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000
FXUS65 KRIW 221811 AAA
AFDRIW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RIVERTON WY
1111 AM MST MON DEC 22 2014

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

CONDITIONS CONTINUE TO GENERALLY IMPROVE ACROSS THE AREA AS ALL
HIGHLIGHTS HAVE BEEN REMOVED. PERIODS OF LIGHT SNOWFALL WILL REMAIN
POSSIBLE THROUGH THE DAY ACROSS MUCH OF THE FORECAST AREA...THOUGH
SNOWFALL WILL MOST SIGNIFICANTLY IMPACT THE EASTERN THIRD OF THE
FORECAST AREA BY THIS AFTERNOON. TEMPERATURES ARE EXPECTED TO BE
COOLER TODAY IN RESPONSE TO THIS SYSTEM.

BUILDING HIGH PRESSURE OVER THE AREA WILL HELP TO END SNOWFALL
ACROSS THE WESTERN MOUNTAINS AND VALLEYS OVERNIGHT. SNOWFALL WILL
ALSO WANE ACROSS EASTERN WYOMING AS THE INFLUENCING SYSTEM MOVES
FURTHER INTO THE CENTRAL PLAINS.

HIGH PRESSURE ACROSS THE AREA WILL GENERALLY BE SHORT LIVED...THOUGH
GENERALLY DRY CONDITIONS WILL BE AROUND LATE TUESDAY THROUGH EARLY
WEDNESDAY. SLIGHTLY WARMER TEMPERATURES WILL BE REALIZED ON
WEDNESDAY AHEAD OF THE NEXT APPROACHING SYSTEM. MODELS TRY TO SHOW
SOME WEAK DISTURBANCES WITHIN THE RIDGE THAT WOULD CREATE SOME
SNOWFALL OVER THE NORTHWESTERN MOUNTAINS BY WEDNESDAY AFTERNOON.
COVERAGE DOES NOT APPEAR TO BECOME SIGNIFICANT UNTIL THE LATE
EVENING HOURS AS A TROUGH APPROACHES THE INTERMOUNTAIN WEST.

THIS TROUGH WILL WORK TO SPREAD SNOWFALL ACROSS THE WESTERN THIRD OF
THE FORECAST AREA THROUGH WEDNESDAY NIGHT.

.LONG TERM...CHRISTMAS DAY THURSDAY THROUGH MONDAY

THE MODELS CONTINUE TO ORDER UP A WHITE CHRISTMAS WITH SOME LIGHT
SNOW ACROSS MOST OF THE AREA DURING THE DAY INTO CHRISTMAS NIGHT.
ACCUMULATIONS AT THE LOWER ELEVATIONS 1 TO 3 INCHES AND 2 TO 5
NEW INCHES FOR THE MOUNTAINS. THE GFS AND ECMWF MODELS ARE STILL
TRENDING SLOWER WITH THE ONSET OF SNOW EAST OF THE DIVIDE...NOW
ACTUALLY LOOKING AT CHRISTMAS MORNING TO AS LATE AS MIDDAY. THE MAIN
CHANCE OF SNOW FOR SOME PLACES MAY OCCUR CHRISTMAS EVENING/NIGHT.
LINGERING LIGHT SNOW ON FRIDAY MORNING THEN MOSTLY DRY FRIDAY
AFTERNOON AND NIGHT EAST OF THE DIVIDE. MOUNTAINS COULD SEE LT SNOW
UNTIL LATE FRI PM OVER THE PEAKS AND PASSES. SATURDAY THROUGH
SATURDAY NIGHT LOOKS DRY EAST OF THE DIVIDE. IN THE WEST...SOME
MOISTURE MOVES BACK SATURDAY AFTERNOON AND NIGHT FOR AN INCREASING
CHANCE OF SNOW. THE NEXT WEATHER SYSTEM IS POISED TO MOVE INTO THE
ROCKY MOUNTAIN REGION SUNDAY THROUGH MONDAY. THIS SYSTEM TAPS SOME
ARCTIC AIR AND SENDS IT INTO WY SUNDAY NIGHT THROUGH MONDAY. LIGHT
FLUFFY SNOW WOULD ALSO OCCUR SUNDAY INTO MONDAY. PLENTY OF TIME TO
WATCH HOW MUCH COLD AIR GETS PULLED SOUTH AND ADJUST FORECAST WITH
TIME. BOTTOM LINE...AN UNSETTLED WEATHER PATTERN FROM CHRISTMAS DAY
INTO THE WEEKEND...IMPACTING TRAVEL FROM TIME TO TIME. HIGH TEMPS
WILL BE AT OR BELOW SEASONAL NORMALS THROUGH THE PERIOD.

.AVIATION.../18Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

AREAS OF GUSTY NORTHWEST WIND WILL REMAIN...ESPECIALLY VCNTY
KDUB-KRIW AND KBYG...THROUGH THE PERIOD.  -SHSN ACTIVITY WILL REMAIN
MOSTLY ISOLD-WDLY SCT WITH MOST OF THIS ACTIVITY VCNTY AND EAST OF A
KCOD-KWRL-KCPR LINE THROUGH MONDAY MORNING WITH MORE NMRS SHSN
OBSCURING THE SURROUNDING MTNS.  MOISTURE AND INSTABILITY WILL
INCREASE AGAIN THIS AFTERNOON WITH SHSN BECOMING MORE SCT ACROSS
THE CENTRAL BASINS. SOME WRAPAROUND MOISTURE IS EXPECTED TO PUSH
BACK FROM AN UPPER LOW OVER THE PLAINS INTO EASTERN WYOMING
TONIGHT...AND THIS MAY BRING MORE WIDESPREAD MVFR/IFR -SN AS FAR
WEST AS THE BIGHORN RANGE TO VCNTY KCPR.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A MOIST AND UNSTABLE NW FLOW WILL REMAIN OVER THE AREA THROUGH
THE AFTERNOON.  AN UPPER LEVEL DISTURBANCE IN THIS FLOW IS
EXPECTED TO CONTINUE TO DIVE SOUTH ALONG THE DIVIDE...EXITING
SOUTH OF INTERSTATE 80 THIS EVENING. SNOW SHOWER ACTIVITY WILL
INCREASE AHEAD OF THIS SYSTEM FROM NW-SE MONDAY MORNING WITH
IMPROVING CONDITIONS AND GUSTY NW WINDS FOLLOWING THE DISTURBANCE
IN THE AFTERNOON AND EVENING. CLEARING CONDITIONS AND DIMINISHING
WIND WILL FOLLOW OVERNIGHT.

.FIRE WEATHER...

GUSTY WIND WILL REMAIN ACROSS MUCH OF THE FORECAST AREA TODAY...WITH
WIND WEAKENING DURING THE EVENING AND OVERNIGHT HOURS. TEMPERATURES
WILL COOL ACROSS THE AREA TODAY...AND CONTINUE TO COOL TUESDAY
BEFORE EXPERIENCING A SLIGHT WARMING ON WEDNESDAY. SNOWFALL WILL
LINGER ACROSS THE AREA TODAY...WITH MUCH OF ITS IMPACT EXPECTED TO
BE FELT ACROSS THE EASTERN THIRD OF THE FORECAST AREA. HIGH PRESSURE
WILL MOVE IN THIS EVENING AND OVERNIGHT TO HELP END MOST SHOWER
ACTIVITY. THE NEXT APPROACHING TROUGH WILL MOVE INTO NORTHWESTERN
WYOMING WEDNESDAY AFTERNOON AND EVENING...AND WILL SPREAD THROUGH
THE OVERNIGHT HOURS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...ALLEN
FIRE WEATHER...BRANHAM





000
FXUS65 KRIW 221811 AAA
AFDRIW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RIVERTON WY
1111 AM MST MON DEC 22 2014

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

CONDITIONS CONTINUE TO GENERALLY IMPROVE ACROSS THE AREA AS ALL
HIGHLIGHTS HAVE BEEN REMOVED. PERIODS OF LIGHT SNOWFALL WILL REMAIN
POSSIBLE THROUGH THE DAY ACROSS MUCH OF THE FORECAST AREA...THOUGH
SNOWFALL WILL MOST SIGNIFICANTLY IMPACT THE EASTERN THIRD OF THE
FORECAST AREA BY THIS AFTERNOON. TEMPERATURES ARE EXPECTED TO BE
COOLER TODAY IN RESPONSE TO THIS SYSTEM.

BUILDING HIGH PRESSURE OVER THE AREA WILL HELP TO END SNOWFALL
ACROSS THE WESTERN MOUNTAINS AND VALLEYS OVERNIGHT. SNOWFALL WILL
ALSO WANE ACROSS EASTERN WYOMING AS THE INFLUENCING SYSTEM MOVES
FURTHER INTO THE CENTRAL PLAINS.

HIGH PRESSURE ACROSS THE AREA WILL GENERALLY BE SHORT LIVED...THOUGH
GENERALLY DRY CONDITIONS WILL BE AROUND LATE TUESDAY THROUGH EARLY
WEDNESDAY. SLIGHTLY WARMER TEMPERATURES WILL BE REALIZED ON
WEDNESDAY AHEAD OF THE NEXT APPROACHING SYSTEM. MODELS TRY TO SHOW
SOME WEAK DISTURBANCES WITHIN THE RIDGE THAT WOULD CREATE SOME
SNOWFALL OVER THE NORTHWESTERN MOUNTAINS BY WEDNESDAY AFTERNOON.
COVERAGE DOES NOT APPEAR TO BECOME SIGNIFICANT UNTIL THE LATE
EVENING HOURS AS A TROUGH APPROACHES THE INTERMOUNTAIN WEST.

THIS TROUGH WILL WORK TO SPREAD SNOWFALL ACROSS THE WESTERN THIRD OF
THE FORECAST AREA THROUGH WEDNESDAY NIGHT.

.LONG TERM...CHRISTMAS DAY THURSDAY THROUGH MONDAY

THE MODELS CONTINUE TO ORDER UP A WHITE CHRISTMAS WITH SOME LIGHT
SNOW ACROSS MOST OF THE AREA DURING THE DAY INTO CHRISTMAS NIGHT.
ACCUMULATIONS AT THE LOWER ELEVATIONS 1 TO 3 INCHES AND 2 TO 5
NEW INCHES FOR THE MOUNTAINS. THE GFS AND ECMWF MODELS ARE STILL
TRENDING SLOWER WITH THE ONSET OF SNOW EAST OF THE DIVIDE...NOW
ACTUALLY LOOKING AT CHRISTMAS MORNING TO AS LATE AS MIDDAY. THE MAIN
CHANCE OF SNOW FOR SOME PLACES MAY OCCUR CHRISTMAS EVENING/NIGHT.
LINGERING LIGHT SNOW ON FRIDAY MORNING THEN MOSTLY DRY FRIDAY
AFTERNOON AND NIGHT EAST OF THE DIVIDE. MOUNTAINS COULD SEE LT SNOW
UNTIL LATE FRI PM OVER THE PEAKS AND PASSES. SATURDAY THROUGH
SATURDAY NIGHT LOOKS DRY EAST OF THE DIVIDE. IN THE WEST...SOME
MOISTURE MOVES BACK SATURDAY AFTERNOON AND NIGHT FOR AN INCREASING
CHANCE OF SNOW. THE NEXT WEATHER SYSTEM IS POISED TO MOVE INTO THE
ROCKY MOUNTAIN REGION SUNDAY THROUGH MONDAY. THIS SYSTEM TAPS SOME
ARCTIC AIR AND SENDS IT INTO WY SUNDAY NIGHT THROUGH MONDAY. LIGHT
FLUFFY SNOW WOULD ALSO OCCUR SUNDAY INTO MONDAY. PLENTY OF TIME TO
WATCH HOW MUCH COLD AIR GETS PULLED SOUTH AND ADJUST FORECAST WITH
TIME. BOTTOM LINE...AN UNSETTLED WEATHER PATTERN FROM CHRISTMAS DAY
INTO THE WEEKEND...IMPACTING TRAVEL FROM TIME TO TIME. HIGH TEMPS
WILL BE AT OR BELOW SEASONAL NORMALS THROUGH THE PERIOD.

.AVIATION.../18Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

AREAS OF GUSTY NORTHWEST WIND WILL REMAIN...ESPECIALLY VCNTY
KDUB-KRIW AND KBYG...THROUGH THE PERIOD.  -SHSN ACTIVITY WILL REMAIN
MOSTLY ISOLD-WDLY SCT WITH MOST OF THIS ACTIVITY VCNTY AND EAST OF A
KCOD-KWRL-KCPR LINE THROUGH MONDAY MORNING WITH MORE NMRS SHSN
OBSCURING THE SURROUNDING MTNS.  MOISTURE AND INSTABILITY WILL
INCREASE AGAIN THIS AFTERNOON WITH SHSN BECOMING MORE SCT ACROSS
THE CENTRAL BASINS. SOME WRAPAROUND MOISTURE IS EXPECTED TO PUSH
BACK FROM AN UPPER LOW OVER THE PLAINS INTO EASTERN WYOMING
TONIGHT...AND THIS MAY BRING MORE WIDESPREAD MVFR/IFR -SN AS FAR
WEST AS THE BIGHORN RANGE TO VCNTY KCPR.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A MOIST AND UNSTABLE NW FLOW WILL REMAIN OVER THE AREA THROUGH
THE AFTERNOON.  AN UPPER LEVEL DISTURBANCE IN THIS FLOW IS
EXPECTED TO CONTINUE TO DIVE SOUTH ALONG THE DIVIDE...EXITING
SOUTH OF INTERSTATE 80 THIS EVENING. SNOW SHOWER ACTIVITY WILL
INCREASE AHEAD OF THIS SYSTEM FROM NW-SE MONDAY MORNING WITH
IMPROVING CONDITIONS AND GUSTY NW WINDS FOLLOWING THE DISTURBANCE
IN THE AFTERNOON AND EVENING. CLEARING CONDITIONS AND DIMINISHING
WIND WILL FOLLOW OVERNIGHT.

.FIRE WEATHER...

GUSTY WIND WILL REMAIN ACROSS MUCH OF THE FORECAST AREA TODAY...WITH
WIND WEAKENING DURING THE EVENING AND OVERNIGHT HOURS. TEMPERATURES
WILL COOL ACROSS THE AREA TODAY...AND CONTINUE TO COOL TUESDAY
BEFORE EXPERIENCING A SLIGHT WARMING ON WEDNESDAY. SNOWFALL WILL
LINGER ACROSS THE AREA TODAY...WITH MUCH OF ITS IMPACT EXPECTED TO
BE FELT ACROSS THE EASTERN THIRD OF THE FORECAST AREA. HIGH PRESSURE
WILL MOVE IN THIS EVENING AND OVERNIGHT TO HELP END MOST SHOWER
ACTIVITY. THE NEXT APPROACHING TROUGH WILL MOVE INTO NORTHWESTERN
WYOMING WEDNESDAY AFTERNOON AND EVENING...AND WILL SPREAD THROUGH
THE OVERNIGHT HOURS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...ALLEN
FIRE WEATHER...BRANHAM





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000
FXUS65 KCYS 221728
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1126 AM MST MON DEC 22 2014

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 525 AM MST MON DEC 22 2014

SNOW AND HIGH WINDS CONTINUE TO BE OUR MAJOR CONCERNS OVER THE NEXT
24 TO 36 HOURS. LIGHT TO MODERATE SNOW SHOWERS HAVE BEEN ONGOING FOR
MUCH OF THE NIGHT ALONG AND EAST OF THE LARAMIE RANGE. ACCUMULATIONS
HAVE NOT BEEN SIGNIFICANT...BUT IT IS CAUSING A FEW TRAVEL HAZARDS
WITH SLICK ROADS AND LOCALLY REDUCED VISIBILITY. SNOW SHOWERS SHOULD
PERSIST TODAY IN THE FAVORED LEFT EXIT REGION OF A 160-180 KT JET AT
H25. NOT SO SURPRISINGLY...THIS PATTERN IS CONTRIBUTING TO QUITE THE
DUMPING OF SNOW IN THE MOUNTAINS. RECENT ANALYSIS OF AREA SNOTEL OBS
ESTIMATES OVER 30 INCHES OVER THE PAST 24 HOURS IN THE SNOWY`S USING
A 15 TO 1 RATIO. EXPECT ANOTHER FOOT OR SO WILL FALL THROUGH EARLY
TUESDAY MORNING WITH MOST MODELS PAINTING SEVERAL TENTHS OF AN INCH
OF QPF IN A VERY FAVORABLE PATTERN FOR MOIST OROGRAPHICS AND EXTREME
DIVERGENCE ALOFT. WINTER STORM WARNING FOR THE MOUNTAINS IS IN GREAT
SHAPE...SO NO CHANGES NECESSARY THERE. WINDS SHOULD BECOME NORTHWEST
ACROSS ALL AREAS IN THE POST FRONTAL AIR MASS...SO ACCUMULATING SNOW
SHOULD END OVER SOUTHWEST CARBON COUNTY WITH THE LOSS OF FAVORABLE
LOW LEVEL UPSLOPE. LATEST HIGHWAY OBSERVATIONS INDICATE LESS THAN 30
MPH WINDS AT ARLINGTON AS WELL. AS SUCH...BELIEVE WE WILL BE ABLE TO
LET THOSE WINTER STORM WARNINGS EXPIRE AT 8 AM.

IT WILL BE WINDY YET AGAIN ACROSS MUCH OF THE AREA TODAY. COLD FRONT
SWEPT ACROSS THE AREA LAST EVENING AND WAS DRAPED ACROSS CENTRAL NE
INTO NORTHWESTERN KS AT 09Z. EXCELLENT COLD ADVECTION IS OCCURRING
ALOFT WITH H7 TEMPS PLUNGING SEVERAL DEG C OVER THE PAST FEW HOURS
PER LAPS SOUNDINGS. THIS IS KEEPING THINGS WELL-MIXED AND IS ALREADY
GIVING WAY TO GUSTS AROUND 40 MPH AT CHADRON. BOTH NAM/GFS FORECAST
SOUNDINGS SHOW AROUND 45 KT AVAILABLE TO MIX THROUGH THE DAY OVER
MOST OF THE PANHANDLE...SO WILL KEEP THE ADVISORY GOING. THINK
WINDS ALOFT ARE NOT QUITE HIGH ENOUGH TO JUSTIFY A WARNING...BUT
WE COULD SEE SOME GUSTS TO 55 MPH IN THE AFTERNOON. BIGGER WIND
CONCERNS ARE FOR THIS EVENING AND OVERNIGHT. THE MODELS STILL
CLOSE OFF THE UPPER LOW OVER THE CENTRAL PLAINS AFTER 00Z WITH
FAST NORTHWESTERLY FLOW ALOFT REMAINING IN PLACE OVER THE CWA. THE
GFS SHOWS A 995 MILLIBAR SURFACE LOW OVER IOWA AT 06Z
TONIGHT...RESULTING IN A STRONG SURFACE PRESSURE GRADIENT ALONG
AND EAST OF THE LARAMIE RANGE. GFS/NAM/ECMWF ALL BRING A BROAD
SWATH OF 55 TO 65 KT FLOW AT H7-H8 DURING THE LATE EVENING AND
OVERNIGHT HOURS. DOWNWARD MOMENTUM TRANSFER IS POSSIBLE AS MODELED
SOUNDINGS SUGGEST A VERY WELL-MIXED BOUNDARY LAYER OWING TO
CONTINUOUS CAA JUST OFF THE SURFACE. BUFKIT SOUNDINGS SUGGEST 30
TO 40 KT SUSTAINED AT THE LOWEST LEVEL AT CHEYENNE AND A FEW
OTHER SITES AROUND 06-08Z...WITH UPWARDS OF 65 KT AT THE TOP OF
THE MIXED LAYER. WILL HOIST A HIGH WIND WATCH STARTING AT 03Z FOR
ALL AREAS ALONG AND EAST OF THE LARAMIE RANGE. EXPECT WINDS WILL
SLOWLY RELAX BY TUESDAY AFTERNOON.

STILL EXPECT SOME ACCUMULATING SNOW OVER PARTS OF THE PANHANDLE THIS
EVENING AND OVERNIGHT WITH A DEVELOPING DEFORMATION AXIS AND MODEST
WRAP-AROUND MOISTURE. STILL LOOKS LIKE THE BEST SUPPORT WILL BE JUST
EAST OF THE CWA THOUGH...SO AMOUNTS WILL MOST LIKELY BE SUB ADVISORY
EXCEPT AT HIGHER ELEVATIONS ALONG THE PINE RIDGE. LATER SHIFTS WILL
NEED TO WATCH HOW THIS INTERACTS WITH HIGH WINDS THOUGH...AS TRAVEL
CONDITIONS MAY GET VERY NASTY. WINTER WEATHER ADVISORIES OR POSSIBLY
WINTER STORM WARNINGS MAY NEED TO BE CONSIDERED LATER ON IF IT LOOKS
LIKE WIDESPREAD SIGNIFICANT BLOWING SNOW WILL BE AN ISSUE. DAWES AND
BOX BUTTE COUNTIES WOULD PROBABLY SEE THE WORST CONDITIONS BASED ON
THE LATEST DATA. NOT THINKING PERSISTENT SNOW WILL BEGIN UNTIL AFTER
00Z TUE...SO WILL LET THE DAY SHIFT DECIDE HOW TO HANDLE THIS.

BROAD UPPER-LEVEL RIDGING IS FORECAST TO BUILD INTO THE AREA THROUGH
THE LATTER PART OF THE SHORT TERM PERIOD. DOWNSLOPE FLOW IS POSSIBLE
EAST OF THE LARAMIE RANGE ON WEDNESDAY WITH H7 TEMPS INCREASING TO
NEAR 0 DEG C. DESPITE THAT...WENT A FEW DEGREES BELOW GUIDANCE FOR
HIGHS AS SOME OF THE ENERGY WILL GO TOWARD MELTING SNOW. OBSERVED
TEMPERATURES WILL HEAVILY DEPEND ON HOW MUCH SNOW FALLS LATE TONIGHT
AND TUESDAY.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 335 AM MST MON DEC 22 2014

FORECAST CHALLENGES WILL FOCUS ON POTENTIAL WINTER STORM SYSTEMS
IMPACTING THE CWA CHRISTMAS DAY/NIGHT AND LATE NEXT WEEKEND.

THE 00Z/06Z DETERMINISTIC MODEL GUIDANCE DEPICTS A SHORTWAVE RIDGE
QUICKLY TRANSLATING EAST FROM THE FRONT RANGE INTO THE GREAT PLAINS
WEDNESDAY NIGHT. THE NEXT PACIFIC TROUGH TRACKS EAST FROM THE
GREAT BASIN ACROSS THE ROCKIES LATE THURSDAY/EARLY FRIDAY. MODEL
DIFFERENCES BECOME APPARENT FRIDAY AS THE ECMWF AND CANADIAN GEM
HANG THE TROUGH FURTHER WEST WHILE THE GFS IS MORE PROGRESSIVE.
PRECIPITATION IS MORE WIDESPREAD WITH THE ECMWF WHILE THE GFS
LIMITS QPF OVER THE SOUTHEAST WY PLAINS AND SOUTHERN NE PANHANDLE
DUE TO THE DOWNSLOPE. MAINTAINED LIKELY POPS ALONG/WEST OF THE
LARAMIE RANGE WITH CHANCE POPS TO THE EAST. WINDS WILL BE
STRONGEST ALONG/WEST OF THE LARAMIE RANGE PRIOR TO FROPA WEDNESDAY
NIGHT/THURSDAY MORNING...THEN DECREASE DURING THE AFTERNOON. SNOW
ACCUMULATIONS WILL BE FAIRLY GENEROUS WITH THIS SYSTEM OVER THE
WEST...WITH UPWARDS OF A HALF FOOT FOR THE SNOWY/SIERRA MADRE AND
NORTH LARAMIE RANGES WITH 2 TO 4 INCHES LOWER ELEVATIONS.

AFTER THIS SYSTEM DEPARTS TO THE EAST...WEAK SHORTWAVE ENERGY AND
OROGRAPHICS WILL KEEP CHANCES FOR SNOW SHOWERS CONFINED TO THE
SOUTHERN MOUNTAINS FRIDAY/FRIDAY EVENING. SATURDAY WILL BE A
TRANSITION DAY WITH THE PASSAGE OF A SHORTWAVE RIDGE.
PRECIPITATION WILL SPREAD EAST INTO CENTRAL AND SOUTHERN WYOMING
/WEST OF A DOUGLAS TO LARAMIE LINE/ SUNDAY WITH THE ARRIVAL OF
ANOTHER PACIFIC TROUGH AND COLD FRONT.

HIGH TEMPERATURES CHRISTMAS DAY WILL RANGE FROM THE 20S AND 30S
NORTH AND WEST TO THE LOWER 40S SOUTHEAST. FRIDAY WILL BE COLDER
WITH HIGHS IN THE TEENS AND 20S. TEMPERATURES MODERATE SLIGHTLY
NEXT WEEKEND WITH 20S AND 30S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY MORNING)
ISSUED AT 1126 AM MST MON DEC 22 2014

VFR OVER THE AERODROME INITIALLY THIS AFTERNOON THOUGH A PD OF MVFR
CIGS/VSBYS POSSIBLE KRWL TO NEAR KCYS IN SNOW SHOWERS.  WINDS WILL
INCREASE TONIGHT AND BE QUITE WINDY OVER THE PLAINS WITH CIGS
LOWERING TO MVFR OVER MANY AREAS WITH SOME PERIODS OF IFR VSBYS IN
SNOW.

&&

.FIRE WEATHER...
ISSUED AT 429 AM MST MON DEC 22 2014

NO CRITICAL FIRE WEATHER OVER THE NEXT FEW DAYS. MOUNTAIN SNOW WILL
CONTINUE THROUGH TUESDAY WITH 2 TO 4 FEET OF TOTAL SNOW ACCUMULATION
IN THE SNOWY`S AND SIERRA MADRES. WINDY CONDITIONS ARE EXPECTED EAST
OF THE LARAMIE RANGE TODAY...WITH STRONGER WINDS POSSIBLE LATE THIS
EVENING THROUGH TUESDAY MORNING. A WIND ADVISORY AND HIGH WIND WATCH
HAVE BEEN ISSUED FOR PARTS OF THE AREA. LIGHT SNOWFALL ACCUMULATIONS
ARE EXPECTED OVER THE PLAINS TONIGHT.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     WYZ101-102-106>108-116>119.

     WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     WINTER WEATHER ADVISORY UNTIL 8 AM MST THIS MORNING FOR WYZ113-
     115.

     WINTER STORM WARNING UNTIL 8 AM MST THIS MORNING FOR WYZ110-111.

NE...WIND ADVISORY FROM 8 AM THIS MORNING TO 5 PM MST THIS AFTERNOON
     FOR NEZ002-003-019>021-054-055-095-096.

     HIGH WIND WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     NEZ019>021-054-055-095-096.

&&

$$

SHORT TERM...CLH
LONG TERM...MJ
AVIATION...RE
FIRE WEATHER...CLH



000
FXUS65 KCYS 221728
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1126 AM MST MON DEC 22 2014

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 525 AM MST MON DEC 22 2014

SNOW AND HIGH WINDS CONTINUE TO BE OUR MAJOR CONCERNS OVER THE NEXT
24 TO 36 HOURS. LIGHT TO MODERATE SNOW SHOWERS HAVE BEEN ONGOING FOR
MUCH OF THE NIGHT ALONG AND EAST OF THE LARAMIE RANGE. ACCUMULATIONS
HAVE NOT BEEN SIGNIFICANT...BUT IT IS CAUSING A FEW TRAVEL HAZARDS
WITH SLICK ROADS AND LOCALLY REDUCED VISIBILITY. SNOW SHOWERS SHOULD
PERSIST TODAY IN THE FAVORED LEFT EXIT REGION OF A 160-180 KT JET AT
H25. NOT SO SURPRISINGLY...THIS PATTERN IS CONTRIBUTING TO QUITE THE
DUMPING OF SNOW IN THE MOUNTAINS. RECENT ANALYSIS OF AREA SNOTEL OBS
ESTIMATES OVER 30 INCHES OVER THE PAST 24 HOURS IN THE SNOWY`S USING
A 15 TO 1 RATIO. EXPECT ANOTHER FOOT OR SO WILL FALL THROUGH EARLY
TUESDAY MORNING WITH MOST MODELS PAINTING SEVERAL TENTHS OF AN INCH
OF QPF IN A VERY FAVORABLE PATTERN FOR MOIST OROGRAPHICS AND EXTREME
DIVERGENCE ALOFT. WINTER STORM WARNING FOR THE MOUNTAINS IS IN GREAT
SHAPE...SO NO CHANGES NECESSARY THERE. WINDS SHOULD BECOME NORTHWEST
ACROSS ALL AREAS IN THE POST FRONTAL AIR MASS...SO ACCUMULATING SNOW
SHOULD END OVER SOUTHWEST CARBON COUNTY WITH THE LOSS OF FAVORABLE
LOW LEVEL UPSLOPE. LATEST HIGHWAY OBSERVATIONS INDICATE LESS THAN 30
MPH WINDS AT ARLINGTON AS WELL. AS SUCH...BELIEVE WE WILL BE ABLE TO
LET THOSE WINTER STORM WARNINGS EXPIRE AT 8 AM.

IT WILL BE WINDY YET AGAIN ACROSS MUCH OF THE AREA TODAY. COLD FRONT
SWEPT ACROSS THE AREA LAST EVENING AND WAS DRAPED ACROSS CENTRAL NE
INTO NORTHWESTERN KS AT 09Z. EXCELLENT COLD ADVECTION IS OCCURRING
ALOFT WITH H7 TEMPS PLUNGING SEVERAL DEG C OVER THE PAST FEW HOURS
PER LAPS SOUNDINGS. THIS IS KEEPING THINGS WELL-MIXED AND IS ALREADY
GIVING WAY TO GUSTS AROUND 40 MPH AT CHADRON. BOTH NAM/GFS FORECAST
SOUNDINGS SHOW AROUND 45 KT AVAILABLE TO MIX THROUGH THE DAY OVER
MOST OF THE PANHANDLE...SO WILL KEEP THE ADVISORY GOING. THINK
WINDS ALOFT ARE NOT QUITE HIGH ENOUGH TO JUSTIFY A WARNING...BUT
WE COULD SEE SOME GUSTS TO 55 MPH IN THE AFTERNOON. BIGGER WIND
CONCERNS ARE FOR THIS EVENING AND OVERNIGHT. THE MODELS STILL
CLOSE OFF THE UPPER LOW OVER THE CENTRAL PLAINS AFTER 00Z WITH
FAST NORTHWESTERLY FLOW ALOFT REMAINING IN PLACE OVER THE CWA. THE
GFS SHOWS A 995 MILLIBAR SURFACE LOW OVER IOWA AT 06Z
TONIGHT...RESULTING IN A STRONG SURFACE PRESSURE GRADIENT ALONG
AND EAST OF THE LARAMIE RANGE. GFS/NAM/ECMWF ALL BRING A BROAD
SWATH OF 55 TO 65 KT FLOW AT H7-H8 DURING THE LATE EVENING AND
OVERNIGHT HOURS. DOWNWARD MOMENTUM TRANSFER IS POSSIBLE AS MODELED
SOUNDINGS SUGGEST A VERY WELL-MIXED BOUNDARY LAYER OWING TO
CONTINUOUS CAA JUST OFF THE SURFACE. BUFKIT SOUNDINGS SUGGEST 30
TO 40 KT SUSTAINED AT THE LOWEST LEVEL AT CHEYENNE AND A FEW
OTHER SITES AROUND 06-08Z...WITH UPWARDS OF 65 KT AT THE TOP OF
THE MIXED LAYER. WILL HOIST A HIGH WIND WATCH STARTING AT 03Z FOR
ALL AREAS ALONG AND EAST OF THE LARAMIE RANGE. EXPECT WINDS WILL
SLOWLY RELAX BY TUESDAY AFTERNOON.

STILL EXPECT SOME ACCUMULATING SNOW OVER PARTS OF THE PANHANDLE THIS
EVENING AND OVERNIGHT WITH A DEVELOPING DEFORMATION AXIS AND MODEST
WRAP-AROUND MOISTURE. STILL LOOKS LIKE THE BEST SUPPORT WILL BE JUST
EAST OF THE CWA THOUGH...SO AMOUNTS WILL MOST LIKELY BE SUB ADVISORY
EXCEPT AT HIGHER ELEVATIONS ALONG THE PINE RIDGE. LATER SHIFTS WILL
NEED TO WATCH HOW THIS INTERACTS WITH HIGH WINDS THOUGH...AS TRAVEL
CONDITIONS MAY GET VERY NASTY. WINTER WEATHER ADVISORIES OR POSSIBLY
WINTER STORM WARNINGS MAY NEED TO BE CONSIDERED LATER ON IF IT LOOKS
LIKE WIDESPREAD SIGNIFICANT BLOWING SNOW WILL BE AN ISSUE. DAWES AND
BOX BUTTE COUNTIES WOULD PROBABLY SEE THE WORST CONDITIONS BASED ON
THE LATEST DATA. NOT THINKING PERSISTENT SNOW WILL BEGIN UNTIL AFTER
00Z TUE...SO WILL LET THE DAY SHIFT DECIDE HOW TO HANDLE THIS.

BROAD UPPER-LEVEL RIDGING IS FORECAST TO BUILD INTO THE AREA THROUGH
THE LATTER PART OF THE SHORT TERM PERIOD. DOWNSLOPE FLOW IS POSSIBLE
EAST OF THE LARAMIE RANGE ON WEDNESDAY WITH H7 TEMPS INCREASING TO
NEAR 0 DEG C. DESPITE THAT...WENT A FEW DEGREES BELOW GUIDANCE FOR
HIGHS AS SOME OF THE ENERGY WILL GO TOWARD MELTING SNOW. OBSERVED
TEMPERATURES WILL HEAVILY DEPEND ON HOW MUCH SNOW FALLS LATE TONIGHT
AND TUESDAY.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 335 AM MST MON DEC 22 2014

FORECAST CHALLENGES WILL FOCUS ON POTENTIAL WINTER STORM SYSTEMS
IMPACTING THE CWA CHRISTMAS DAY/NIGHT AND LATE NEXT WEEKEND.

THE 00Z/06Z DETERMINISTIC MODEL GUIDANCE DEPICTS A SHORTWAVE RIDGE
QUICKLY TRANSLATING EAST FROM THE FRONT RANGE INTO THE GREAT PLAINS
WEDNESDAY NIGHT. THE NEXT PACIFIC TROUGH TRACKS EAST FROM THE
GREAT BASIN ACROSS THE ROCKIES LATE THURSDAY/EARLY FRIDAY. MODEL
DIFFERENCES BECOME APPARENT FRIDAY AS THE ECMWF AND CANADIAN GEM
HANG THE TROUGH FURTHER WEST WHILE THE GFS IS MORE PROGRESSIVE.
PRECIPITATION IS MORE WIDESPREAD WITH THE ECMWF WHILE THE GFS
LIMITS QPF OVER THE SOUTHEAST WY PLAINS AND SOUTHERN NE PANHANDLE
DUE TO THE DOWNSLOPE. MAINTAINED LIKELY POPS ALONG/WEST OF THE
LARAMIE RANGE WITH CHANCE POPS TO THE EAST. WINDS WILL BE
STRONGEST ALONG/WEST OF THE LARAMIE RANGE PRIOR TO FROPA WEDNESDAY
NIGHT/THURSDAY MORNING...THEN DECREASE DURING THE AFTERNOON. SNOW
ACCUMULATIONS WILL BE FAIRLY GENEROUS WITH THIS SYSTEM OVER THE
WEST...WITH UPWARDS OF A HALF FOOT FOR THE SNOWY/SIERRA MADRE AND
NORTH LARAMIE RANGES WITH 2 TO 4 INCHES LOWER ELEVATIONS.

AFTER THIS SYSTEM DEPARTS TO THE EAST...WEAK SHORTWAVE ENERGY AND
OROGRAPHICS WILL KEEP CHANCES FOR SNOW SHOWERS CONFINED TO THE
SOUTHERN MOUNTAINS FRIDAY/FRIDAY EVENING. SATURDAY WILL BE A
TRANSITION DAY WITH THE PASSAGE OF A SHORTWAVE RIDGE.
PRECIPITATION WILL SPREAD EAST INTO CENTRAL AND SOUTHERN WYOMING
/WEST OF A DOUGLAS TO LARAMIE LINE/ SUNDAY WITH THE ARRIVAL OF
ANOTHER PACIFIC TROUGH AND COLD FRONT.

HIGH TEMPERATURES CHRISTMAS DAY WILL RANGE FROM THE 20S AND 30S
NORTH AND WEST TO THE LOWER 40S SOUTHEAST. FRIDAY WILL BE COLDER
WITH HIGHS IN THE TEENS AND 20S. TEMPERATURES MODERATE SLIGHTLY
NEXT WEEKEND WITH 20S AND 30S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY MORNING)
ISSUED AT 1126 AM MST MON DEC 22 2014

VFR OVER THE AERODROME INITIALLY THIS AFTERNOON THOUGH A PD OF MVFR
CIGS/VSBYS POSSIBLE KRWL TO NEAR KCYS IN SNOW SHOWERS.  WINDS WILL
INCREASE TONIGHT AND BE QUITE WINDY OVER THE PLAINS WITH CIGS
LOWERING TO MVFR OVER MANY AREAS WITH SOME PERIODS OF IFR VSBYS IN
SNOW.

&&

.FIRE WEATHER...
ISSUED AT 429 AM MST MON DEC 22 2014

NO CRITICAL FIRE WEATHER OVER THE NEXT FEW DAYS. MOUNTAIN SNOW WILL
CONTINUE THROUGH TUESDAY WITH 2 TO 4 FEET OF TOTAL SNOW ACCUMULATION
IN THE SNOWY`S AND SIERRA MADRES. WINDY CONDITIONS ARE EXPECTED EAST
OF THE LARAMIE RANGE TODAY...WITH STRONGER WINDS POSSIBLE LATE THIS
EVENING THROUGH TUESDAY MORNING. A WIND ADVISORY AND HIGH WIND WATCH
HAVE BEEN ISSUED FOR PARTS OF THE AREA. LIGHT SNOWFALL ACCUMULATIONS
ARE EXPECTED OVER THE PLAINS TONIGHT.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     WYZ101-102-106>108-116>119.

     WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     WINTER WEATHER ADVISORY UNTIL 8 AM MST THIS MORNING FOR WYZ113-
     115.

     WINTER STORM WARNING UNTIL 8 AM MST THIS MORNING FOR WYZ110-111.

NE...WIND ADVISORY FROM 8 AM THIS MORNING TO 5 PM MST THIS AFTERNOON
     FOR NEZ002-003-019>021-054-055-095-096.

     HIGH WIND WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     NEZ019>021-054-055-095-096.

&&

$$

SHORT TERM...CLH
LONG TERM...MJ
AVIATION...RE
FIRE WEATHER...CLH



  [top]

000
FXUS63 KUNR 221710
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1010 AM MST MON DEC 22 2014

.UPDATE...
ISSUED AT 851 AM MST MON DEC 22 2014

SURFACE LOW IS OVER NORTHEAST SD...CREATING A TIGHT PRESSURE
GRADIENT OVER WESTERN SD AND SOME STRONG NORTHWESTERLY WINDS. MODELS
ARE STILL SHOWING A LULL IN PRECIP EARLY TODAY...WITH RAIN/SNOW MAINLY
STARTING LATE THIS AFTERNOON. DECREASED POPS LATE THIS MORNING AND
EARLY THIS AFTERNOON. ALSO LOWERED PRECIP/SNOW AMOUNTS THIS
MORNING. TOOK OUT THE BLOWING SNOW FOR EARLY THIS AFTERNOON...AS
MUCH OF THE PRECIP MAY FALL AS RAIN. REST OF FORECAST LOOKS ON
TRACK AND LEFT HEADLINES AS THEY ARE.

&&

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 333 AM MST MON DEC 22 2014

WATER VAPOR IMAGERY SHOWS AMPLIFYING TROUGH ACROSS THE CENTRAL CONUS
WITH PLENTY OF ENERGY DIVING DOWN THE BACKSIDE FROM BC CANADA TO THE
NORTHERN AND CENTRAL ROCKIES TO THE CENTRAL/SOUTHERN PLAINS. SURFACE
ANALYSIS SHOWS LOW PRESSURE ACROSS THE DAKOTAS INTO NEBRASKA. KUDX
RADAR SHOWS -RA ACROSS SOUTH CENTRAL TO SOUTHWEST SOUTH DAKOTA AND
VERY LIGHT SNOW FALLING ACROSS NORTHERN/CENTRAL PORTIONS OF THE
BLACK HILLS WITH MORE UPSTREAM SHOWERS DEVELOPING.

MODELS HAVE MADE FURTHER ADJUSTMENTS WITH THE 00Z RUN WHICH TAKES
THE TRACK OF THE DEVELOPING UPPER LOW INTO CENTRAL SD/NEB...THEN
REDEVELOPS IT FARTHER SOUTHEAST TOWARD IA. THIS DOES BRING SOME
CHANGES TO THE FORECAST. IT NOW LOOKS LIKE THERE WILL BE A LULL IN
THE PRECIP FOR MOST LOCATIONS THIS MORNING BEFORE THE UPPER LOW CAN
ACTUALLY CLOSE OFF ON A BROADER SCALE. THIS IS EXPECTED TO HAPPEN
LATER IN THE DAY/TONIGHT WITH WRAP AROUND PRECIP DEVELOPING ACROSS
THE AREA THROUGH THE AFTERNOON AND TONIGHT. THIS WILL DROP SNOW
AMOUNTS ACROSS THE CWA TODAY...BUT FOR THE MOST PART STORM TOTAL
SNOW ACCUMULATIONS ARE STILL ON TRACK AS THE END OF THE EVENT ALSO
GETS DELAYED UNTIL MORE MIDDAY TUESDAY.

WILL CONTINUE WITH PREVIOUS SHIFTS HEADLINES...WILL JUST MAKE
MENTION OF DELAYED ONSET OF SNOWFALL. WINTER STORM WARNING STILL
LOOKS GOOD FOR NORTHERN/WYOMING BLACK HILLS WITH 6 TO 12 INCH
WORDING. LOOKS LIKE UPSLOPE SNOW WILL END LATER...MORE IN THE EARLY
AFTERNOON HOURS...BUT WITH MINIMAL ADDITIONAL ACCUMULATION AFTER 19Z
WILL LEAVE TIMING OF THE HEADLINES THE SAME. WHILE WNW UPSLOPE WINDS
ARE STILL EXPECTED TODAY...MODELS ARE NOW SHOWING A SLIGHTLY MORE
NORTHERLY COMPONENT TONIGHT TO MORE OF A NW DIRECTION. THIS WOULD
FAVOR GREATER SNOW AMOUNTS OVER THE NORTHERN FOOTHILLS/SPEARFISH
AREA...SO WILL UPGRADE THAT ZONE TO A WINTER STORM WARNING WITH 5 TO
10 INCH WORDING. WINTER WEATHER ADVISORIES ACROSS THE PLAINS ARE IN
GOOD SHAPE. WILL ADD SOUTH CENTRAL SD TO THE ADVISORY AS MODELS
CONTINUE TO SHOW 3 TO 6 INCH ACCUMULATIONS ALONG WITH BLOWING SNOW
THREAT. GIVEN THE DELAY IN PRECIP...WILL NOT START THAT SEGMENT OF
THE ADVISORY UNTIL 01Z...BUT WILL LEAVE THE TIMING ALONE FOR THE
REST OF THE HEADLINES SINCE THEY ARE ALREADY IN EFFECT. WIND
HEADLINES FOR REMAINING SD PLAINS ZONES...INCLUDING RAPID
CITY...ARE IN GOOD SHAPE.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 333 AM MST MON DEC 22 2014

DOMINANT NORTHERN STREAM EXPECTED IN THE PERIOD. EARLY WEEK LONG
WAVE TROUGH WILL SUPPORT MASSIVE RIDGING INTO GREENLAND. THIS WILL
FAVOR A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A
CP/MODIFIED ARCTIC AIRMASS INTRUSION INTO THE NORTHERN CONUS LATER
IN THE WEEK PER A WAVE TRAIN OF TROUGHS EMANATING FROM THE
NORTHERN PAC UPPER LOW. THIS COLD INTRUSION WILL ARRIVE WITH A
DECENT/STRONG SHORTWAVE EXPECTED IN THE THUR PERIOD...WITH ANOTHER
SHOT OF COLDER AIR LIKELY THIS WEEKEND PER WESTERN NOAM RIDGING
AND ANOTHER FRONT SIDE NORTHERN STREAM IMPULSE. AFTER A MILD DAY
WED...BELOW NORMAL TEMPS CAN BE EXPECTED FOR THE REMAINDER OF THE
PERIOD.

WED-THUR...STRONG WESTERN CONUS TROUGH WILL ADVECT SE ACROSS THE
ROCKIES...SUPPORTING LOCAL WAA/HEIGHT RISES. WESTERLY FLOW SHOULD
ALLOW PARTIAL MIX DOWN OF THIS WARMER AIR ACROSS MUCH OF THE
FA...SUPPORTING A MILD DAY WED WITH 40S EXPECTED AT SEVERAL
LOCATIONS. LL WARM WEDGE WILL CONTINUE TO AMPLIFY AHEAD OF THE MAIN
UPPER TROUGH. FORECAST MODELS HAVE STARTED TO TREND TO NEGATIVE TILT
TENDENCIES WITH THIS SYSTEM...WHICH IS OFFERING A SLOWER EVOLUTION
AND DELAYED ARRIVAL INTO THE FA...ALONG WITH MUCH WARMER LL THERMAL
FIELDS. THIS HAS OFFERED A SIG CHANGE TO THE LOCAL WX IMPACTS...WITH
A STRONG WARM WEDGE OFFERING THE POTENTIAL FOR RAIN OR FREEZING RAIN
IN ADDITION TO SNOW. SLOWER ARRIVAL OF COLDER AIR /MOST PRONOUNCED
IN THE GFS/ WOULD SUPPORT A NW SHIFT OF STRONGEST FGEN AND RESULTING
SNOW ACCUMS...EVIDENT WELL IN THE 06Z DGEX...WITH MUCH OF THE FA NOT
SEEING MUCH PRECIP UNTIL POSSIBLY THUR AFTERNOON OR THUR NIGHT. HAVE
TRIED TO INCORPORATED THIS IDEA INTO THE CURRENT FORECAST
PACKAGE...THE BIGGEST CHANGE WAS ADDING A MIXED PRECIP POTENTIAL.
DID ADD A CHANCE FOR ZR GIVEN WARM WEDGE. HOWEVER...IF A NW SHIFT
OCCURS WITH THIS SYSTEM...THE ZR POTENTIAL WOULD DIMINISH GIVEN A
DELAY IN LSA AND ASSOCIATED PRECIP. IF CURRENT NEGATIVE TILT
TENDENCIES MATURE IN FUTURE MODEL RUNS...THEN A NW SHIFT OF BEST
PRECIP CHANCES AS WELL AS A WARMER DAY WOULD BE IN STORE FOR THUR.

FRI-SUN...DRY WEATHER EXPECTED THROUGH MOST OF THE PERIOD...ALTHOUGH
INDICATIONS FOR ANOTHER STRONG LONG WAVE TROUGH ARE DEVELOPING IN
MODEL TRENDS. INTRODUCED LOW PRECIP CHANCES SUN. DID SIDE WITH THE
COOL SIDE OF GUIDANCE GIVEN GREENLAND BLOCKING AND EXPECTED WESTERN
NOAM RIDGING. THERE IS THE POTENTIAL FOR AN ARCTIC OUTBREAK EARLY NEXT
WEEK AS MASSIVE WESTERN NOAM RIDGING CONTINUES TO BE FAVORED IN
FORECAST MODELS. SOMETHING TO KEEP AN EYE ON.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY)
ISSUED AT 1002 AM MST MON DEC 22 2014

SN/RA SHOWERS HAVE TAPERED DOWN SINCE THIS MORNING RESULTING IN
WIDESPREAD VRF CONDITIONS ACROSS THE REGION AT THIS TIME. ANOTHER
ROUND OF SNOW WILL MOVE INTO THE AREA LATE THIS AFTERNOON AND
LOWER CIGS/VIS. EXPECT MVFR/IFR CONDITIONS MOST PLACES AWAY FROM
BLACK HILLS DOWNSLOPING... WHILE LOCALIZED VLIFR CONDITIONS IN NRN
BLACK HILLS AND NERN WYOMING ARE POSSIBLE. WINDS WILL BE STRONG
AND GUSTY THROUGH THE AFTERNOON/EVENING ACROSS THE AREA... WHICH
WILL CREATE SOME BLOWING SNOW AND VISIBILITY ISSUES. THE SNOW WILL
BEGIN TO TAPER DOWN BY SUNRISE TUESDAY MORNING AND CIGS/VIS WILL
GRADUALLY IMPROVE.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR SDZ024-025.

     WINTER WEATHER ADVISORY UNTIL NOON MST TUESDAY FOR SDZ013-014-
     028-031-032-042>044-072-073.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST
     TUESDAY FOR SDZ046-047-049.

     WIND ADVISORY UNTIL 6 PM MST THIS EVENING FOR SDZ027-030-041-074.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR SDZ001-002-
     012.

     HIGH WIND WARNING UNTIL 8 PM MST THIS EVENING FOR SDZ026.

WY...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR WYZ057.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR WYZ056-071.

&&

$$

UPDATE...POJORLIE
SHORT TERM...13
LONG TERM...JC
AVIATION...MCKEMY







000
FXUS63 KUNR 221710
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1010 AM MST MON DEC 22 2014

.UPDATE...
ISSUED AT 851 AM MST MON DEC 22 2014

SURFACE LOW IS OVER NORTHEAST SD...CREATING A TIGHT PRESSURE
GRADIENT OVER WESTERN SD AND SOME STRONG NORTHWESTERLY WINDS. MODELS
ARE STILL SHOWING A LULL IN PRECIP EARLY TODAY...WITH RAIN/SNOW MAINLY
STARTING LATE THIS AFTERNOON. DECREASED POPS LATE THIS MORNING AND
EARLY THIS AFTERNOON. ALSO LOWERED PRECIP/SNOW AMOUNTS THIS
MORNING. TOOK OUT THE BLOWING SNOW FOR EARLY THIS AFTERNOON...AS
MUCH OF THE PRECIP MAY FALL AS RAIN. REST OF FORECAST LOOKS ON
TRACK AND LEFT HEADLINES AS THEY ARE.

&&

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 333 AM MST MON DEC 22 2014

WATER VAPOR IMAGERY SHOWS AMPLIFYING TROUGH ACROSS THE CENTRAL CONUS
WITH PLENTY OF ENERGY DIVING DOWN THE BACKSIDE FROM BC CANADA TO THE
NORTHERN AND CENTRAL ROCKIES TO THE CENTRAL/SOUTHERN PLAINS. SURFACE
ANALYSIS SHOWS LOW PRESSURE ACROSS THE DAKOTAS INTO NEBRASKA. KUDX
RADAR SHOWS -RA ACROSS SOUTH CENTRAL TO SOUTHWEST SOUTH DAKOTA AND
VERY LIGHT SNOW FALLING ACROSS NORTHERN/CENTRAL PORTIONS OF THE
BLACK HILLS WITH MORE UPSTREAM SHOWERS DEVELOPING.

MODELS HAVE MADE FURTHER ADJUSTMENTS WITH THE 00Z RUN WHICH TAKES
THE TRACK OF THE DEVELOPING UPPER LOW INTO CENTRAL SD/NEB...THEN
REDEVELOPS IT FARTHER SOUTHEAST TOWARD IA. THIS DOES BRING SOME
CHANGES TO THE FORECAST. IT NOW LOOKS LIKE THERE WILL BE A LULL IN
THE PRECIP FOR MOST LOCATIONS THIS MORNING BEFORE THE UPPER LOW CAN
ACTUALLY CLOSE OFF ON A BROADER SCALE. THIS IS EXPECTED TO HAPPEN
LATER IN THE DAY/TONIGHT WITH WRAP AROUND PRECIP DEVELOPING ACROSS
THE AREA THROUGH THE AFTERNOON AND TONIGHT. THIS WILL DROP SNOW
AMOUNTS ACROSS THE CWA TODAY...BUT FOR THE MOST PART STORM TOTAL
SNOW ACCUMULATIONS ARE STILL ON TRACK AS THE END OF THE EVENT ALSO
GETS DELAYED UNTIL MORE MIDDAY TUESDAY.

WILL CONTINUE WITH PREVIOUS SHIFTS HEADLINES...WILL JUST MAKE
MENTION OF DELAYED ONSET OF SNOWFALL. WINTER STORM WARNING STILL
LOOKS GOOD FOR NORTHERN/WYOMING BLACK HILLS WITH 6 TO 12 INCH
WORDING. LOOKS LIKE UPSLOPE SNOW WILL END LATER...MORE IN THE EARLY
AFTERNOON HOURS...BUT WITH MINIMAL ADDITIONAL ACCUMULATION AFTER 19Z
WILL LEAVE TIMING OF THE HEADLINES THE SAME. WHILE WNW UPSLOPE WINDS
ARE STILL EXPECTED TODAY...MODELS ARE NOW SHOWING A SLIGHTLY MORE
NORTHERLY COMPONENT TONIGHT TO MORE OF A NW DIRECTION. THIS WOULD
FAVOR GREATER SNOW AMOUNTS OVER THE NORTHERN FOOTHILLS/SPEARFISH
AREA...SO WILL UPGRADE THAT ZONE TO A WINTER STORM WARNING WITH 5 TO
10 INCH WORDING. WINTER WEATHER ADVISORIES ACROSS THE PLAINS ARE IN
GOOD SHAPE. WILL ADD SOUTH CENTRAL SD TO THE ADVISORY AS MODELS
CONTINUE TO SHOW 3 TO 6 INCH ACCUMULATIONS ALONG WITH BLOWING SNOW
THREAT. GIVEN THE DELAY IN PRECIP...WILL NOT START THAT SEGMENT OF
THE ADVISORY UNTIL 01Z...BUT WILL LEAVE THE TIMING ALONE FOR THE
REST OF THE HEADLINES SINCE THEY ARE ALREADY IN EFFECT. WIND
HEADLINES FOR REMAINING SD PLAINS ZONES...INCLUDING RAPID
CITY...ARE IN GOOD SHAPE.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 333 AM MST MON DEC 22 2014

DOMINANT NORTHERN STREAM EXPECTED IN THE PERIOD. EARLY WEEK LONG
WAVE TROUGH WILL SUPPORT MASSIVE RIDGING INTO GREENLAND. THIS WILL
FAVOR A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A
CP/MODIFIED ARCTIC AIRMASS INTRUSION INTO THE NORTHERN CONUS LATER
IN THE WEEK PER A WAVE TRAIN OF TROUGHS EMANATING FROM THE
NORTHERN PAC UPPER LOW. THIS COLD INTRUSION WILL ARRIVE WITH A
DECENT/STRONG SHORTWAVE EXPECTED IN THE THUR PERIOD...WITH ANOTHER
SHOT OF COLDER AIR LIKELY THIS WEEKEND PER WESTERN NOAM RIDGING
AND ANOTHER FRONT SIDE NORTHERN STREAM IMPULSE. AFTER A MILD DAY
WED...BELOW NORMAL TEMPS CAN BE EXPECTED FOR THE REMAINDER OF THE
PERIOD.

WED-THUR...STRONG WESTERN CONUS TROUGH WILL ADVECT SE ACROSS THE
ROCKIES...SUPPORTING LOCAL WAA/HEIGHT RISES. WESTERLY FLOW SHOULD
ALLOW PARTIAL MIX DOWN OF THIS WARMER AIR ACROSS MUCH OF THE
FA...SUPPORTING A MILD DAY WED WITH 40S EXPECTED AT SEVERAL
LOCATIONS. LL WARM WEDGE WILL CONTINUE TO AMPLIFY AHEAD OF THE MAIN
UPPER TROUGH. FORECAST MODELS HAVE STARTED TO TREND TO NEGATIVE TILT
TENDENCIES WITH THIS SYSTEM...WHICH IS OFFERING A SLOWER EVOLUTION
AND DELAYED ARRIVAL INTO THE FA...ALONG WITH MUCH WARMER LL THERMAL
FIELDS. THIS HAS OFFERED A SIG CHANGE TO THE LOCAL WX IMPACTS...WITH
A STRONG WARM WEDGE OFFERING THE POTENTIAL FOR RAIN OR FREEZING RAIN
IN ADDITION TO SNOW. SLOWER ARRIVAL OF COLDER AIR /MOST PRONOUNCED
IN THE GFS/ WOULD SUPPORT A NW SHIFT OF STRONGEST FGEN AND RESULTING
SNOW ACCUMS...EVIDENT WELL IN THE 06Z DGEX...WITH MUCH OF THE FA NOT
SEEING MUCH PRECIP UNTIL POSSIBLY THUR AFTERNOON OR THUR NIGHT. HAVE
TRIED TO INCORPORATED THIS IDEA INTO THE CURRENT FORECAST
PACKAGE...THE BIGGEST CHANGE WAS ADDING A MIXED PRECIP POTENTIAL.
DID ADD A CHANCE FOR ZR GIVEN WARM WEDGE. HOWEVER...IF A NW SHIFT
OCCURS WITH THIS SYSTEM...THE ZR POTENTIAL WOULD DIMINISH GIVEN A
DELAY IN LSA AND ASSOCIATED PRECIP. IF CURRENT NEGATIVE TILT
TENDENCIES MATURE IN FUTURE MODEL RUNS...THEN A NW SHIFT OF BEST
PRECIP CHANCES AS WELL AS A WARMER DAY WOULD BE IN STORE FOR THUR.

FRI-SUN...DRY WEATHER EXPECTED THROUGH MOST OF THE PERIOD...ALTHOUGH
INDICATIONS FOR ANOTHER STRONG LONG WAVE TROUGH ARE DEVELOPING IN
MODEL TRENDS. INTRODUCED LOW PRECIP CHANCES SUN. DID SIDE WITH THE
COOL SIDE OF GUIDANCE GIVEN GREENLAND BLOCKING AND EXPECTED WESTERN
NOAM RIDGING. THERE IS THE POTENTIAL FOR AN ARCTIC OUTBREAK EARLY NEXT
WEEK AS MASSIVE WESTERN NOAM RIDGING CONTINUES TO BE FAVORED IN
FORECAST MODELS. SOMETHING TO KEEP AN EYE ON.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY)
ISSUED AT 1002 AM MST MON DEC 22 2014

SN/RA SHOWERS HAVE TAPERED DOWN SINCE THIS MORNING RESULTING IN
WIDESPREAD VRF CONDITIONS ACROSS THE REGION AT THIS TIME. ANOTHER
ROUND OF SNOW WILL MOVE INTO THE AREA LATE THIS AFTERNOON AND
LOWER CIGS/VIS. EXPECT MVFR/IFR CONDITIONS MOST PLACES AWAY FROM
BLACK HILLS DOWNSLOPING... WHILE LOCALIZED VLIFR CONDITIONS IN NRN
BLACK HILLS AND NERN WYOMING ARE POSSIBLE. WINDS WILL BE STRONG
AND GUSTY THROUGH THE AFTERNOON/EVENING ACROSS THE AREA... WHICH
WILL CREATE SOME BLOWING SNOW AND VISIBILITY ISSUES. THE SNOW WILL
BEGIN TO TAPER DOWN BY SUNRISE TUESDAY MORNING AND CIGS/VIS WILL
GRADUALLY IMPROVE.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR SDZ024-025.

     WINTER WEATHER ADVISORY UNTIL NOON MST TUESDAY FOR SDZ013-014-
     028-031-032-042>044-072-073.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST
     TUESDAY FOR SDZ046-047-049.

     WIND ADVISORY UNTIL 6 PM MST THIS EVENING FOR SDZ027-030-041-074.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR SDZ001-002-
     012.

     HIGH WIND WARNING UNTIL 8 PM MST THIS EVENING FOR SDZ026.

WY...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR WYZ057.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR WYZ056-071.

&&

$$

UPDATE...POJORLIE
SHORT TERM...13
LONG TERM...JC
AVIATION...MCKEMY






000
FXUS63 KUNR 221623
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
923 AM MST MON DEC 22 2014

.UPDATE...
ISSUED AT 851 AM MST MON DEC 22 2014

SURFACE LOW IS OVER NORTHEAST SD...CREATING A TIGHT PRESSURE
GRADIENT OVER WESTERN SD AND SOME STRONG NORTHWESTERLY WINDS. MODELS
ARE STILL SHOWING A LULL IN PRECIP EARLY TODAY...WITH RAIN/SNOW MAINLY
STARTING LATE THIS AFTERNOON. DECREASED POPS LATE THIS MORNING AND
EARLY THIS AFTERNOON. ALSO LOWERED PRECIP/SNOW AMOUNTS THIS
MORNING. TOOK OUT THE BLOWING SNOW FOR EARLY THIS AFTERNOON...AS
MUCH OF THE PRECIP MAY FALL AS RAIN. REST OF FORECAST LOOKS ON
TRACK AND LEFT HEADLINES AS THEY ARE.

&&

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 333 AM MST MON DEC 22 2014

WATER VAPOR IMAGERY SHOWS AMPLIFYING TROUGH ACROSS THE CENTRAL CONUS
WITH PLENTY OF ENERGY DIVING DOWN THE BACKSIDE FROM BC CANADA TO THE
NORTHERN AND CENTRAL ROCKIES TO THE CENTRAL/SOUTHERN PLAINS. SURFACE
ANALYSIS SHOWS LOW PRESSURE ACROSS THE DAKOTAS INTO NEBRASKA. KUDX
RADAR SHOWS -RA ACROSS SOUTH CENTRAL TO SOUTHWEST SOUTH DAKOTA AND
VERY LIGHT SNOW FALLING ACROSS NORTHERN/CENTRAL PORTIONS OF THE
BLACK HILLS WITH MORE UPSTREAM SHOWERS DEVELOPING.

MODELS HAVE MADE FURTHER ADJUSTMENTS WITH THE 00Z RUN WHICH TAKES
THE TRACK OF THE DEVELOPING UPPER LOW INTO CENTRAL SD/NEB...THEN
REDEVELOPS IT FARTHER SOUTHEAST TOWARD IA. THIS DOES BRING SOME
CHANGES TO THE FORECAST. IT NOW LOOKS LIKE THERE WILL BE A LULL IN
THE PRECIP FOR MOST LOCATIONS THIS MORNING BEFORE THE UPPER LOW CAN
ACTUALLY CLOSE OFF ON A BROADER SCALE. THIS IS EXPECTED TO HAPPEN
LATER IN THE DAY/TONIGHT WITH WRAP AROUND PRECIP DEVELOPING ACROSS
THE AREA THROUGH THE AFTERNOON AND TONIGHT. THIS WILL DROP SNOW
AMOUNTS ACROSS THE CWA TODAY...BUT FOR THE MOST PART STORM TOTAL
SNOW ACCUMULATIONS ARE STILL ON TRACK AS THE END OF THE EVENT ALSO
GETS DELAYED UNTIL MORE MIDDAY TUESDAY.

WILL CONTINUE WITH PREVIOUS SHIFTS HEADLINES...WILL JUST MAKE
MENTION OF DELAYED ONSET OF SNOWFALL. WINTER STORM WARNING STILL
LOOKS GOOD FOR NORTHERN/WYOMING BLACK HILLS WITH 6 TO 12 INCH
WORDING. LOOKS LIKE UPSLOPE SNOW WILL END LATER...MORE IN THE EARLY
AFTERNOON HOURS...BUT WITH MINIMAL ADDITIONAL ACCUMULATION AFTER 19Z
WILL LEAVE TIMING OF THE HEADLINES THE SAME. WHILE WNW UPSLOPE WINDS
ARE STILL EXPECTED TODAY...MODELS ARE NOW SHOWING A SLIGHTLY MORE
NORTHERLY COMPONENT TONIGHT TO MORE OF A NW DIRECTION. THIS WOULD
FAVOR GREATER SNOW AMOUNTS OVER THE NORTHERN FOOTHILLS/SPEARFISH
AREA...SO WILL UPGRADE THAT ZONE TO A WINTER STORM WARNING WITH 5 TO
10 INCH WORDING. WINTER WEATHER ADVISORIES ACROSS THE PLAINS ARE IN
GOOD SHAPE. WILL ADD SOUTH CENTRAL SD TO THE ADVISORY AS MODELS
CONTINUE TO SHOW 3 TO 6 INCH ACCUMULATIONS ALONG WITH BLOWING SNOW
THREAT. GIVEN THE DELAY IN PRECIP...WILL NOT START THAT SEGMENT OF
THE ADVISORY UNTIL 01Z...BUT WILL LEAVE THE TIMING ALONE FOR THE
REST OF THE HEADLINES SINCE THEY ARE ALREADY IN EFFECT. WIND
HEADLINES FOR REMAINING SD PLAINS ZONES...INCLUDING RAPID
CITY...ARE IN GOOD SHAPE.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 333 AM MST MON DEC 22 2014

DOMINANT NORTHERN STREAM EXPECTED IN THE PERIOD. EARLY WEEK LONG
WAVE TROUGH WILL SUPPORT MASSIVE RIDGING INTO GREENLAND. THIS WILL
FAVOR A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A
CP/MODIFIED ARCTIC AIRMASS INTRUSION INTO THE NORTHERN CONUS LATER
IN THE WEEK PER A WAVE TRAIN OF TROUGHS EMANATING FROM THE
NORTHERN PAC UPPER LOW. THIS COLD INTRUSION WILL ARRIVE WITH A
DECENT/STRONG SHORTWAVE EXPECTED IN THE THUR PERIOD...WITH ANOTHER
SHOT OF COLDER AIR LIKELY THIS WEEKEND PER WESTERN NOAM RIDGING
AND ANOTHER FRONT SIDE NORTHERN STREAM IMPULSE. AFTER A MILD DAY
WED...BELOW NORMAL TEMPS CAN BE EXPECTED FOR THE REMAINDER OF THE
PERIOD.

WED-THUR...STRONG WESTERN CONUS TROUGH WILL ADVECT SE ACROSS THE
ROCKIES...SUPPORTING LOCAL WAA/HEIGHT RISES. WESTERLY FLOW SHOULD
ALLOW PARTIAL MIX DOWN OF THIS WARMER AIR ACROSS MUCH OF THE
FA...SUPPORTING A MILD DAY WED WITH 40S EXPECTED AT SEVERAL
LOCATIONS. LL WARM WEDGE WILL CONTINUE TO AMPLIFY AHEAD OF THE MAIN
UPPER TROUGH. FORECAST MODELS HAVE STARTED TO TREND TO NEGATIVE TILT
TENDENCIES WITH THIS SYSTEM...WHICH IS OFFERING A SLOWER EVOLUTION
AND DELAYED ARRIVAL INTO THE FA...ALONG WITH MUCH WARMER LL THERMAL
FIELDS. THIS HAS OFFERED A SIG CHANGE TO THE LOCAL WX IMPACTS...WITH
A STRONG WARM WEDGE OFFERING THE POTENTIAL FOR RAIN OR FREEZING RAIN
IN ADDITION TO SNOW. SLOWER ARRIVAL OF COLDER AIR /MOST PRONOUNCED
IN THE GFS/ WOULD SUPPORT A NW SHIFT OF STRONGEST FGEN AND RESULTING
SNOW ACCUMS...EVIDENT WELL IN THE 06Z DGEX...WITH MUCH OF THE FA NOT
SEEING MUCH PRECIP UNTIL POSSIBLY THUR AFTERNOON OR THUR NIGHT. HAVE
TRIED TO INCORPORATED THIS IDEA INTO THE CURRENT FORECAST
PACKAGE...THE BIGGEST CHANGE WAS ADDING A MIXED PRECIP POTENTIAL.
DID ADD A CHANCE FOR ZR GIVEN WARM WEDGE. HOWEVER...IF A NW SHIFT
OCCURS WITH THIS SYSTEM...THE ZR POTENTIAL WOULD DIMINISH GIVEN A
DELAY IN LSA AND ASSOCIATED PRECIP. IF CURRENT NEGATIVE TILT
TENDENCIES MATURE IN FUTURE MODEL RUNS...THEN A NW SHIFT OF BEST
PRECIP CHANCES AS WELL AS A WARMER DAY WOULD BE IN STORE FOR THUR.

FRI-SUN...DRY WEATHER EXPECTED THROUGH MOST OF THE PERIOD...ALTHOUGH
INDICATIONS FOR ANOTHER STRONG LONG WAVE TROUGH ARE DEVELOPING IN
MODEL TRENDS. INTRODUCED LOW PRECIP CHANCES SUN. DID SIDE WITH THE
COOL SIDE OF GUIDANCE GIVEN GREENLAND BLOCKING AND EXPECTED WESTERN
NOAM RIDGING. THERE IS THE POTENTIAL FOR AN ARCTIC OUTBREAK EARLY NEXT
WEEK AS MASSIVE WESTERN NOAM RIDGING CONTINUES TO BE FAVORED IN
FORECAST MODELS. SOMETHING TO KEEP AN EYE ON.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 416 AM MST MON DEC 22 2014

AREAS OF MVFR CONDITIONS AND LOCALIZED IFR CONDITIONS /MAINLY IN
THE NRN BLKHLS/ EXPECTED THROUGH THE DAY TODAY. GUSTY NW WINDS TO
50KTS EXPECTED...STRONGEST ALONG THE ERN SLOPES OF THE BLKHLS. A
SECONDARY WAVE WILL BRING ANOTHER ROUND OF SNOW AND LOWER CIGS/VIS
TO THE REGION LATE THIS AFTERNOON AND TONIGHT. EXPECT MVFR TO IFR
CONDS MOST PLACES AWAY FROM BLACK HILLS DOWNSLOPING. LOCALIZED
VLIFR POSSIBLE IN HEAVIER SNOWS...ESP IN THE NORTHERN BLACK HILLS.


&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR SDZ024-025.

     WINTER WEATHER ADVISORY UNTIL NOON MST TUESDAY FOR SDZ013-014-
     028-031-032-042>044-072-073.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST
     TUESDAY FOR SDZ046-047-049.

     WIND ADVISORY UNTIL 6 PM MST THIS EVENING FOR SDZ027-030-041-074.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR SDZ001-002-
     012.

     HIGH WIND WARNING UNTIL 8 PM MST THIS EVENING FOR SDZ026.

WY...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR WYZ057.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR WYZ056-071.

&&

$$

UPDATE...POJORLIE
SHORT TERM...13
LONG TERM...JC
AVIATION...JC







000
FXUS63 KUNR 221623
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
923 AM MST MON DEC 22 2014

.UPDATE...
ISSUED AT 851 AM MST MON DEC 22 2014

SURFACE LOW IS OVER NORTHEAST SD...CREATING A TIGHT PRESSURE
GRADIENT OVER WESTERN SD AND SOME STRONG NORTHWESTERLY WINDS. MODELS
ARE STILL SHOWING A LULL IN PRECIP EARLY TODAY...WITH RAIN/SNOW MAINLY
STARTING LATE THIS AFTERNOON. DECREASED POPS LATE THIS MORNING AND
EARLY THIS AFTERNOON. ALSO LOWERED PRECIP/SNOW AMOUNTS THIS
MORNING. TOOK OUT THE BLOWING SNOW FOR EARLY THIS AFTERNOON...AS
MUCH OF THE PRECIP MAY FALL AS RAIN. REST OF FORECAST LOOKS ON
TRACK AND LEFT HEADLINES AS THEY ARE.

&&

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 333 AM MST MON DEC 22 2014

WATER VAPOR IMAGERY SHOWS AMPLIFYING TROUGH ACROSS THE CENTRAL CONUS
WITH PLENTY OF ENERGY DIVING DOWN THE BACKSIDE FROM BC CANADA TO THE
NORTHERN AND CENTRAL ROCKIES TO THE CENTRAL/SOUTHERN PLAINS. SURFACE
ANALYSIS SHOWS LOW PRESSURE ACROSS THE DAKOTAS INTO NEBRASKA. KUDX
RADAR SHOWS -RA ACROSS SOUTH CENTRAL TO SOUTHWEST SOUTH DAKOTA AND
VERY LIGHT SNOW FALLING ACROSS NORTHERN/CENTRAL PORTIONS OF THE
BLACK HILLS WITH MORE UPSTREAM SHOWERS DEVELOPING.

MODELS HAVE MADE FURTHER ADJUSTMENTS WITH THE 00Z RUN WHICH TAKES
THE TRACK OF THE DEVELOPING UPPER LOW INTO CENTRAL SD/NEB...THEN
REDEVELOPS IT FARTHER SOUTHEAST TOWARD IA. THIS DOES BRING SOME
CHANGES TO THE FORECAST. IT NOW LOOKS LIKE THERE WILL BE A LULL IN
THE PRECIP FOR MOST LOCATIONS THIS MORNING BEFORE THE UPPER LOW CAN
ACTUALLY CLOSE OFF ON A BROADER SCALE. THIS IS EXPECTED TO HAPPEN
LATER IN THE DAY/TONIGHT WITH WRAP AROUND PRECIP DEVELOPING ACROSS
THE AREA THROUGH THE AFTERNOON AND TONIGHT. THIS WILL DROP SNOW
AMOUNTS ACROSS THE CWA TODAY...BUT FOR THE MOST PART STORM TOTAL
SNOW ACCUMULATIONS ARE STILL ON TRACK AS THE END OF THE EVENT ALSO
GETS DELAYED UNTIL MORE MIDDAY TUESDAY.

WILL CONTINUE WITH PREVIOUS SHIFTS HEADLINES...WILL JUST MAKE
MENTION OF DELAYED ONSET OF SNOWFALL. WINTER STORM WARNING STILL
LOOKS GOOD FOR NORTHERN/WYOMING BLACK HILLS WITH 6 TO 12 INCH
WORDING. LOOKS LIKE UPSLOPE SNOW WILL END LATER...MORE IN THE EARLY
AFTERNOON HOURS...BUT WITH MINIMAL ADDITIONAL ACCUMULATION AFTER 19Z
WILL LEAVE TIMING OF THE HEADLINES THE SAME. WHILE WNW UPSLOPE WINDS
ARE STILL EXPECTED TODAY...MODELS ARE NOW SHOWING A SLIGHTLY MORE
NORTHERLY COMPONENT TONIGHT TO MORE OF A NW DIRECTION. THIS WOULD
FAVOR GREATER SNOW AMOUNTS OVER THE NORTHERN FOOTHILLS/SPEARFISH
AREA...SO WILL UPGRADE THAT ZONE TO A WINTER STORM WARNING WITH 5 TO
10 INCH WORDING. WINTER WEATHER ADVISORIES ACROSS THE PLAINS ARE IN
GOOD SHAPE. WILL ADD SOUTH CENTRAL SD TO THE ADVISORY AS MODELS
CONTINUE TO SHOW 3 TO 6 INCH ACCUMULATIONS ALONG WITH BLOWING SNOW
THREAT. GIVEN THE DELAY IN PRECIP...WILL NOT START THAT SEGMENT OF
THE ADVISORY UNTIL 01Z...BUT WILL LEAVE THE TIMING ALONE FOR THE
REST OF THE HEADLINES SINCE THEY ARE ALREADY IN EFFECT. WIND
HEADLINES FOR REMAINING SD PLAINS ZONES...INCLUDING RAPID
CITY...ARE IN GOOD SHAPE.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 333 AM MST MON DEC 22 2014

DOMINANT NORTHERN STREAM EXPECTED IN THE PERIOD. EARLY WEEK LONG
WAVE TROUGH WILL SUPPORT MASSIVE RIDGING INTO GREENLAND. THIS WILL
FAVOR A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A
CP/MODIFIED ARCTIC AIRMASS INTRUSION INTO THE NORTHERN CONUS LATER
IN THE WEEK PER A WAVE TRAIN OF TROUGHS EMANATING FROM THE
NORTHERN PAC UPPER LOW. THIS COLD INTRUSION WILL ARRIVE WITH A
DECENT/STRONG SHORTWAVE EXPECTED IN THE THUR PERIOD...WITH ANOTHER
SHOT OF COLDER AIR LIKELY THIS WEEKEND PER WESTERN NOAM RIDGING
AND ANOTHER FRONT SIDE NORTHERN STREAM IMPULSE. AFTER A MILD DAY
WED...BELOW NORMAL TEMPS CAN BE EXPECTED FOR THE REMAINDER OF THE
PERIOD.

WED-THUR...STRONG WESTERN CONUS TROUGH WILL ADVECT SE ACROSS THE
ROCKIES...SUPPORTING LOCAL WAA/HEIGHT RISES. WESTERLY FLOW SHOULD
ALLOW PARTIAL MIX DOWN OF THIS WARMER AIR ACROSS MUCH OF THE
FA...SUPPORTING A MILD DAY WED WITH 40S EXPECTED AT SEVERAL
LOCATIONS. LL WARM WEDGE WILL CONTINUE TO AMPLIFY AHEAD OF THE MAIN
UPPER TROUGH. FORECAST MODELS HAVE STARTED TO TREND TO NEGATIVE TILT
TENDENCIES WITH THIS SYSTEM...WHICH IS OFFERING A SLOWER EVOLUTION
AND DELAYED ARRIVAL INTO THE FA...ALONG WITH MUCH WARMER LL THERMAL
FIELDS. THIS HAS OFFERED A SIG CHANGE TO THE LOCAL WX IMPACTS...WITH
A STRONG WARM WEDGE OFFERING THE POTENTIAL FOR RAIN OR FREEZING RAIN
IN ADDITION TO SNOW. SLOWER ARRIVAL OF COLDER AIR /MOST PRONOUNCED
IN THE GFS/ WOULD SUPPORT A NW SHIFT OF STRONGEST FGEN AND RESULTING
SNOW ACCUMS...EVIDENT WELL IN THE 06Z DGEX...WITH MUCH OF THE FA NOT
SEEING MUCH PRECIP UNTIL POSSIBLY THUR AFTERNOON OR THUR NIGHT. HAVE
TRIED TO INCORPORATED THIS IDEA INTO THE CURRENT FORECAST
PACKAGE...THE BIGGEST CHANGE WAS ADDING A MIXED PRECIP POTENTIAL.
DID ADD A CHANCE FOR ZR GIVEN WARM WEDGE. HOWEVER...IF A NW SHIFT
OCCURS WITH THIS SYSTEM...THE ZR POTENTIAL WOULD DIMINISH GIVEN A
DELAY IN LSA AND ASSOCIATED PRECIP. IF CURRENT NEGATIVE TILT
TENDENCIES MATURE IN FUTURE MODEL RUNS...THEN A NW SHIFT OF BEST
PRECIP CHANCES AS WELL AS A WARMER DAY WOULD BE IN STORE FOR THUR.

FRI-SUN...DRY WEATHER EXPECTED THROUGH MOST OF THE PERIOD...ALTHOUGH
INDICATIONS FOR ANOTHER STRONG LONG WAVE TROUGH ARE DEVELOPING IN
MODEL TRENDS. INTRODUCED LOW PRECIP CHANCES SUN. DID SIDE WITH THE
COOL SIDE OF GUIDANCE GIVEN GREENLAND BLOCKING AND EXPECTED WESTERN
NOAM RIDGING. THERE IS THE POTENTIAL FOR AN ARCTIC OUTBREAK EARLY NEXT
WEEK AS MASSIVE WESTERN NOAM RIDGING CONTINUES TO BE FAVORED IN
FORECAST MODELS. SOMETHING TO KEEP AN EYE ON.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 416 AM MST MON DEC 22 2014

AREAS OF MVFR CONDITIONS AND LOCALIZED IFR CONDITIONS /MAINLY IN
THE NRN BLKHLS/ EXPECTED THROUGH THE DAY TODAY. GUSTY NW WINDS TO
50KTS EXPECTED...STRONGEST ALONG THE ERN SLOPES OF THE BLKHLS. A
SECONDARY WAVE WILL BRING ANOTHER ROUND OF SNOW AND LOWER CIGS/VIS
TO THE REGION LATE THIS AFTERNOON AND TONIGHT. EXPECT MVFR TO IFR
CONDS MOST PLACES AWAY FROM BLACK HILLS DOWNSLOPING. LOCALIZED
VLIFR POSSIBLE IN HEAVIER SNOWS...ESP IN THE NORTHERN BLACK HILLS.


&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR SDZ024-025.

     WINTER WEATHER ADVISORY UNTIL NOON MST TUESDAY FOR SDZ013-014-
     028-031-032-042>044-072-073.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST
     TUESDAY FOR SDZ046-047-049.

     WIND ADVISORY UNTIL 6 PM MST THIS EVENING FOR SDZ027-030-041-074.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR SDZ001-002-
     012.

     HIGH WIND WARNING UNTIL 8 PM MST THIS EVENING FOR SDZ026.

WY...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR WYZ057.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR WYZ056-071.

&&

$$

UPDATE...POJORLIE
SHORT TERM...13
LONG TERM...JC
AVIATION...JC







000
FXUS63 KUNR 221623
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
923 AM MST MON DEC 22 2014

.UPDATE...
ISSUED AT 851 AM MST MON DEC 22 2014

SURFACE LOW IS OVER NORTHEAST SD...CREATING A TIGHT PRESSURE
GRADIENT OVER WESTERN SD AND SOME STRONG NORTHWESTERLY WINDS. MODELS
ARE STILL SHOWING A LULL IN PRECIP EARLY TODAY...WITH RAIN/SNOW MAINLY
STARTING LATE THIS AFTERNOON. DECREASED POPS LATE THIS MORNING AND
EARLY THIS AFTERNOON. ALSO LOWERED PRECIP/SNOW AMOUNTS THIS
MORNING. TOOK OUT THE BLOWING SNOW FOR EARLY THIS AFTERNOON...AS
MUCH OF THE PRECIP MAY FALL AS RAIN. REST OF FORECAST LOOKS ON
TRACK AND LEFT HEADLINES AS THEY ARE.

&&

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 333 AM MST MON DEC 22 2014

WATER VAPOR IMAGERY SHOWS AMPLIFYING TROUGH ACROSS THE CENTRAL CONUS
WITH PLENTY OF ENERGY DIVING DOWN THE BACKSIDE FROM BC CANADA TO THE
NORTHERN AND CENTRAL ROCKIES TO THE CENTRAL/SOUTHERN PLAINS. SURFACE
ANALYSIS SHOWS LOW PRESSURE ACROSS THE DAKOTAS INTO NEBRASKA. KUDX
RADAR SHOWS -RA ACROSS SOUTH CENTRAL TO SOUTHWEST SOUTH DAKOTA AND
VERY LIGHT SNOW FALLING ACROSS NORTHERN/CENTRAL PORTIONS OF THE
BLACK HILLS WITH MORE UPSTREAM SHOWERS DEVELOPING.

MODELS HAVE MADE FURTHER ADJUSTMENTS WITH THE 00Z RUN WHICH TAKES
THE TRACK OF THE DEVELOPING UPPER LOW INTO CENTRAL SD/NEB...THEN
REDEVELOPS IT FARTHER SOUTHEAST TOWARD IA. THIS DOES BRING SOME
CHANGES TO THE FORECAST. IT NOW LOOKS LIKE THERE WILL BE A LULL IN
THE PRECIP FOR MOST LOCATIONS THIS MORNING BEFORE THE UPPER LOW CAN
ACTUALLY CLOSE OFF ON A BROADER SCALE. THIS IS EXPECTED TO HAPPEN
LATER IN THE DAY/TONIGHT WITH WRAP AROUND PRECIP DEVELOPING ACROSS
THE AREA THROUGH THE AFTERNOON AND TONIGHT. THIS WILL DROP SNOW
AMOUNTS ACROSS THE CWA TODAY...BUT FOR THE MOST PART STORM TOTAL
SNOW ACCUMULATIONS ARE STILL ON TRACK AS THE END OF THE EVENT ALSO
GETS DELAYED UNTIL MORE MIDDAY TUESDAY.

WILL CONTINUE WITH PREVIOUS SHIFTS HEADLINES...WILL JUST MAKE
MENTION OF DELAYED ONSET OF SNOWFALL. WINTER STORM WARNING STILL
LOOKS GOOD FOR NORTHERN/WYOMING BLACK HILLS WITH 6 TO 12 INCH
WORDING. LOOKS LIKE UPSLOPE SNOW WILL END LATER...MORE IN THE EARLY
AFTERNOON HOURS...BUT WITH MINIMAL ADDITIONAL ACCUMULATION AFTER 19Z
WILL LEAVE TIMING OF THE HEADLINES THE SAME. WHILE WNW UPSLOPE WINDS
ARE STILL EXPECTED TODAY...MODELS ARE NOW SHOWING A SLIGHTLY MORE
NORTHERLY COMPONENT TONIGHT TO MORE OF A NW DIRECTION. THIS WOULD
FAVOR GREATER SNOW AMOUNTS OVER THE NORTHERN FOOTHILLS/SPEARFISH
AREA...SO WILL UPGRADE THAT ZONE TO A WINTER STORM WARNING WITH 5 TO
10 INCH WORDING. WINTER WEATHER ADVISORIES ACROSS THE PLAINS ARE IN
GOOD SHAPE. WILL ADD SOUTH CENTRAL SD TO THE ADVISORY AS MODELS
CONTINUE TO SHOW 3 TO 6 INCH ACCUMULATIONS ALONG WITH BLOWING SNOW
THREAT. GIVEN THE DELAY IN PRECIP...WILL NOT START THAT SEGMENT OF
THE ADVISORY UNTIL 01Z...BUT WILL LEAVE THE TIMING ALONE FOR THE
REST OF THE HEADLINES SINCE THEY ARE ALREADY IN EFFECT. WIND
HEADLINES FOR REMAINING SD PLAINS ZONES...INCLUDING RAPID
CITY...ARE IN GOOD SHAPE.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 333 AM MST MON DEC 22 2014

DOMINANT NORTHERN STREAM EXPECTED IN THE PERIOD. EARLY WEEK LONG
WAVE TROUGH WILL SUPPORT MASSIVE RIDGING INTO GREENLAND. THIS WILL
FAVOR A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A
CP/MODIFIED ARCTIC AIRMASS INTRUSION INTO THE NORTHERN CONUS LATER
IN THE WEEK PER A WAVE TRAIN OF TROUGHS EMANATING FROM THE
NORTHERN PAC UPPER LOW. THIS COLD INTRUSION WILL ARRIVE WITH A
DECENT/STRONG SHORTWAVE EXPECTED IN THE THUR PERIOD...WITH ANOTHER
SHOT OF COLDER AIR LIKELY THIS WEEKEND PER WESTERN NOAM RIDGING
AND ANOTHER FRONT SIDE NORTHERN STREAM IMPULSE. AFTER A MILD DAY
WED...BELOW NORMAL TEMPS CAN BE EXPECTED FOR THE REMAINDER OF THE
PERIOD.

WED-THUR...STRONG WESTERN CONUS TROUGH WILL ADVECT SE ACROSS THE
ROCKIES...SUPPORTING LOCAL WAA/HEIGHT RISES. WESTERLY FLOW SHOULD
ALLOW PARTIAL MIX DOWN OF THIS WARMER AIR ACROSS MUCH OF THE
FA...SUPPORTING A MILD DAY WED WITH 40S EXPECTED AT SEVERAL
LOCATIONS. LL WARM WEDGE WILL CONTINUE TO AMPLIFY AHEAD OF THE MAIN
UPPER TROUGH. FORECAST MODELS HAVE STARTED TO TREND TO NEGATIVE TILT
TENDENCIES WITH THIS SYSTEM...WHICH IS OFFERING A SLOWER EVOLUTION
AND DELAYED ARRIVAL INTO THE FA...ALONG WITH MUCH WARMER LL THERMAL
FIELDS. THIS HAS OFFERED A SIG CHANGE TO THE LOCAL WX IMPACTS...WITH
A STRONG WARM WEDGE OFFERING THE POTENTIAL FOR RAIN OR FREEZING RAIN
IN ADDITION TO SNOW. SLOWER ARRIVAL OF COLDER AIR /MOST PRONOUNCED
IN THE GFS/ WOULD SUPPORT A NW SHIFT OF STRONGEST FGEN AND RESULTING
SNOW ACCUMS...EVIDENT WELL IN THE 06Z DGEX...WITH MUCH OF THE FA NOT
SEEING MUCH PRECIP UNTIL POSSIBLY THUR AFTERNOON OR THUR NIGHT. HAVE
TRIED TO INCORPORATED THIS IDEA INTO THE CURRENT FORECAST
PACKAGE...THE BIGGEST CHANGE WAS ADDING A MIXED PRECIP POTENTIAL.
DID ADD A CHANCE FOR ZR GIVEN WARM WEDGE. HOWEVER...IF A NW SHIFT
OCCURS WITH THIS SYSTEM...THE ZR POTENTIAL WOULD DIMINISH GIVEN A
DELAY IN LSA AND ASSOCIATED PRECIP. IF CURRENT NEGATIVE TILT
TENDENCIES MATURE IN FUTURE MODEL RUNS...THEN A NW SHIFT OF BEST
PRECIP CHANCES AS WELL AS A WARMER DAY WOULD BE IN STORE FOR THUR.

FRI-SUN...DRY WEATHER EXPECTED THROUGH MOST OF THE PERIOD...ALTHOUGH
INDICATIONS FOR ANOTHER STRONG LONG WAVE TROUGH ARE DEVELOPING IN
MODEL TRENDS. INTRODUCED LOW PRECIP CHANCES SUN. DID SIDE WITH THE
COOL SIDE OF GUIDANCE GIVEN GREENLAND BLOCKING AND EXPECTED WESTERN
NOAM RIDGING. THERE IS THE POTENTIAL FOR AN ARCTIC OUTBREAK EARLY NEXT
WEEK AS MASSIVE WESTERN NOAM RIDGING CONTINUES TO BE FAVORED IN
FORECAST MODELS. SOMETHING TO KEEP AN EYE ON.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 416 AM MST MON DEC 22 2014

AREAS OF MVFR CONDITIONS AND LOCALIZED IFR CONDITIONS /MAINLY IN
THE NRN BLKHLS/ EXPECTED THROUGH THE DAY TODAY. GUSTY NW WINDS TO
50KTS EXPECTED...STRONGEST ALONG THE ERN SLOPES OF THE BLKHLS. A
SECONDARY WAVE WILL BRING ANOTHER ROUND OF SNOW AND LOWER CIGS/VIS
TO THE REGION LATE THIS AFTERNOON AND TONIGHT. EXPECT MVFR TO IFR
CONDS MOST PLACES AWAY FROM BLACK HILLS DOWNSLOPING. LOCALIZED
VLIFR POSSIBLE IN HEAVIER SNOWS...ESP IN THE NORTHERN BLACK HILLS.


&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR SDZ024-025.

     WINTER WEATHER ADVISORY UNTIL NOON MST TUESDAY FOR SDZ013-014-
     028-031-032-042>044-072-073.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST
     TUESDAY FOR SDZ046-047-049.

     WIND ADVISORY UNTIL 6 PM MST THIS EVENING FOR SDZ027-030-041-074.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR SDZ001-002-
     012.

     HIGH WIND WARNING UNTIL 8 PM MST THIS EVENING FOR SDZ026.

WY...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR WYZ057.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR WYZ056-071.

&&

$$

UPDATE...POJORLIE
SHORT TERM...13
LONG TERM...JC
AVIATION...JC







000
FXUS63 KUNR 221623
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
923 AM MST MON DEC 22 2014

.UPDATE...
ISSUED AT 851 AM MST MON DEC 22 2014

SURFACE LOW IS OVER NORTHEAST SD...CREATING A TIGHT PRESSURE
GRADIENT OVER WESTERN SD AND SOME STRONG NORTHWESTERLY WINDS. MODELS
ARE STILL SHOWING A LULL IN PRECIP EARLY TODAY...WITH RAIN/SNOW MAINLY
STARTING LATE THIS AFTERNOON. DECREASED POPS LATE THIS MORNING AND
EARLY THIS AFTERNOON. ALSO LOWERED PRECIP/SNOW AMOUNTS THIS
MORNING. TOOK OUT THE BLOWING SNOW FOR EARLY THIS AFTERNOON...AS
MUCH OF THE PRECIP MAY FALL AS RAIN. REST OF FORECAST LOOKS ON
TRACK AND LEFT HEADLINES AS THEY ARE.

&&

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 333 AM MST MON DEC 22 2014

WATER VAPOR IMAGERY SHOWS AMPLIFYING TROUGH ACROSS THE CENTRAL CONUS
WITH PLENTY OF ENERGY DIVING DOWN THE BACKSIDE FROM BC CANADA TO THE
NORTHERN AND CENTRAL ROCKIES TO THE CENTRAL/SOUTHERN PLAINS. SURFACE
ANALYSIS SHOWS LOW PRESSURE ACROSS THE DAKOTAS INTO NEBRASKA. KUDX
RADAR SHOWS -RA ACROSS SOUTH CENTRAL TO SOUTHWEST SOUTH DAKOTA AND
VERY LIGHT SNOW FALLING ACROSS NORTHERN/CENTRAL PORTIONS OF THE
BLACK HILLS WITH MORE UPSTREAM SHOWERS DEVELOPING.

MODELS HAVE MADE FURTHER ADJUSTMENTS WITH THE 00Z RUN WHICH TAKES
THE TRACK OF THE DEVELOPING UPPER LOW INTO CENTRAL SD/NEB...THEN
REDEVELOPS IT FARTHER SOUTHEAST TOWARD IA. THIS DOES BRING SOME
CHANGES TO THE FORECAST. IT NOW LOOKS LIKE THERE WILL BE A LULL IN
THE PRECIP FOR MOST LOCATIONS THIS MORNING BEFORE THE UPPER LOW CAN
ACTUALLY CLOSE OFF ON A BROADER SCALE. THIS IS EXPECTED TO HAPPEN
LATER IN THE DAY/TONIGHT WITH WRAP AROUND PRECIP DEVELOPING ACROSS
THE AREA THROUGH THE AFTERNOON AND TONIGHT. THIS WILL DROP SNOW
AMOUNTS ACROSS THE CWA TODAY...BUT FOR THE MOST PART STORM TOTAL
SNOW ACCUMULATIONS ARE STILL ON TRACK AS THE END OF THE EVENT ALSO
GETS DELAYED UNTIL MORE MIDDAY TUESDAY.

WILL CONTINUE WITH PREVIOUS SHIFTS HEADLINES...WILL JUST MAKE
MENTION OF DELAYED ONSET OF SNOWFALL. WINTER STORM WARNING STILL
LOOKS GOOD FOR NORTHERN/WYOMING BLACK HILLS WITH 6 TO 12 INCH
WORDING. LOOKS LIKE UPSLOPE SNOW WILL END LATER...MORE IN THE EARLY
AFTERNOON HOURS...BUT WITH MINIMAL ADDITIONAL ACCUMULATION AFTER 19Z
WILL LEAVE TIMING OF THE HEADLINES THE SAME. WHILE WNW UPSLOPE WINDS
ARE STILL EXPECTED TODAY...MODELS ARE NOW SHOWING A SLIGHTLY MORE
NORTHERLY COMPONENT TONIGHT TO MORE OF A NW DIRECTION. THIS WOULD
FAVOR GREATER SNOW AMOUNTS OVER THE NORTHERN FOOTHILLS/SPEARFISH
AREA...SO WILL UPGRADE THAT ZONE TO A WINTER STORM WARNING WITH 5 TO
10 INCH WORDING. WINTER WEATHER ADVISORIES ACROSS THE PLAINS ARE IN
GOOD SHAPE. WILL ADD SOUTH CENTRAL SD TO THE ADVISORY AS MODELS
CONTINUE TO SHOW 3 TO 6 INCH ACCUMULATIONS ALONG WITH BLOWING SNOW
THREAT. GIVEN THE DELAY IN PRECIP...WILL NOT START THAT SEGMENT OF
THE ADVISORY UNTIL 01Z...BUT WILL LEAVE THE TIMING ALONE FOR THE
REST OF THE HEADLINES SINCE THEY ARE ALREADY IN EFFECT. WIND
HEADLINES FOR REMAINING SD PLAINS ZONES...INCLUDING RAPID
CITY...ARE IN GOOD SHAPE.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 333 AM MST MON DEC 22 2014

DOMINANT NORTHERN STREAM EXPECTED IN THE PERIOD. EARLY WEEK LONG
WAVE TROUGH WILL SUPPORT MASSIVE RIDGING INTO GREENLAND. THIS WILL
FAVOR A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A
CP/MODIFIED ARCTIC AIRMASS INTRUSION INTO THE NORTHERN CONUS LATER
IN THE WEEK PER A WAVE TRAIN OF TROUGHS EMANATING FROM THE
NORTHERN PAC UPPER LOW. THIS COLD INTRUSION WILL ARRIVE WITH A
DECENT/STRONG SHORTWAVE EXPECTED IN THE THUR PERIOD...WITH ANOTHER
SHOT OF COLDER AIR LIKELY THIS WEEKEND PER WESTERN NOAM RIDGING
AND ANOTHER FRONT SIDE NORTHERN STREAM IMPULSE. AFTER A MILD DAY
WED...BELOW NORMAL TEMPS CAN BE EXPECTED FOR THE REMAINDER OF THE
PERIOD.

WED-THUR...STRONG WESTERN CONUS TROUGH WILL ADVECT SE ACROSS THE
ROCKIES...SUPPORTING LOCAL WAA/HEIGHT RISES. WESTERLY FLOW SHOULD
ALLOW PARTIAL MIX DOWN OF THIS WARMER AIR ACROSS MUCH OF THE
FA...SUPPORTING A MILD DAY WED WITH 40S EXPECTED AT SEVERAL
LOCATIONS. LL WARM WEDGE WILL CONTINUE TO AMPLIFY AHEAD OF THE MAIN
UPPER TROUGH. FORECAST MODELS HAVE STARTED TO TREND TO NEGATIVE TILT
TENDENCIES WITH THIS SYSTEM...WHICH IS OFFERING A SLOWER EVOLUTION
AND DELAYED ARRIVAL INTO THE FA...ALONG WITH MUCH WARMER LL THERMAL
FIELDS. THIS HAS OFFERED A SIG CHANGE TO THE LOCAL WX IMPACTS...WITH
A STRONG WARM WEDGE OFFERING THE POTENTIAL FOR RAIN OR FREEZING RAIN
IN ADDITION TO SNOW. SLOWER ARRIVAL OF COLDER AIR /MOST PRONOUNCED
IN THE GFS/ WOULD SUPPORT A NW SHIFT OF STRONGEST FGEN AND RESULTING
SNOW ACCUMS...EVIDENT WELL IN THE 06Z DGEX...WITH MUCH OF THE FA NOT
SEEING MUCH PRECIP UNTIL POSSIBLY THUR AFTERNOON OR THUR NIGHT. HAVE
TRIED TO INCORPORATED THIS IDEA INTO THE CURRENT FORECAST
PACKAGE...THE BIGGEST CHANGE WAS ADDING A MIXED PRECIP POTENTIAL.
DID ADD A CHANCE FOR ZR GIVEN WARM WEDGE. HOWEVER...IF A NW SHIFT
OCCURS WITH THIS SYSTEM...THE ZR POTENTIAL WOULD DIMINISH GIVEN A
DELAY IN LSA AND ASSOCIATED PRECIP. IF CURRENT NEGATIVE TILT
TENDENCIES MATURE IN FUTURE MODEL RUNS...THEN A NW SHIFT OF BEST
PRECIP CHANCES AS WELL AS A WARMER DAY WOULD BE IN STORE FOR THUR.

FRI-SUN...DRY WEATHER EXPECTED THROUGH MOST OF THE PERIOD...ALTHOUGH
INDICATIONS FOR ANOTHER STRONG LONG WAVE TROUGH ARE DEVELOPING IN
MODEL TRENDS. INTRODUCED LOW PRECIP CHANCES SUN. DID SIDE WITH THE
COOL SIDE OF GUIDANCE GIVEN GREENLAND BLOCKING AND EXPECTED WESTERN
NOAM RIDGING. THERE IS THE POTENTIAL FOR AN ARCTIC OUTBREAK EARLY NEXT
WEEK AS MASSIVE WESTERN NOAM RIDGING CONTINUES TO BE FAVORED IN
FORECAST MODELS. SOMETHING TO KEEP AN EYE ON.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 416 AM MST MON DEC 22 2014

AREAS OF MVFR CONDITIONS AND LOCALIZED IFR CONDITIONS /MAINLY IN
THE NRN BLKHLS/ EXPECTED THROUGH THE DAY TODAY. GUSTY NW WINDS TO
50KTS EXPECTED...STRONGEST ALONG THE ERN SLOPES OF THE BLKHLS. A
SECONDARY WAVE WILL BRING ANOTHER ROUND OF SNOW AND LOWER CIGS/VIS
TO THE REGION LATE THIS AFTERNOON AND TONIGHT. EXPECT MVFR TO IFR
CONDS MOST PLACES AWAY FROM BLACK HILLS DOWNSLOPING. LOCALIZED
VLIFR POSSIBLE IN HEAVIER SNOWS...ESP IN THE NORTHERN BLACK HILLS.


&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR SDZ024-025.

     WINTER WEATHER ADVISORY UNTIL NOON MST TUESDAY FOR SDZ013-014-
     028-031-032-042>044-072-073.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST
     TUESDAY FOR SDZ046-047-049.

     WIND ADVISORY UNTIL 6 PM MST THIS EVENING FOR SDZ027-030-041-074.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR SDZ001-002-
     012.

     HIGH WIND WARNING UNTIL 8 PM MST THIS EVENING FOR SDZ026.

WY...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR WYZ057.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR WYZ056-071.

&&

$$

UPDATE...POJORLIE
SHORT TERM...13
LONG TERM...JC
AVIATION...JC







000
FXUS65 KCYS 221226
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
526 AM MST MON DEC 22 2014

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 525 AM MST MON DEC 22 2014

SNOW AND HIGH WINDS CONTINUE TO BE OUR MAJOR CONCERNS OVER THE NEXT
24 TO 36 HOURS. LIGHT TO MODERATE SNOW SHOWERS HAVE BEEN ONGOING FOR
MUCH OF THE NIGHT ALONG AND EAST OF THE LARAMIE RANGE. ACCUMULATIONS
HAVE NOT BEEN SIGNIFICANT...BUT IT IS CAUSING A FEW TRAVEL HAZARDS
WITH SLICK ROADS AND LOCALLY REDUCED VISIBILITY. SNOW SHOWERS SHOULD
PERSIST TODAY IN THE FAVORED LEFT EXIT REGION OF A 160-180 KT JET AT
H25. NOT SO SURPRISINGLY...THIS PATTERN IS CONTRIBUTING TO QUITE THE
DUMPING OF SNOW IN THE MOUNTAINS. RECENT ANALYSIS OF AREA SNOTEL OBS
ESTIMATES OVER 30 INCHES OVER THE PAST 24 HOURS IN THE SNOWIES USING
A 15 TO 1 RATIO. EXPECT ANOTHER FOOT OR SO WILL FALL THROUGH EARLY
TUESDAY MORNING WITH MOST MODELS PAINTING SEVERAL TENTHS OF AN INCH
OF QPF IN A VERY FAVORABLE PATTERN FOR MOIST OROGRAPHICS AND EXTREME
DIVERGENCE ALOFT. WINTER STORM WARNING FOR THE MOUNTAINS IS IN GREAT
SHAPE...SO NO CHANGES NECESSARY THERE. WINDS SHOULD BECOME NORTHWEST
ACROSS ALL AREAS IN THE POST FRONTAL AIR MASS...SO ACCUMULATING SNOW
SHOULD END OVER SOUTHWEST CARBON COUNTY WITH THE LOSS OF FAVORABLE
LOW LEVEL UPSLOPE. LATEST HIGHWAY OBSERVATIONS INDICATE LESS THAN 30
MPH WINDS AT ARLINGTON AS WELL. AS SUCH...BELIEVE WE WILL BE ABLE TO
LET THOSE WINTER STORM WARNINGS EXPIRE AT 8 AM.

IT WILL BE WINDY YET AGAIN ACROSS MUCH OF THE AREA TODAY. COLD FRONT
SWEPT ACROSS THE AREA LAST EVENING AND WAS DRAPED ACROSS CENTRAL NE
INTO NORTHWESTERN KS AT 09Z. EXCELLENT COLD ADVECTION IS OCCURRING
ALOFT WITH H7 TEMPS PLUNGING SEVERAL DEG C OVER THE PAST FEW HOURS
PER LAPS SOUNDINGS. THIS IS KEEPING THINGS WELL-MIXED AND IS ALREADY
GIVING WAY TO GUSTS AROUND 40 MPH AT CHADRON. BOTH NAM/GFS FORECAST
SOUNDINGS SHOW AROUND 45 KT AVAILABLE TO MIX THROUGH THE DAY OVER
MOST OF THE PANHANDLE...SO WILL KEEP THE ADVISORY GOING. THINK
WINDS ALOFT ARE NOT QUITE HIGH ENOUGH TO JUSTIFY A WARNING...BUT
WE COULD SEE SOME GUSTS TO 55 MPH IN THE AFTERNOON. BIGGER WIND
CONCERNS ARE FOR THIS EVENING AND OVERNIGHT. THE MODELS STILL
CLOSE OFF THE UPPER LOW OVER THE CENTRAL PLAINS AFTER 00Z WITH
FAST NORTHWESTERLY FLOW ALOFT REMAINING IN PLACE OVER THE CWA. THE
GFS SHOWS A 995 MILLIBAR SURFACE LOW OVER IOWA AT 06Z
TONIGHT...RESULTING IN A STRONG SURFACE PRESSURE GRADIENT ALONG
AND EAST OF THE LARAMIE RANGE. GFS/NAM/ECMWF ALL BRING A BROAD
SWATH OF 55 TO 65 KT FLOW AT H7-H8 DURING THE LATE EVENING AND
OVERNIGHT HOURS. DOWNWARD MOMENTUM TRANSFER IS POSSIBLE AS MODELED
SOUNDINGS SUGGEST A VERY WELL-MIXED BOUNDARY LAYER OWING TO
CONTINUOUS CAA JUST OFF THE SURFACE. BUFKIT SOUNDINGS SUGGEST 30
TO 40 KT SUSTAINED AT THE LOWEST LEVEL AT CHEYENNE AND A FEW
OTHER SITES AROUND 06-08Z...WITH UPWARDS OF 65 KT AT THE TOP OF
THE MIXED LAYER. WILL HOIST A HIGH WIND WATCH STARTING AT 03Z FOR
ALL AREAS ALONG AND EAST OF THE LARAMIE RANGE. EXPECT WINDS WILL
SLOWLY RELAX BY TUESDAY AFTERNOON.

STILL EXPECT SOME ACCUMULATING SNOW OVER PARTS OF THE PANHANDLE THIS
EVENING AND OVERNIGHT WITH A DEVELOPING DEFORMATION AXIS AND MODEST
WRAP-AROUND MOISTURE. STILL LOOKS LIKE THE BEST SUPPORT WILL BE JUST
EAST OF THE CWA THOUGH...SO AMOUNTS WILL MOST LIKELY BE SUB ADVISORY
EXCEPT AT HIGHER ELEVATIONS ALONG THE PINE RIDGE. LATER SHIFTS WILL
NEED TO WATCH HOW THIS INTERACTS WITH HIGH WINDS THOUGH...AS TRAVEL
CONDITIONS MAY GET VERY NASTY. WINTER WEATHER ADVISORIES OR POSSIBLY
WINTER STORM WARNINGS MAY NEED TO BE CONSIDERED LATER ON IF IT LOOKS
LIKE WIDESPREAD SIGNIFICANT BLOWING SNOW WILL BE AN ISSUE. DAWES AND
BOX BUTTE COUNTIES WOULD PROBABLY SEE THE WORST CONDITIONS BASED ON
THE LATEST DATA. NOT THINKING PERSISTENT SNOW WILL BEGIN UNTIL AFTER
00Z TUE...SO WILL LET THE DAY SHIFT DECIDE HOW TO HANDLE THIS.

BROAD UPPER-LEVEL RIDGING IS FORECAST TO BUILD INTO THE AREA THROUGH
THE LATTER PART OF THE SHORT TERM PERIOD. DOWNSLOPE FLOW IS POSSIBLE
EAST OF THE LARAMIE RANGE ON WEDNESDAY WITH H7 TEMPS INCREASING TO
NEAR 0 DEG C. DESPITE THAT...WENT A FEW DEGREES BELOW GUIDANCE FOR
HIGHS AS SOME OF THE ENERGY WILL GO TOWARD MELTING SNOW. OBSERVED
TEMPERATURES WILL HEAVILY DEPEND ON HOW MUCH SNOW FALLS LATE TONIGHT
AND TUESDAY.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 335 AM MST MON DEC 22 2014

FORECAST CHALLENGES WILL FOCUS ON POTENTIAL WINTER STORM SYSTEMS
IMPACTING THE CWA CHRISTMAS DAY/NIGHT AND LATE NEXT WEEKEND.

THE 00Z/06Z DETERMINISTIC MODEL GUIDANCE DEPICTS A SHORTWAVE RIDGE
QUICKLY TRANSLATING EAST FROM THE FRONT RANGE INTO THE GREAT PLAINS
WEDNESDAY NIGHT. THE NEXT PACIFIC TROUGH TRACKS EAST FROM THE
GREAT BASIN ACROSS THE ROCKIES LATE THURSDAY/EARLY FRIDAY. MODEL
DIFFERENCES BECOME APPARENT FRIDAY AS THE ECMWF AND CANADIAN GEM
HANG THE TROUGH FURTHER WEST WHILE THE GFS IS MORE PROGRESSIVE.
PRECIPITATION IS MORE WIDESPREAD WITH THE ECMWF WHILE THE GFS
LIMITS QPF OVER THE SOUTHEAST WY PLAINS AND SOUTHERN NE PANHANDLE
DUE TO THE DOWNSLOPE. MAINTAINED LIKELY POPS ALONG/WEST OF THE
LARAMIE RANGE WITH CHANCE POPS TO THE EAST. WINDS WILL BE
STRONGEST ALONG/WEST OF THE LARAMIE RANGE PRIOR TO FROPA WEDNESDAY
NIGHT/THURSDAY MORNING...THEN DECREASE DURING THE AFTERNOON. SNOW
ACCUMULATIONS WILL BE FAIRLY GENEROUS WITH THIS SYSTEM OVER THE
WEST...WITH UPWARDS OF A HALF FOOT FOR THE SNOWY/SIERRA MADRE AND
NORTH LARAMIE RANGES WITH 2 TO 4 INCHES LOWER ELEVATIONS.

AFTER THIS SYSTEM DEPARTS TO THE EAST...WEAK SHORTWAVE ENERGY AND
OROGRAPHICS WILL KEEP CHANCES FOR SNOW SHOWERS CONFINED TO THE
SOUTHERN MOUNTAINS FRIDAY/FRIDAY EVENING. SATURDAY WILL BE A
TRANSITION DAY WITH THE PASSAGE OF A SHORTWAVE RIDGE.
PRECIPITATION WILL SPREAD EAST INTO CENTRAL AND SOUTHERN WYOMING
/WEST OF A DOUGLAS TO LARAMIE LINE/ SUNDAY WITH THE ARRIVAL OF
ANOTHER PACIFIC TROUGH AND COLD FRONT.

HIGH TEMPERATURES CHRISTMAS DAY WILL RANGE FROM THE 20S AND 30S
NORTH AND WEST TO THE LOWER 40S SOUTHEAST. FRIDAY WILL BE COLDER
WITH HIGHS IN THE TEENS AND 20S. TEMPERATURES MODERATE SLIGHTLY
NEXT WEEKEND WITH 20S AND 30S.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 335 AM MST MON DEC 22 2014

ACTIVE WINTER WEATHER PATTERN WILL CONTINUE THROUGH THE FORECAST
PERIOD. OCCASIONAL MVFR CEILINGS WILL BE POSSIBLE EAST OF THE
LARAMIE RANGE THIS MORNING...OTHERWISE EXPECT VFR CEILINGS AOA
5000 FT AGL. ALONG AND WEST OF THE LARAMIE RANGE WILL BE PERIODIC
MVFR TO IFR CEILINGS/VISIBILITIES IN SNOW SHOWERS. THE MOUNTAINS
WILL BE OBSCURED. GUSTY NORTHWEST WINDS OF 35 TO 45 KT WILL BE
COMMON TODAY AND TONIGHT...WITH AREAS OF BLOWING/DRIFTING SNOW
LIMITING VISIBILITIES AT TIMES IN THE VICINITY OF THE MOUNTAINS
AND HIGH VALLEYS. THERE IS A CHANCE FOR LIGHT SNOW TONIGHT ALONG
WITH OCCASIONAL MVFR CEILINGS/VISIBILITIES.

&&

.FIRE WEATHER...
ISSUED AT 429 AM MST MON DEC 22 2014

NO CRITICAL FIRE WEATHER OVER THE NEXT FEW DAYS. MOUNTAIN SNOW WILL
CONTINUE THROUGH TUESDAY WITH 2 TO 4 FEET OF TOTAL SNOW ACCUMULATION
IN THE SNOWIES AND SIERRA MADRES. WINDY CONDITIONS ARE EXPECTED EAST
OF THE LARAMIE RANGE TODAY...WITH STRONGER WINDS POSSIBLE LATE THIS
EVENING THROUGH TUESDAY MORNING. A WIND ADVISORY AND HIGH WIND WATCH
HAVE BEEN ISSUED FOR PARTS OF THE AREA. LIGHT SNOWFALL ACCUMULATIONS
ARE EXPECTED OVER THE PLAINS TONIGHT.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     WYZ101-102-106>108-116>119.

     WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     WINTER WEATHER ADVISORY UNTIL 8 AM MST THIS MORNING FOR WYZ113-
     115.

     WINTER STORM WARNING UNTIL 8 AM MST THIS MORNING FOR WYZ110-111.

NE...WIND ADVISORY FROM 8 AM THIS MORNING TO 5 PM MST THIS AFTERNOON
     FOR NEZ002-003-019>021-054-055-095-096.

     HIGH WIND WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     NEZ019>021-054-055-095-096.

&&

$$

SHORT TERM...CLH
LONG TERM...MJ
AVIATION...MJ
FIRE WEATHER...CLH



000
FXUS63 KUNR 221120
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
420 AM MST MON DEC 22 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 333 AM MST MON DEC 22 2014

WATER VAPOR IMAGERY SHOWS AMPLIFYING TROUGH ACROSS THE CENTRAL CONUS
WITH PLENTY OF ENERGY DIVING DOWN THE BACKSIDE FROM BC CANADA TO THE
NORTHERN AND CENTRAL ROCKIES TO THE CENTRAL/SOUTHERN PLAINS. SURFACE
ANALYSIS SHOWS LOW PRESSURE ACROSS THE DAKOTAS INTO NEBRASKA. KUDX
RADAR SHOWS -RA ACROSS SOUTH CENTRAL TO SOUTHWEST SOUTH DAKOTA AND
VERY LIGHT SNOW FALLING ACROSS NORTHERN/CENTRAL PORTIONS OF THE
BLACK HILLS WITH MORE UPSTREAM SHOWERS DEVELOPING.

MODELS HAVE MADE FURTHER ADJUSTMENTS WITH THE 00Z RUN WHICH TAKES
THE TRACK OF THE DEVELOPING UPPER LOW INTO CENTRAL SD/NEB...THEN
REDEVELOPS IT FARTHER SOUTHEAST TOWARD IA. THIS DOES BRING SOME
CHANGES TO THE FORECAST. IT NOW LOOKS LIKE THERE WILL BE A LULL IN
THE PRECIP FOR MOST LOCATIONS THIS MORNING BEFORE THE UPPER LOW CAN
ACTUALLY CLOSE OFF ON A BROADER SCALE. THIS IS EXPECTED TO HAPPEN
LATER IN THE DAY/TONIGHT WITH WRAP AROUND PRECIP DEVELOPING ACROSS
THE AREA THROUGH THE AFTERNOON AND TONIGHT. THIS WILL DROP SNOW
AMOUNTS ACROSS THE CWA TODAY...BUT FOR THE MOST PART STORM TOTAL
SNOW ACCUMULATIONS ARE STILL ON TRACK AS THE END OF THE EVENT ALSO
GETS DELAYED UNTIL MORE MIDDAY TUESDAY.

WILL CONTINUE WITH PREVIOUS SHIFTS HEADLINES...WILL JUST MAKE
MENTION OF DELAYED ONSET OF SNOWFALL. WINTER STORM WARNING STILL
LOOKS GOOD FOR NORTHERN/WYOMING BLACK HILLS WITH 6 TO 12 INCH
WORDING. LOOKS LIKE UPSLOPE SNOW WILL END LATER...MORE IN THE EARLY
AFTERNOON HOURS...BUT WITH MINIMAL ADDITIONAL ACCUMULATION AFTER 19Z
WILL LEAVE TIMING OF THE HEADLINES THE SAME. WHILE WNW UPSLOPE WINDS
ARE STILL EXPECTED TODAY...MODELS ARE NOW SHOWING A SLIGHTLY MORE
NORTHERLY COMPONENT TONIGHT TO MORE OF A NW DIRECTION. THIS WOULD
FAVOR GREATER SNOW AMOUNTS OVER THE NORTHERN FOOTHILLS/SPEARFISH
AREA...SO WILL UPGRADE THAT ZONE TO A WINTER STORM WARNING WITH 5 TO
10 INCH WORDING. WINTER WEATHER ADVISORIES ACROSS THE PLAINS ARE IN
GOOD SHAPE. WILL ADD SOUTH CENTRAL SD TO THE ADVISORY AS MODELS
CONTINUE TO SHOW 3 TO 6 INCH ACCUMULATIONS ALONG WITH BLOWING SNOW
THREAT. GIVEN THE DELAY IN PRECIP...WILL NOT START THAT SEGMENT OF
THE ADVISORY UNTIL 01Z...BUT WILL LEAVE THE TIMING ALONE FOR THE
REST OF THE HEADLINES SINCE THEY ARE ALREADY IN EFFECT. WIND
HEADLINES FOR REMAINING SD PLAINS ZONES...INCLUDING RAPID
CITY...ARE IN GOOD SHAPE.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 333 AM MST MON DEC 22 2014

DOMINANT NORTHERN STREAM EXPECTED IN THE PERIOD. EARLY WEEK LONG
WAVE TROUGH WILL SUPPORT MASSIVE RIDGING INTO GREENLAND. THIS WILL
FAVOR A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A
CP/MODIFIED ARCTIC AIRMASS INTRUSION INTO THE NORTHERN CONUS LATER
IN THE WEEK PER A WAVE TRAIN OF TROUGHS EMANATING FROM THE
NORTHERN PAC UPPER LOW. THIS COLD INTRUSION WILL ARRIVE WITH A
DECENT/STRONG SHORTWAVE EXPECTED IN THE THUR PERIOD...WITH ANOTHER
SHOT OF COLDER AIR LIKELY THIS WEEKEND PER WESTERN NOAM RIDGING
AND ANOTHER FRONT SIDE NORTHERN STREAM IMPULSE. AFTER A MILD DAY
WED...BELOW NORMAL TEMPS CAN BE EXPECTED FOR THE REMAINDER OF THE
PERIOD.

WED-THUR...STRONG WESTERN CONUS TROUGH WILL ADVECT SE ACROSS THE
ROCKIES...SUPPORTING LOCAL WAA/HEIGHT RISES. WESTERLY FLOW SHOULD
ALLOW PARTIAL MIX DOWN OF THIS WARMER AIR ACROSS MUCH OF THE
FA...SUPPORTING A MILD DAY WED WITH 40S EXPECTED AT SEVERAL
LOCATIONS. LL WARM WEDGE WILL CONTINUE TO AMPLIFY AHEAD OF THE MAIN
UPPER TROUGH. FORECAST MODELS HAVE STARTED TO TREND TO NEGATIVE TILT
TENDENCIES WITH THIS SYSTEM...WHICH IS OFFERING A SLOWER EVOLUTION
AND DELAYED ARRIVAL INTO THE FA...ALONG WITH MUCH WARMER LL THERMAL
FIELDS. THIS HAS OFFERED A SIG CHANGE TO THE LOCAL WX IMPACTS...WITH
A STRONG WARM WEDGE OFFERING THE POTENTIAL FOR RAIN OR FREEZING RAIN
IN ADDITION TO SNOW. SLOWER ARRIVAL OF COLDER AIR /MOST PRONOUNCED
IN THE GFS/ WOULD SUPPORT A NW SHIFT OF STRONGEST FGEN AND RESULTING
SNOW ACCUMS...EVIDENT WELL IN THE 06Z DGEX...WITH MUCH OF THE FA NOT
SEEING MUCH PRECIP UNTIL POSSIBLY THUR AFTERNOON OR THUR NIGHT. HAVE
TRIED TO INCORPORATED THIS IDEA INTO THE CURRENT FORECAST
PACKAGE...THE BIGGEST CHANGE WAS ADDING A MIXED PRECIP POTENTIAL.
DID ADD A CHANCE FOR ZR GIVEN WARM WEDGE. HOWEVER...IF A NW SHIFT
OCCURS WITH THIS SYSTEM...THE ZR POTENTIAL WOULD DIMINISH GIVEN A
DELAY IN LSA AND ASSOCIATED PRECIP. IF CURRENT NEGATIVE TILT
TENDENCIES MATURE IN FUTURE MODEL RUNS...THEN A NW SHIFT OF BEST
PRECIP CHANCES AS WELL AS A WARMER DAY WOULD BE IN STORE FOR THUR.

FRI-SUN...DRY WEATHER EXPECTED THROUGH MOST OF THE PERIOD...ALTHOUGH
INDICATIONS FOR ANOTHER STRONG LONG WAVE TROUGH ARE DEVELOPING IN
MODEL TRENDS. INTRODUCED LOW PRECIP CHANCES SUN. DID SIDE WITH THE
COOL SIDE OF GUIDANCE GIVEN GREENLAND BLOCKING AND EXPECTED WESTERN
NOAM RIDGING. THERE IS THE POTENTIAL FOR AN ARCTIC OUTBREAK EARLY NEXT
WEEK AS MASSIVE WESTERN NOAM RIDGING CONTINUES TO BE FAVORED IN
FORECAST MODELS. SOMETHING TO KEEP AN EYE ON.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 416 AM MST MON DEC 22 2014

AREAS OF MVFR CONDITIONS AND LOCALIZED IFR CONDITIONS /MAINLY IN
THE NRN BLKHLS/ EXPECTED THROUGH THE DAY TODAY. GUSTY NW WINDS TO
50KTS EXPECTED...STRONGEST ALONG THE ERN SLOPES OF THE BLKHLS. A
SECONDARY WAVE WILL BRING ANOTHER ROUND OF SNOW AND LOWER CIGS/VIS
TO THE REGION LATE THIS AFTERNOON AND TONIGHT. EXPECT MVFR TO IFR
CONDS MOST PLACES AWAY FROM BLACK HILLS DOWNSLOPING. LOCALIZED
VLIFR POSSIBLE IN HEAVIER SNOWS...ESP IN THE NORTHERN BLACK HILLS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR SDZ024-025.

     WINTER WEATHER ADVISORY UNTIL NOON MST TUESDAY FOR SDZ013-014-
     028-031-032-042>044-072-073.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST
     TUESDAY FOR SDZ046-047-049.

     WIND ADVISORY FROM 8 AM THIS MORNING TO 6 PM MST THIS EVENING
     FOR SDZ027-030-041-074.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR SDZ001-002-
     012.

     HIGH WIND WARNING FROM 8 AM THIS MORNING TO 8 PM MST THIS
     EVENING FOR SDZ026.

WY...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR WYZ057.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR WYZ056-071.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC







000
FXUS63 KUNR 221120
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
420 AM MST MON DEC 22 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 333 AM MST MON DEC 22 2014

WATER VAPOR IMAGERY SHOWS AMPLIFYING TROUGH ACROSS THE CENTRAL CONUS
WITH PLENTY OF ENERGY DIVING DOWN THE BACKSIDE FROM BC CANADA TO THE
NORTHERN AND CENTRAL ROCKIES TO THE CENTRAL/SOUTHERN PLAINS. SURFACE
ANALYSIS SHOWS LOW PRESSURE ACROSS THE DAKOTAS INTO NEBRASKA. KUDX
RADAR SHOWS -RA ACROSS SOUTH CENTRAL TO SOUTHWEST SOUTH DAKOTA AND
VERY LIGHT SNOW FALLING ACROSS NORTHERN/CENTRAL PORTIONS OF THE
BLACK HILLS WITH MORE UPSTREAM SHOWERS DEVELOPING.

MODELS HAVE MADE FURTHER ADJUSTMENTS WITH THE 00Z RUN WHICH TAKES
THE TRACK OF THE DEVELOPING UPPER LOW INTO CENTRAL SD/NEB...THEN
REDEVELOPS IT FARTHER SOUTHEAST TOWARD IA. THIS DOES BRING SOME
CHANGES TO THE FORECAST. IT NOW LOOKS LIKE THERE WILL BE A LULL IN
THE PRECIP FOR MOST LOCATIONS THIS MORNING BEFORE THE UPPER LOW CAN
ACTUALLY CLOSE OFF ON A BROADER SCALE. THIS IS EXPECTED TO HAPPEN
LATER IN THE DAY/TONIGHT WITH WRAP AROUND PRECIP DEVELOPING ACROSS
THE AREA THROUGH THE AFTERNOON AND TONIGHT. THIS WILL DROP SNOW
AMOUNTS ACROSS THE CWA TODAY...BUT FOR THE MOST PART STORM TOTAL
SNOW ACCUMULATIONS ARE STILL ON TRACK AS THE END OF THE EVENT ALSO
GETS DELAYED UNTIL MORE MIDDAY TUESDAY.

WILL CONTINUE WITH PREVIOUS SHIFTS HEADLINES...WILL JUST MAKE
MENTION OF DELAYED ONSET OF SNOWFALL. WINTER STORM WARNING STILL
LOOKS GOOD FOR NORTHERN/WYOMING BLACK HILLS WITH 6 TO 12 INCH
WORDING. LOOKS LIKE UPSLOPE SNOW WILL END LATER...MORE IN THE EARLY
AFTERNOON HOURS...BUT WITH MINIMAL ADDITIONAL ACCUMULATION AFTER 19Z
WILL LEAVE TIMING OF THE HEADLINES THE SAME. WHILE WNW UPSLOPE WINDS
ARE STILL EXPECTED TODAY...MODELS ARE NOW SHOWING A SLIGHTLY MORE
NORTHERLY COMPONENT TONIGHT TO MORE OF A NW DIRECTION. THIS WOULD
FAVOR GREATER SNOW AMOUNTS OVER THE NORTHERN FOOTHILLS/SPEARFISH
AREA...SO WILL UPGRADE THAT ZONE TO A WINTER STORM WARNING WITH 5 TO
10 INCH WORDING. WINTER WEATHER ADVISORIES ACROSS THE PLAINS ARE IN
GOOD SHAPE. WILL ADD SOUTH CENTRAL SD TO THE ADVISORY AS MODELS
CONTINUE TO SHOW 3 TO 6 INCH ACCUMULATIONS ALONG WITH BLOWING SNOW
THREAT. GIVEN THE DELAY IN PRECIP...WILL NOT START THAT SEGMENT OF
THE ADVISORY UNTIL 01Z...BUT WILL LEAVE THE TIMING ALONE FOR THE
REST OF THE HEADLINES SINCE THEY ARE ALREADY IN EFFECT. WIND
HEADLINES FOR REMAINING SD PLAINS ZONES...INCLUDING RAPID
CITY...ARE IN GOOD SHAPE.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 333 AM MST MON DEC 22 2014

DOMINANT NORTHERN STREAM EXPECTED IN THE PERIOD. EARLY WEEK LONG
WAVE TROUGH WILL SUPPORT MASSIVE RIDGING INTO GREENLAND. THIS WILL
FAVOR A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A
CP/MODIFIED ARCTIC AIRMASS INTRUSION INTO THE NORTHERN CONUS LATER
IN THE WEEK PER A WAVE TRAIN OF TROUGHS EMANATING FROM THE
NORTHERN PAC UPPER LOW. THIS COLD INTRUSION WILL ARRIVE WITH A
DECENT/STRONG SHORTWAVE EXPECTED IN THE THUR PERIOD...WITH ANOTHER
SHOT OF COLDER AIR LIKELY THIS WEEKEND PER WESTERN NOAM RIDGING
AND ANOTHER FRONT SIDE NORTHERN STREAM IMPULSE. AFTER A MILD DAY
WED...BELOW NORMAL TEMPS CAN BE EXPECTED FOR THE REMAINDER OF THE
PERIOD.

WED-THUR...STRONG WESTERN CONUS TROUGH WILL ADVECT SE ACROSS THE
ROCKIES...SUPPORTING LOCAL WAA/HEIGHT RISES. WESTERLY FLOW SHOULD
ALLOW PARTIAL MIX DOWN OF THIS WARMER AIR ACROSS MUCH OF THE
FA...SUPPORTING A MILD DAY WED WITH 40S EXPECTED AT SEVERAL
LOCATIONS. LL WARM WEDGE WILL CONTINUE TO AMPLIFY AHEAD OF THE MAIN
UPPER TROUGH. FORECAST MODELS HAVE STARTED TO TREND TO NEGATIVE TILT
TENDENCIES WITH THIS SYSTEM...WHICH IS OFFERING A SLOWER EVOLUTION
AND DELAYED ARRIVAL INTO THE FA...ALONG WITH MUCH WARMER LL THERMAL
FIELDS. THIS HAS OFFERED A SIG CHANGE TO THE LOCAL WX IMPACTS...WITH
A STRONG WARM WEDGE OFFERING THE POTENTIAL FOR RAIN OR FREEZING RAIN
IN ADDITION TO SNOW. SLOWER ARRIVAL OF COLDER AIR /MOST PRONOUNCED
IN THE GFS/ WOULD SUPPORT A NW SHIFT OF STRONGEST FGEN AND RESULTING
SNOW ACCUMS...EVIDENT WELL IN THE 06Z DGEX...WITH MUCH OF THE FA NOT
SEEING MUCH PRECIP UNTIL POSSIBLY THUR AFTERNOON OR THUR NIGHT. HAVE
TRIED TO INCORPORATED THIS IDEA INTO THE CURRENT FORECAST
PACKAGE...THE BIGGEST CHANGE WAS ADDING A MIXED PRECIP POTENTIAL.
DID ADD A CHANCE FOR ZR GIVEN WARM WEDGE. HOWEVER...IF A NW SHIFT
OCCURS WITH THIS SYSTEM...THE ZR POTENTIAL WOULD DIMINISH GIVEN A
DELAY IN LSA AND ASSOCIATED PRECIP. IF CURRENT NEGATIVE TILT
TENDENCIES MATURE IN FUTURE MODEL RUNS...THEN A NW SHIFT OF BEST
PRECIP CHANCES AS WELL AS A WARMER DAY WOULD BE IN STORE FOR THUR.

FRI-SUN...DRY WEATHER EXPECTED THROUGH MOST OF THE PERIOD...ALTHOUGH
INDICATIONS FOR ANOTHER STRONG LONG WAVE TROUGH ARE DEVELOPING IN
MODEL TRENDS. INTRODUCED LOW PRECIP CHANCES SUN. DID SIDE WITH THE
COOL SIDE OF GUIDANCE GIVEN GREENLAND BLOCKING AND EXPECTED WESTERN
NOAM RIDGING. THERE IS THE POTENTIAL FOR AN ARCTIC OUTBREAK EARLY NEXT
WEEK AS MASSIVE WESTERN NOAM RIDGING CONTINUES TO BE FAVORED IN
FORECAST MODELS. SOMETHING TO KEEP AN EYE ON.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 416 AM MST MON DEC 22 2014

AREAS OF MVFR CONDITIONS AND LOCALIZED IFR CONDITIONS /MAINLY IN
THE NRN BLKHLS/ EXPECTED THROUGH THE DAY TODAY. GUSTY NW WINDS TO
50KTS EXPECTED...STRONGEST ALONG THE ERN SLOPES OF THE BLKHLS. A
SECONDARY WAVE WILL BRING ANOTHER ROUND OF SNOW AND LOWER CIGS/VIS
TO THE REGION LATE THIS AFTERNOON AND TONIGHT. EXPECT MVFR TO IFR
CONDS MOST PLACES AWAY FROM BLACK HILLS DOWNSLOPING. LOCALIZED
VLIFR POSSIBLE IN HEAVIER SNOWS...ESP IN THE NORTHERN BLACK HILLS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR SDZ024-025.

     WINTER WEATHER ADVISORY UNTIL NOON MST TUESDAY FOR SDZ013-014-
     028-031-032-042>044-072-073.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST
     TUESDAY FOR SDZ046-047-049.

     WIND ADVISORY FROM 8 AM THIS MORNING TO 6 PM MST THIS EVENING
     FOR SDZ027-030-041-074.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR SDZ001-002-
     012.

     HIGH WIND WARNING FROM 8 AM THIS MORNING TO 8 PM MST THIS
     EVENING FOR SDZ026.

WY...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR WYZ057.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR WYZ056-071.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC






000
FXUS63 KUNR 221038
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
338 AM MST MON DEC 22 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 333 AM MST MON DEC 22 2014

WATER VAPOR IMAGERY SHOWS AMPLIFYING TROUGH ACROSS THE CENTRAL CONUS
WITH PLENTY OF ENERGY DIVING DOWN THE BACKSIDE FROM BC CANADA TO THE
NORTHERN AND CENTRAL ROCKIES TO THE CENTRAL/SOUTHERN PLAINS. SURFACE
ANALYSIS SHOWS LOW PRESSURE ACROSS THE DAKOTAS INTO NEBRASKA. KUDX
RADAR SHOWS -RA ACROSS SOUTH CENTRAL TO SOUTHWEST SOUTH DAKOTA AND
VERY LIGHT SNOW FALLING ACROSS NORTHERN/CENTRAL PORTIONS OF THE
BLACK HILLS WITH MORE UPSTREAM SHOWERS DEVELOPING.

MODELS HAVE MADE FURTHER ADJUSTMENTS WITH THE 00Z RUN WHICH TAKES
THE TRACK OF THE DEVELOPING UPPER LOW INTO CENTRAL SD/NEB...THEN
REDEVELOPS IT FARTHER SOUTHEAST TOWARD IA. THIS DOES BRING SOME
CHANGES TO THE FORECAST. IT NOW LOOKS LIKE THERE WILL BE A LULL IN
THE PRECIP FOR MOST LOCATIONS THIS MORNING BEFORE THE UPPER LOW CAN
ACTUALLY CLOSE OFF ON A BROADER SCALE. THIS IS EXPECTED TO HAPPEN
LATER IN THE DAY/TONIGHT WITH WRAP AROUND PRECIP DEVELOPING ACROSS
THE AREA THROUGH THE AFTERNOON AND TONIGHT. THIS WILL DROP SNOW
AMOUNTS ACROSS THE CWA TODAY...BUT FOR THE MOST PART STORM TOTAL
SNOW ACCUMULATIONS ARE STILL ON TRACK AS THE END OF THE EVENT ALSO
GETS DELAYED UNTIL MORE MIDDAY TUESDAY.

WILL CONTINUE WITH PREVIOUS SHIFTS HEADLINES...WILL JUST MAKE
MENTION OF DELAYED ONSET OF SNOWFALL. WINTER STORM WARNING STILL
LOOKS GOOD FOR NORTHERN/WYOMING BLACK HILLS WITH 6 TO 12 INCH
WORDING. LOOKS LIKE UPSLOPE SNOW WILL END LATER...MORE IN THE EARLY
AFTERNOON HOURS...BUT WITH MINIMAL ADDITIONAL ACCUMULATION AFTER 19Z
WILL LEAVE TIMING OF THE HEADLINES THE SAME. WHILE WNW UPSLOPE WINDS
ARE STILL EXPECTED TODAY...MODELS ARE NOW SHOWING A SLIGHTLY MORE
NORTHERLY COMPONENT TONIGHT TO MORE OF A NW DIRECTION. THIS WOULD
FAVOR GREATER SNOW AMOUNTS OVER THE NORTHERN FOOTHILLS/SPEARFISH
AREA...SO WILL UPGRADE THAT ZONE TO A WINTER STORM WARNING WITH 5 TO
10 INCH WORDING. WINTER WEATHER ADVISORIES ACROSS THE PLAINS ARE IN
GOOD SHAPE. WILL ADD SOUTH CENTRAL SD TO THE ADVISORY AS MODELS
CONTINUE TO SHOW 3 TO 6 INCH ACCUMULATIONS ALONG WITH BLOWING SNOW
THREAT. GIVEN THE DELAY IN PRECIP...WILL NOT START THAT SEGMENT OF
THE ADVISORY UNTIL 01Z...BUT WILL LEAVE THE TIMING ALONE FOR THE
REST OF THE HEADLINES SINCE THEY ARE ALREADY IN EFFECT. WIND
HEADLINES FOR REMAINING SD PLAINS ZONES...INCLUDING RAPID
CITY...ARE IN GOOD SHAPE.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 333 AM MST MON DEC 22 2014

DOMINANT NORTHERN STREAM EXPECTED IN THE PERIOD. EARLY WEEK LONG
WAVE TROUGH WILL SUPPORT MASSIVE RIDGING INTO GREENLAND. THIS WILL
FAVOR A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A
CP/MODIFIED ARCTIC AIRMASS INTRUSION INTO THE NORTHERN CONUS LATER
IN THE WEEK PER A WAVE TRAIN OF TROUGHS EMANATING FROM THE
NORTHERN PAC UPPER LOW. THIS COLD INTRUSION WILL ARRIVE WITH A
DECENT/STRONG SHORTWAVE EXPECTED IN THE THUR PERIOD...WITH ANOTHER
SHOT OF COLDER AIR LIKELY THIS WEEKEND PER WESTERN NOAM RIDGING
AND ANOTHER FRONT SIDE NORTHERN STREAM IMPULSE. AFTER A MILD DAY
WED...BELOW NORMAL TEMPS CAN BE EXPECTED FOR THE REMAINDER OF THE
PERIOD.

WED-THUR...STRONG WESTERN CONUS TROUGH WILL ADVECT SE ACROSS THE
ROCKIES...SUPPORTING LOCAL WAA/HEIGHT RISES. WESTERLY FLOW SHOULD
ALLOW PARTIAL MIX DOWN OF THIS WARMER AIR ACROSS MUCH OF THE
FA...SUPPORTING A MILD DAY WED WITH 40S EXPECTED AT SEVERAL
LOCATIONS. LL WARM WEDGE WILL CONTINUE TO AMPLIFY AHEAD OF THE MAIN
UPPER TROUGH. FORECAST MODELS HAVE STARTED TO TREND TO NEGATIVE TILT
TENDENCIES WITH THIS SYSTEM...WHICH IS OFFERING A SLOWER EVOLUTION
AND DELAYED ARRIVAL INTO THE FA...ALONG WITH MUCH WARMER LL THERMAL
FIELDS. THIS HAS OFFERED A SIG CHANGE TO THE LOCAL WX IMPACTS...WITH
A STRONG WARM WEDGE OFFERING THE POTENTIAL FOR RAIN OR FREEZING RAIN
IN ADDITION TO SNOW. SLOWER ARRIVAL OF COLDER AIR /MOST PRONOUNCED
IN THE GFS/ WOULD SUPPORT A NW SHIFT OF STRONGEST FGEN AND RESULTING
SNOW ACCUMS...EVIDENT WELL IN THE 06Z DGEX...WITH MUCH OF THE FA NOT
SEEING MUCH PRECIP UNTIL POSSIBLY THUR AFTERNOON OR THUR NIGHT. HAVE
TRIED TO INCORPORATED THIS IDEA INTO THE CURRENT FORECAST
PACKAGE...THE BIGGEST CHANGE WAS ADDING A MIXED PRECIP POTENTIAL.
DID ADD A CHANCE FOR ZR GIVEN WARM WEDGE. HOWEVER...IF A NW SHIFT
OCCURS WITH THIS SYSTEM...THE ZR POTENTIAL WOULD DIMINISH GIVEN A
DELAY IN LSA AND ASSOCIATED PRECIP. IF CURRENT NEGATIVE TILT
TENDENCIES MATURE IN FUTURE MODEL RUNS...THEN A NW SHIFT OF BEST
PRECIP CHANCES AS WELL AS A WARMER DAY WOULD BE IN STORE FOR THUR.

FRI-SUN...DRY WEATHER EXPECTED THROUGH MOST OF THE PERIOD...ALTHOUGH
INDICATIONS FOR ANOTHER STRONG LONG WAVE TROUGH ARE DEVELOPING IN
MODEL TRENDS. INTRODUCED LOW PRECIP CHANCES SUN. DID SIDE WITH THE
COOL SIDE OF GUIDANCE GIVEN GREENLAND BLOCKING AND EXPECTED WESTERN
NOAM RIDGING. THERE IS THE POTENTIAL FOR AN ARCTIC OUTBREAK EARLY NEXT
WEEK AS MASSIVE WESTERN NOAM RIDGING CONTINUES TO BE FAVORED IN
FORECAST MODELS. SOMETHING TO KEEP AN EYE ON.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING
ISSUED AT 333 AM MST MON DEC 22 2014

AREAS OF MVFR CONDITIONS AND LOCALIZED IFR CONDITIONS /MAINLY IN
THE NRN BLKHLS/ EXPECTED THROUGH THE DAY TODAY. GUSTY NW WINDS TO
50KTS EXPECTED...STRONGEST ALONG THE ERN SLOPES OF THE BLKHLS. A
SECONDARY WAVE WILL BRING ANOTHER ROUND OF SNOW AND LOWER CIGS/VIS
TO THE REGION TONIGHT. EXPECT MVFR TO IFR CONDS MOST PLACES AWAY
FROM BLACK HILLS DOWNSLOPING.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR SDZ024-025.

     WINTER WEATHER ADVISORY UNTIL NOON MST TUESDAY FOR SDZ013-014-
     028-031-032-042>044-072-073.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST
     TUESDAY FOR SDZ046-047-049.

     WIND ADVISORY FROM 8 AM THIS MORNING TO 6 PM MST THIS EVENING
     FOR SDZ027-030-041-074.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR SDZ001-002-
     012.

     HIGH WIND WARNING FROM 8 AM THIS MORNING TO 8 PM MST THIS
     EVENING FOR SDZ026.

WY...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR WYZ057.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR WYZ056-071.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC








000
FXUS63 KUNR 221038
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
338 AM MST MON DEC 22 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 333 AM MST MON DEC 22 2014

WATER VAPOR IMAGERY SHOWS AMPLIFYING TROUGH ACROSS THE CENTRAL CONUS
WITH PLENTY OF ENERGY DIVING DOWN THE BACKSIDE FROM BC CANADA TO THE
NORTHERN AND CENTRAL ROCKIES TO THE CENTRAL/SOUTHERN PLAINS. SURFACE
ANALYSIS SHOWS LOW PRESSURE ACROSS THE DAKOTAS INTO NEBRASKA. KUDX
RADAR SHOWS -RA ACROSS SOUTH CENTRAL TO SOUTHWEST SOUTH DAKOTA AND
VERY LIGHT SNOW FALLING ACROSS NORTHERN/CENTRAL PORTIONS OF THE
BLACK HILLS WITH MORE UPSTREAM SHOWERS DEVELOPING.

MODELS HAVE MADE FURTHER ADJUSTMENTS WITH THE 00Z RUN WHICH TAKES
THE TRACK OF THE DEVELOPING UPPER LOW INTO CENTRAL SD/NEB...THEN
REDEVELOPS IT FARTHER SOUTHEAST TOWARD IA. THIS DOES BRING SOME
CHANGES TO THE FORECAST. IT NOW LOOKS LIKE THERE WILL BE A LULL IN
THE PRECIP FOR MOST LOCATIONS THIS MORNING BEFORE THE UPPER LOW CAN
ACTUALLY CLOSE OFF ON A BROADER SCALE. THIS IS EXPECTED TO HAPPEN
LATER IN THE DAY/TONIGHT WITH WRAP AROUND PRECIP DEVELOPING ACROSS
THE AREA THROUGH THE AFTERNOON AND TONIGHT. THIS WILL DROP SNOW
AMOUNTS ACROSS THE CWA TODAY...BUT FOR THE MOST PART STORM TOTAL
SNOW ACCUMULATIONS ARE STILL ON TRACK AS THE END OF THE EVENT ALSO
GETS DELAYED UNTIL MORE MIDDAY TUESDAY.

WILL CONTINUE WITH PREVIOUS SHIFTS HEADLINES...WILL JUST MAKE
MENTION OF DELAYED ONSET OF SNOWFALL. WINTER STORM WARNING STILL
LOOKS GOOD FOR NORTHERN/WYOMING BLACK HILLS WITH 6 TO 12 INCH
WORDING. LOOKS LIKE UPSLOPE SNOW WILL END LATER...MORE IN THE EARLY
AFTERNOON HOURS...BUT WITH MINIMAL ADDITIONAL ACCUMULATION AFTER 19Z
WILL LEAVE TIMING OF THE HEADLINES THE SAME. WHILE WNW UPSLOPE WINDS
ARE STILL EXPECTED TODAY...MODELS ARE NOW SHOWING A SLIGHTLY MORE
NORTHERLY COMPONENT TONIGHT TO MORE OF A NW DIRECTION. THIS WOULD
FAVOR GREATER SNOW AMOUNTS OVER THE NORTHERN FOOTHILLS/SPEARFISH
AREA...SO WILL UPGRADE THAT ZONE TO A WINTER STORM WARNING WITH 5 TO
10 INCH WORDING. WINTER WEATHER ADVISORIES ACROSS THE PLAINS ARE IN
GOOD SHAPE. WILL ADD SOUTH CENTRAL SD TO THE ADVISORY AS MODELS
CONTINUE TO SHOW 3 TO 6 INCH ACCUMULATIONS ALONG WITH BLOWING SNOW
THREAT. GIVEN THE DELAY IN PRECIP...WILL NOT START THAT SEGMENT OF
THE ADVISORY UNTIL 01Z...BUT WILL LEAVE THE TIMING ALONE FOR THE
REST OF THE HEADLINES SINCE THEY ARE ALREADY IN EFFECT. WIND
HEADLINES FOR REMAINING SD PLAINS ZONES...INCLUDING RAPID
CITY...ARE IN GOOD SHAPE.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 333 AM MST MON DEC 22 2014

DOMINANT NORTHERN STREAM EXPECTED IN THE PERIOD. EARLY WEEK LONG
WAVE TROUGH WILL SUPPORT MASSIVE RIDGING INTO GREENLAND. THIS WILL
FAVOR A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A
CP/MODIFIED ARCTIC AIRMASS INTRUSION INTO THE NORTHERN CONUS LATER
IN THE WEEK PER A WAVE TRAIN OF TROUGHS EMANATING FROM THE
NORTHERN PAC UPPER LOW. THIS COLD INTRUSION WILL ARRIVE WITH A
DECENT/STRONG SHORTWAVE EXPECTED IN THE THUR PERIOD...WITH ANOTHER
SHOT OF COLDER AIR LIKELY THIS WEEKEND PER WESTERN NOAM RIDGING
AND ANOTHER FRONT SIDE NORTHERN STREAM IMPULSE. AFTER A MILD DAY
WED...BELOW NORMAL TEMPS CAN BE EXPECTED FOR THE REMAINDER OF THE
PERIOD.

WED-THUR...STRONG WESTERN CONUS TROUGH WILL ADVECT SE ACROSS THE
ROCKIES...SUPPORTING LOCAL WAA/HEIGHT RISES. WESTERLY FLOW SHOULD
ALLOW PARTIAL MIX DOWN OF THIS WARMER AIR ACROSS MUCH OF THE
FA...SUPPORTING A MILD DAY WED WITH 40S EXPECTED AT SEVERAL
LOCATIONS. LL WARM WEDGE WILL CONTINUE TO AMPLIFY AHEAD OF THE MAIN
UPPER TROUGH. FORECAST MODELS HAVE STARTED TO TREND TO NEGATIVE TILT
TENDENCIES WITH THIS SYSTEM...WHICH IS OFFERING A SLOWER EVOLUTION
AND DELAYED ARRIVAL INTO THE FA...ALONG WITH MUCH WARMER LL THERMAL
FIELDS. THIS HAS OFFERED A SIG CHANGE TO THE LOCAL WX IMPACTS...WITH
A STRONG WARM WEDGE OFFERING THE POTENTIAL FOR RAIN OR FREEZING RAIN
IN ADDITION TO SNOW. SLOWER ARRIVAL OF COLDER AIR /MOST PRONOUNCED
IN THE GFS/ WOULD SUPPORT A NW SHIFT OF STRONGEST FGEN AND RESULTING
SNOW ACCUMS...EVIDENT WELL IN THE 06Z DGEX...WITH MUCH OF THE FA NOT
SEEING MUCH PRECIP UNTIL POSSIBLY THUR AFTERNOON OR THUR NIGHT. HAVE
TRIED TO INCORPORATED THIS IDEA INTO THE CURRENT FORECAST
PACKAGE...THE BIGGEST CHANGE WAS ADDING A MIXED PRECIP POTENTIAL.
DID ADD A CHANCE FOR ZR GIVEN WARM WEDGE. HOWEVER...IF A NW SHIFT
OCCURS WITH THIS SYSTEM...THE ZR POTENTIAL WOULD DIMINISH GIVEN A
DELAY IN LSA AND ASSOCIATED PRECIP. IF CURRENT NEGATIVE TILT
TENDENCIES MATURE IN FUTURE MODEL RUNS...THEN A NW SHIFT OF BEST
PRECIP CHANCES AS WELL AS A WARMER DAY WOULD BE IN STORE FOR THUR.

FRI-SUN...DRY WEATHER EXPECTED THROUGH MOST OF THE PERIOD...ALTHOUGH
INDICATIONS FOR ANOTHER STRONG LONG WAVE TROUGH ARE DEVELOPING IN
MODEL TRENDS. INTRODUCED LOW PRECIP CHANCES SUN. DID SIDE WITH THE
COOL SIDE OF GUIDANCE GIVEN GREENLAND BLOCKING AND EXPECTED WESTERN
NOAM RIDGING. THERE IS THE POTENTIAL FOR AN ARCTIC OUTBREAK EARLY NEXT
WEEK AS MASSIVE WESTERN NOAM RIDGING CONTINUES TO BE FAVORED IN
FORECAST MODELS. SOMETHING TO KEEP AN EYE ON.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING
ISSUED AT 333 AM MST MON DEC 22 2014

AREAS OF MVFR CONDITIONS AND LOCALIZED IFR CONDITIONS /MAINLY IN
THE NRN BLKHLS/ EXPECTED THROUGH THE DAY TODAY. GUSTY NW WINDS TO
50KTS EXPECTED...STRONGEST ALONG THE ERN SLOPES OF THE BLKHLS. A
SECONDARY WAVE WILL BRING ANOTHER ROUND OF SNOW AND LOWER CIGS/VIS
TO THE REGION TONIGHT. EXPECT MVFR TO IFR CONDS MOST PLACES AWAY
FROM BLACK HILLS DOWNSLOPING.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR SDZ024-025.

     WINTER WEATHER ADVISORY UNTIL NOON MST TUESDAY FOR SDZ013-014-
     028-031-032-042>044-072-073.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST
     TUESDAY FOR SDZ046-047-049.

     WIND ADVISORY FROM 8 AM THIS MORNING TO 6 PM MST THIS EVENING
     FOR SDZ027-030-041-074.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR SDZ001-002-
     012.

     HIGH WIND WARNING FROM 8 AM THIS MORNING TO 8 PM MST THIS
     EVENING FOR SDZ026.

WY...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR WYZ057.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR WYZ056-071.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC








000
FXUS63 KUNR 221038
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
338 AM MST MON DEC 22 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 333 AM MST MON DEC 22 2014

WATER VAPOR IMAGERY SHOWS AMPLIFYING TROUGH ACROSS THE CENTRAL CONUS
WITH PLENTY OF ENERGY DIVING DOWN THE BACKSIDE FROM BC CANADA TO THE
NORTHERN AND CENTRAL ROCKIES TO THE CENTRAL/SOUTHERN PLAINS. SURFACE
ANALYSIS SHOWS LOW PRESSURE ACROSS THE DAKOTAS INTO NEBRASKA. KUDX
RADAR SHOWS -RA ACROSS SOUTH CENTRAL TO SOUTHWEST SOUTH DAKOTA AND
VERY LIGHT SNOW FALLING ACROSS NORTHERN/CENTRAL PORTIONS OF THE
BLACK HILLS WITH MORE UPSTREAM SHOWERS DEVELOPING.

MODELS HAVE MADE FURTHER ADJUSTMENTS WITH THE 00Z RUN WHICH TAKES
THE TRACK OF THE DEVELOPING UPPER LOW INTO CENTRAL SD/NEB...THEN
REDEVELOPS IT FARTHER SOUTHEAST TOWARD IA. THIS DOES BRING SOME
CHANGES TO THE FORECAST. IT NOW LOOKS LIKE THERE WILL BE A LULL IN
THE PRECIP FOR MOST LOCATIONS THIS MORNING BEFORE THE UPPER LOW CAN
ACTUALLY CLOSE OFF ON A BROADER SCALE. THIS IS EXPECTED TO HAPPEN
LATER IN THE DAY/TONIGHT WITH WRAP AROUND PRECIP DEVELOPING ACROSS
THE AREA THROUGH THE AFTERNOON AND TONIGHT. THIS WILL DROP SNOW
AMOUNTS ACROSS THE CWA TODAY...BUT FOR THE MOST PART STORM TOTAL
SNOW ACCUMULATIONS ARE STILL ON TRACK AS THE END OF THE EVENT ALSO
GETS DELAYED UNTIL MORE MIDDAY TUESDAY.

WILL CONTINUE WITH PREVIOUS SHIFTS HEADLINES...WILL JUST MAKE
MENTION OF DELAYED ONSET OF SNOWFALL. WINTER STORM WARNING STILL
LOOKS GOOD FOR NORTHERN/WYOMING BLACK HILLS WITH 6 TO 12 INCH
WORDING. LOOKS LIKE UPSLOPE SNOW WILL END LATER...MORE IN THE EARLY
AFTERNOON HOURS...BUT WITH MINIMAL ADDITIONAL ACCUMULATION AFTER 19Z
WILL LEAVE TIMING OF THE HEADLINES THE SAME. WHILE WNW UPSLOPE WINDS
ARE STILL EXPECTED TODAY...MODELS ARE NOW SHOWING A SLIGHTLY MORE
NORTHERLY COMPONENT TONIGHT TO MORE OF A NW DIRECTION. THIS WOULD
FAVOR GREATER SNOW AMOUNTS OVER THE NORTHERN FOOTHILLS/SPEARFISH
AREA...SO WILL UPGRADE THAT ZONE TO A WINTER STORM WARNING WITH 5 TO
10 INCH WORDING. WINTER WEATHER ADVISORIES ACROSS THE PLAINS ARE IN
GOOD SHAPE. WILL ADD SOUTH CENTRAL SD TO THE ADVISORY AS MODELS
CONTINUE TO SHOW 3 TO 6 INCH ACCUMULATIONS ALONG WITH BLOWING SNOW
THREAT. GIVEN THE DELAY IN PRECIP...WILL NOT START THAT SEGMENT OF
THE ADVISORY UNTIL 01Z...BUT WILL LEAVE THE TIMING ALONE FOR THE
REST OF THE HEADLINES SINCE THEY ARE ALREADY IN EFFECT. WIND
HEADLINES FOR REMAINING SD PLAINS ZONES...INCLUDING RAPID
CITY...ARE IN GOOD SHAPE.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 333 AM MST MON DEC 22 2014

DOMINANT NORTHERN STREAM EXPECTED IN THE PERIOD. EARLY WEEK LONG
WAVE TROUGH WILL SUPPORT MASSIVE RIDGING INTO GREENLAND. THIS WILL
FAVOR A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A
CP/MODIFIED ARCTIC AIRMASS INTRUSION INTO THE NORTHERN CONUS LATER
IN THE WEEK PER A WAVE TRAIN OF TROUGHS EMANATING FROM THE
NORTHERN PAC UPPER LOW. THIS COLD INTRUSION WILL ARRIVE WITH A
DECENT/STRONG SHORTWAVE EXPECTED IN THE THUR PERIOD...WITH ANOTHER
SHOT OF COLDER AIR LIKELY THIS WEEKEND PER WESTERN NOAM RIDGING
AND ANOTHER FRONT SIDE NORTHERN STREAM IMPULSE. AFTER A MILD DAY
WED...BELOW NORMAL TEMPS CAN BE EXPECTED FOR THE REMAINDER OF THE
PERIOD.

WED-THUR...STRONG WESTERN CONUS TROUGH WILL ADVECT SE ACROSS THE
ROCKIES...SUPPORTING LOCAL WAA/HEIGHT RISES. WESTERLY FLOW SHOULD
ALLOW PARTIAL MIX DOWN OF THIS WARMER AIR ACROSS MUCH OF THE
FA...SUPPORTING A MILD DAY WED WITH 40S EXPECTED AT SEVERAL
LOCATIONS. LL WARM WEDGE WILL CONTINUE TO AMPLIFY AHEAD OF THE MAIN
UPPER TROUGH. FORECAST MODELS HAVE STARTED TO TREND TO NEGATIVE TILT
TENDENCIES WITH THIS SYSTEM...WHICH IS OFFERING A SLOWER EVOLUTION
AND DELAYED ARRIVAL INTO THE FA...ALONG WITH MUCH WARMER LL THERMAL
FIELDS. THIS HAS OFFERED A SIG CHANGE TO THE LOCAL WX IMPACTS...WITH
A STRONG WARM WEDGE OFFERING THE POTENTIAL FOR RAIN OR FREEZING RAIN
IN ADDITION TO SNOW. SLOWER ARRIVAL OF COLDER AIR /MOST PRONOUNCED
IN THE GFS/ WOULD SUPPORT A NW SHIFT OF STRONGEST FGEN AND RESULTING
SNOW ACCUMS...EVIDENT WELL IN THE 06Z DGEX...WITH MUCH OF THE FA NOT
SEEING MUCH PRECIP UNTIL POSSIBLY THUR AFTERNOON OR THUR NIGHT. HAVE
TRIED TO INCORPORATED THIS IDEA INTO THE CURRENT FORECAST
PACKAGE...THE BIGGEST CHANGE WAS ADDING A MIXED PRECIP POTENTIAL.
DID ADD A CHANCE FOR ZR GIVEN WARM WEDGE. HOWEVER...IF A NW SHIFT
OCCURS WITH THIS SYSTEM...THE ZR POTENTIAL WOULD DIMINISH GIVEN A
DELAY IN LSA AND ASSOCIATED PRECIP. IF CURRENT NEGATIVE TILT
TENDENCIES MATURE IN FUTURE MODEL RUNS...THEN A NW SHIFT OF BEST
PRECIP CHANCES AS WELL AS A WARMER DAY WOULD BE IN STORE FOR THUR.

FRI-SUN...DRY WEATHER EXPECTED THROUGH MOST OF THE PERIOD...ALTHOUGH
INDICATIONS FOR ANOTHER STRONG LONG WAVE TROUGH ARE DEVELOPING IN
MODEL TRENDS. INTRODUCED LOW PRECIP CHANCES SUN. DID SIDE WITH THE
COOL SIDE OF GUIDANCE GIVEN GREENLAND BLOCKING AND EXPECTED WESTERN
NOAM RIDGING. THERE IS THE POTENTIAL FOR AN ARCTIC OUTBREAK EARLY NEXT
WEEK AS MASSIVE WESTERN NOAM RIDGING CONTINUES TO BE FAVORED IN
FORECAST MODELS. SOMETHING TO KEEP AN EYE ON.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING
ISSUED AT 333 AM MST MON DEC 22 2014

AREAS OF MVFR CONDITIONS AND LOCALIZED IFR CONDITIONS /MAINLY IN
THE NRN BLKHLS/ EXPECTED THROUGH THE DAY TODAY. GUSTY NW WINDS TO
50KTS EXPECTED...STRONGEST ALONG THE ERN SLOPES OF THE BLKHLS. A
SECONDARY WAVE WILL BRING ANOTHER ROUND OF SNOW AND LOWER CIGS/VIS
TO THE REGION TONIGHT. EXPECT MVFR TO IFR CONDS MOST PLACES AWAY
FROM BLACK HILLS DOWNSLOPING.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR SDZ024-025.

     WINTER WEATHER ADVISORY UNTIL NOON MST TUESDAY FOR SDZ013-014-
     028-031-032-042>044-072-073.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST
     TUESDAY FOR SDZ046-047-049.

     WIND ADVISORY FROM 8 AM THIS MORNING TO 6 PM MST THIS EVENING
     FOR SDZ027-030-041-074.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR SDZ001-002-
     012.

     HIGH WIND WARNING FROM 8 AM THIS MORNING TO 8 PM MST THIS
     EVENING FOR SDZ026.

WY...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR WYZ057.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR WYZ056-071.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC








000
FXUS63 KUNR 221038
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
338 AM MST MON DEC 22 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 333 AM MST MON DEC 22 2014

WATER VAPOR IMAGERY SHOWS AMPLIFYING TROUGH ACROSS THE CENTRAL CONUS
WITH PLENTY OF ENERGY DIVING DOWN THE BACKSIDE FROM BC CANADA TO THE
NORTHERN AND CENTRAL ROCKIES TO THE CENTRAL/SOUTHERN PLAINS. SURFACE
ANALYSIS SHOWS LOW PRESSURE ACROSS THE DAKOTAS INTO NEBRASKA. KUDX
RADAR SHOWS -RA ACROSS SOUTH CENTRAL TO SOUTHWEST SOUTH DAKOTA AND
VERY LIGHT SNOW FALLING ACROSS NORTHERN/CENTRAL PORTIONS OF THE
BLACK HILLS WITH MORE UPSTREAM SHOWERS DEVELOPING.

MODELS HAVE MADE FURTHER ADJUSTMENTS WITH THE 00Z RUN WHICH TAKES
THE TRACK OF THE DEVELOPING UPPER LOW INTO CENTRAL SD/NEB...THEN
REDEVELOPS IT FARTHER SOUTHEAST TOWARD IA. THIS DOES BRING SOME
CHANGES TO THE FORECAST. IT NOW LOOKS LIKE THERE WILL BE A LULL IN
THE PRECIP FOR MOST LOCATIONS THIS MORNING BEFORE THE UPPER LOW CAN
ACTUALLY CLOSE OFF ON A BROADER SCALE. THIS IS EXPECTED TO HAPPEN
LATER IN THE DAY/TONIGHT WITH WRAP AROUND PRECIP DEVELOPING ACROSS
THE AREA THROUGH THE AFTERNOON AND TONIGHT. THIS WILL DROP SNOW
AMOUNTS ACROSS THE CWA TODAY...BUT FOR THE MOST PART STORM TOTAL
SNOW ACCUMULATIONS ARE STILL ON TRACK AS THE END OF THE EVENT ALSO
GETS DELAYED UNTIL MORE MIDDAY TUESDAY.

WILL CONTINUE WITH PREVIOUS SHIFTS HEADLINES...WILL JUST MAKE
MENTION OF DELAYED ONSET OF SNOWFALL. WINTER STORM WARNING STILL
LOOKS GOOD FOR NORTHERN/WYOMING BLACK HILLS WITH 6 TO 12 INCH
WORDING. LOOKS LIKE UPSLOPE SNOW WILL END LATER...MORE IN THE EARLY
AFTERNOON HOURS...BUT WITH MINIMAL ADDITIONAL ACCUMULATION AFTER 19Z
WILL LEAVE TIMING OF THE HEADLINES THE SAME. WHILE WNW UPSLOPE WINDS
ARE STILL EXPECTED TODAY...MODELS ARE NOW SHOWING A SLIGHTLY MORE
NORTHERLY COMPONENT TONIGHT TO MORE OF A NW DIRECTION. THIS WOULD
FAVOR GREATER SNOW AMOUNTS OVER THE NORTHERN FOOTHILLS/SPEARFISH
AREA...SO WILL UPGRADE THAT ZONE TO A WINTER STORM WARNING WITH 5 TO
10 INCH WORDING. WINTER WEATHER ADVISORIES ACROSS THE PLAINS ARE IN
GOOD SHAPE. WILL ADD SOUTH CENTRAL SD TO THE ADVISORY AS MODELS
CONTINUE TO SHOW 3 TO 6 INCH ACCUMULATIONS ALONG WITH BLOWING SNOW
THREAT. GIVEN THE DELAY IN PRECIP...WILL NOT START THAT SEGMENT OF
THE ADVISORY UNTIL 01Z...BUT WILL LEAVE THE TIMING ALONE FOR THE
REST OF THE HEADLINES SINCE THEY ARE ALREADY IN EFFECT. WIND
HEADLINES FOR REMAINING SD PLAINS ZONES...INCLUDING RAPID
CITY...ARE IN GOOD SHAPE.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 333 AM MST MON DEC 22 2014

DOMINANT NORTHERN STREAM EXPECTED IN THE PERIOD. EARLY WEEK LONG
WAVE TROUGH WILL SUPPORT MASSIVE RIDGING INTO GREENLAND. THIS WILL
FAVOR A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A
CP/MODIFIED ARCTIC AIRMASS INTRUSION INTO THE NORTHERN CONUS LATER
IN THE WEEK PER A WAVE TRAIN OF TROUGHS EMANATING FROM THE
NORTHERN PAC UPPER LOW. THIS COLD INTRUSION WILL ARRIVE WITH A
DECENT/STRONG SHORTWAVE EXPECTED IN THE THUR PERIOD...WITH ANOTHER
SHOT OF COLDER AIR LIKELY THIS WEEKEND PER WESTERN NOAM RIDGING
AND ANOTHER FRONT SIDE NORTHERN STREAM IMPULSE. AFTER A MILD DAY
WED...BELOW NORMAL TEMPS CAN BE EXPECTED FOR THE REMAINDER OF THE
PERIOD.

WED-THUR...STRONG WESTERN CONUS TROUGH WILL ADVECT SE ACROSS THE
ROCKIES...SUPPORTING LOCAL WAA/HEIGHT RISES. WESTERLY FLOW SHOULD
ALLOW PARTIAL MIX DOWN OF THIS WARMER AIR ACROSS MUCH OF THE
FA...SUPPORTING A MILD DAY WED WITH 40S EXPECTED AT SEVERAL
LOCATIONS. LL WARM WEDGE WILL CONTINUE TO AMPLIFY AHEAD OF THE MAIN
UPPER TROUGH. FORECAST MODELS HAVE STARTED TO TREND TO NEGATIVE TILT
TENDENCIES WITH THIS SYSTEM...WHICH IS OFFERING A SLOWER EVOLUTION
AND DELAYED ARRIVAL INTO THE FA...ALONG WITH MUCH WARMER LL THERMAL
FIELDS. THIS HAS OFFERED A SIG CHANGE TO THE LOCAL WX IMPACTS...WITH
A STRONG WARM WEDGE OFFERING THE POTENTIAL FOR RAIN OR FREEZING RAIN
IN ADDITION TO SNOW. SLOWER ARRIVAL OF COLDER AIR /MOST PRONOUNCED
IN THE GFS/ WOULD SUPPORT A NW SHIFT OF STRONGEST FGEN AND RESULTING
SNOW ACCUMS...EVIDENT WELL IN THE 06Z DGEX...WITH MUCH OF THE FA NOT
SEEING MUCH PRECIP UNTIL POSSIBLY THUR AFTERNOON OR THUR NIGHT. HAVE
TRIED TO INCORPORATED THIS IDEA INTO THE CURRENT FORECAST
PACKAGE...THE BIGGEST CHANGE WAS ADDING A MIXED PRECIP POTENTIAL.
DID ADD A CHANCE FOR ZR GIVEN WARM WEDGE. HOWEVER...IF A NW SHIFT
OCCURS WITH THIS SYSTEM...THE ZR POTENTIAL WOULD DIMINISH GIVEN A
DELAY IN LSA AND ASSOCIATED PRECIP. IF CURRENT NEGATIVE TILT
TENDENCIES MATURE IN FUTURE MODEL RUNS...THEN A NW SHIFT OF BEST
PRECIP CHANCES AS WELL AS A WARMER DAY WOULD BE IN STORE FOR THUR.

FRI-SUN...DRY WEATHER EXPECTED THROUGH MOST OF THE PERIOD...ALTHOUGH
INDICATIONS FOR ANOTHER STRONG LONG WAVE TROUGH ARE DEVELOPING IN
MODEL TRENDS. INTRODUCED LOW PRECIP CHANCES SUN. DID SIDE WITH THE
COOL SIDE OF GUIDANCE GIVEN GREENLAND BLOCKING AND EXPECTED WESTERN
NOAM RIDGING. THERE IS THE POTENTIAL FOR AN ARCTIC OUTBREAK EARLY NEXT
WEEK AS MASSIVE WESTERN NOAM RIDGING CONTINUES TO BE FAVORED IN
FORECAST MODELS. SOMETHING TO KEEP AN EYE ON.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING
ISSUED AT 333 AM MST MON DEC 22 2014

AREAS OF MVFR CONDITIONS AND LOCALIZED IFR CONDITIONS /MAINLY IN
THE NRN BLKHLS/ EXPECTED THROUGH THE DAY TODAY. GUSTY NW WINDS TO
50KTS EXPECTED...STRONGEST ALONG THE ERN SLOPES OF THE BLKHLS. A
SECONDARY WAVE WILL BRING ANOTHER ROUND OF SNOW AND LOWER CIGS/VIS
TO THE REGION TONIGHT. EXPECT MVFR TO IFR CONDS MOST PLACES AWAY
FROM BLACK HILLS DOWNSLOPING.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR SDZ024-025.

     WINTER WEATHER ADVISORY UNTIL NOON MST TUESDAY FOR SDZ013-014-
     028-031-032-042>044-072-073.

     WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST
     TUESDAY FOR SDZ046-047-049.

     WIND ADVISORY FROM 8 AM THIS MORNING TO 6 PM MST THIS EVENING
     FOR SDZ027-030-041-074.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR SDZ001-002-
     012.

     HIGH WIND WARNING FROM 8 AM THIS MORNING TO 8 PM MST THIS
     EVENING FOR SDZ026.

WY...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR WYZ057.

     WINTER WEATHER ADVISORY UNTIL 5 AM MST TUESDAY FOR WYZ056-071.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC








000
FXUS65 KRIW 221003
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
303 AM MST MON DEC 22 2014

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

CONDITIONS CONTINUE TO GENERALLY IMPROVE ACROSS THE AREA AS ALL
HIGHLIGHTS HAVE BEEN REMOVED. PERIODS OF LIGHT SNOWFALL WILL REMAIN
POSSIBLE THROUGH THE DAY ACROSS MUCH OF THE FORECAST AREA...THOUGH
SNOWFALL WILL MOST SIGNIFICANTLY IMPACT THE EASTERN THIRD OF THE
FORECAST AREA BY THIS AFTERNOON. TEMPERATURES ARE EXPECTED TO BE
COOLER TODAY IN RESPONSE TO THIS SYSTEM.

BUILDING HIGH PRESSURE OVER THE AREA WILL HELP TO END SNOWFALL
ACROSS THE WESTERN MOUNTAINS AND VALLEYS OVERNIGHT. SNOWFALL WILL
ALSO WANE ACROSS EASTERN WYOMING AS THE INFLUENCING SYSTEM MOVES
FURTHER INTO THE CENTRAL PLAINS.

HIGH PRESSURE ACROSS THE AREA WILL GENERALLY BE SHORT LIVED...THOUGH
GENERALLY DRY CONDITIONS WILL BE AROUND LATE TUESDAY THROUGH EARLY
WEDNESDAY. SLIGHTLY WARMER TEMPERATURES WILL BE REALIZED ON
WEDNESDAY AHEAD OF THE NEXT APPROACHING SYSTEM. MODELS TRY TO SHOW
SOME WEAK DISTURBANCES WITHIN THE RIDGE THAT WOULD CREATE SOME
SNOWFALL OVER THE NORTHWESTERN MOUNTAINS BY WEDNESDAY AFTERNOON.
COVERAGE DOES NOT APPEAR TO BECOME SIGNIFICANT UNTIL THE LATE
EVENING HOURS AS A TROUGH APPROACHES THE INTERMOUNTAIN WEST.

THIS TROUGH WILL WORK TO SPREAD SNOWFALL ACROSS THE WESTERN THIRD OF
THE FORECAST AREA THROUGH WEDNESDAY NIGHT.

.LONG TERM...CHRISTMAS DAY THURSDAY THROUGH MONDAY

THE MODELS CONTINUE TO ORDER UP A WHITE CHRISTMAS WITH SOME LIGHT
SNOW ACROSS MOST OF THE AREA DURING THE DAY INTO CHRISTMAS NIGHT.
ACCUMULATIONS AT THE LOWER ELEVATIONS 1 TO 3 INCHES AND 2 TO 5
NEW INCHES FOR THE MOUNTAINS. THE GFS AND ECMWF MODELS ARE STILL
TRENDING SLOWER WITH THE ONSET OF SNOW EAST OF THE DIVIDE...NOW
ACTUALLY LOOKING AT CHRISTMAS MORNING TO AS LATE AS MIDDAY. THE MAIN
CHANCE OF SNOW FOR SOME PLACES MAY OCCUR CHRISTMAS EVENING/NIGHT.
LINGERING LIGHT SNOW ON FRIDAY MORNING THEN MOSTLY DRY FRIDAY
AFTERNOON AND NIGHT EAST OF THE DIVIDE. MOUNTAINS COULD SEE LT SNOW
UNTIL LATE FRI PM OVER THE PEAKS AND PASSES. SATURDAY THROUGH
SATURDAY NIGHT LOOKS DRY EAST OF THE DIVIDE. IN THE WEST...SOME
MOISTURE MOVES BACK SATURDAY AFTERNOON AND NIGHT FOR AN INCREASING
CHANCE OF SNOW. THE NEXT WEATHER SYSTEM IS POISED TO MOVE INTO THE
ROCKY MOUNTAIN REGION SUNDAY THROUGH MONDAY. THIS SYSTEM TAPS SOME
ARCTIC AIR AND SENDS IT INTO WY SUNDAY NIGHT THROUGH MONDAY. LIGHT
FLUFFY SNOW WOULD ALSO OCCUR SUNDAY INTO MONDAY. PLENTY OF TIME TO
WATCH HOW MUCH COLD AIR GETS PULLED SOUTH AND ADJUST FORECAST WITH
TIME. BOTTOM LINE...AN UNSETTLED WEATHER PATTERN FROM CHRISTMAS DAY
INTO THE WEEKEND...IMPACTING TRAVEL FROM TIME TO TIME. HIGH TEMPS
WILL BE AT OR BELOW SEASONAL NORMALS THROUGH THE PERIOD.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

AREAS OF GUSTY NORTHWEST WIND WILL REMAIN...ESPECIALLY VCNTY
KDUB-KRIW AND KBYG...THROUGH THE PERIOD.  -SHSN ACTIVITY WILL REMAIN
MOSTLY ISOLD-WDLY SCT WITH MOST OF THIS ACTIVITY VCNTY AND EAST OF A
KCOD-KWRL-KCPR LINE THROUGH MONDAY MORNING WITH MORE NMRS SHSN
OBSCURING THE SURROUNDING MTNS.  MOISTURE AND INSTABILITY WILL
INCREASE MONDAY AFTERNOON WITH SHSN BECOMING MORE SCT ACROSS THE
CENTRAL BASINS.  SOME WRAPAROUND MOISTURE IS EXPECTED TO PUSH BACK
FROM AN UPPER LOW OVER THE PLAINS INTO EASTERN WYOMING MONDAY
NIGHT...AND THIS MAY BRING MORE WIDESPREAD MVFR/IFR -SN AS FAR WEST
AS THE BIGHORN RANGE TO VCNTY KCPR.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A MOIST AND UNSTABLE NW FLOW WILL REMAIN OVER THE AREA THROUGH
MONDAY AFTERNOON.  AN UPPER LEVEL DISTURBANCE IN THIS FLOW IS
EXPECTED TO DIVE SOUTH ALONG THE DIVIDE LATE MONDAY MORNING AND
MONDAY AFTERNOON...EXITING SOUTH OF INTERSTATE 80 MONDAY EVENING.
SNOW SHOWER ACTIVITY WILL INCREASE AHEAD OF THIS SYSTEM FROM NW-SE
MONDAY MORNING WITH IMPROVING CONDITIONS AND GUSTY NW WINDS
FOLLOWING THE DISTURBANCE MONDAY AFTERNOON AND MONDAY EVENING.
CLEARING CONDITIONS AND DIMINISHING WIND WILL FOLLOW OVERNIGHT
MONDAY.

&&

.FIRE WEATHER...

GUSTY WIND WILL REMAIN ACROSS MUCH OF THE FORECAST AREA TODAY...WITH
WIND WEAKENING DURING THE EVENING AND OVERNIGHT HOURS. TEMPERATURES
WILL COOL ACROSS THE AREA TODAY...AND CONTINUE TO COOL TUESDAY
BEFORE EXPERIENCING A SLIGHT WARMING ON WEDNESDAY. SNOWFALL WILL
LINGER ACROSS THE AREA TODAY...WITH MUCH OF ITS IMPACT EXPECTED TO
BE FELT ACROSS THE EASTERN THIRD OF THE FORECAST AREA. HIGH PRESSURE
WILL MOVE IN THIS EVENING AND OVERNIGHT TO HELP END MOST SHOWER
ACTIVITY. THE NEXT APPROACHING TROUGH WILL MOVE INTO NORTHWESTERN
WYOMING WEDNESDAY AFTERNOON AND EVENING...AND WILL SPREAD THROUGH
THE OVERNIGHT HOURS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...BRANHAM









000
FXUS65 KRIW 221003
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
303 AM MST MON DEC 22 2014

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

CONDITIONS CONTINUE TO GENERALLY IMPROVE ACROSS THE AREA AS ALL
HIGHLIGHTS HAVE BEEN REMOVED. PERIODS OF LIGHT SNOWFALL WILL REMAIN
POSSIBLE THROUGH THE DAY ACROSS MUCH OF THE FORECAST AREA...THOUGH
SNOWFALL WILL MOST SIGNIFICANTLY IMPACT THE EASTERN THIRD OF THE
FORECAST AREA BY THIS AFTERNOON. TEMPERATURES ARE EXPECTED TO BE
COOLER TODAY IN RESPONSE TO THIS SYSTEM.

BUILDING HIGH PRESSURE OVER THE AREA WILL HELP TO END SNOWFALL
ACROSS THE WESTERN MOUNTAINS AND VALLEYS OVERNIGHT. SNOWFALL WILL
ALSO WANE ACROSS EASTERN WYOMING AS THE INFLUENCING SYSTEM MOVES
FURTHER INTO THE CENTRAL PLAINS.

HIGH PRESSURE ACROSS THE AREA WILL GENERALLY BE SHORT LIVED...THOUGH
GENERALLY DRY CONDITIONS WILL BE AROUND LATE TUESDAY THROUGH EARLY
WEDNESDAY. SLIGHTLY WARMER TEMPERATURES WILL BE REALIZED ON
WEDNESDAY AHEAD OF THE NEXT APPROACHING SYSTEM. MODELS TRY TO SHOW
SOME WEAK DISTURBANCES WITHIN THE RIDGE THAT WOULD CREATE SOME
SNOWFALL OVER THE NORTHWESTERN MOUNTAINS BY WEDNESDAY AFTERNOON.
COVERAGE DOES NOT APPEAR TO BECOME SIGNIFICANT UNTIL THE LATE
EVENING HOURS AS A TROUGH APPROACHES THE INTERMOUNTAIN WEST.

THIS TROUGH WILL WORK TO SPREAD SNOWFALL ACROSS THE WESTERN THIRD OF
THE FORECAST AREA THROUGH WEDNESDAY NIGHT.

.LONG TERM...CHRISTMAS DAY THURSDAY THROUGH MONDAY

THE MODELS CONTINUE TO ORDER UP A WHITE CHRISTMAS WITH SOME LIGHT
SNOW ACROSS MOST OF THE AREA DURING THE DAY INTO CHRISTMAS NIGHT.
ACCUMULATIONS AT THE LOWER ELEVATIONS 1 TO 3 INCHES AND 2 TO 5
NEW INCHES FOR THE MOUNTAINS. THE GFS AND ECMWF MODELS ARE STILL
TRENDING SLOWER WITH THE ONSET OF SNOW EAST OF THE DIVIDE...NOW
ACTUALLY LOOKING AT CHRISTMAS MORNING TO AS LATE AS MIDDAY. THE MAIN
CHANCE OF SNOW FOR SOME PLACES MAY OCCUR CHRISTMAS EVENING/NIGHT.
LINGERING LIGHT SNOW ON FRIDAY MORNING THEN MOSTLY DRY FRIDAY
AFTERNOON AND NIGHT EAST OF THE DIVIDE. MOUNTAINS COULD SEE LT SNOW
UNTIL LATE FRI PM OVER THE PEAKS AND PASSES. SATURDAY THROUGH
SATURDAY NIGHT LOOKS DRY EAST OF THE DIVIDE. IN THE WEST...SOME
MOISTURE MOVES BACK SATURDAY AFTERNOON AND NIGHT FOR AN INCREASING
CHANCE OF SNOW. THE NEXT WEATHER SYSTEM IS POISED TO MOVE INTO THE
ROCKY MOUNTAIN REGION SUNDAY THROUGH MONDAY. THIS SYSTEM TAPS SOME
ARCTIC AIR AND SENDS IT INTO WY SUNDAY NIGHT THROUGH MONDAY. LIGHT
FLUFFY SNOW WOULD ALSO OCCUR SUNDAY INTO MONDAY. PLENTY OF TIME TO
WATCH HOW MUCH COLD AIR GETS PULLED SOUTH AND ADJUST FORECAST WITH
TIME. BOTTOM LINE...AN UNSETTLED WEATHER PATTERN FROM CHRISTMAS DAY
INTO THE WEEKEND...IMPACTING TRAVEL FROM TIME TO TIME. HIGH TEMPS
WILL BE AT OR BELOW SEASONAL NORMALS THROUGH THE PERIOD.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

AREAS OF GUSTY NORTHWEST WIND WILL REMAIN...ESPECIALLY VCNTY
KDUB-KRIW AND KBYG...THROUGH THE PERIOD.  -SHSN ACTIVITY WILL REMAIN
MOSTLY ISOLD-WDLY SCT WITH MOST OF THIS ACTIVITY VCNTY AND EAST OF A
KCOD-KWRL-KCPR LINE THROUGH MONDAY MORNING WITH MORE NMRS SHSN
OBSCURING THE SURROUNDING MTNS.  MOISTURE AND INSTABILITY WILL
INCREASE MONDAY AFTERNOON WITH SHSN BECOMING MORE SCT ACROSS THE
CENTRAL BASINS.  SOME WRAPAROUND MOISTURE IS EXPECTED TO PUSH BACK
FROM AN UPPER LOW OVER THE PLAINS INTO EASTERN WYOMING MONDAY
NIGHT...AND THIS MAY BRING MORE WIDESPREAD MVFR/IFR -SN AS FAR WEST
AS THE BIGHORN RANGE TO VCNTY KCPR.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A MOIST AND UNSTABLE NW FLOW WILL REMAIN OVER THE AREA THROUGH
MONDAY AFTERNOON.  AN UPPER LEVEL DISTURBANCE IN THIS FLOW IS
EXPECTED TO DIVE SOUTH ALONG THE DIVIDE LATE MONDAY MORNING AND
MONDAY AFTERNOON...EXITING SOUTH OF INTERSTATE 80 MONDAY EVENING.
SNOW SHOWER ACTIVITY WILL INCREASE AHEAD OF THIS SYSTEM FROM NW-SE
MONDAY MORNING WITH IMPROVING CONDITIONS AND GUSTY NW WINDS
FOLLOWING THE DISTURBANCE MONDAY AFTERNOON AND MONDAY EVENING.
CLEARING CONDITIONS AND DIMINISHING WIND WILL FOLLOW OVERNIGHT
MONDAY.

&&

.FIRE WEATHER...

GUSTY WIND WILL REMAIN ACROSS MUCH OF THE FORECAST AREA TODAY...WITH
WIND WEAKENING DURING THE EVENING AND OVERNIGHT HOURS. TEMPERATURES
WILL COOL ACROSS THE AREA TODAY...AND CONTINUE TO COOL TUESDAY
BEFORE EXPERIENCING A SLIGHT WARMING ON WEDNESDAY. SNOWFALL WILL
LINGER ACROSS THE AREA TODAY...WITH MUCH OF ITS IMPACT EXPECTED TO
BE FELT ACROSS THE EASTERN THIRD OF THE FORECAST AREA. HIGH PRESSURE
WILL MOVE IN THIS EVENING AND OVERNIGHT TO HELP END MOST SHOWER
ACTIVITY. THE NEXT APPROACHING TROUGH WILL MOVE INTO NORTHWESTERN
WYOMING WEDNESDAY AFTERNOON AND EVENING...AND WILL SPREAD THROUGH
THE OVERNIGHT HOURS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...BRANHAM








000
FXUS65 KRIW 220640
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1140 PM MST SUN DEC 21 2014

.UPDATE...

CANCELLED REMAINING HIGH WIND WARNINGS FOR SOUTHERN
WYOMING...SO NO REMAINING WINTER STORM OR HIGH WIND WARNINGS ARE IN
EFFECT ACROSS THE CWA.

AVIATION.../06Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

AREAS OF GUSTY NORTHWEST WIND WILL REMAIN...ESPECIALLY VCNTY
KDUB-KRIW AND KBYG...THROUGH THE PERIOD.  -SHSN ACTIVITY WILL REMAIN
MOSTLY ISOLD-WDLY SCT WITH MOST OF THIS ACTIVITY VCNTY AND EAST OF A
KCOD-KWRL-KCPR LINE THROUGH MONDAY MORNING WITH MORE NMRS SHSN
OBSCURING THE SURROUNDING MTNS.  MOISTURE AND INSTABILITY WILL
INCREASE MONDAY AFTERNOON WITH SHSN BECOMING MORE SCT ACROSS THE
CENTRAL BASINS.  SOME WRAPAROUND MOISTURE IS EXPECTED TO PUSH BACK
FROM AN UPPER LOW OVER THE PLAINS INTO EASTERN WYOMING MONDAY
NIGHT...AND THIS MAY BRING MORE WIDESPREAD MVFR/IFR -SN AS FAR WEST
AS THE BIGHORN RANGE TO VCNTY KCPR.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A MOIST AND UNSTABLE NW FLOW WILL REMAIN OVER THE AREA THROUGH
MONDAY AFTERNOON.  AN UPPER LEVEL DISTURBANCE IN THIS FLOW IS
EXPECTED TO DIVE SOUTH ALONG THE DIVIDE LATE MONDAY MORNING AND
MONDAY AFTERNOON...EXITING SOUTH OF INTERSTATE 80 MONDAY EVENING.
SNOW SHOWER ACTIVITY WILL INCREASE AHEAD OF THIS SYSTEM FROM NW-SE
MONDAY MORNING WITH IMPROVING CONDITIONS AND GUSTY NW WINDS
FOLLOWING THE DISTURBANCE MONDAY AFTERNOON AND MONDAY EVENING.
CLEARING CONDITIONS AND DIMINISHING WIND WILL FOLLOW OVERNIGHT
MONDAY.

&&

.PREV DISCUSSION... /ISSUED 304 PM MST SUN DEC 21 2014/

SHORT TERM...TONIGHT THROUGH WEDNESDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES WITH MORE VALLEY
LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX OR FROM A WET SNOW TO A
DRIER ACCUMULATING SNOW TONIGHT. AS THE STRONG WESTERLY FLOW
SWITCHES TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT THERE COULD BE
PERIODS OF GUSTY WIND MOVING INTO ARES MORE PRONE TO STRONG
NORTHWEST FLOW...SPECIFICALLY INTO THE WIND RIVER BASIN AND
BUFFALO/PINEY CREEK AREA. THERE DOES NOT APPEAR TO BE MUCH DOWNWARD
FORCING AS THE LEFT FRONT QUAD OF THE JET REMAINS IN THE
AREA...THERE ARE SOME 50 TO 60KT BARBS AT 700MB BUT THERE IS NOT
EXPECTED TO BE WIDESPREAD TRANSLATION TO THE SURFACE AS FORCING FOR
ASCENT WILL LIKELY WIN OUT. HOWEVER THERE WILL BE A FEW SPOTS
FLIRTING WITH HIGH WIND CRITERIA...ESPECIALLY NORTHWEST OF BUFFALO.
THE NORTHWEST FLOW WILL ALSO BRING DOWN A COLD POOL
ALOFT...INCREASING LOW AND MID LEVEL LAPSE RATES TO OVER 8.5DEG/KM
IN SOME CASES...ESPECIALLY ALONG AND EAST OF THE DIVIDE...AS WELL AS
IN SOME LOCATIONS WEST OF THE DIVIDE LIKE THE TETONS AND YELLOWSTONE.
COULD BE AN INTERESTING EVENING FOR SNOW BANDING. ONE BAND HAS
ALREADY MOVED ACROSS DUBOIS...DROPPING ABOUT AN INCH OF SNOW IN LESS
THAN ONE HOUR.

ON MONDAY...THE MAIN TROUGH MOVES EAST AND UNDERGOES RAPID
CYCLOGENESIS IN THE PLAINS. AROUND THE BACK OF THE TROUGH WE ARE
LOOKING AT A SHORT WAVE THAT IS SET TO MOVE THROUGH LATE TOMORROW
AFTERNOON. LOOKING AT STRICTLY THE MODEL QPF...IT WOULD APPEAR AS IF
NOT MUCH WILL COME OV IT. HOWEVER...THERE WILL STILL BE SOME DECENT
MOISTURE HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS A
SECOND COLD POOL ALOFT SETTLES IN COMBINING WITH A SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ALONG THE BIGHORNS INTO JOHNSON
COUNTY...POPS WERE ALSO INCREASED FOR POTENTIAL SNOW BANDING
ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM SHOSHONI THROUGH CASPER
AND AREAS SOUTHEAST OF THE EASTERN TIP OF THE WIND RIVER MOUNTAINS.
STAYED FAIRLY CONSERVATIVE WITH QPF AND SNOW AMOUNTS GIVEN THE
CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ON TUESDAY...HIGH PRESSURE BUILDS INTO THE WEST WITH ANOTHER SNOW
SHOWER OR TWO POSSIBLE ALONG THE I25 CORRIDOR AND IN THE BIGHORNS.
ELSEWHERE...CLEARING AND COOL WITH DECREASING WINDS. ON
WEDNESDAY...A RIDGE BUILDS IN ALOFT WHILE A LEE TROUGH DIGS AT THE
SURFACE...INCREASING WINDS FROM ROCK SPRINGS TO CASPER IN THE
AFTERNOON. OTHERWISE...INCREASING CLOUDS WITH MORE SNOW EXPECTED
ACROSS THE WEST AND NORTH LATE IN THE AFTERNOON.

LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

GOING INTO THE CHRISTMAS DAY FORECAST STILL BRINGS
CHALLENGES...ESPECIALLY EAST OF THE DIVIDE. ONE THING IS CERTAIN...
A COLD FRONT WILL BRING COLDER TEMPERATURES TO THE REGION BY EARLY
CHRISTMAS MORNING.

ECMWF MODEL STILL DIGS SYSTEM TO THE SOUTHWEST OF FORECAST AREA ON
CHRISTMAS MORNING. THE LOW COMES OVER THE ROCKIES AS AN OPEN WAVE.
BUT THERE SHOULD BE A LONG ENOUGH PERIOD OF UPSLOPE FLOW ON BOTH
SIDES OF THE DIVIDE FOR A FEW INCHES OF SNOW. THIS IS TYPICAL MOST
LOCATIONS EAST OF THE DIVIDE AFTER FROPA. HOWEVER...LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE ALONG FAVORED NORTHEAST MOUNTAIN SLOPES
ON CHRISTMAS. DID NOT CHANGE POPS MUCH ON THURSDAY INTO THURSDAY
NIGHT. REGARDLESS...THIS IS NOT SHAPING UP TO BE A BIG SNOW EVENT.

FLOW ALOFT THEN SUPPORTS SCATTERED SNOW SHOWERS ON FRIDAY. THINKING
IS THAT THERE WILL BE ENOUGH INSTABILITY ALOFT...ESPECIALLY OVER THE
WESTERN AND NORTHERN MOUNTAIN RANGES. BOTH THURSDAY AND FRIDAY
NIGHTS SHOULD BE QUITE COLD...ESPECIALLY WITH ANY FRESH SNOW COVER.

MOSTLY DRY W-NW FLOW THEN SETS UP OVER THE FORECAST AREA SATURDAY
INTO SUNDAY. DETAILS VARY A BIT WITH EACH MEDIUM RANGE MODEL...BUT
LOOKS LIKE TEMPERATURES WILL MODERATE NEXT WEEKEND. POSSIBLY BETTER
CHANCE FOR SNOW NORTHWEST WYOMING MOUNTAINS BY SUNDAY AFTERNOON.

AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE MIXING OUT. EXPECT PERIODS OF 20 TO 30KT WINDS WITH GUSTS MAINLY
IN THE 35-45KT RANGE BUT A FEW MORE WIND PRONE AREAS COULD SEE GUSTS
UP TO 55KT...BUT NOT AT ANY OF THE FORECAST TERMINALS. A STRONG NW
FLOW WILL FOLLOW THIS SYSTEM TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW
SHOWERS POSSIBLE ALONG THE FRONT ACROSS THE LOWER ELEVATIONS THIS
EVENING...ESPECIALLY VCNTY AND EAST OF INTERSTATE 25. DRIER AIR
PREVAIL NW-SE BUT GUSTY NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

STRONG MTN TOP WINDS RESULTING IN AREAS MDT-SVR TURBULENCE AND
LLWS...WILL CONTINUE THROUGH THE NIGHT. A COLD FRONT WILL CONTINUE
TO PUSH SOUTH ACROSS THE AREA CROSSING INTERSTATE 80 AROUND 03Z
MONDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

UPDATE...AEM
SHORT TERM...ALLEN
LONG TERM...KPL
AVIATION...AEM
FIRE WEATHER...ALLEN










000
FXUS65 KRIW 220640
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1140 PM MST SUN DEC 21 2014

.UPDATE...

CANCELLED REMAINING HIGH WIND WARNINGS FOR SOUTHERN
WYOMING...SO NO REMAINING WINTER STORM OR HIGH WIND WARNINGS ARE IN
EFFECT ACROSS THE CWA.

AVIATION.../06Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

AREAS OF GUSTY NORTHWEST WIND WILL REMAIN...ESPECIALLY VCNTY
KDUB-KRIW AND KBYG...THROUGH THE PERIOD.  -SHSN ACTIVITY WILL REMAIN
MOSTLY ISOLD-WDLY SCT WITH MOST OF THIS ACTIVITY VCNTY AND EAST OF A
KCOD-KWRL-KCPR LINE THROUGH MONDAY MORNING WITH MORE NMRS SHSN
OBSCURING THE SURROUNDING MTNS.  MOISTURE AND INSTABILITY WILL
INCREASE MONDAY AFTERNOON WITH SHSN BECOMING MORE SCT ACROSS THE
CENTRAL BASINS.  SOME WRAPAROUND MOISTURE IS EXPECTED TO PUSH BACK
FROM AN UPPER LOW OVER THE PLAINS INTO EASTERN WYOMING MONDAY
NIGHT...AND THIS MAY BRING MORE WIDESPREAD MVFR/IFR -SN AS FAR WEST
AS THE BIGHORN RANGE TO VCNTY KCPR.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A MOIST AND UNSTABLE NW FLOW WILL REMAIN OVER THE AREA THROUGH
MONDAY AFTERNOON.  AN UPPER LEVEL DISTURBANCE IN THIS FLOW IS
EXPECTED TO DIVE SOUTH ALONG THE DIVIDE LATE MONDAY MORNING AND
MONDAY AFTERNOON...EXITING SOUTH OF INTERSTATE 80 MONDAY EVENING.
SNOW SHOWER ACTIVITY WILL INCREASE AHEAD OF THIS SYSTEM FROM NW-SE
MONDAY MORNING WITH IMPROVING CONDITIONS AND GUSTY NW WINDS
FOLLOWING THE DISTURBANCE MONDAY AFTERNOON AND MONDAY EVENING.
CLEARING CONDITIONS AND DIMINISHING WIND WILL FOLLOW OVERNIGHT
MONDAY.

&&

.PREV DISCUSSION... /ISSUED 304 PM MST SUN DEC 21 2014/

SHORT TERM...TONIGHT THROUGH WEDNESDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES WITH MORE VALLEY
LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX OR FROM A WET SNOW TO A
DRIER ACCUMULATING SNOW TONIGHT. AS THE STRONG WESTERLY FLOW
SWITCHES TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT THERE COULD BE
PERIODS OF GUSTY WIND MOVING INTO ARES MORE PRONE TO STRONG
NORTHWEST FLOW...SPECIFICALLY INTO THE WIND RIVER BASIN AND
BUFFALO/PINEY CREEK AREA. THERE DOES NOT APPEAR TO BE MUCH DOWNWARD
FORCING AS THE LEFT FRONT QUAD OF THE JET REMAINS IN THE
AREA...THERE ARE SOME 50 TO 60KT BARBS AT 700MB BUT THERE IS NOT
EXPECTED TO BE WIDESPREAD TRANSLATION TO THE SURFACE AS FORCING FOR
ASCENT WILL LIKELY WIN OUT. HOWEVER THERE WILL BE A FEW SPOTS
FLIRTING WITH HIGH WIND CRITERIA...ESPECIALLY NORTHWEST OF BUFFALO.
THE NORTHWEST FLOW WILL ALSO BRING DOWN A COLD POOL
ALOFT...INCREASING LOW AND MID LEVEL LAPSE RATES TO OVER 8.5DEG/KM
IN SOME CASES...ESPECIALLY ALONG AND EAST OF THE DIVIDE...AS WELL AS
IN SOME LOCATIONS WEST OF THE DIVIDE LIKE THE TETONS AND YELLOWSTONE.
COULD BE AN INTERESTING EVENING FOR SNOW BANDING. ONE BAND HAS
ALREADY MOVED ACROSS DUBOIS...DROPPING ABOUT AN INCH OF SNOW IN LESS
THAN ONE HOUR.

ON MONDAY...THE MAIN TROUGH MOVES EAST AND UNDERGOES RAPID
CYCLOGENESIS IN THE PLAINS. AROUND THE BACK OF THE TROUGH WE ARE
LOOKING AT A SHORT WAVE THAT IS SET TO MOVE THROUGH LATE TOMORROW
AFTERNOON. LOOKING AT STRICTLY THE MODEL QPF...IT WOULD APPEAR AS IF
NOT MUCH WILL COME OV IT. HOWEVER...THERE WILL STILL BE SOME DECENT
MOISTURE HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS A
SECOND COLD POOL ALOFT SETTLES IN COMBINING WITH A SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ALONG THE BIGHORNS INTO JOHNSON
COUNTY...POPS WERE ALSO INCREASED FOR POTENTIAL SNOW BANDING
ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM SHOSHONI THROUGH CASPER
AND AREAS SOUTHEAST OF THE EASTERN TIP OF THE WIND RIVER MOUNTAINS.
STAYED FAIRLY CONSERVATIVE WITH QPF AND SNOW AMOUNTS GIVEN THE
CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ON TUESDAY...HIGH PRESSURE BUILDS INTO THE WEST WITH ANOTHER SNOW
SHOWER OR TWO POSSIBLE ALONG THE I25 CORRIDOR AND IN THE BIGHORNS.
ELSEWHERE...CLEARING AND COOL WITH DECREASING WINDS. ON
WEDNESDAY...A RIDGE BUILDS IN ALOFT WHILE A LEE TROUGH DIGS AT THE
SURFACE...INCREASING WINDS FROM ROCK SPRINGS TO CASPER IN THE
AFTERNOON. OTHERWISE...INCREASING CLOUDS WITH MORE SNOW EXPECTED
ACROSS THE WEST AND NORTH LATE IN THE AFTERNOON.

LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

GOING INTO THE CHRISTMAS DAY FORECAST STILL BRINGS
CHALLENGES...ESPECIALLY EAST OF THE DIVIDE. ONE THING IS CERTAIN...
A COLD FRONT WILL BRING COLDER TEMPERATURES TO THE REGION BY EARLY
CHRISTMAS MORNING.

ECMWF MODEL STILL DIGS SYSTEM TO THE SOUTHWEST OF FORECAST AREA ON
CHRISTMAS MORNING. THE LOW COMES OVER THE ROCKIES AS AN OPEN WAVE.
BUT THERE SHOULD BE A LONG ENOUGH PERIOD OF UPSLOPE FLOW ON BOTH
SIDES OF THE DIVIDE FOR A FEW INCHES OF SNOW. THIS IS TYPICAL MOST
LOCATIONS EAST OF THE DIVIDE AFTER FROPA. HOWEVER...LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE ALONG FAVORED NORTHEAST MOUNTAIN SLOPES
ON CHRISTMAS. DID NOT CHANGE POPS MUCH ON THURSDAY INTO THURSDAY
NIGHT. REGARDLESS...THIS IS NOT SHAPING UP TO BE A BIG SNOW EVENT.

FLOW ALOFT THEN SUPPORTS SCATTERED SNOW SHOWERS ON FRIDAY. THINKING
IS THAT THERE WILL BE ENOUGH INSTABILITY ALOFT...ESPECIALLY OVER THE
WESTERN AND NORTHERN MOUNTAIN RANGES. BOTH THURSDAY AND FRIDAY
NIGHTS SHOULD BE QUITE COLD...ESPECIALLY WITH ANY FRESH SNOW COVER.

MOSTLY DRY W-NW FLOW THEN SETS UP OVER THE FORECAST AREA SATURDAY
INTO SUNDAY. DETAILS VARY A BIT WITH EACH MEDIUM RANGE MODEL...BUT
LOOKS LIKE TEMPERATURES WILL MODERATE NEXT WEEKEND. POSSIBLY BETTER
CHANCE FOR SNOW NORTHWEST WYOMING MOUNTAINS BY SUNDAY AFTERNOON.

AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE MIXING OUT. EXPECT PERIODS OF 20 TO 30KT WINDS WITH GUSTS MAINLY
IN THE 35-45KT RANGE BUT A FEW MORE WIND PRONE AREAS COULD SEE GUSTS
UP TO 55KT...BUT NOT AT ANY OF THE FORECAST TERMINALS. A STRONG NW
FLOW WILL FOLLOW THIS SYSTEM TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW
SHOWERS POSSIBLE ALONG THE FRONT ACROSS THE LOWER ELEVATIONS THIS
EVENING...ESPECIALLY VCNTY AND EAST OF INTERSTATE 25. DRIER AIR
PREVAIL NW-SE BUT GUSTY NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

STRONG MTN TOP WINDS RESULTING IN AREAS MDT-SVR TURBULENCE AND
LLWS...WILL CONTINUE THROUGH THE NIGHT. A COLD FRONT WILL CONTINUE
TO PUSH SOUTH ACROSS THE AREA CROSSING INTERSTATE 80 AROUND 03Z
MONDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

UPDATE...AEM
SHORT TERM...ALLEN
LONG TERM...KPL
AVIATION...AEM
FIRE WEATHER...ALLEN










000
FXUS65 KRIW 220640
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1140 PM MST SUN DEC 21 2014

.UPDATE...

CANCELLED REMAINING HIGH WIND WARNINGS FOR SOUTHERN
WYOMING...SO NO REMAINING WINTER STORM OR HIGH WIND WARNINGS ARE IN
EFFECT ACROSS THE CWA.

AVIATION.../06Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

AREAS OF GUSTY NORTHWEST WIND WILL REMAIN...ESPECIALLY VCNTY
KDUB-KRIW AND KBYG...THROUGH THE PERIOD.  -SHSN ACTIVITY WILL REMAIN
MOSTLY ISOLD-WDLY SCT WITH MOST OF THIS ACTIVITY VCNTY AND EAST OF A
KCOD-KWRL-KCPR LINE THROUGH MONDAY MORNING WITH MORE NMRS SHSN
OBSCURING THE SURROUNDING MTNS.  MOISTURE AND INSTABILITY WILL
INCREASE MONDAY AFTERNOON WITH SHSN BECOMING MORE SCT ACROSS THE
CENTRAL BASINS.  SOME WRAPAROUND MOISTURE IS EXPECTED TO PUSH BACK
FROM AN UPPER LOW OVER THE PLAINS INTO EASTERN WYOMING MONDAY
NIGHT...AND THIS MAY BRING MORE WIDESPREAD MVFR/IFR -SN AS FAR WEST
AS THE BIGHORN RANGE TO VCNTY KCPR.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A MOIST AND UNSTABLE NW FLOW WILL REMAIN OVER THE AREA THROUGH
MONDAY AFTERNOON.  AN UPPER LEVEL DISTURBANCE IN THIS FLOW IS
EXPECTED TO DIVE SOUTH ALONG THE DIVIDE LATE MONDAY MORNING AND
MONDAY AFTERNOON...EXITING SOUTH OF INTERSTATE 80 MONDAY EVENING.
SNOW SHOWER ACTIVITY WILL INCREASE AHEAD OF THIS SYSTEM FROM NW-SE
MONDAY MORNING WITH IMPROVING CONDITIONS AND GUSTY NW WINDS
FOLLOWING THE DISTURBANCE MONDAY AFTERNOON AND MONDAY EVENING.
CLEARING CONDITIONS AND DIMINISHING WIND WILL FOLLOW OVERNIGHT
MONDAY.

&&

.PREV DISCUSSION... /ISSUED 304 PM MST SUN DEC 21 2014/

SHORT TERM...TONIGHT THROUGH WEDNESDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES WITH MORE VALLEY
LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX OR FROM A WET SNOW TO A
DRIER ACCUMULATING SNOW TONIGHT. AS THE STRONG WESTERLY FLOW
SWITCHES TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT THERE COULD BE
PERIODS OF GUSTY WIND MOVING INTO ARES MORE PRONE TO STRONG
NORTHWEST FLOW...SPECIFICALLY INTO THE WIND RIVER BASIN AND
BUFFALO/PINEY CREEK AREA. THERE DOES NOT APPEAR TO BE MUCH DOWNWARD
FORCING AS THE LEFT FRONT QUAD OF THE JET REMAINS IN THE
AREA...THERE ARE SOME 50 TO 60KT BARBS AT 700MB BUT THERE IS NOT
EXPECTED TO BE WIDESPREAD TRANSLATION TO THE SURFACE AS FORCING FOR
ASCENT WILL LIKELY WIN OUT. HOWEVER THERE WILL BE A FEW SPOTS
FLIRTING WITH HIGH WIND CRITERIA...ESPECIALLY NORTHWEST OF BUFFALO.
THE NORTHWEST FLOW WILL ALSO BRING DOWN A COLD POOL
ALOFT...INCREASING LOW AND MID LEVEL LAPSE RATES TO OVER 8.5DEG/KM
IN SOME CASES...ESPECIALLY ALONG AND EAST OF THE DIVIDE...AS WELL AS
IN SOME LOCATIONS WEST OF THE DIVIDE LIKE THE TETONS AND YELLOWSTONE.
COULD BE AN INTERESTING EVENING FOR SNOW BANDING. ONE BAND HAS
ALREADY MOVED ACROSS DUBOIS...DROPPING ABOUT AN INCH OF SNOW IN LESS
THAN ONE HOUR.

ON MONDAY...THE MAIN TROUGH MOVES EAST AND UNDERGOES RAPID
CYCLOGENESIS IN THE PLAINS. AROUND THE BACK OF THE TROUGH WE ARE
LOOKING AT A SHORT WAVE THAT IS SET TO MOVE THROUGH LATE TOMORROW
AFTERNOON. LOOKING AT STRICTLY THE MODEL QPF...IT WOULD APPEAR AS IF
NOT MUCH WILL COME OV IT. HOWEVER...THERE WILL STILL BE SOME DECENT
MOISTURE HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS A
SECOND COLD POOL ALOFT SETTLES IN COMBINING WITH A SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ALONG THE BIGHORNS INTO JOHNSON
COUNTY...POPS WERE ALSO INCREASED FOR POTENTIAL SNOW BANDING
ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM SHOSHONI THROUGH CASPER
AND AREAS SOUTHEAST OF THE EASTERN TIP OF THE WIND RIVER MOUNTAINS.
STAYED FAIRLY CONSERVATIVE WITH QPF AND SNOW AMOUNTS GIVEN THE
CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ON TUESDAY...HIGH PRESSURE BUILDS INTO THE WEST WITH ANOTHER SNOW
SHOWER OR TWO POSSIBLE ALONG THE I25 CORRIDOR AND IN THE BIGHORNS.
ELSEWHERE...CLEARING AND COOL WITH DECREASING WINDS. ON
WEDNESDAY...A RIDGE BUILDS IN ALOFT WHILE A LEE TROUGH DIGS AT THE
SURFACE...INCREASING WINDS FROM ROCK SPRINGS TO CASPER IN THE
AFTERNOON. OTHERWISE...INCREASING CLOUDS WITH MORE SNOW EXPECTED
ACROSS THE WEST AND NORTH LATE IN THE AFTERNOON.

LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

GOING INTO THE CHRISTMAS DAY FORECAST STILL BRINGS
CHALLENGES...ESPECIALLY EAST OF THE DIVIDE. ONE THING IS CERTAIN...
A COLD FRONT WILL BRING COLDER TEMPERATURES TO THE REGION BY EARLY
CHRISTMAS MORNING.

ECMWF MODEL STILL DIGS SYSTEM TO THE SOUTHWEST OF FORECAST AREA ON
CHRISTMAS MORNING. THE LOW COMES OVER THE ROCKIES AS AN OPEN WAVE.
BUT THERE SHOULD BE A LONG ENOUGH PERIOD OF UPSLOPE FLOW ON BOTH
SIDES OF THE DIVIDE FOR A FEW INCHES OF SNOW. THIS IS TYPICAL MOST
LOCATIONS EAST OF THE DIVIDE AFTER FROPA. HOWEVER...LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE ALONG FAVORED NORTHEAST MOUNTAIN SLOPES
ON CHRISTMAS. DID NOT CHANGE POPS MUCH ON THURSDAY INTO THURSDAY
NIGHT. REGARDLESS...THIS IS NOT SHAPING UP TO BE A BIG SNOW EVENT.

FLOW ALOFT THEN SUPPORTS SCATTERED SNOW SHOWERS ON FRIDAY. THINKING
IS THAT THERE WILL BE ENOUGH INSTABILITY ALOFT...ESPECIALLY OVER THE
WESTERN AND NORTHERN MOUNTAIN RANGES. BOTH THURSDAY AND FRIDAY
NIGHTS SHOULD BE QUITE COLD...ESPECIALLY WITH ANY FRESH SNOW COVER.

MOSTLY DRY W-NW FLOW THEN SETS UP OVER THE FORECAST AREA SATURDAY
INTO SUNDAY. DETAILS VARY A BIT WITH EACH MEDIUM RANGE MODEL...BUT
LOOKS LIKE TEMPERATURES WILL MODERATE NEXT WEEKEND. POSSIBLY BETTER
CHANCE FOR SNOW NORTHWEST WYOMING MOUNTAINS BY SUNDAY AFTERNOON.

AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE MIXING OUT. EXPECT PERIODS OF 20 TO 30KT WINDS WITH GUSTS MAINLY
IN THE 35-45KT RANGE BUT A FEW MORE WIND PRONE AREAS COULD SEE GUSTS
UP TO 55KT...BUT NOT AT ANY OF THE FORECAST TERMINALS. A STRONG NW
FLOW WILL FOLLOW THIS SYSTEM TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW
SHOWERS POSSIBLE ALONG THE FRONT ACROSS THE LOWER ELEVATIONS THIS
EVENING...ESPECIALLY VCNTY AND EAST OF INTERSTATE 25. DRIER AIR
PREVAIL NW-SE BUT GUSTY NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

STRONG MTN TOP WINDS RESULTING IN AREAS MDT-SVR TURBULENCE AND
LLWS...WILL CONTINUE THROUGH THE NIGHT. A COLD FRONT WILL CONTINUE
TO PUSH SOUTH ACROSS THE AREA CROSSING INTERSTATE 80 AROUND 03Z
MONDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

UPDATE...AEM
SHORT TERM...ALLEN
LONG TERM...KPL
AVIATION...AEM
FIRE WEATHER...ALLEN










000
FXUS65 KRIW 220640
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1140 PM MST SUN DEC 21 2014

.UPDATE...

CANCELLED REMAINING HIGH WIND WARNINGS FOR SOUTHERN
WYOMING...SO NO REMAINING WINTER STORM OR HIGH WIND WARNINGS ARE IN
EFFECT ACROSS THE CWA.

AVIATION.../06Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

AREAS OF GUSTY NORTHWEST WIND WILL REMAIN...ESPECIALLY VCNTY
KDUB-KRIW AND KBYG...THROUGH THE PERIOD.  -SHSN ACTIVITY WILL REMAIN
MOSTLY ISOLD-WDLY SCT WITH MOST OF THIS ACTIVITY VCNTY AND EAST OF A
KCOD-KWRL-KCPR LINE THROUGH MONDAY MORNING WITH MORE NMRS SHSN
OBSCURING THE SURROUNDING MTNS.  MOISTURE AND INSTABILITY WILL
INCREASE MONDAY AFTERNOON WITH SHSN BECOMING MORE SCT ACROSS THE
CENTRAL BASINS.  SOME WRAPAROUND MOISTURE IS EXPECTED TO PUSH BACK
FROM AN UPPER LOW OVER THE PLAINS INTO EASTERN WYOMING MONDAY
NIGHT...AND THIS MAY BRING MORE WIDESPREAD MVFR/IFR -SN AS FAR WEST
AS THE BIGHORN RANGE TO VCNTY KCPR.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

A MOIST AND UNSTABLE NW FLOW WILL REMAIN OVER THE AREA THROUGH
MONDAY AFTERNOON.  AN UPPER LEVEL DISTURBANCE IN THIS FLOW IS
EXPECTED TO DIVE SOUTH ALONG THE DIVIDE LATE MONDAY MORNING AND
MONDAY AFTERNOON...EXITING SOUTH OF INTERSTATE 80 MONDAY EVENING.
SNOW SHOWER ACTIVITY WILL INCREASE AHEAD OF THIS SYSTEM FROM NW-SE
MONDAY MORNING WITH IMPROVING CONDITIONS AND GUSTY NW WINDS
FOLLOWING THE DISTURBANCE MONDAY AFTERNOON AND MONDAY EVENING.
CLEARING CONDITIONS AND DIMINISHING WIND WILL FOLLOW OVERNIGHT
MONDAY.

&&

.PREV DISCUSSION... /ISSUED 304 PM MST SUN DEC 21 2014/

SHORT TERM...TONIGHT THROUGH WEDNESDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES WITH MORE VALLEY
LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX OR FROM A WET SNOW TO A
DRIER ACCUMULATING SNOW TONIGHT. AS THE STRONG WESTERLY FLOW
SWITCHES TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT THERE COULD BE
PERIODS OF GUSTY WIND MOVING INTO ARES MORE PRONE TO STRONG
NORTHWEST FLOW...SPECIFICALLY INTO THE WIND RIVER BASIN AND
BUFFALO/PINEY CREEK AREA. THERE DOES NOT APPEAR TO BE MUCH DOWNWARD
FORCING AS THE LEFT FRONT QUAD OF THE JET REMAINS IN THE
AREA...THERE ARE SOME 50 TO 60KT BARBS AT 700MB BUT THERE IS NOT
EXPECTED TO BE WIDESPREAD TRANSLATION TO THE SURFACE AS FORCING FOR
ASCENT WILL LIKELY WIN OUT. HOWEVER THERE WILL BE A FEW SPOTS
FLIRTING WITH HIGH WIND CRITERIA...ESPECIALLY NORTHWEST OF BUFFALO.
THE NORTHWEST FLOW WILL ALSO BRING DOWN A COLD POOL
ALOFT...INCREASING LOW AND MID LEVEL LAPSE RATES TO OVER 8.5DEG/KM
IN SOME CASES...ESPECIALLY ALONG AND EAST OF THE DIVIDE...AS WELL AS
IN SOME LOCATIONS WEST OF THE DIVIDE LIKE THE TETONS AND YELLOWSTONE.
COULD BE AN INTERESTING EVENING FOR SNOW BANDING. ONE BAND HAS
ALREADY MOVED ACROSS DUBOIS...DROPPING ABOUT AN INCH OF SNOW IN LESS
THAN ONE HOUR.

ON MONDAY...THE MAIN TROUGH MOVES EAST AND UNDERGOES RAPID
CYCLOGENESIS IN THE PLAINS. AROUND THE BACK OF THE TROUGH WE ARE
LOOKING AT A SHORT WAVE THAT IS SET TO MOVE THROUGH LATE TOMORROW
AFTERNOON. LOOKING AT STRICTLY THE MODEL QPF...IT WOULD APPEAR AS IF
NOT MUCH WILL COME OV IT. HOWEVER...THERE WILL STILL BE SOME DECENT
MOISTURE HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS A
SECOND COLD POOL ALOFT SETTLES IN COMBINING WITH A SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ALONG THE BIGHORNS INTO JOHNSON
COUNTY...POPS WERE ALSO INCREASED FOR POTENTIAL SNOW BANDING
ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM SHOSHONI THROUGH CASPER
AND AREAS SOUTHEAST OF THE EASTERN TIP OF THE WIND RIVER MOUNTAINS.
STAYED FAIRLY CONSERVATIVE WITH QPF AND SNOW AMOUNTS GIVEN THE
CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ON TUESDAY...HIGH PRESSURE BUILDS INTO THE WEST WITH ANOTHER SNOW
SHOWER OR TWO POSSIBLE ALONG THE I25 CORRIDOR AND IN THE BIGHORNS.
ELSEWHERE...CLEARING AND COOL WITH DECREASING WINDS. ON
WEDNESDAY...A RIDGE BUILDS IN ALOFT WHILE A LEE TROUGH DIGS AT THE
SURFACE...INCREASING WINDS FROM ROCK SPRINGS TO CASPER IN THE
AFTERNOON. OTHERWISE...INCREASING CLOUDS WITH MORE SNOW EXPECTED
ACROSS THE WEST AND NORTH LATE IN THE AFTERNOON.

LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

GOING INTO THE CHRISTMAS DAY FORECAST STILL BRINGS
CHALLENGES...ESPECIALLY EAST OF THE DIVIDE. ONE THING IS CERTAIN...
A COLD FRONT WILL BRING COLDER TEMPERATURES TO THE REGION BY EARLY
CHRISTMAS MORNING.

ECMWF MODEL STILL DIGS SYSTEM TO THE SOUTHWEST OF FORECAST AREA ON
CHRISTMAS MORNING. THE LOW COMES OVER THE ROCKIES AS AN OPEN WAVE.
BUT THERE SHOULD BE A LONG ENOUGH PERIOD OF UPSLOPE FLOW ON BOTH
SIDES OF THE DIVIDE FOR A FEW INCHES OF SNOW. THIS IS TYPICAL MOST
LOCATIONS EAST OF THE DIVIDE AFTER FROPA. HOWEVER...LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE ALONG FAVORED NORTHEAST MOUNTAIN SLOPES
ON CHRISTMAS. DID NOT CHANGE POPS MUCH ON THURSDAY INTO THURSDAY
NIGHT. REGARDLESS...THIS IS NOT SHAPING UP TO BE A BIG SNOW EVENT.

FLOW ALOFT THEN SUPPORTS SCATTERED SNOW SHOWERS ON FRIDAY. THINKING
IS THAT THERE WILL BE ENOUGH INSTABILITY ALOFT...ESPECIALLY OVER THE
WESTERN AND NORTHERN MOUNTAIN RANGES. BOTH THURSDAY AND FRIDAY
NIGHTS SHOULD BE QUITE COLD...ESPECIALLY WITH ANY FRESH SNOW COVER.

MOSTLY DRY W-NW FLOW THEN SETS UP OVER THE FORECAST AREA SATURDAY
INTO SUNDAY. DETAILS VARY A BIT WITH EACH MEDIUM RANGE MODEL...BUT
LOOKS LIKE TEMPERATURES WILL MODERATE NEXT WEEKEND. POSSIBLY BETTER
CHANCE FOR SNOW NORTHWEST WYOMING MOUNTAINS BY SUNDAY AFTERNOON.

AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE MIXING OUT. EXPECT PERIODS OF 20 TO 30KT WINDS WITH GUSTS MAINLY
IN THE 35-45KT RANGE BUT A FEW MORE WIND PRONE AREAS COULD SEE GUSTS
UP TO 55KT...BUT NOT AT ANY OF THE FORECAST TERMINALS. A STRONG NW
FLOW WILL FOLLOW THIS SYSTEM TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW
SHOWERS POSSIBLE ALONG THE FRONT ACROSS THE LOWER ELEVATIONS THIS
EVENING...ESPECIALLY VCNTY AND EAST OF INTERSTATE 25. DRIER AIR
PREVAIL NW-SE BUT GUSTY NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

STRONG MTN TOP WINDS RESULTING IN AREAS MDT-SVR TURBULENCE AND
LLWS...WILL CONTINUE THROUGH THE NIGHT. A COLD FRONT WILL CONTINUE
TO PUSH SOUTH ACROSS THE AREA CROSSING INTERSTATE 80 AROUND 03Z
MONDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

UPDATE...AEM
SHORT TERM...ALLEN
LONG TERM...KPL
AVIATION...AEM
FIRE WEATHER...ALLEN










000
FXUS65 KCYS 220537
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1037 PM MST SUN DEC 21 2014

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

POWERFUL PACIFIC LOW PRESSURE SYSTEM CONTINUES TO MOVE INTO THE
AREA FROM THE WEST THIS AFTERNOON...BRINGING WIDESPREAD STRONG
WINDS AND NEAR BLIZZARD CONDITIONS ALONG PORTIONS OF INTERSTATE 80
OUT NEAR ARLINGTON. HAVE SEEN SOME REPORTS OF WIND GUSTS
APPROACHING 70MPH AND HAD AN 80MPH GUST REPORTED AT A UPR SITE UP
ON THE SOUTH LARAMIE RANGE. FORECAST CHALLENGES CONTINUE TO BE
MAINLY WINDS...BUT LATER THIS EVENING...WINTER WEATHER CONDITIONS
WILL TAKE SHAPE.

CURRENTLY...1015MB SURFACE LOW CURRENTLY OVER CENTRAL UTAH EARLY
THIS AFTERNOON. PERHAPS OUR STRONGEST GRADIENT IS YET TO COME AS
SURFACE ANALYSIS SHOWS THE STRONG PRESSURE GRADIENT STILL OVER
NORTHWESTERN COLORADO AND NORTHEASTERN UTAH. CRAIG TO CASPER
SURFACE GRADIENT RIGHT AROUND 12MBS AT 1 PM THIS AFTERNOON. LATEST
WRKHGT PRODUCTS HAS 850/700MB CRAIG TO CASPER HEIGHT GRADIENTS OF
75 AND 73MTRS RESPECTIVELY. MOSAIC RADAR SHOWING MOST OF THE SNOW
OVER NORTHWESTERN COLORADO AND UP OVER NORTHWESTERN WYOMING.

HEIGHT GRADIENTS REMAIN STRONG OVER SOUTHEAST WYOMING THROUGH THE
EVENING HOURS. WILL KEEP ALL WIND HEADLINES GOING AS THEY ARE FOR
NOW AS THE GFS SHOWS 700MB WINDS STILL AROUND 60-65KTS AT 06Z
TONIGHT. ECMWF SHOWS THE 500MB SHORTWAVE MOVING THROUGH CENTRAL
WYOMING INTO WESTERN NEBRASKA AFTER 06Z WITH WINDS SHIFTING
NORTHWEST BEHIND THE FRONT TONIGHT. AREAS WEST OF THE LARAMIE
RANGE STAY IN THE FAVORABLE LEFT FRONT QUADRANT OF A 170+ KT
JET...SO HEAVY SNOW LOOKS TO CONTINUE FOR THE SNOWY AND SIERRA
MADRE RANGES. LOWER ELEVATIONS WILL CONTINUE TO SEE STRONG
WINDS...THOUGH NOT AS STRONG AS TODAY...BUT ENOUGH TO KEEP WINTER
HEADLINES GOING OUT THERE THROUGH THE OVERNIGHT HOURS.

ATTENTION TURNS TO THE PANHANDLE FOR MONDAY. GFS 850MB WINDS
BEHIND THE FRONT OUT OVER THE PANHANDLE INCREASE SIGNIFICANTLY
OVERNIGHT. LOOKING AT 850MB WIND SPEEDS OF 40-45KTS FOR MUCH OF
THE PANHANDLE. WENT AHEAD WITH A WIND ADVISORY FOR NOW COVERING
MUCH OF THE DAY. LATER SHIFTS MAY NEED TO UPGRADE TO HIGH WIND
WARNINGS IF LATER GUIDANCE SHOWS ANYTHING STRONGER THAN WHAT I AM
SEEING NOW. HEAVY SNOW CONTINUES FOR THE SNOWY AND SIERRA MADRE
RANGES ALL DAY MONDAY.

FINALLY BEGIN TO SEE AN EASING ON THE SNOW OUT WEST MONDAY NIGHT
INTO TUESDAY AS THE UPPER LOW MOVES EAST. CURRENT WINTER STORM
WARNING FOR THE MOUNTAINS LOOKS GOOD THROUGH 12Z TUESDAY...NO
CHANGES MADE IN HEADLINES.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY EVENING THROUGH
FRIDAY DUE TO HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER
WEATHER ON CHRISTMAS DAY. MODELS ARE MAINTAINING RUN TO RUN
CONSISTENCY FOR THE POTENTIAL WINTER WEATHER ON CHRISTMAS...BUT
WITH SUCH A LARGE DISCREPANCY BETWEEN INDIVIDUAL MODEL RUNS...THE
PICTURE IS NOT LOOKING ANY CLEARER TODAY IN TERMS OF THE WEATHER.

EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY TRAVEL
PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS DOWNSLOPE FLOW
DEVELOPS...WITH HIGHS IN THE MID 30S TO MID 40S...WARMEST ALONG
THE I25 CORRIDOR DUE TO DOWNSLOPE FLOW NEAR THE SURFACE. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS INDICATE A RAPIDLY MOVING
PACIFIC UPPER LEVEL TROUGH PUSHING INTO THE AREA FROM THE
NORTHWEST UNITED STATES. A STRONG PACIFIC COLD FRONT IS FORECAST
TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME CHRISTMAS MORNING WITH
SNOW DEVELOPING BEHIND THE FRONT. THERE IS THE POTENTIAL FOR A
HIGH WIND EVENT ACROSS THE WIND PRONE AREAS OF SOUTHEAST WYOMING
AHEAD OF THIS FRONT...SO CONTINUED TO INCREASE WINDS OVER THE
ARLINGTON AND BORDEAUX AREAS. WIND IMPACTS SHOULD BE MINIMAL
HOWEVER FOR HOLIDAY TRAVELERS...DUE TO A RELATIVELY BRIEF PERIOD
OF STRONG WINDS...AND THE WINDS MAINLY AFFECTING HIGH PROFILE
VEHICLES.

FORECAST BECOMES TRICKY ON CHRISTMAS DAY IN TERMS OF SNOW
POTENTIAL AS THERE IS ONLY SLIGHTLY MORE CONFIDENCE COMPARED TO
YESTERDAY THAT A DECENT PORTION OF THE AREA WILL RECEIVE
ACCUMULATING SNOW. ALL MODELS NOW SHOW THE SYSTEM MOVING RAPIDLY
ACROSS THE AREA INTO THURSDAY NIGHT...WHICH IS IMPORTANT BECAUSE
IT GREATLY LOWERS THE CHANCE OF WINTER STORM CONDITIONS. THE 12Z
ECMWF IS SLIGHTLY FASTER AND SHOWING WIDESPREAD LIGHT TO MODERATE
SNOWFALL NEARLY EVERYWHERE ACROSS SOUTHEAST WYOMING AND WESTERN
NEBRASKA. THE 12Z GFS HAS BEEN CONSISTENTLY FURTHER NORTH WITH THE
TROUGH AXIS AND PORT MAX...AND THUS MUCH LESS SNOW DUE TO
DOWNSLOPE WINDS. THE PRIMARY DIFFERENCE BETWEEN THESE TWO
SOLUTIONS...OTHER THAN THE QPF...IS THE STORM TRACK AND JET STREAM
LOCATION. THE ECMWF HAS THE JET DIGGING FURTHER SOUTH WITH A
SURFACE LOW DEVELOPING NEAR THE WYOMING/COLORADO BORDER AND MOVING
SOUTHEAST. THE GFS ON THE OTHER HAND SHOWS THE JET STREAM OVER THE
STATE OF WYOMING WITH A SURFACE LOW MUCH FURTHER NORTH ACROSS
MONTANA AND THE DAKOTAS. THE NET RESULT IS BROAD DRY DOWNSLOPE
FLOW AND LLVL SUBSIDENCE COMPARED TO THE ECMWF WHICH SHOWS PLENTY
OF NORTHEAST UPSLOPE FLOW. THE GEM IS SOMEWHERE IN BETWEEN THESE
TWO EXTREMES BUT A LITTLE CLOSER TO THE GFS. ECMWF QPF VALUES
RANGE FROM ONE QUARTER OF AN INCH TO ABOUT A THIRD OF AN INCH.
WHICH MEANS THERE IS POTENTIAL FOR LIGHT TO MODERATE SNOW AMOUNTS.
INCREASED POP SLIGHTLY ACROSS THE I80 CORRIDOR TO AROUND 30 TO 40
PERCENT FOR NOW...WITH VALUES NEAR 80 PERCENT FOR THE MOUNTAINS
WHICH HAVE THE BEST CHANCE OF SEEING 6+ INCHES OF SNOW.
HOPEFULLY...MODELS TREND TOWARD A SIMILAR SOLUTION OVER THE NEXT
24 HOURS...BUT HAVE A FEELING THAT MAY NOT HAPPEN UNTIL TUESDAY
WHEN THE SYSTEM BEGINS TO MOVE ONSHORE. THERE IS HIGH CONFIDENCE
THAT MUCH COLDER TEMPERATURES WILL ENTER THE REGION FOR THE
REMAINDER OF THE WEEK AND INTO NEXT WEEKEND WITH HIGHS IN THE 20S
TO MID 30S...AND LOWS IN THE SINGLE DIGITS (ABOVE AND BELOW ZERO)
AND TEENS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1036 PM MST SUN DEC 21 2014

VFR PREVAILS WITH LOCALIZED MVFR AT LARAMIE THROUGH 09Z...AND
LOCALIZED IFR AT RAWLINS MONDAY EVENING.

&&

.FIRE WEATHER...
ISSUED AT 110 PM MST SUN DEC 21 2014

NO FIRE WEATHER CONCERNS THROUGH THE MIDDLE OF THE WEEK. VERY WINDY
CONDITIONS ARE EXPECTED THROUGH THIS EVENING ALONG AND WEST OF
THE LARAMIE RANGE WITH GUSTS BETWEEN 60 AND 70 MPH LIKELY.
INCREASING MOISTURE WILL KEEP THE RISK FOR RAPID FIRE GROWTH LOW.
SIGNIFICANT MOUNTAIN SNOWS WILL PERSIST OVER THE NEXT 24 TO 48
HOURS WITH TOTAL ACCUMULATIONS IN EXCESS OF 2 FEET POSSIBLE IN THE
SNOWY AND SIERRA MADRES BEFORE ALL IS SAID AND DONE.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     WINTER WEATHER ADVISORY UNTIL 8 AM MST MONDAY FOR WYZ113-115.

     WINTER STORM WARNING UNTIL 11 AM MST MONDAY FOR WYZ110-111.

NE...WIND ADVISORY FROM 8 AM TO 5 PM MST MONDAY FOR NEZ002-003-
     019>021-054-055-095-096.

&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...RUBIN
FIRE WEATHER...GCC




000
FXUS65 KCYS 220537
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1037 PM MST SUN DEC 21 2014

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

POWERFUL PACIFIC LOW PRESSURE SYSTEM CONTINUES TO MOVE INTO THE
AREA FROM THE WEST THIS AFTERNOON...BRINGING WIDESPREAD STRONG
WINDS AND NEAR BLIZZARD CONDITIONS ALONG PORTIONS OF INTERSTATE 80
OUT NEAR ARLINGTON. HAVE SEEN SOME REPORTS OF WIND GUSTS
APPROACHING 70MPH AND HAD AN 80MPH GUST REPORTED AT A UPR SITE UP
ON THE SOUTH LARAMIE RANGE. FORECAST CHALLENGES CONTINUE TO BE
MAINLY WINDS...BUT LATER THIS EVENING...WINTER WEATHER CONDITIONS
WILL TAKE SHAPE.

CURRENTLY...1015MB SURFACE LOW CURRENTLY OVER CENTRAL UTAH EARLY
THIS AFTERNOON. PERHAPS OUR STRONGEST GRADIENT IS YET TO COME AS
SURFACE ANALYSIS SHOWS THE STRONG PRESSURE GRADIENT STILL OVER
NORTHWESTERN COLORADO AND NORTHEASTERN UTAH. CRAIG TO CASPER
SURFACE GRADIENT RIGHT AROUND 12MBS AT 1 PM THIS AFTERNOON. LATEST
WRKHGT PRODUCTS HAS 850/700MB CRAIG TO CASPER HEIGHT GRADIENTS OF
75 AND 73MTRS RESPECTIVELY. MOSAIC RADAR SHOWING MOST OF THE SNOW
OVER NORTHWESTERN COLORADO AND UP OVER NORTHWESTERN WYOMING.

HEIGHT GRADIENTS REMAIN STRONG OVER SOUTHEAST WYOMING THROUGH THE
EVENING HOURS. WILL KEEP ALL WIND HEADLINES GOING AS THEY ARE FOR
NOW AS THE GFS SHOWS 700MB WINDS STILL AROUND 60-65KTS AT 06Z
TONIGHT. ECMWF SHOWS THE 500MB SHORTWAVE MOVING THROUGH CENTRAL
WYOMING INTO WESTERN NEBRASKA AFTER 06Z WITH WINDS SHIFTING
NORTHWEST BEHIND THE FRONT TONIGHT. AREAS WEST OF THE LARAMIE
RANGE STAY IN THE FAVORABLE LEFT FRONT QUADRANT OF A 170+ KT
JET...SO HEAVY SNOW LOOKS TO CONTINUE FOR THE SNOWY AND SIERRA
MADRE RANGES. LOWER ELEVATIONS WILL CONTINUE TO SEE STRONG
WINDS...THOUGH NOT AS STRONG AS TODAY...BUT ENOUGH TO KEEP WINTER
HEADLINES GOING OUT THERE THROUGH THE OVERNIGHT HOURS.

ATTENTION TURNS TO THE PANHANDLE FOR MONDAY. GFS 850MB WINDS
BEHIND THE FRONT OUT OVER THE PANHANDLE INCREASE SIGNIFICANTLY
OVERNIGHT. LOOKING AT 850MB WIND SPEEDS OF 40-45KTS FOR MUCH OF
THE PANHANDLE. WENT AHEAD WITH A WIND ADVISORY FOR NOW COVERING
MUCH OF THE DAY. LATER SHIFTS MAY NEED TO UPGRADE TO HIGH WIND
WARNINGS IF LATER GUIDANCE SHOWS ANYTHING STRONGER THAN WHAT I AM
SEEING NOW. HEAVY SNOW CONTINUES FOR THE SNOWY AND SIERRA MADRE
RANGES ALL DAY MONDAY.

FINALLY BEGIN TO SEE AN EASING ON THE SNOW OUT WEST MONDAY NIGHT
INTO TUESDAY AS THE UPPER LOW MOVES EAST. CURRENT WINTER STORM
WARNING FOR THE MOUNTAINS LOOKS GOOD THROUGH 12Z TUESDAY...NO
CHANGES MADE IN HEADLINES.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY EVENING THROUGH
FRIDAY DUE TO HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER
WEATHER ON CHRISTMAS DAY. MODELS ARE MAINTAINING RUN TO RUN
CONSISTENCY FOR THE POTENTIAL WINTER WEATHER ON CHRISTMAS...BUT
WITH SUCH A LARGE DISCREPANCY BETWEEN INDIVIDUAL MODEL RUNS...THE
PICTURE IS NOT LOOKING ANY CLEARER TODAY IN TERMS OF THE WEATHER.

EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY TRAVEL
PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS DOWNSLOPE FLOW
DEVELOPS...WITH HIGHS IN THE MID 30S TO MID 40S...WARMEST ALONG
THE I25 CORRIDOR DUE TO DOWNSLOPE FLOW NEAR THE SURFACE. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS INDICATE A RAPIDLY MOVING
PACIFIC UPPER LEVEL TROUGH PUSHING INTO THE AREA FROM THE
NORTHWEST UNITED STATES. A STRONG PACIFIC COLD FRONT IS FORECAST
TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME CHRISTMAS MORNING WITH
SNOW DEVELOPING BEHIND THE FRONT. THERE IS THE POTENTIAL FOR A
HIGH WIND EVENT ACROSS THE WIND PRONE AREAS OF SOUTHEAST WYOMING
AHEAD OF THIS FRONT...SO CONTINUED TO INCREASE WINDS OVER THE
ARLINGTON AND BORDEAUX AREAS. WIND IMPACTS SHOULD BE MINIMAL
HOWEVER FOR HOLIDAY TRAVELERS...DUE TO A RELATIVELY BRIEF PERIOD
OF STRONG WINDS...AND THE WINDS MAINLY AFFECTING HIGH PROFILE
VEHICLES.

FORECAST BECOMES TRICKY ON CHRISTMAS DAY IN TERMS OF SNOW
POTENTIAL AS THERE IS ONLY SLIGHTLY MORE CONFIDENCE COMPARED TO
YESTERDAY THAT A DECENT PORTION OF THE AREA WILL RECEIVE
ACCUMULATING SNOW. ALL MODELS NOW SHOW THE SYSTEM MOVING RAPIDLY
ACROSS THE AREA INTO THURSDAY NIGHT...WHICH IS IMPORTANT BECAUSE
IT GREATLY LOWERS THE CHANCE OF WINTER STORM CONDITIONS. THE 12Z
ECMWF IS SLIGHTLY FASTER AND SHOWING WIDESPREAD LIGHT TO MODERATE
SNOWFALL NEARLY EVERYWHERE ACROSS SOUTHEAST WYOMING AND WESTERN
NEBRASKA. THE 12Z GFS HAS BEEN CONSISTENTLY FURTHER NORTH WITH THE
TROUGH AXIS AND PORT MAX...AND THUS MUCH LESS SNOW DUE TO
DOWNSLOPE WINDS. THE PRIMARY DIFFERENCE BETWEEN THESE TWO
SOLUTIONS...OTHER THAN THE QPF...IS THE STORM TRACK AND JET STREAM
LOCATION. THE ECMWF HAS THE JET DIGGING FURTHER SOUTH WITH A
SURFACE LOW DEVELOPING NEAR THE WYOMING/COLORADO BORDER AND MOVING
SOUTHEAST. THE GFS ON THE OTHER HAND SHOWS THE JET STREAM OVER THE
STATE OF WYOMING WITH A SURFACE LOW MUCH FURTHER NORTH ACROSS
MONTANA AND THE DAKOTAS. THE NET RESULT IS BROAD DRY DOWNSLOPE
FLOW AND LLVL SUBSIDENCE COMPARED TO THE ECMWF WHICH SHOWS PLENTY
OF NORTHEAST UPSLOPE FLOW. THE GEM IS SOMEWHERE IN BETWEEN THESE
TWO EXTREMES BUT A LITTLE CLOSER TO THE GFS. ECMWF QPF VALUES
RANGE FROM ONE QUARTER OF AN INCH TO ABOUT A THIRD OF AN INCH.
WHICH MEANS THERE IS POTENTIAL FOR LIGHT TO MODERATE SNOW AMOUNTS.
INCREASED POP SLIGHTLY ACROSS THE I80 CORRIDOR TO AROUND 30 TO 40
PERCENT FOR NOW...WITH VALUES NEAR 80 PERCENT FOR THE MOUNTAINS
WHICH HAVE THE BEST CHANCE OF SEEING 6+ INCHES OF SNOW.
HOPEFULLY...MODELS TREND TOWARD A SIMILAR SOLUTION OVER THE NEXT
24 HOURS...BUT HAVE A FEELING THAT MAY NOT HAPPEN UNTIL TUESDAY
WHEN THE SYSTEM BEGINS TO MOVE ONSHORE. THERE IS HIGH CONFIDENCE
THAT MUCH COLDER TEMPERATURES WILL ENTER THE REGION FOR THE
REMAINDER OF THE WEEK AND INTO NEXT WEEKEND WITH HIGHS IN THE 20S
TO MID 30S...AND LOWS IN THE SINGLE DIGITS (ABOVE AND BELOW ZERO)
AND TEENS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1036 PM MST SUN DEC 21 2014

VFR PREVAILS WITH LOCALIZED MVFR AT LARAMIE THROUGH 09Z...AND
LOCALIZED IFR AT RAWLINS MONDAY EVENING.

&&

.FIRE WEATHER...
ISSUED AT 110 PM MST SUN DEC 21 2014

NO FIRE WEATHER CONCERNS THROUGH THE MIDDLE OF THE WEEK. VERY WINDY
CONDITIONS ARE EXPECTED THROUGH THIS EVENING ALONG AND WEST OF
THE LARAMIE RANGE WITH GUSTS BETWEEN 60 AND 70 MPH LIKELY.
INCREASING MOISTURE WILL KEEP THE RISK FOR RAPID FIRE GROWTH LOW.
SIGNIFICANT MOUNTAIN SNOWS WILL PERSIST OVER THE NEXT 24 TO 48
HOURS WITH TOTAL ACCUMULATIONS IN EXCESS OF 2 FEET POSSIBLE IN THE
SNOWY AND SIERRA MADRES BEFORE ALL IS SAID AND DONE.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     WINTER WEATHER ADVISORY UNTIL 8 AM MST MONDAY FOR WYZ113-115.

     WINTER STORM WARNING UNTIL 11 AM MST MONDAY FOR WYZ110-111.

NE...WIND ADVISORY FROM 8 AM TO 5 PM MST MONDAY FOR NEZ002-003-
     019>021-054-055-095-096.

&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...RUBIN
FIRE WEATHER...GCC



000
FXUS65 KRIW 220424
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
924 PM MST SUN DEC 21 2014

.UPDATE...DRIER AIRMASS IN NW FLOW HAS PREVAILED ACROSS THE WEST
WITH LITTLE IN THE WAY OF ADDITIONAL SNOWFALL OVER THE LAST FEW
HOURS. CANCELLED ALL WINTER STORM WARNINGS ACROSS THE WEST. COLD
FRONT IS MOVING SOUTH ACROSS SOUTHERN WYOMING AND HAS SHUT OFF THE
WIND MACHINE ACROSS SOUTH PASS AND BEAVER RIM AREAS...SO HIGH WIND
WARNING HAS BEEN TAKEN DOWN THERE. LOCATIONS FURTHER SOUTH ARE
STILL BLOWING HIGH WIND OR NEAR HIGH WIND SO LET THE WARNINGS
CONTINUE...BUT COLD FRONT AND NW FLOW WILL SOON END THE EVENT
THERE AS WELL.

&&

.PREV DISCUSSION... /ISSUED 304 PM MST SUN DEC 21 2014/

SHORT TERM...TONIGHT THROUGH WEDNESDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES WITH MORE VALLEY
LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX OR FROM A WET SNOW TO A
DRIER ACCUMULATING SNOW TONIGHT. AS THE STRONG WESTERLY FLOW
SWITCHES TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT THERE COULD BE
PERIODS OF GUSTY WIND MOVING INTO ARES MORE PRONE TO STRONG
NORTHWEST FLOW...SPECIFICALLY INTO THE WIND RIVER BASIN AND
BUFFALO/PINEY CREEK AREA. THERE DOES NOT APPEAR TO BE MUCH DOWNWARD
FORCING AS THE LEFT FRONT QUAD OF THE JET REMAINS IN THE
AREA...THERE ARE SOME 50 TO 60KT BARBS AT 700MB BUT THERE IS NOT
EXPECTED TO BE WIDESPREAD TRANSLATION TO THE SURFACE AS FORCING FOR
ASCENT WILL LIKELY WIN OUT. HOWEVER THERE WILL BE A FEW SPOTS
FLIRTING WITH HIGH WIND CRITERIA...ESPECIALLY NORTHWEST OF BUFFALO.
THE NORTHWEST FLOW WILL ALSO BRING DOWN A COLD POOL
ALOFT...INCREASING LOW AND MID LEVEL LAPSE RATES TO OVER 8.5DEG/KM
IN SOME CASES...ESPECIALLY ALONG AND EAST OF THE DIVIDE...AS WELL AS
IN SOME LOCATIONS WEST OF THE DIVIDE LIKE THE TETONS AND YELLOWSTONE.
COULD BE AN INTERESTING EVENING FOR SNOW BANDING. ONE BAND HAS
ALREADY MOVED ACROSS DUBOIS...DROPPING ABOUT AN INCH OF SNOW IN LESS
THAN ONE HOUR.

ON MONDAY...THE MAIN TROUGH MOVES EAST AND UNDERGOES RAPID
CYCLOGENESIS IN THE PLAINS. AROUND THE BACK OF THE TROUGH WE ARE
LOOKING AT A SHORT WAVE THAT IS SET TO MOVE THROUGH LATE TOMORROW
AFTERNOON. LOOKING AT STRICTLY THE MODEL QPF...IT WOULD APPEAR AS IF
NOT MUCH WILL COME OV IT. HOWEVER...THERE WILL STILL BE SOME DECENT
MOISTURE HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS A
SECOND COLD POOL ALOFT SETTLES IN COMBINING WITH A SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ALONG THE BIGHORNS INTO JOHNSON
COUNTY...POPS WERE ALSO INCREASED FOR POTENTIAL SNOW BANDING
ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM SHOSHONI THROUGH CASPER
AND AREAS SOUTHEAST OF THE EASTERN TIP OF THE WIND RIVER MOUNTAINS.
STAYED FAIRLY CONSERVATIVE WITH QPF AND SNOW AMOUNTS GIVEN THE
CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ON TUESDAY...HIGH PRESSURE BUILDS INTO THE WEST WITH ANOTHER SNOW
SHOWER OR TWO POSSIBLE ALONG THE I25 CORRIDOR AND IN THE BIGHORNS.
ELSEWHERE...CLEARING AND COOL WITH DECREASING WINDS. ON
WEDNESDAY...A RIDGE BUILDS IN ALOFT WHILE A LEE TROUGH DIGS AT THE
SURFACE...INCREASING WINDS FROM ROCK SPRINGS TO CASPER IN THE
AFTERNOON. OTHERWISE...INCREASING CLOUDS WITH MORE SNOW EXPECTED
ACROSS THE WEST AND NORTH LATE IN THE AFTERNOON.

LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

GOING INTO THE CHRISTMAS DAY FORECAST STILL BRINGS
CHALLENGES...ESPECIALLY EAST OF THE DIVIDE. ONE THING IS CERTAIN...
A COLD FRONT WILL BRING COLDER TEMPERATURES TO THE REGION BY EARLY
CHRISTMAS MORNING.

ECMWF MODEL STILL DIGS SYSTEM TO THE SOUTHWEST OF FORECAST AREA ON
CHRISTMAS MORNING. THE LOW COMES OVER THE ROCKIES AS AN OPEN WAVE.
BUT THERE SHOULD BE A LONG ENOUGH PERIOD OF UPSLOPE FLOW ON BOTH
SIDES OF THE DIVIDE FOR A FEW INCHES OF SNOW. THIS IS TYPICAL MOST
LOCATIONS EAST OF THE DIVIDE AFTER FROPA. HOWEVER...LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE ALONG FAVORED NORTHEAST MOUNTAIN SLOPES
ON CHRISTMAS. DID NOT CHANGE POPS MUCH ON THURSDAY INTO THURSDAY
NIGHT. REGARDLESS...THIS IS NOT SHAPING UP TO BE A BIG SNOW EVENT.

FLOW ALOFT THEN SUPPORTS SCATTERED SNOW SHOWERS ON FRIDAY. THINKING
IS THAT THERE WILL BE ENOUGH INSTABILITY ALOFT...ESPECIALLY OVER THE
WESTERN AND NORTHERN MOUNTAIN RANGES. BOTH THURSDAY AND FRIDAY
NIGHTS SHOULD BE QUITE COLD...ESPECIALLY WITH ANY FRESH SNOW COVER.

MOSTLY DRY W-NW FLOW THEN SETS UP OVER THE FORECAST AREA SATURDAY
INTO SUNDAY. DETAILS VARY A BIT WITH EACH MEDIUM RANGE MODEL...BUT
LOOKS LIKE TEMPERATURES WILL MODERATE NEXT WEEKEND. POSSIBLY BETTER
CHANCE FOR SNOW NORTHWEST WYOMING MOUNTAINS BY SUNDAY AFTERNOON.

AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE MIXING OUT. EXPECT PERIODS OF 20 TO 30KT WINDS WITH GUSTS MAINLY
IN THE 35-45KT RANGE BUT A FEW MORE WIND PRONE AREAS COULD SEE GUSTS
UP TO 55KT...BUT NOT AT ANY OF THE FORECAST TERMINALS. A STRONG NW
FLOW WILL FOLLOW THIS SYSTEM TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW
SHOWERS POSSIBLE ALONG THE FRONT ACROSS THE LOWER ELEVATIONS THIS
EVENING...ESPECIALLY VCNTY AND EAST OF INTERSTATE 25. DRIER AIR
PREVAIL NW-SE BUT GUSTY NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

STRONG MTN TOP WINDS RESULTING IN AREAS MDT-SVR TURBULENCE AND
LLWS...WILL CONTINUE THROUGH THE NIGHT. A COLD FRONT WILL CONTINUE
TO PUSH SOUTH ACROSS THE AREA CROSSING INTERSTATE 80 AROUND 03Z
MONDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

&&

$$

UPDATE...AEM
SHORT TERM...ALLEN
LONG TERM...KPL
AVIATION...ALLEN
FIRE WEATHER...ALLEN






000
FXUS65 KRIW 220424
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
924 PM MST SUN DEC 21 2014

.UPDATE...DRIER AIRMASS IN NW FLOW HAS PREVAILED ACROSS THE WEST
WITH LITTLE IN THE WAY OF ADDITIONAL SNOWFALL OVER THE LAST FEW
HOURS. CANCELLED ALL WINTER STORM WARNINGS ACROSS THE WEST. COLD
FRONT IS MOVING SOUTH ACROSS SOUTHERN WYOMING AND HAS SHUT OFF THE
WIND MACHINE ACROSS SOUTH PASS AND BEAVER RIM AREAS...SO HIGH WIND
WARNING HAS BEEN TAKEN DOWN THERE. LOCATIONS FURTHER SOUTH ARE
STILL BLOWING HIGH WIND OR NEAR HIGH WIND SO LET THE WARNINGS
CONTINUE...BUT COLD FRONT AND NW FLOW WILL SOON END THE EVENT
THERE AS WELL.

&&

.PREV DISCUSSION... /ISSUED 304 PM MST SUN DEC 21 2014/

SHORT TERM...TONIGHT THROUGH WEDNESDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES WITH MORE VALLEY
LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX OR FROM A WET SNOW TO A
DRIER ACCUMULATING SNOW TONIGHT. AS THE STRONG WESTERLY FLOW
SWITCHES TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT THERE COULD BE
PERIODS OF GUSTY WIND MOVING INTO ARES MORE PRONE TO STRONG
NORTHWEST FLOW...SPECIFICALLY INTO THE WIND RIVER BASIN AND
BUFFALO/PINEY CREEK AREA. THERE DOES NOT APPEAR TO BE MUCH DOWNWARD
FORCING AS THE LEFT FRONT QUAD OF THE JET REMAINS IN THE
AREA...THERE ARE SOME 50 TO 60KT BARBS AT 700MB BUT THERE IS NOT
EXPECTED TO BE WIDESPREAD TRANSLATION TO THE SURFACE AS FORCING FOR
ASCENT WILL LIKELY WIN OUT. HOWEVER THERE WILL BE A FEW SPOTS
FLIRTING WITH HIGH WIND CRITERIA...ESPECIALLY NORTHWEST OF BUFFALO.
THE NORTHWEST FLOW WILL ALSO BRING DOWN A COLD POOL
ALOFT...INCREASING LOW AND MID LEVEL LAPSE RATES TO OVER 8.5DEG/KM
IN SOME CASES...ESPECIALLY ALONG AND EAST OF THE DIVIDE...AS WELL AS
IN SOME LOCATIONS WEST OF THE DIVIDE LIKE THE TETONS AND YELLOWSTONE.
COULD BE AN INTERESTING EVENING FOR SNOW BANDING. ONE BAND HAS
ALREADY MOVED ACROSS DUBOIS...DROPPING ABOUT AN INCH OF SNOW IN LESS
THAN ONE HOUR.

ON MONDAY...THE MAIN TROUGH MOVES EAST AND UNDERGOES RAPID
CYCLOGENESIS IN THE PLAINS. AROUND THE BACK OF THE TROUGH WE ARE
LOOKING AT A SHORT WAVE THAT IS SET TO MOVE THROUGH LATE TOMORROW
AFTERNOON. LOOKING AT STRICTLY THE MODEL QPF...IT WOULD APPEAR AS IF
NOT MUCH WILL COME OV IT. HOWEVER...THERE WILL STILL BE SOME DECENT
MOISTURE HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS A
SECOND COLD POOL ALOFT SETTLES IN COMBINING WITH A SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ALONG THE BIGHORNS INTO JOHNSON
COUNTY...POPS WERE ALSO INCREASED FOR POTENTIAL SNOW BANDING
ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM SHOSHONI THROUGH CASPER
AND AREAS SOUTHEAST OF THE EASTERN TIP OF THE WIND RIVER MOUNTAINS.
STAYED FAIRLY CONSERVATIVE WITH QPF AND SNOW AMOUNTS GIVEN THE
CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ON TUESDAY...HIGH PRESSURE BUILDS INTO THE WEST WITH ANOTHER SNOW
SHOWER OR TWO POSSIBLE ALONG THE I25 CORRIDOR AND IN THE BIGHORNS.
ELSEWHERE...CLEARING AND COOL WITH DECREASING WINDS. ON
WEDNESDAY...A RIDGE BUILDS IN ALOFT WHILE A LEE TROUGH DIGS AT THE
SURFACE...INCREASING WINDS FROM ROCK SPRINGS TO CASPER IN THE
AFTERNOON. OTHERWISE...INCREASING CLOUDS WITH MORE SNOW EXPECTED
ACROSS THE WEST AND NORTH LATE IN THE AFTERNOON.

LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

GOING INTO THE CHRISTMAS DAY FORECAST STILL BRINGS
CHALLENGES...ESPECIALLY EAST OF THE DIVIDE. ONE THING IS CERTAIN...
A COLD FRONT WILL BRING COLDER TEMPERATURES TO THE REGION BY EARLY
CHRISTMAS MORNING.

ECMWF MODEL STILL DIGS SYSTEM TO THE SOUTHWEST OF FORECAST AREA ON
CHRISTMAS MORNING. THE LOW COMES OVER THE ROCKIES AS AN OPEN WAVE.
BUT THERE SHOULD BE A LONG ENOUGH PERIOD OF UPSLOPE FLOW ON BOTH
SIDES OF THE DIVIDE FOR A FEW INCHES OF SNOW. THIS IS TYPICAL MOST
LOCATIONS EAST OF THE DIVIDE AFTER FROPA. HOWEVER...LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE ALONG FAVORED NORTHEAST MOUNTAIN SLOPES
ON CHRISTMAS. DID NOT CHANGE POPS MUCH ON THURSDAY INTO THURSDAY
NIGHT. REGARDLESS...THIS IS NOT SHAPING UP TO BE A BIG SNOW EVENT.

FLOW ALOFT THEN SUPPORTS SCATTERED SNOW SHOWERS ON FRIDAY. THINKING
IS THAT THERE WILL BE ENOUGH INSTABILITY ALOFT...ESPECIALLY OVER THE
WESTERN AND NORTHERN MOUNTAIN RANGES. BOTH THURSDAY AND FRIDAY
NIGHTS SHOULD BE QUITE COLD...ESPECIALLY WITH ANY FRESH SNOW COVER.

MOSTLY DRY W-NW FLOW THEN SETS UP OVER THE FORECAST AREA SATURDAY
INTO SUNDAY. DETAILS VARY A BIT WITH EACH MEDIUM RANGE MODEL...BUT
LOOKS LIKE TEMPERATURES WILL MODERATE NEXT WEEKEND. POSSIBLY BETTER
CHANCE FOR SNOW NORTHWEST WYOMING MOUNTAINS BY SUNDAY AFTERNOON.

AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE MIXING OUT. EXPECT PERIODS OF 20 TO 30KT WINDS WITH GUSTS MAINLY
IN THE 35-45KT RANGE BUT A FEW MORE WIND PRONE AREAS COULD SEE GUSTS
UP TO 55KT...BUT NOT AT ANY OF THE FORECAST TERMINALS. A STRONG NW
FLOW WILL FOLLOW THIS SYSTEM TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW
SHOWERS POSSIBLE ALONG THE FRONT ACROSS THE LOWER ELEVATIONS THIS
EVENING...ESPECIALLY VCNTY AND EAST OF INTERSTATE 25. DRIER AIR
PREVAIL NW-SE BUT GUSTY NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

STRONG MTN TOP WINDS RESULTING IN AREAS MDT-SVR TURBULENCE AND
LLWS...WILL CONTINUE THROUGH THE NIGHT. A COLD FRONT WILL CONTINUE
TO PUSH SOUTH ACROSS THE AREA CROSSING INTERSTATE 80 AROUND 03Z
MONDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

&&

$$

UPDATE...AEM
SHORT TERM...ALLEN
LONG TERM...KPL
AVIATION...ALLEN
FIRE WEATHER...ALLEN







000
FXUS63 KUNR 220324
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
824 PM MST SUN DEC 21 2014

.UPDATE...
ISSUED AT 808 PM MST SUN DEC 21 2014

ONLY MINOR ADJUSTMENTS NECESSARY TO THE FCST THIS EVENING. FIRST
ROUND OF UPSLOPE PCPN IS NOW REACHING THE NRN BLKHLS. LATEST
GUIDANCE SHOWING THERE WILL BE BREAKS IN THE PCPN DURING THE DAY
MONDAY IN BOTH THE NRN BLKHLS AND THE PLAINS...THEN BECOME MORE
WDSPRD MONDAY NIGHT AS NEXT DISTURBANCE MOVES IN. WIND STILL LOOKS
TO BE A BIG ISSUE LATER TONIGHT AND THROUGH MONDAY...STRONGEST
AROUND THE EAST SIDE OF THE BLKHLS. OF COURSE...ANY SNOW COMBINED
WITH THE WIND COULD CREATE VERY POOR VSBYS. CURRENT HIGHLIGHTS
COVER THINGS WELL.

&&

.SHORT TERM...THIS EVENING THROUGH MONDAY NIGHT
ISSUED AT 354 PM MST SUN DEC 21 2014

CURRENT SURFACE ANALYSIS SHOWS LOW PRESSURE OVER SOUTHWEST
SK...WITH FRONTAL BOUNDARY STRETCHING SOUTHEASTWARD INTO THE
WESTERN DAKOTAS. MAIN COLD FRONT LIES SOUTH AND WEST OF THE LOW
FROM NORTHEAST MT TO CENTRAL WY. UPPER LEVEL ANALYSIS SHOWS ZONAL
FLOW OVER THE REGION...WITH A VERY STRONG UPPER JET...150
KT+...STRETCHING ACROSS THE PACIFIC NW INTO THE ROCKIES. UPPER
LEVEL ENERGY IS MOVING QUICKLY EAST ACROSS THE PACIFIC NW AND
SOUTHWEST CANADA. A SHORTWAVE TROF IS STRENGTHENING AND DIGGING
SOUTH ACROSS MT RIGHT NOW. SKIES HAVE BECOME MOSTLY CLOUDY ACROSS
MUCH OF THE AREA...WITH SCATTERED RAIN SHOWERS NOW OVER NORTHEAST
WY AND WESTERN SD. TEMPS ARE MOSTLY IN THE 40S TO AROUND 50
DEGREES.

A UNSETTLED BEGINNING TO THE WEEK CAN BE EXPECTED AS A STORM SYSTEM
DEVELOPS AND INTENSIFIES OVER THE REGION TONIGHT AND MONDAY. VARIOUS
SHORT RANGE MODELS ARE IN GOOD AGREEMENT ON GENERAL DEVELOPMENT...
BUT STILL HAVE DIFFERENCES WITH REGARD TO TRACK AND STRENGTH BETWEEN
TONIGHT AND TUESDAY. THE TRACK OF THE STORM WILL BE IMPORTANT WITH
REGARD TO WHERE AREAS OF HEAVIER PCPN MAY DEVELOP OVER THE
PLAINS...WITH STRONG WINDS ALSO COMPLICATING THINGS. THE GFS AND NAM
DIG THE DEVELOPING LOW FURTHER SOUTH AND QUICKER THAN THE ECMWF AND
GEM. WILL LEAN MORE TOWARD A BLEND OF THE GFS AND ECMWF FOR THIS
FORECAST.

FOR TONIGHT...PCPN WILL EXPAND ACROSS THE AREA FROM WEST TO EAST AS
THE FRONT PASSES AND THE NEXT DISTURBANCE ALOFT CROSSES. THE CHANGE
OVER TO SNOW SHOULD BE GRADUAL FROM WEST TO EAST AS THE AIR BEHIND
THE FRONT IS NOT THAT COLD. PCPN WILL CHANGE OVER THE QUICKEST OVER
THE BLACK HILLS...DURING THE EVENING HOURS...WITH A MORE GRADUAL
CHANGE OVERNIGHT ACROSS THE PLAINS. SNOWFALL AMOUNTS OF UP TO AN
INCH OR SO IS EXPECTED ON THE PLAINS...WITH 2 TO 4 INCHES POSSIBLE
BY MORNING OVER THE TERRAIN FAVORED AREAS OF THE BLACK HILLS.
NORTHWESTERLY WINDS WILL GRADUALLY INCREASE BEHIND THE FRONT
OVERNIGHT...BECOMING BREEZY TO WINDY IN MOST AREAS BY EARLY MORNING.
LOWS WILL MOSTLY BE IN THE UPPER 20S AND LOWER 30S...A BIT COLDER
OVER THE HIGHER BLACK HILLS.

ON MONDAY...AREAS OF SNOW CAN BE EXPECTED IN THE MORNING...WITH THE
MOST PERSISTENT SNOW OVER THE NORTHERN BLACK HILLS AREA. AS THE
STACKED LOW PRESSURE SYSTEM MOVES INTO EASTERN SD/EASTERN NEB DURING
THE DAY...WINDS WILL FURTHER INCREASE AND PCPN WILL EXPAND ACROSS
THE AREA ON THE BACK SIDE OF THE SYSTEM AS SHORTWAVE ENERGY WRAPS
AROUND THE SYSTEM...ESPECIALLY DURING THE AFTERNOON AND EVENING.
PERIODS OF SNOW AND BLOWING SNOW ARE LIKELY ACROSS A GOOD PORTION OF
THE PLAINS THROUGH MONDAY NIGHT. THE EXCEPTION WILL LIKELY BE
DOWNSLOPED AREAS OF SOUTHWESTERN SD...FROM NEAR RAPID CITY TO THE
SOUTHERN BLACK HILLS...HOT SPRINGS...AND EDGEMONT...WHERE THIS
SHOULD MOSTLY BE A WIND EVENT.

A MYRIAD OF WARNINGS AND ADVISORIES HAVE BEEN ISSUED FOR MOST OF THE
CWA...POSSIBLY SUBJECT TO SOME CHANGE OVER THE NEXT 12 TO 24 HOURS
AS CONDITIONS WARRANT. SOUTH CENTRAL SD WILL LIKELY NEED TO BE ADDED
TO THE WINTER WX HEADLINES FOR LATER MONDAY AND MONDAY NIGHT IF THE
CURRENT TRENDS HOLD...BUT WILL LET THE NIGHT SHIFT HAVE ANOTHER LOOK
AT THE POTENTIAL THERE. FORECASTED SNOWFALL TOTALS FOR NOW RANGE
FROM 2 TO 5 INCHES ACROSS MUCH OF FAR NORTHEAST WY AND THE WESTERN
AND SOUTH CENTRAL SOUTH DAKOTA PLAINS TO 6 TO 12+ OVER THE NORTHERN
BLACK HILLS. UP TO AN INCH OR TWO IS POSSIBLE ACROSS DOWNSLOPED
AREAS OF SOUTHWESTERN SD.

.LONG TERM...TUESDAY THROUGH SUNDAY
ISSUED AT 354 PM MST SUN DEC 21 2014

UPPER TROF MOVES EASTWARD INTO MN-MISSOURI VALLEY BY EARLY TUES...
WITH NORTHERLY FLOW ASSOCIATED WITH 120KT JET OVER FRONT RANGE.
MODELS IN GOOD AGREEMENT WITH GENERAL SURFACE LOW PLACEMENT OVER IA
AND STRONG PRESSURE GRADIENT OVER FORECAST AREA MEANS GUSTY WINDS
WILL PERSIST EARLY TUES...AS WELL AS SOME SNOW LINGERING OVER SOUTH
CENTRAL SD AND NORTHERN BLACK HILLS...THEN GRADIENT DECREASES AS
HIGH PRESSURE BUILDS OVER THE GREAT BASIN. NEXT UPPER TROF COMING
ONSHORE PACIFIC NORTHWEST FORMS A BROAD RIDGE OVER THE ROCKIES AND
HIGH PLAINS WED...BUT TROF MOVES EASTWARD ONTO THE PLAINS. GFS HAS
SURFACE LOW WITH TRAILING COLD FRONT DROPPING ACROSS AREA CHRISTMAS
DAY...WHICH WOULD KEEP BETTER CHANCE OF SNOW OVER ND...AND MOSTLY
LIGHT POST-FRONTAL SNOW SHOWERS OVER SD...WHILE ECMWF FORMS LOW OVER
THE CENTRAL PLAINS...AND BAND OF SNOW IS FARTHER SOUTH OVER SOUTHERN
SD AND NE. CYCLONIC NORTHWEST FLOW REMAINS OVER THE AREA BEHIND THE
TROF...WITH OCCASIONAL WAVES DROPPING INTO MAIN TROF PRODUCING
CHANCES OF SNOW. ARCTIC SURFACE HI PRESSURE WILL KEEP TEMPERATURES
COLD.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 808 PM MST SUN DEC 21 2014

MAINLY VFR CONDITIONS EARLY THIS EVE WILL CONTINUE TO DETERIORATE
LATE TONIGHT AS SNOW DEVELOPS FROM NW TO SE. IFR/LIFR CONDITIONS
POSSIBLE IN THE NRN BLKHLS DUE TO UPSLOPE SNOW. WDSPRD MVFR
CONDITIONS AND LOCALIZED IFR CONDITIONS (MAINLY IN THE NRN BLKHLS) EXPECTED
THROUGH THE DAY MONDAY. GUSTY NW WINDS TO 50KTS EXPECTED LATER
TONIGHT AND MONDAY...STRONGEST ALONG THE ERN SLOPES OF THE BLKHLS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR SDZ024.

     WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 5 AM MST
     TUESDAY FOR SDZ001-002-012>014-025-031-032-042>044-072-073.

     WIND ADVISORY FROM 8 AM TO 6 PM MST MONDAY FOR SDZ027-030-041-
     074.

     WINTER WEATHER ADVISORY UNTIL NOON MST TUESDAY FOR SDZ028.

     HIGH WIND WARNING FROM 8 AM TO 8 PM MST MONDAY FOR SDZ026.

WY...WINTER STORM WARNING UNTIL NOON MST TUESDAY FOR WYZ057.

     WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 5 AM MST
     TUESDAY FOR WYZ056-071.

&&

$$

UPDATE...JOHNSON
SHORT TERM...26
LONG TERM...55
AVIATION...JOHNSON







000
FXUS65 KCYS 220035
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
535 PM MST SUN DEC 21 2014

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

POWERFUL PACIFIC LOW PRESSURE SYSTEM CONTINUES TO MOVE INTO THE
AREA FROM THE WEST THIS AFTERNOON...BRINGING WIDESPREAD STRONG
WINDS AND NEAR BLIZZARD CONDITIONS ALONG PORTIONS OF INTERSTATE 80
OUT NEAR ARLINGTON. HAVE SEEN SOME REPORTS OF WIND GUSTS
APPROACHING 70MPH AND HAD AN 80MPH GUST REPORTED AT A UPR SITE UP
ON THE SOUTH LARAMIE RANGE. FORECAST CHALLENGES CONTINUE TO BE
MAINLY WINDS...BUT LATER THIS EVENING...WINTER WEATHER CONDITIONS
WILL TAKE SHAPE.

CURRENTLY...1015MB SURFACE LOW CURRENTLY OVER CENTRAL UTAH EARLY
THIS AFTERNOON. PERHAPS OUR STRONGEST GRADIENT IS YET TO COME AS
SURFACE ANALYSIS SHOWS THE STRONG PRESSURE GRADIENT STILL OVER
NORTHWESTERN COLORADO AND NORTHEASTERN UTAH. CRAIG TO CASPER
SURFACE GRADIENT RIGHT AROUND 12MBS AT 1 PM THIS AFTERNOON. LATEST
WRKHGT PRODUCTS HAS 850/700MB CRAIG TO CASPER HEIGHT GRADIENTS OF
75 AND 73MTRS RESPECTIVELY. MOSAIC RADAR SHOWING MOST OF THE SNOW
OVER NORTHWESTERN COLORADO AND UP OVER NORTHWESTERN WYOMING.

HEIGHT GRADIENTS REMAIN STRONG OVER SOUTHEAST WYOMING THROUGH THE
EVENING HOURS. WILL KEEP ALL WIND HEADLINES GOING AS THEY ARE FOR
NOW AS THE GFS SHOWS 700MB WINDS STILL AROUND 60-65KTS AT 06Z
TONIGHT. ECMWF SHOWS THE 500MB SHORTWAVE MOVING THROUGH CENTRAL
WYOMING INTO WESTERN NEBRASKA AFTER 06Z WITH WINDS SHIFTING
NORTHWEST BEHIND THE FRONT TONIGHT. AREAS WEST OF THE LARAMIE
RANGE STAY IN THE FAVORABLE LEFT FRONT QUADRANT OF A 170+ KT
JET...SO HEAVY SNOW LOOKS TO CONTINUE FOR THE SNOWY AND SIERRA
MADRE RANGES. LOWER ELEVATIONS WILL CONTINUE TO SEE STRONG
WINDS...THOUGH NOT AS STRONG AS TODAY...BUT ENOUGH TO KEEP WINTER
HEADLINES GOING OUT THERE THROUGH THE OVERNIGHT HOURS.

ATTENTION TURNS TO THE PANHANDLE FOR MONDAY. GFS 850MB WINDS
BEHIND THE FRONT OUT OVER THE PANHANDLE INCREASE SIGNIFICANTLY
OVERNIGHT. LOOKING AT 850MB WIND SPEEDS OF 40-45KTS FOR MUCH OF
THE PANHANDLE. WENT AHEAD WITH A WIND ADVISORY FOR NOW COVERING
MUCH OF THE DAY. LATER SHIFTS MAY NEED TO UPGRADE TO HIGH WIND
WARNINGS IF LATER GUIDANCE SHOWS ANYTHING STRONGER THAN WHAT I AM
SEEING NOW. HEAVY SNOW CONTINUES FOR THE SNOWY AND SIERRA MADRE
RANGES ALL DAY MONDAY.

FINALLY BEGIN TO SEE AN EASING ON THE SNOW OUT WEST MONDAY NIGHT
INTO TUESDAY AS THE UPPER LOW MOVES EAST. CURRENT WINTER STORM
WARNING FOR THE MOUNTAINS LOOKS GOOD THROUGH 12Z TUESDAY...NO
CHANGES MADE IN HEADLINES.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY EVENING THROUGH
FRIDAY DUE TO HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER
WEATHER ON CHRISTMAS DAY. MODELS ARE MAINTAINING RUN TO RUN
CONSISTENCY FOR THE POTENTIAL WINTER WEATHER ON CHRISTMAS...BUT
WITH SUCH A LARGE DISCREPANCY BETWEEN INDIVIDUAL MODEL RUNS...THE
PICTURE IS NOT LOOKING ANY CLEARER TODAY IN TERMS OF THE WEATHER.

EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY TRAVEL
PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS DOWNSLOPE FLOW
DEVELOPS...WITH HIGHS IN THE MID 30S TO MID 40S...WARMEST ALONG
THE I25 CORRIDOR DUE TO DOWNSLOPE FLOW NEAR THE SURFACE. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS INDICATE A RAPIDLY MOVING
PACIFIC UPPER LEVEL TROUGH PUSHING INTO THE AREA FROM THE
NORTHWEST UNITED STATES. A STRONG PACIFIC COLD FRONT IS FORECAST
TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME CHRISTMAS MORNING WITH
SNOW DEVELOPING BEHIND THE FRONT. THERE IS THE POTENTIAL FOR A
HIGH WIND EVENT ACROSS THE WIND PRONE AREAS OF SOUTHEAST WYOMING
AHEAD OF THIS FRONT...SO CONTINUED TO INCREASE WINDS OVER THE
ARLINGTON AND BORDEAUX AREAS. WIND IMPACTS SHOULD BE MINIMAL
HOWEVER FOR HOLIDAY TRAVELERS...DUE TO A RELATIVELY BRIEF PERIOD
OF STRONG WINDS...AND THE WINDS MAINLY AFFECTING HIGH PROFILE
VEHICLES.

FORECAST BECOMES TRICKY ON CHRISTMAS DAY IN TERMS OF SNOW
POTENTIAL AS THERE IS ONLY SLIGHTLY MORE CONFIDENCE COMPARED TO
YESTERDAY THAT A DECENT PORTION OF THE AREA WILL RECEIVE
ACCUMULATING SNOW. ALL MODELS NOW SHOW THE SYSTEM MOVING RAPIDLY
ACROSS THE AREA INTO THURSDAY NIGHT...WHICH IS IMPORTANT BECAUSE
IT GREATLY LOWERS THE CHANCE OF WINTER STORM CONDITIONS. THE 12Z
ECMWF IS SLIGHTLY FASTER AND SHOWING WIDESPREAD LIGHT TO MODERATE
SNOWFALL NEARLY EVERYWHERE ACROSS SOUTHEAST WYOMING AND WESTERN
NEBRASKA. THE 12Z GFS HAS BEEN CONSISTENTLY FURTHER NORTH WITH THE
TROUGH AXIS AND PORT MAX...AND THUS MUCH LESS SNOW DUE TO
DOWNSLOPE WINDS. THE PRIMARY DIFFERENCE BETWEEN THESE TWO
SOLUTIONS...OTHER THAN THE QPF...IS THE STORM TRACK AND JET STREAM
LOCATION. THE ECMWF HAS THE JET DIGGING FURTHER SOUTH WITH A
SURFACE LOW DEVELOPING NEAR THE WYOMING/COLORADO BORDER AND MOVING
SOUTHEAST. THE GFS ON THE OTHER HAND SHOWS THE JET STREAM OVER THE
STATE OF WYOMING WITH A SURFACE LOW MUCH FURTHER NORTH ACROSS
MONTANA AND THE DAKOTAS. THE NET RESULT IS BROAD DRY DOWNSLOPE
FLOW AND LLVL SUBSIDENCE COMPARED TO THE ECMWF WHICH SHOWS PLENTY
OF NORTHEAST UPSLOPE FLOW. THE GEM IS SOMEWHERE IN BETWEEN THESE
TWO EXTREMES BUT A LITTLE CLOSER TO THE GFS. ECMWF QPF VALUES
RANGE FROM ONE QUARTER OF AN INCH TO ABOUT A THIRD OF AN INCH.
WHICH MEANS THERE IS POTENTIAL FOR LIGHT TO MODERATE SNOW AMOUNTS.
INCREASED POP SLIGHTLY ACROSS THE I80 CORRIDOR TO AROUND 30 TO 40
PERCENT FOR NOW...WITH VALUES NEAR 80 PERCENT FOR THE MOUNTAINS
WHICH HAVE THE BEST CHANCE OF SEEING 6+ INCHES OF SNOW.
HOPEFULLY...MODELS TREND TOWARD A SIMILAR SOLUTION OVER THE NEXT
24 HOURS...BUT HAVE A FEELING THAT MAY NOT HAPPEN UNTIL TUESDAY
WHEN THE SYSTEM BEGINS TO MOVE ONSHORE. THERE IS HIGH CONFIDENCE
THAT MUCH COLDER TEMPERATURES WILL ENTER THE REGION FOR THE
REMAINDER OF THE WEEK AND INTO NEXT WEEKEND WITH HIGHS IN THE 20S
TO MID 30S...AND LOWS IN THE SINGLE DIGITS (ABOVE AND BELOW ZERO)
AND TEENS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 527 PM MST SUN DEC 21 2014

WYOMING TAFS...VFR AT CHEYENNE WITH WIND GUSTS DECREASING THIS
EVENING...THEN WIND GUSTS INCREASING AFTER DAYBREAK MONDAY.
OCCASIONAL MVFR AT LARAMIE THIS EVENING...OTHERWISE VFR WITH
WIND GUSTS INCREASING OVER 40 KNOTS AFTER 15Z MONDAY. OCCASIONAL
IFR AND PERIODS OF MVFR AT RAWLINS THROUGH 09Z...THEN BECOMING
VFR WITH WIND GUSTS INCREASING NEAR 35 KNOTS AFTER 15Z.

NEBRASKA TAFS...VFR...ASIDE FROM OCCASIONAL MVFR THIS EVENING
AT SCOTTSBLUFF IN SNOW SHOWERS. STRONG NORTHWEST WIND 25 TO 35
KNOTS AFTER 15Z MONDAY WITH GUSTS 45 TO 50 KNOTS.

&&

.FIRE WEATHER...
ISSUED AT 110 PM MST SUN DEC 21 2014

NO FIRE WEATHER CONCERNS THROUGH THE MIDDLE OF THE WEEK. VERY WINDY
CONDITIONS ARE EXPECTED THROUGH THIS EVENING ALONG AND WEST OF
THE LARAMIE RANGE WITH GUSTS BETWEEN 60 AND 70 MPH LIKELY.
INCREASING MOISTURE WILL KEEP THE RISK FOR RAPID FIRE GROWTH LOW.
SIGNIFICANT MOUNTAIN SNOWS WILL PERSIST OVER THE NEXT 24 TO 48
HOURS WITH TOTAL ACCUMULATIONS IN EXCESS OF 2 FEET POSSIBLE IN THE
SNOWY AND SIERRA MADRES BEFORE ALL IS SAID AND DONE.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING UNTIL MIDNIGHT MST TONIGHT FOR WYZ104>107-109-
     116>118.

     WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     WINTER WEATHER ADVISORY UNTIL 8 AM MST MONDAY FOR WYZ113-115.

     WINTER STORM WARNING UNTIL 11 AM MST MONDAY FOR WYZ110-111.

NE...WIND ADVISORY FROM 8 AM TO 5 PM MST MONDAY FOR NEZ002-003-
     019>021-054-055-095-096.

&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...RUBIN
FIRE WEATHER...GCC




000
FXUS65 KCYS 220035
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
535 PM MST SUN DEC 21 2014

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

POWERFUL PACIFIC LOW PRESSURE SYSTEM CONTINUES TO MOVE INTO THE
AREA FROM THE WEST THIS AFTERNOON...BRINGING WIDESPREAD STRONG
WINDS AND NEAR BLIZZARD CONDITIONS ALONG PORTIONS OF INTERSTATE 80
OUT NEAR ARLINGTON. HAVE SEEN SOME REPORTS OF WIND GUSTS
APPROACHING 70MPH AND HAD AN 80MPH GUST REPORTED AT A UPR SITE UP
ON THE SOUTH LARAMIE RANGE. FORECAST CHALLENGES CONTINUE TO BE
MAINLY WINDS...BUT LATER THIS EVENING...WINTER WEATHER CONDITIONS
WILL TAKE SHAPE.

CURRENTLY...1015MB SURFACE LOW CURRENTLY OVER CENTRAL UTAH EARLY
THIS AFTERNOON. PERHAPS OUR STRONGEST GRADIENT IS YET TO COME AS
SURFACE ANALYSIS SHOWS THE STRONG PRESSURE GRADIENT STILL OVER
NORTHWESTERN COLORADO AND NORTHEASTERN UTAH. CRAIG TO CASPER
SURFACE GRADIENT RIGHT AROUND 12MBS AT 1 PM THIS AFTERNOON. LATEST
WRKHGT PRODUCTS HAS 850/700MB CRAIG TO CASPER HEIGHT GRADIENTS OF
75 AND 73MTRS RESPECTIVELY. MOSAIC RADAR SHOWING MOST OF THE SNOW
OVER NORTHWESTERN COLORADO AND UP OVER NORTHWESTERN WYOMING.

HEIGHT GRADIENTS REMAIN STRONG OVER SOUTHEAST WYOMING THROUGH THE
EVENING HOURS. WILL KEEP ALL WIND HEADLINES GOING AS THEY ARE FOR
NOW AS THE GFS SHOWS 700MB WINDS STILL AROUND 60-65KTS AT 06Z
TONIGHT. ECMWF SHOWS THE 500MB SHORTWAVE MOVING THROUGH CENTRAL
WYOMING INTO WESTERN NEBRASKA AFTER 06Z WITH WINDS SHIFTING
NORTHWEST BEHIND THE FRONT TONIGHT. AREAS WEST OF THE LARAMIE
RANGE STAY IN THE FAVORABLE LEFT FRONT QUADRANT OF A 170+ KT
JET...SO HEAVY SNOW LOOKS TO CONTINUE FOR THE SNOWY AND SIERRA
MADRE RANGES. LOWER ELEVATIONS WILL CONTINUE TO SEE STRONG
WINDS...THOUGH NOT AS STRONG AS TODAY...BUT ENOUGH TO KEEP WINTER
HEADLINES GOING OUT THERE THROUGH THE OVERNIGHT HOURS.

ATTENTION TURNS TO THE PANHANDLE FOR MONDAY. GFS 850MB WINDS
BEHIND THE FRONT OUT OVER THE PANHANDLE INCREASE SIGNIFICANTLY
OVERNIGHT. LOOKING AT 850MB WIND SPEEDS OF 40-45KTS FOR MUCH OF
THE PANHANDLE. WENT AHEAD WITH A WIND ADVISORY FOR NOW COVERING
MUCH OF THE DAY. LATER SHIFTS MAY NEED TO UPGRADE TO HIGH WIND
WARNINGS IF LATER GUIDANCE SHOWS ANYTHING STRONGER THAN WHAT I AM
SEEING NOW. HEAVY SNOW CONTINUES FOR THE SNOWY AND SIERRA MADRE
RANGES ALL DAY MONDAY.

FINALLY BEGIN TO SEE AN EASING ON THE SNOW OUT WEST MONDAY NIGHT
INTO TUESDAY AS THE UPPER LOW MOVES EAST. CURRENT WINTER STORM
WARNING FOR THE MOUNTAINS LOOKS GOOD THROUGH 12Z TUESDAY...NO
CHANGES MADE IN HEADLINES.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY EVENING THROUGH
FRIDAY DUE TO HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER
WEATHER ON CHRISTMAS DAY. MODELS ARE MAINTAINING RUN TO RUN
CONSISTENCY FOR THE POTENTIAL WINTER WEATHER ON CHRISTMAS...BUT
WITH SUCH A LARGE DISCREPANCY BETWEEN INDIVIDUAL MODEL RUNS...THE
PICTURE IS NOT LOOKING ANY CLEARER TODAY IN TERMS OF THE WEATHER.

EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY TRAVEL
PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS DOWNSLOPE FLOW
DEVELOPS...WITH HIGHS IN THE MID 30S TO MID 40S...WARMEST ALONG
THE I25 CORRIDOR DUE TO DOWNSLOPE FLOW NEAR THE SURFACE. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS INDICATE A RAPIDLY MOVING
PACIFIC UPPER LEVEL TROUGH PUSHING INTO THE AREA FROM THE
NORTHWEST UNITED STATES. A STRONG PACIFIC COLD FRONT IS FORECAST
TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME CHRISTMAS MORNING WITH
SNOW DEVELOPING BEHIND THE FRONT. THERE IS THE POTENTIAL FOR A
HIGH WIND EVENT ACROSS THE WIND PRONE AREAS OF SOUTHEAST WYOMING
AHEAD OF THIS FRONT...SO CONTINUED TO INCREASE WINDS OVER THE
ARLINGTON AND BORDEAUX AREAS. WIND IMPACTS SHOULD BE MINIMAL
HOWEVER FOR HOLIDAY TRAVELERS...DUE TO A RELATIVELY BRIEF PERIOD
OF STRONG WINDS...AND THE WINDS MAINLY AFFECTING HIGH PROFILE
VEHICLES.

FORECAST BECOMES TRICKY ON CHRISTMAS DAY IN TERMS OF SNOW
POTENTIAL AS THERE IS ONLY SLIGHTLY MORE CONFIDENCE COMPARED TO
YESTERDAY THAT A DECENT PORTION OF THE AREA WILL RECEIVE
ACCUMULATING SNOW. ALL MODELS NOW SHOW THE SYSTEM MOVING RAPIDLY
ACROSS THE AREA INTO THURSDAY NIGHT...WHICH IS IMPORTANT BECAUSE
IT GREATLY LOWERS THE CHANCE OF WINTER STORM CONDITIONS. THE 12Z
ECMWF IS SLIGHTLY FASTER AND SHOWING WIDESPREAD LIGHT TO MODERATE
SNOWFALL NEARLY EVERYWHERE ACROSS SOUTHEAST WYOMING AND WESTERN
NEBRASKA. THE 12Z GFS HAS BEEN CONSISTENTLY FURTHER NORTH WITH THE
TROUGH AXIS AND PORT MAX...AND THUS MUCH LESS SNOW DUE TO
DOWNSLOPE WINDS. THE PRIMARY DIFFERENCE BETWEEN THESE TWO
SOLUTIONS...OTHER THAN THE QPF...IS THE STORM TRACK AND JET STREAM
LOCATION. THE ECMWF HAS THE JET DIGGING FURTHER SOUTH WITH A
SURFACE LOW DEVELOPING NEAR THE WYOMING/COLORADO BORDER AND MOVING
SOUTHEAST. THE GFS ON THE OTHER HAND SHOWS THE JET STREAM OVER THE
STATE OF WYOMING WITH A SURFACE LOW MUCH FURTHER NORTH ACROSS
MONTANA AND THE DAKOTAS. THE NET RESULT IS BROAD DRY DOWNSLOPE
FLOW AND LLVL SUBSIDENCE COMPARED TO THE ECMWF WHICH SHOWS PLENTY
OF NORTHEAST UPSLOPE FLOW. THE GEM IS SOMEWHERE IN BETWEEN THESE
TWO EXTREMES BUT A LITTLE CLOSER TO THE GFS. ECMWF QPF VALUES
RANGE FROM ONE QUARTER OF AN INCH TO ABOUT A THIRD OF AN INCH.
WHICH MEANS THERE IS POTENTIAL FOR LIGHT TO MODERATE SNOW AMOUNTS.
INCREASED POP SLIGHTLY ACROSS THE I80 CORRIDOR TO AROUND 30 TO 40
PERCENT FOR NOW...WITH VALUES NEAR 80 PERCENT FOR THE MOUNTAINS
WHICH HAVE THE BEST CHANCE OF SEEING 6+ INCHES OF SNOW.
HOPEFULLY...MODELS TREND TOWARD A SIMILAR SOLUTION OVER THE NEXT
24 HOURS...BUT HAVE A FEELING THAT MAY NOT HAPPEN UNTIL TUESDAY
WHEN THE SYSTEM BEGINS TO MOVE ONSHORE. THERE IS HIGH CONFIDENCE
THAT MUCH COLDER TEMPERATURES WILL ENTER THE REGION FOR THE
REMAINDER OF THE WEEK AND INTO NEXT WEEKEND WITH HIGHS IN THE 20S
TO MID 30S...AND LOWS IN THE SINGLE DIGITS (ABOVE AND BELOW ZERO)
AND TEENS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 527 PM MST SUN DEC 21 2014

WYOMING TAFS...VFR AT CHEYENNE WITH WIND GUSTS DECREASING THIS
EVENING...THEN WIND GUSTS INCREASING AFTER DAYBREAK MONDAY.
OCCASIONAL MVFR AT LARAMIE THIS EVENING...OTHERWISE VFR WITH
WIND GUSTS INCREASING OVER 40 KNOTS AFTER 15Z MONDAY. OCCASIONAL
IFR AND PERIODS OF MVFR AT RAWLINS THROUGH 09Z...THEN BECOMING
VFR WITH WIND GUSTS INCREASING NEAR 35 KNOTS AFTER 15Z.

NEBRASKA TAFS...VFR...ASIDE FROM OCCASIONAL MVFR THIS EVENING
AT SCOTTSBLUFF IN SNOW SHOWERS. STRONG NORTHWEST WIND 25 TO 35
KNOTS AFTER 15Z MONDAY WITH GUSTS 45 TO 50 KNOTS.

&&

.FIRE WEATHER...
ISSUED AT 110 PM MST SUN DEC 21 2014

NO FIRE WEATHER CONCERNS THROUGH THE MIDDLE OF THE WEEK. VERY WINDY
CONDITIONS ARE EXPECTED THROUGH THIS EVENING ALONG AND WEST OF
THE LARAMIE RANGE WITH GUSTS BETWEEN 60 AND 70 MPH LIKELY.
INCREASING MOISTURE WILL KEEP THE RISK FOR RAPID FIRE GROWTH LOW.
SIGNIFICANT MOUNTAIN SNOWS WILL PERSIST OVER THE NEXT 24 TO 48
HOURS WITH TOTAL ACCUMULATIONS IN EXCESS OF 2 FEET POSSIBLE IN THE
SNOWY AND SIERRA MADRES BEFORE ALL IS SAID AND DONE.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING UNTIL MIDNIGHT MST TONIGHT FOR WYZ104>107-109-
     116>118.

     WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     WINTER WEATHER ADVISORY UNTIL 8 AM MST MONDAY FOR WYZ113-115.

     WINTER STORM WARNING UNTIL 11 AM MST MONDAY FOR WYZ110-111.

NE...WIND ADVISORY FROM 8 AM TO 5 PM MST MONDAY FOR NEZ002-003-
     019>021-054-055-095-096.

&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...RUBIN
FIRE WEATHER...GCC



000
FXUS65 KCYS 220035
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
535 PM MST SUN DEC 21 2014

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

POWERFUL PACIFIC LOW PRESSURE SYSTEM CONTINUES TO MOVE INTO THE
AREA FROM THE WEST THIS AFTERNOON...BRINGING WIDESPREAD STRONG
WINDS AND NEAR BLIZZARD CONDITIONS ALONG PORTIONS OF INTERSTATE 80
OUT NEAR ARLINGTON. HAVE SEEN SOME REPORTS OF WIND GUSTS
APPROACHING 70MPH AND HAD AN 80MPH GUST REPORTED AT A UPR SITE UP
ON THE SOUTH LARAMIE RANGE. FORECAST CHALLENGES CONTINUE TO BE
MAINLY WINDS...BUT LATER THIS EVENING...WINTER WEATHER CONDITIONS
WILL TAKE SHAPE.

CURRENTLY...1015MB SURFACE LOW CURRENTLY OVER CENTRAL UTAH EARLY
THIS AFTERNOON. PERHAPS OUR STRONGEST GRADIENT IS YET TO COME AS
SURFACE ANALYSIS SHOWS THE STRONG PRESSURE GRADIENT STILL OVER
NORTHWESTERN COLORADO AND NORTHEASTERN UTAH. CRAIG TO CASPER
SURFACE GRADIENT RIGHT AROUND 12MBS AT 1 PM THIS AFTERNOON. LATEST
WRKHGT PRODUCTS HAS 850/700MB CRAIG TO CASPER HEIGHT GRADIENTS OF
75 AND 73MTRS RESPECTIVELY. MOSAIC RADAR SHOWING MOST OF THE SNOW
OVER NORTHWESTERN COLORADO AND UP OVER NORTHWESTERN WYOMING.

HEIGHT GRADIENTS REMAIN STRONG OVER SOUTHEAST WYOMING THROUGH THE
EVENING HOURS. WILL KEEP ALL WIND HEADLINES GOING AS THEY ARE FOR
NOW AS THE GFS SHOWS 700MB WINDS STILL AROUND 60-65KTS AT 06Z
TONIGHT. ECMWF SHOWS THE 500MB SHORTWAVE MOVING THROUGH CENTRAL
WYOMING INTO WESTERN NEBRASKA AFTER 06Z WITH WINDS SHIFTING
NORTHWEST BEHIND THE FRONT TONIGHT. AREAS WEST OF THE LARAMIE
RANGE STAY IN THE FAVORABLE LEFT FRONT QUADRANT OF A 170+ KT
JET...SO HEAVY SNOW LOOKS TO CONTINUE FOR THE SNOWY AND SIERRA
MADRE RANGES. LOWER ELEVATIONS WILL CONTINUE TO SEE STRONG
WINDS...THOUGH NOT AS STRONG AS TODAY...BUT ENOUGH TO KEEP WINTER
HEADLINES GOING OUT THERE THROUGH THE OVERNIGHT HOURS.

ATTENTION TURNS TO THE PANHANDLE FOR MONDAY. GFS 850MB WINDS
BEHIND THE FRONT OUT OVER THE PANHANDLE INCREASE SIGNIFICANTLY
OVERNIGHT. LOOKING AT 850MB WIND SPEEDS OF 40-45KTS FOR MUCH OF
THE PANHANDLE. WENT AHEAD WITH A WIND ADVISORY FOR NOW COVERING
MUCH OF THE DAY. LATER SHIFTS MAY NEED TO UPGRADE TO HIGH WIND
WARNINGS IF LATER GUIDANCE SHOWS ANYTHING STRONGER THAN WHAT I AM
SEEING NOW. HEAVY SNOW CONTINUES FOR THE SNOWY AND SIERRA MADRE
RANGES ALL DAY MONDAY.

FINALLY BEGIN TO SEE AN EASING ON THE SNOW OUT WEST MONDAY NIGHT
INTO TUESDAY AS THE UPPER LOW MOVES EAST. CURRENT WINTER STORM
WARNING FOR THE MOUNTAINS LOOKS GOOD THROUGH 12Z TUESDAY...NO
CHANGES MADE IN HEADLINES.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY EVENING THROUGH
FRIDAY DUE TO HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER
WEATHER ON CHRISTMAS DAY. MODELS ARE MAINTAINING RUN TO RUN
CONSISTENCY FOR THE POTENTIAL WINTER WEATHER ON CHRISTMAS...BUT
WITH SUCH A LARGE DISCREPANCY BETWEEN INDIVIDUAL MODEL RUNS...THE
PICTURE IS NOT LOOKING ANY CLEARER TODAY IN TERMS OF THE WEATHER.

EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY TRAVEL
PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS DOWNSLOPE FLOW
DEVELOPS...WITH HIGHS IN THE MID 30S TO MID 40S...WARMEST ALONG
THE I25 CORRIDOR DUE TO DOWNSLOPE FLOW NEAR THE SURFACE. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS INDICATE A RAPIDLY MOVING
PACIFIC UPPER LEVEL TROUGH PUSHING INTO THE AREA FROM THE
NORTHWEST UNITED STATES. A STRONG PACIFIC COLD FRONT IS FORECAST
TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME CHRISTMAS MORNING WITH
SNOW DEVELOPING BEHIND THE FRONT. THERE IS THE POTENTIAL FOR A
HIGH WIND EVENT ACROSS THE WIND PRONE AREAS OF SOUTHEAST WYOMING
AHEAD OF THIS FRONT...SO CONTINUED TO INCREASE WINDS OVER THE
ARLINGTON AND BORDEAUX AREAS. WIND IMPACTS SHOULD BE MINIMAL
HOWEVER FOR HOLIDAY TRAVELERS...DUE TO A RELATIVELY BRIEF PERIOD
OF STRONG WINDS...AND THE WINDS MAINLY AFFECTING HIGH PROFILE
VEHICLES.

FORECAST BECOMES TRICKY ON CHRISTMAS DAY IN TERMS OF SNOW
POTENTIAL AS THERE IS ONLY SLIGHTLY MORE CONFIDENCE COMPARED TO
YESTERDAY THAT A DECENT PORTION OF THE AREA WILL RECEIVE
ACCUMULATING SNOW. ALL MODELS NOW SHOW THE SYSTEM MOVING RAPIDLY
ACROSS THE AREA INTO THURSDAY NIGHT...WHICH IS IMPORTANT BECAUSE
IT GREATLY LOWERS THE CHANCE OF WINTER STORM CONDITIONS. THE 12Z
ECMWF IS SLIGHTLY FASTER AND SHOWING WIDESPREAD LIGHT TO MODERATE
SNOWFALL NEARLY EVERYWHERE ACROSS SOUTHEAST WYOMING AND WESTERN
NEBRASKA. THE 12Z GFS HAS BEEN CONSISTENTLY FURTHER NORTH WITH THE
TROUGH AXIS AND PORT MAX...AND THUS MUCH LESS SNOW DUE TO
DOWNSLOPE WINDS. THE PRIMARY DIFFERENCE BETWEEN THESE TWO
SOLUTIONS...OTHER THAN THE QPF...IS THE STORM TRACK AND JET STREAM
LOCATION. THE ECMWF HAS THE JET DIGGING FURTHER SOUTH WITH A
SURFACE LOW DEVELOPING NEAR THE WYOMING/COLORADO BORDER AND MOVING
SOUTHEAST. THE GFS ON THE OTHER HAND SHOWS THE JET STREAM OVER THE
STATE OF WYOMING WITH A SURFACE LOW MUCH FURTHER NORTH ACROSS
MONTANA AND THE DAKOTAS. THE NET RESULT IS BROAD DRY DOWNSLOPE
FLOW AND LLVL SUBSIDENCE COMPARED TO THE ECMWF WHICH SHOWS PLENTY
OF NORTHEAST UPSLOPE FLOW. THE GEM IS SOMEWHERE IN BETWEEN THESE
TWO EXTREMES BUT A LITTLE CLOSER TO THE GFS. ECMWF QPF VALUES
RANGE FROM ONE QUARTER OF AN INCH TO ABOUT A THIRD OF AN INCH.
WHICH MEANS THERE IS POTENTIAL FOR LIGHT TO MODERATE SNOW AMOUNTS.
INCREASED POP SLIGHTLY ACROSS THE I80 CORRIDOR TO AROUND 30 TO 40
PERCENT FOR NOW...WITH VALUES NEAR 80 PERCENT FOR THE MOUNTAINS
WHICH HAVE THE BEST CHANCE OF SEEING 6+ INCHES OF SNOW.
HOPEFULLY...MODELS TREND TOWARD A SIMILAR SOLUTION OVER THE NEXT
24 HOURS...BUT HAVE A FEELING THAT MAY NOT HAPPEN UNTIL TUESDAY
WHEN THE SYSTEM BEGINS TO MOVE ONSHORE. THERE IS HIGH CONFIDENCE
THAT MUCH COLDER TEMPERATURES WILL ENTER THE REGION FOR THE
REMAINDER OF THE WEEK AND INTO NEXT WEEKEND WITH HIGHS IN THE 20S
TO MID 30S...AND LOWS IN THE SINGLE DIGITS (ABOVE AND BELOW ZERO)
AND TEENS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 527 PM MST SUN DEC 21 2014

WYOMING TAFS...VFR AT CHEYENNE WITH WIND GUSTS DECREASING THIS
EVENING...THEN WIND GUSTS INCREASING AFTER DAYBREAK MONDAY.
OCCASIONAL MVFR AT LARAMIE THIS EVENING...OTHERWISE VFR WITH
WIND GUSTS INCREASING OVER 40 KNOTS AFTER 15Z MONDAY. OCCASIONAL
IFR AND PERIODS OF MVFR AT RAWLINS THROUGH 09Z...THEN BECOMING
VFR WITH WIND GUSTS INCREASING NEAR 35 KNOTS AFTER 15Z.

NEBRASKA TAFS...VFR...ASIDE FROM OCCASIONAL MVFR THIS EVENING
AT SCOTTSBLUFF IN SNOW SHOWERS. STRONG NORTHWEST WIND 25 TO 35
KNOTS AFTER 15Z MONDAY WITH GUSTS 45 TO 50 KNOTS.

&&

.FIRE WEATHER...
ISSUED AT 110 PM MST SUN DEC 21 2014

NO FIRE WEATHER CONCERNS THROUGH THE MIDDLE OF THE WEEK. VERY WINDY
CONDITIONS ARE EXPECTED THROUGH THIS EVENING ALONG AND WEST OF
THE LARAMIE RANGE WITH GUSTS BETWEEN 60 AND 70 MPH LIKELY.
INCREASING MOISTURE WILL KEEP THE RISK FOR RAPID FIRE GROWTH LOW.
SIGNIFICANT MOUNTAIN SNOWS WILL PERSIST OVER THE NEXT 24 TO 48
HOURS WITH TOTAL ACCUMULATIONS IN EXCESS OF 2 FEET POSSIBLE IN THE
SNOWY AND SIERRA MADRES BEFORE ALL IS SAID AND DONE.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING UNTIL MIDNIGHT MST TONIGHT FOR WYZ104>107-109-
     116>118.

     WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     WINTER WEATHER ADVISORY UNTIL 8 AM MST MONDAY FOR WYZ113-115.

     WINTER STORM WARNING UNTIL 11 AM MST MONDAY FOR WYZ110-111.

NE...WIND ADVISORY FROM 8 AM TO 5 PM MST MONDAY FOR NEZ002-003-
     019>021-054-055-095-096.

&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...RUBIN
FIRE WEATHER...GCC




000
FXUS65 KCYS 220035
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
535 PM MST SUN DEC 21 2014

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

POWERFUL PACIFIC LOW PRESSURE SYSTEM CONTINUES TO MOVE INTO THE
AREA FROM THE WEST THIS AFTERNOON...BRINGING WIDESPREAD STRONG
WINDS AND NEAR BLIZZARD CONDITIONS ALONG PORTIONS OF INTERSTATE 80
OUT NEAR ARLINGTON. HAVE SEEN SOME REPORTS OF WIND GUSTS
APPROACHING 70MPH AND HAD AN 80MPH GUST REPORTED AT A UPR SITE UP
ON THE SOUTH LARAMIE RANGE. FORECAST CHALLENGES CONTINUE TO BE
MAINLY WINDS...BUT LATER THIS EVENING...WINTER WEATHER CONDITIONS
WILL TAKE SHAPE.

CURRENTLY...1015MB SURFACE LOW CURRENTLY OVER CENTRAL UTAH EARLY
THIS AFTERNOON. PERHAPS OUR STRONGEST GRADIENT IS YET TO COME AS
SURFACE ANALYSIS SHOWS THE STRONG PRESSURE GRADIENT STILL OVER
NORTHWESTERN COLORADO AND NORTHEASTERN UTAH. CRAIG TO CASPER
SURFACE GRADIENT RIGHT AROUND 12MBS AT 1 PM THIS AFTERNOON. LATEST
WRKHGT PRODUCTS HAS 850/700MB CRAIG TO CASPER HEIGHT GRADIENTS OF
75 AND 73MTRS RESPECTIVELY. MOSAIC RADAR SHOWING MOST OF THE SNOW
OVER NORTHWESTERN COLORADO AND UP OVER NORTHWESTERN WYOMING.

HEIGHT GRADIENTS REMAIN STRONG OVER SOUTHEAST WYOMING THROUGH THE
EVENING HOURS. WILL KEEP ALL WIND HEADLINES GOING AS THEY ARE FOR
NOW AS THE GFS SHOWS 700MB WINDS STILL AROUND 60-65KTS AT 06Z
TONIGHT. ECMWF SHOWS THE 500MB SHORTWAVE MOVING THROUGH CENTRAL
WYOMING INTO WESTERN NEBRASKA AFTER 06Z WITH WINDS SHIFTING
NORTHWEST BEHIND THE FRONT TONIGHT. AREAS WEST OF THE LARAMIE
RANGE STAY IN THE FAVORABLE LEFT FRONT QUADRANT OF A 170+ KT
JET...SO HEAVY SNOW LOOKS TO CONTINUE FOR THE SNOWY AND SIERRA
MADRE RANGES. LOWER ELEVATIONS WILL CONTINUE TO SEE STRONG
WINDS...THOUGH NOT AS STRONG AS TODAY...BUT ENOUGH TO KEEP WINTER
HEADLINES GOING OUT THERE THROUGH THE OVERNIGHT HOURS.

ATTENTION TURNS TO THE PANHANDLE FOR MONDAY. GFS 850MB WINDS
BEHIND THE FRONT OUT OVER THE PANHANDLE INCREASE SIGNIFICANTLY
OVERNIGHT. LOOKING AT 850MB WIND SPEEDS OF 40-45KTS FOR MUCH OF
THE PANHANDLE. WENT AHEAD WITH A WIND ADVISORY FOR NOW COVERING
MUCH OF THE DAY. LATER SHIFTS MAY NEED TO UPGRADE TO HIGH WIND
WARNINGS IF LATER GUIDANCE SHOWS ANYTHING STRONGER THAN WHAT I AM
SEEING NOW. HEAVY SNOW CONTINUES FOR THE SNOWY AND SIERRA MADRE
RANGES ALL DAY MONDAY.

FINALLY BEGIN TO SEE AN EASING ON THE SNOW OUT WEST MONDAY NIGHT
INTO TUESDAY AS THE UPPER LOW MOVES EAST. CURRENT WINTER STORM
WARNING FOR THE MOUNTAINS LOOKS GOOD THROUGH 12Z TUESDAY...NO
CHANGES MADE IN HEADLINES.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY EVENING THROUGH
FRIDAY DUE TO HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER
WEATHER ON CHRISTMAS DAY. MODELS ARE MAINTAINING RUN TO RUN
CONSISTENCY FOR THE POTENTIAL WINTER WEATHER ON CHRISTMAS...BUT
WITH SUCH A LARGE DISCREPANCY BETWEEN INDIVIDUAL MODEL RUNS...THE
PICTURE IS NOT LOOKING ANY CLEARER TODAY IN TERMS OF THE WEATHER.

EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY TRAVEL
PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS DOWNSLOPE FLOW
DEVELOPS...WITH HIGHS IN THE MID 30S TO MID 40S...WARMEST ALONG
THE I25 CORRIDOR DUE TO DOWNSLOPE FLOW NEAR THE SURFACE. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS INDICATE A RAPIDLY MOVING
PACIFIC UPPER LEVEL TROUGH PUSHING INTO THE AREA FROM THE
NORTHWEST UNITED STATES. A STRONG PACIFIC COLD FRONT IS FORECAST
TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME CHRISTMAS MORNING WITH
SNOW DEVELOPING BEHIND THE FRONT. THERE IS THE POTENTIAL FOR A
HIGH WIND EVENT ACROSS THE WIND PRONE AREAS OF SOUTHEAST WYOMING
AHEAD OF THIS FRONT...SO CONTINUED TO INCREASE WINDS OVER THE
ARLINGTON AND BORDEAUX AREAS. WIND IMPACTS SHOULD BE MINIMAL
HOWEVER FOR HOLIDAY TRAVELERS...DUE TO A RELATIVELY BRIEF PERIOD
OF STRONG WINDS...AND THE WINDS MAINLY AFFECTING HIGH PROFILE
VEHICLES.

FORECAST BECOMES TRICKY ON CHRISTMAS DAY IN TERMS OF SNOW
POTENTIAL AS THERE IS ONLY SLIGHTLY MORE CONFIDENCE COMPARED TO
YESTERDAY THAT A DECENT PORTION OF THE AREA WILL RECEIVE
ACCUMULATING SNOW. ALL MODELS NOW SHOW THE SYSTEM MOVING RAPIDLY
ACROSS THE AREA INTO THURSDAY NIGHT...WHICH IS IMPORTANT BECAUSE
IT GREATLY LOWERS THE CHANCE OF WINTER STORM CONDITIONS. THE 12Z
ECMWF IS SLIGHTLY FASTER AND SHOWING WIDESPREAD LIGHT TO MODERATE
SNOWFALL NEARLY EVERYWHERE ACROSS SOUTHEAST WYOMING AND WESTERN
NEBRASKA. THE 12Z GFS HAS BEEN CONSISTENTLY FURTHER NORTH WITH THE
TROUGH AXIS AND PORT MAX...AND THUS MUCH LESS SNOW DUE TO
DOWNSLOPE WINDS. THE PRIMARY DIFFERENCE BETWEEN THESE TWO
SOLUTIONS...OTHER THAN THE QPF...IS THE STORM TRACK AND JET STREAM
LOCATION. THE ECMWF HAS THE JET DIGGING FURTHER SOUTH WITH A
SURFACE LOW DEVELOPING NEAR THE WYOMING/COLORADO BORDER AND MOVING
SOUTHEAST. THE GFS ON THE OTHER HAND SHOWS THE JET STREAM OVER THE
STATE OF WYOMING WITH A SURFACE LOW MUCH FURTHER NORTH ACROSS
MONTANA AND THE DAKOTAS. THE NET RESULT IS BROAD DRY DOWNSLOPE
FLOW AND LLVL SUBSIDENCE COMPARED TO THE ECMWF WHICH SHOWS PLENTY
OF NORTHEAST UPSLOPE FLOW. THE GEM IS SOMEWHERE IN BETWEEN THESE
TWO EXTREMES BUT A LITTLE CLOSER TO THE GFS. ECMWF QPF VALUES
RANGE FROM ONE QUARTER OF AN INCH TO ABOUT A THIRD OF AN INCH.
WHICH MEANS THERE IS POTENTIAL FOR LIGHT TO MODERATE SNOW AMOUNTS.
INCREASED POP SLIGHTLY ACROSS THE I80 CORRIDOR TO AROUND 30 TO 40
PERCENT FOR NOW...WITH VALUES NEAR 80 PERCENT FOR THE MOUNTAINS
WHICH HAVE THE BEST CHANCE OF SEEING 6+ INCHES OF SNOW.
HOPEFULLY...MODELS TREND TOWARD A SIMILAR SOLUTION OVER THE NEXT
24 HOURS...BUT HAVE A FEELING THAT MAY NOT HAPPEN UNTIL TUESDAY
WHEN THE SYSTEM BEGINS TO MOVE ONSHORE. THERE IS HIGH CONFIDENCE
THAT MUCH COLDER TEMPERATURES WILL ENTER THE REGION FOR THE
REMAINDER OF THE WEEK AND INTO NEXT WEEKEND WITH HIGHS IN THE 20S
TO MID 30S...AND LOWS IN THE SINGLE DIGITS (ABOVE AND BELOW ZERO)
AND TEENS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 527 PM MST SUN DEC 21 2014

WYOMING TAFS...VFR AT CHEYENNE WITH WIND GUSTS DECREASING THIS
EVENING...THEN WIND GUSTS INCREASING AFTER DAYBREAK MONDAY.
OCCASIONAL MVFR AT LARAMIE THIS EVENING...OTHERWISE VFR WITH
WIND GUSTS INCREASING OVER 40 KNOTS AFTER 15Z MONDAY. OCCASIONAL
IFR AND PERIODS OF MVFR AT RAWLINS THROUGH 09Z...THEN BECOMING
VFR WITH WIND GUSTS INCREASING NEAR 35 KNOTS AFTER 15Z.

NEBRASKA TAFS...VFR...ASIDE FROM OCCASIONAL MVFR THIS EVENING
AT SCOTTSBLUFF IN SNOW SHOWERS. STRONG NORTHWEST WIND 25 TO 35
KNOTS AFTER 15Z MONDAY WITH GUSTS 45 TO 50 KNOTS.

&&

.FIRE WEATHER...
ISSUED AT 110 PM MST SUN DEC 21 2014

NO FIRE WEATHER CONCERNS THROUGH THE MIDDLE OF THE WEEK. VERY WINDY
CONDITIONS ARE EXPECTED THROUGH THIS EVENING ALONG AND WEST OF
THE LARAMIE RANGE WITH GUSTS BETWEEN 60 AND 70 MPH LIKELY.
INCREASING MOISTURE WILL KEEP THE RISK FOR RAPID FIRE GROWTH LOW.
SIGNIFICANT MOUNTAIN SNOWS WILL PERSIST OVER THE NEXT 24 TO 48
HOURS WITH TOTAL ACCUMULATIONS IN EXCESS OF 2 FEET POSSIBLE IN THE
SNOWY AND SIERRA MADRES BEFORE ALL IS SAID AND DONE.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING UNTIL MIDNIGHT MST TONIGHT FOR WYZ104>107-109-
     116>118.

     WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     WINTER WEATHER ADVISORY UNTIL 8 AM MST MONDAY FOR WYZ113-115.

     WINTER STORM WARNING UNTIL 11 AM MST MONDAY FOR WYZ110-111.

NE...WIND ADVISORY FROM 8 AM TO 5 PM MST MONDAY FOR NEZ002-003-
     019>021-054-055-095-096.

&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...RUBIN
FIRE WEATHER...GCC



000
FXUS63 KUNR 212257
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
357 PM MST SUN DEC 21 2014

.SHORT TERM...THIS EVENING THROUGH MONDAY NIGHT
ISSUED AT 354 PM MST SUN DEC 21 2014

CURRENT SURFACE ANALYSIS SHOWS LOW PRESSURE OVER SOUTHWEST
SK...WITH FRONTAL BOUNDARY STRETCHING SOUTHEASTWARD INTO THE
WESTERN DAKOTAS. MAIN COLD FRONT LIES SOUTH AND WEST OF THE LOW
FROM NORTHEAST MT TO CENTRAL WY. UPPER LEVEL ANALYSIS SHOWS ZONAL
FLOW OVER THE REGION...WITH A VERY STRONG UPPER JET...150
KT+...STRETCHING ACROSS THE PACIFIC NW INTO THE ROCKIES. UPPER
LEVEL ENERGY IS MOVING QUICKLY EAST ACROSS THE PACIFIC NW AND
SOUTHWEST CANADA. A SHORTWAVE TROF IS STRENGTHENING AND DIGGING
SOUTH ACROSS MT RIGHT NOW. SKIES HAVE BECOME MOSTLY CLOUDY ACROSS
MUCH OF THE AREA...WITH SCATTERED RAIN SHOWERS NOW OVER NORTHEAST
WY AND WESTERN SD. TEMPS ARE MOSTLY IN THE 40S TO AROUND 50
DEGREES.

A UNSETTLED BEGINNING TO THE WEEK CAN BE EXPECTED AS A STORM SYSTEM
DEVELOPS AND INTENSIFIES OVER THE REGION TONIGHT AND MONDAY. VARIOUS
SHORT RANGE MODELS ARE IN GOOD AGREEMENT ON GENERAL DEVELOPMENT...
BUT STILL HAVE DIFFERENCES WITH REGARD TO TRACK AND STRENGTH BETWEEN
TONIGHT AND TUESDAY. THE TRACK OF THE STORM WILL BE IMPORTANT WITH
REGARD TO WHERE AREAS OF HEAVIER PCPN MAY DEVELOP OVER THE
PLAINS...WITH STRONG WINDS ALSO COMPLICATING THINGS. THE GFS AND NAM
DIG THE DEVELOPING LOW FURTHER SOUTH AND QUICKER THAN THE ECMWF AND
GEM. WILL LEAN MORE TOWARD A BLEND OF THE GFS AND ECMWF FOR THIS
FORECAST.

FOR TONIGHT...PCPN WILL EXPAND ACROSS THE AREA FROM WEST TO EAST AS
THE FRONT PASSES AND THE NEXT DISTURBANCE ALOFT CROSSES. THE CHANGE
OVER TO SNOW SHOULD BE GRADUAL FROM WEST TO EAST AS THE AIR BEHIND
THE FRONT IS NOT THAT COLD. PCPN WILL CHANGE OVER THE QUICKEST OVER
THE BLACK HILLS...DURING THE EVENING HOURS...WITH A MORE GRADUAL
CHANGE OVERNIGHT ACROSS THE PLAINS. SNOWFALL AMOUNTS OF UP TO AN
INCH OR SO IS EXPECTED ON THE PLAINS...WITH 2 TO 4 INCHES POSSIBLE
BY MORNING OVER THE TERRAIN FAVORED AREAS OF THE BLACK HILLS.
NORTHWESTERLY WINDS WILL GRADUALLY INCREASE BEHIND THE FRONT
OVERNIGHT...BECOMING BREEZY TO WINDY IN MOST AREAS BY EARLY MORNING.
LOWS WILL MOSTLY BE IN THE UPPER 20S AND LOWER 30S...A BIT COLDER
OVER THE HIGHER BLACK HILLS.

ON MONDAY...AREAS OF SNOW CAN BE EXPECTED IN THE MORNING...WITH THE
MOST PERSISTENT SNOW OVER THE NORTHERN BLACK HILLS AREA. AS THE
STACKED LOW PRESSURE SYSTEM MOVES INTO EASTERN SD/EASTERN NEB DURING
THE DAY...WINDS WILL FURTHER INCREASE AND PCPN WILL EXPAND ACROSS
THE AREA ON THE BACK SIDE OF THE SYSTEM AS SHORTWAVE ENERGY WRAPS
AROUND THE SYSTEM...ESPECIALLY DURING THE AFTERNOON AND EVENING.
PERIODS OF SNOW AND BLOWING SNOW ARE LIKELY ACROSS A GOOD PORTION OF
THE PLAINS THROUGH MONDAY NIGHT. THE EXCEPTION WILL LIKELY BE
DOWNSLOPED AREAS OF SOUTHWESTERN SD...FROM NEAR RAPID CITY TO THE
SOUTHERN BLACK HILLS...HOT SPRINGS...AND EDGEMONT...WHERE THIS
SHOULD MOSTLY BE A WIND EVENT.

A MYRIAD OF WARNINGS AND ADVISORIES HAVE BEEN ISSUED FOR MOST OF THE
CWA...POSSIBLY SUBJECT TO SOME CHANGE OVER THE NEXT 12 TO 24 HOURS
AS CONDITIONS WARRANT. SOUTH CENTRAL SD WILL LIKELY NEED TO BE ADDED
TO THE WINTER WX HEADLINES FOR LATER MONDAY AND MONDAY NIGHT IF THE
CURRENT TRENDS HOLD...BUT WILL LET THE NIGHT SHIFT HAVE ANOTHER LOOK
AT THE POTENTIAL THERE. FORECASTED SNOWFALL TOTALS FOR NOW RANGE
FROM 2 TO 5 INCHES ACROSS MUCH OF FAR NORTHEAST WY AND THE WESTERN
AND SOUTH CENTRAL SOUTH DAKOTA PLAINS TO 6 TO 12+ OVER THE NORTHERN
BLACK HILLS. UP TO AN INCH OR TWO IS POSSIBLE ACROSS DOWNSLOPED
AREAS OF SOUTHWESTERN SD.

.LONG TERM...TUESDAY THROUGH SUNDAY
ISSUED AT 354 PM MST SUN DEC 21 2014

UPPER TROF MOVES EASTWARD INTO MN-MISSOURI VALLEY BY EARLY TUES...
WITH NORTHERLY FLOW ASSOCIATED WITH 120KT JET OVER FRONT RANGE.
MODELS IN GOOD AGREEMENT WITH GENERAL SURFACE LOW PLACEMENT OVER IA
AND STRONG PRESSURE GRADIENT OVER FORECAST AREA MEANS GUSTY WINDS
WILL PERSIST EARLY TUES...AS WELL AS SOME SNOW LINGERING OVER SOUTH
CENTRAL SD AND NORTHERN BLACK HILLS...THEN GRADIENT DECREASES AS
HIGH PRESSURE BUILDS OVER THE GREAT BASIN. NEXT UPPER TROF COMING
ONSHORE PACIFIC NORTHWEST FORMS A BROAD RIDGE OVER THE ROCKIES AND
HIGH PLAINS WED...BUT TROF MOVES EASTWARD ONTO THE PLAINS. GFS HAS
SURFACE LOW WITH TRAILING COLD FRONT DROPPING ACROSS AREA CHRISTMAS
DAY...WHICH WOULD KEEP BETTER CHANCE OF SNOW OVER ND...AND MOSTLY
LIGHT POST-FRONTAL SNOW SHOWERS OVER SD...WHILE ECMWF FORMS LOW OVER
THE CENTRAL PLAINS...AND BAND OF SNOW IS FARTHER SOUTH OVER SOUTHERN
SD AND NE. CYCLONIC NORTHWEST FLOW REMAINS OVER THE AREA BEHIND THE
TROF...WITH OCCASIONAL WAVES DROPPING INTO MAIN TROF PRODUCING
CHANCES OF SNOW. ARCTIC SURFACE HI PRESSURE WILL KEEP TEMPERATURES
COLD.

&&

AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY)
ISSUED AT 354 PM MST SUN DEC 21 2014

PRECIP IS SPREADING ACRS FCST AREA THIS AFTN AHD OF A STORM
SYSTEM OVR NWRN WY. LGT RAIN SHWRS OVR NERN WY AND FAR WRN SD THIS
AFTN WL TRANSITION TO LGT SNW THIS EVEN...W/ CIGS LOWERING TO
MVFR...AND IFR IN HEAVIER SNW OVR NRN BLACK HILLS. A STRONG COLD
FRONT WL CROSS THE REGION TONITE...W/ NW WINDS INCSG TO 20-30 KT
AND GUSTS TO 45KT.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING FROM 8 PM THIS EVENING TO NOON MST TUESDAY
     FOR SDZ024.

     WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 5 AM MST
     TUESDAY FOR SDZ001-002-012>014-025-031-032-042>044-072-073.

     WIND ADVISORY FROM 8 AM TO 6 PM MST MONDAY FOR SDZ027-030-041-
     074.

     WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO NOON MST
     TUESDAY FOR SDZ028.

     HIGH WIND WARNING FROM 8 AM TO 8 PM MST MONDAY FOR SDZ026.

WY...WINTER STORM WARNING FROM 8 PM THIS EVENING TO NOON MST TUESDAY
     FOR WYZ057.

     WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 5 AM MST
     TUESDAY FOR WYZ056-071.

&&

$$

SHORT TERM...26
LONG TERM...55
AVIATION...55






000
FXUS63 KUNR 212257
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
357 PM MST SUN DEC 21 2014

.SHORT TERM...THIS EVENING THROUGH MONDAY NIGHT
ISSUED AT 354 PM MST SUN DEC 21 2014

CURRENT SURFACE ANALYSIS SHOWS LOW PRESSURE OVER SOUTHWEST
SK...WITH FRONTAL BOUNDARY STRETCHING SOUTHEASTWARD INTO THE
WESTERN DAKOTAS. MAIN COLD FRONT LIES SOUTH AND WEST OF THE LOW
FROM NORTHEAST MT TO CENTRAL WY. UPPER LEVEL ANALYSIS SHOWS ZONAL
FLOW OVER THE REGION...WITH A VERY STRONG UPPER JET...150
KT+...STRETCHING ACROSS THE PACIFIC NW INTO THE ROCKIES. UPPER
LEVEL ENERGY IS MOVING QUICKLY EAST ACROSS THE PACIFIC NW AND
SOUTHWEST CANADA. A SHORTWAVE TROF IS STRENGTHENING AND DIGGING
SOUTH ACROSS MT RIGHT NOW. SKIES HAVE BECOME MOSTLY CLOUDY ACROSS
MUCH OF THE AREA...WITH SCATTERED RAIN SHOWERS NOW OVER NORTHEAST
WY AND WESTERN SD. TEMPS ARE MOSTLY IN THE 40S TO AROUND 50
DEGREES.

A UNSETTLED BEGINNING TO THE WEEK CAN BE EXPECTED AS A STORM SYSTEM
DEVELOPS AND INTENSIFIES OVER THE REGION TONIGHT AND MONDAY. VARIOUS
SHORT RANGE MODELS ARE IN GOOD AGREEMENT ON GENERAL DEVELOPMENT...
BUT STILL HAVE DIFFERENCES WITH REGARD TO TRACK AND STRENGTH BETWEEN
TONIGHT AND TUESDAY. THE TRACK OF THE STORM WILL BE IMPORTANT WITH
REGARD TO WHERE AREAS OF HEAVIER PCPN MAY DEVELOP OVER THE
PLAINS...WITH STRONG WINDS ALSO COMPLICATING THINGS. THE GFS AND NAM
DIG THE DEVELOPING LOW FURTHER SOUTH AND QUICKER THAN THE ECMWF AND
GEM. WILL LEAN MORE TOWARD A BLEND OF THE GFS AND ECMWF FOR THIS
FORECAST.

FOR TONIGHT...PCPN WILL EXPAND ACROSS THE AREA FROM WEST TO EAST AS
THE FRONT PASSES AND THE NEXT DISTURBANCE ALOFT CROSSES. THE CHANGE
OVER TO SNOW SHOULD BE GRADUAL FROM WEST TO EAST AS THE AIR BEHIND
THE FRONT IS NOT THAT COLD. PCPN WILL CHANGE OVER THE QUICKEST OVER
THE BLACK HILLS...DURING THE EVENING HOURS...WITH A MORE GRADUAL
CHANGE OVERNIGHT ACROSS THE PLAINS. SNOWFALL AMOUNTS OF UP TO AN
INCH OR SO IS EXPECTED ON THE PLAINS...WITH 2 TO 4 INCHES POSSIBLE
BY MORNING OVER THE TERRAIN FAVORED AREAS OF THE BLACK HILLS.
NORTHWESTERLY WINDS WILL GRADUALLY INCREASE BEHIND THE FRONT
OVERNIGHT...BECOMING BREEZY TO WINDY IN MOST AREAS BY EARLY MORNING.
LOWS WILL MOSTLY BE IN THE UPPER 20S AND LOWER 30S...A BIT COLDER
OVER THE HIGHER BLACK HILLS.

ON MONDAY...AREAS OF SNOW CAN BE EXPECTED IN THE MORNING...WITH THE
MOST PERSISTENT SNOW OVER THE NORTHERN BLACK HILLS AREA. AS THE
STACKED LOW PRESSURE SYSTEM MOVES INTO EASTERN SD/EASTERN NEB DURING
THE DAY...WINDS WILL FURTHER INCREASE AND PCPN WILL EXPAND ACROSS
THE AREA ON THE BACK SIDE OF THE SYSTEM AS SHORTWAVE ENERGY WRAPS
AROUND THE SYSTEM...ESPECIALLY DURING THE AFTERNOON AND EVENING.
PERIODS OF SNOW AND BLOWING SNOW ARE LIKELY ACROSS A GOOD PORTION OF
THE PLAINS THROUGH MONDAY NIGHT. THE EXCEPTION WILL LIKELY BE
DOWNSLOPED AREAS OF SOUTHWESTERN SD...FROM NEAR RAPID CITY TO THE
SOUTHERN BLACK HILLS...HOT SPRINGS...AND EDGEMONT...WHERE THIS
SHOULD MOSTLY BE A WIND EVENT.

A MYRIAD OF WARNINGS AND ADVISORIES HAVE BEEN ISSUED FOR MOST OF THE
CWA...POSSIBLY SUBJECT TO SOME CHANGE OVER THE NEXT 12 TO 24 HOURS
AS CONDITIONS WARRANT. SOUTH CENTRAL SD WILL LIKELY NEED TO BE ADDED
TO THE WINTER WX HEADLINES FOR LATER MONDAY AND MONDAY NIGHT IF THE
CURRENT TRENDS HOLD...BUT WILL LET THE NIGHT SHIFT HAVE ANOTHER LOOK
AT THE POTENTIAL THERE. FORECASTED SNOWFALL TOTALS FOR NOW RANGE
FROM 2 TO 5 INCHES ACROSS MUCH OF FAR NORTHEAST WY AND THE WESTERN
AND SOUTH CENTRAL SOUTH DAKOTA PLAINS TO 6 TO 12+ OVER THE NORTHERN
BLACK HILLS. UP TO AN INCH OR TWO IS POSSIBLE ACROSS DOWNSLOPED
AREAS OF SOUTHWESTERN SD.

.LONG TERM...TUESDAY THROUGH SUNDAY
ISSUED AT 354 PM MST SUN DEC 21 2014

UPPER TROF MOVES EASTWARD INTO MN-MISSOURI VALLEY BY EARLY TUES...
WITH NORTHERLY FLOW ASSOCIATED WITH 120KT JET OVER FRONT RANGE.
MODELS IN GOOD AGREEMENT WITH GENERAL SURFACE LOW PLACEMENT OVER IA
AND STRONG PRESSURE GRADIENT OVER FORECAST AREA MEANS GUSTY WINDS
WILL PERSIST EARLY TUES...AS WELL AS SOME SNOW LINGERING OVER SOUTH
CENTRAL SD AND NORTHERN BLACK HILLS...THEN GRADIENT DECREASES AS
HIGH PRESSURE BUILDS OVER THE GREAT BASIN. NEXT UPPER TROF COMING
ONSHORE PACIFIC NORTHWEST FORMS A BROAD RIDGE OVER THE ROCKIES AND
HIGH PLAINS WED...BUT TROF MOVES EASTWARD ONTO THE PLAINS. GFS HAS
SURFACE LOW WITH TRAILING COLD FRONT DROPPING ACROSS AREA CHRISTMAS
DAY...WHICH WOULD KEEP BETTER CHANCE OF SNOW OVER ND...AND MOSTLY
LIGHT POST-FRONTAL SNOW SHOWERS OVER SD...WHILE ECMWF FORMS LOW OVER
THE CENTRAL PLAINS...AND BAND OF SNOW IS FARTHER SOUTH OVER SOUTHERN
SD AND NE. CYCLONIC NORTHWEST FLOW REMAINS OVER THE AREA BEHIND THE
TROF...WITH OCCASIONAL WAVES DROPPING INTO MAIN TROF PRODUCING
CHANCES OF SNOW. ARCTIC SURFACE HI PRESSURE WILL KEEP TEMPERATURES
COLD.

&&

AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY)
ISSUED AT 354 PM MST SUN DEC 21 2014

PRECIP IS SPREADING ACRS FCST AREA THIS AFTN AHD OF A STORM
SYSTEM OVR NWRN WY. LGT RAIN SHWRS OVR NERN WY AND FAR WRN SD THIS
AFTN WL TRANSITION TO LGT SNW THIS EVEN...W/ CIGS LOWERING TO
MVFR...AND IFR IN HEAVIER SNW OVR NRN BLACK HILLS. A STRONG COLD
FRONT WL CROSS THE REGION TONITE...W/ NW WINDS INCSG TO 20-30 KT
AND GUSTS TO 45KT.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING FROM 8 PM THIS EVENING TO NOON MST TUESDAY
     FOR SDZ024.

     WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 5 AM MST
     TUESDAY FOR SDZ001-002-012>014-025-031-032-042>044-072-073.

     WIND ADVISORY FROM 8 AM TO 6 PM MST MONDAY FOR SDZ027-030-041-
     074.

     WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO NOON MST
     TUESDAY FOR SDZ028.

     HIGH WIND WARNING FROM 8 AM TO 8 PM MST MONDAY FOR SDZ026.

WY...WINTER STORM WARNING FROM 8 PM THIS EVENING TO NOON MST TUESDAY
     FOR WYZ057.

     WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 5 AM MST
     TUESDAY FOR WYZ056-071.

&&

$$

SHORT TERM...26
LONG TERM...55
AVIATION...55







000
FXUS65 KRIW 212204
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
304 PM MST SUN DEC 21 2014

.SHORT TERM...TONIGHT THROUGH WEDNESDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES WITH MORE VALLEY
LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX OR FROM A WET SNOW TO A
DRIER ACCUMULATING SNOW TONIGHT. AS THE STRONG WESTERLY FLOW
SWITCHES TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT THERE COULD BE
PERIODS OF GUSTY WIND MOVING INTO ARES MORE PRONE TO STRONG
NORTHWEST FLOW...SPECIFICALLY INTO THE WIND RIVER BASIN AND
BUFFALO/PINEY CREEK AREA. THERE DOES NOT APPEAR TO BE MUCH DOWNWARD
FORCING AS THE LEFT FRONT QUAD OF THE JET REMAINS IN THE
AREA...THERE ARE SOME 50 TO 60KT BARBS AT 700MB BUT THERE IS NOT
EXPECTED TO BE WIDESPREAD TRANSLATION TO THE SURFACE AS FORCING FOR
ASCENT WILL LIKELY WIN OUT. HOWEVER THERE WILL BE A FEW SPOTS
FLIRTING WITH HIGH WIND CRITERIA...ESPECIALLY NORTHWEST OF BUFFALO.
THE NORTHWEST FLOW WILL ALSO BRING DOWN A COLD POOL
ALOFT...INCREASING LOW AND MID LEVEL LAPSE RATES TO OVER 8.5DEG/KM
IN SOME CASES...ESPECIALLY ALONG AND EAST OF THE DIVIDE...AS WELL AS
IN SOME LOCATIONS WEST OF THE DIVIDE LIKE THE TETONS AND YELLOWSTONE.
COULD BE AN INTERESTING EVENING FOR SNOW BANDING. ONE BAND HAS
ALREADY MOVED ACROSS DUBOIS...DROPPING ABOUT AN INCH OF SNOW IN LESS
THAN ONE HOUR.

ON MONDAY...THE MAIN TROUGH MOVES EAST AND UNDERGOES RAPID
CYCLOGENESIS IN THE PLAINS. AROUND THE BACK OF THE TROUGH WE ARE
LOOKING AT A SHORT WAVE THAT IS SET TO MOVE THROUGH LATE TOMORROW
AFTERNOON. LOOKING AT STRICTLY THE MODEL QPF...IT WOULD APPEAR AS IF
NOT MUCH WILL COME OV IT. HOWEVER...THERE WILL STILL BE SOME DECENT
MOISTURE HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS A
SECOND COLD POOL ALOFT SETTLES IN COMBINING WITH A SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ALONG THE BIGHORNS INTO JOHNSON
COUNTY...POPS WERE ALSO INCREASED FOR POTENTIAL SNOW BANDING
ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM SHOSHONI THROUGH CASPER
AND AREAS SOUTHEAST OF THE EASTERN TIP OF THE WIND RIVER MOUNTAINS.
STAYED FAIRLY CONSERVATIVE WITH QPF AND SNOW AMOUNTS GIVEN THE
CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ON TUESDAY...HIGH PRESSURE BUILDS INTO THE WEST WITH ANOTHER SNOW
SHOWER OR TWO POSSIBLE ALONG THE I25 CORRIDOR AND IN THE BIGHORNS.
ELSEWHERE...CLEARING AND COOL WITH DECREASING WINDS. ON
WEDNESDAY...A RIDGE BUILDS IN ALOFT WHILE A LEE TROUGH DIGS AT THE
SURFACE...INCREASING WINDS FROM ROCK SPRINGS TO CASPER IN THE
AFTERNOON. OTHERWISE...INCREASING CLOUDS WITH MORE SNOW EXPECTED
ACROSS THE WEST AND NORTH LATE IN THE AFTERNOON.

.LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

GOING INTO THE CHRISTMAS DAY FORECAST STILL BRINGS
CHALLENGES...ESPECIALLY EAST OF THE DIVIDE. ONE THING IS CERTAIN...
A COLD FRONT WILL BRING COLDER TEMPERATURES TO THE REGION BY EARLY
CHRISTMAS MORNING.

ECMWF MODEL STILL DIGS SYSTEM TO THE SOUTHWEST OF FORECAST AREA ON
CHRISTMAS MORNING. THE LOW COMES OVER THE ROCKIES AS AN OPEN WAVE.
BUT THERE SHOULD BE A LONG ENOUGH PERIOD OF UPSLOPE FLOW ON BOTH
SIDES OF THE DIVIDE FOR A FEW INCHES OF SNOW. THIS IS TYPICAL MOST
LOCATIONS EAST OF THE DIVIDE AFTER FROPA. HOWEVER...LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE ALONG FAVORED NORTHEAST MOUNTAIN SLOPES
ON CHRISTMAS. DID NOT CHANGE POPS MUCH ON THURSDAY INTO THURSDAY
NIGHT. REGARDLESS...THIS IS NOT SHAPING UP TO BE A BIG SNOW EVENT.

FLOW ALOFT THEN SUPPORTS SCATTERED SNOW SHOWERS ON FRIDAY. THINKING
IS THAT THERE WILL BE ENOUGH INSTABILITY ALOFT...ESPECIALLY OVER THE
WESTERN AND NORTHERN MOUNTAIN RANGES. BOTH THURSDAY AND FRIDAY
NIGHTS SHOULD BE QUITE COLD...ESPECIALLY WITH ANY FRESH SNOW COVER.

MOSTLY DRY W-NW FLOW THEN SETS UP OVER THE FORECAST AREA SATURDAY
INTO SUNDAY. DETAILS VARY A BIT WITH EACH MEDIUM RANGE MODEL...BUT
LOOKS LIKE TEMPERATURES WILL MODERATE NEXT WEEKEND. POSSIBLY BETTER
CHANCE FOR SNOW NORTHWEST WYOMING MOUNTAINS BY SUNDAY AFTERNOON.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE MIXING OUT. EXPECT PERIODS OF 20 TO 30KT WINDS WITH GUSTS MAINLY
IN THE 35-45KT RANGE BUT A FEW MORE WIND PRONE AREAS COULD SEE GUSTS
UP TO 55KT...BUT NOT AT ANY OF THE FORECAST TERMINALS. A STRONG NW
FLOW WILL FOLLOW THIS SYSTEM TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW
SHOWERS POSSIBLE ALONG THE FRONT ACROSS THE LOWER ELEVATIONS THIS
EVENING...ESPECIALLY VCNTY AND EAST OF INTERSTATE 25. DRIER AIR
PREVAIL NW-SE BUT GUSTY NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

STRONG MTN TOP WINDS RESULTING IN AREAS MDT-SVR TURBULENCE AND
LLWS...WILL CONTINUE THROUGH THE NIGHT. A COLD FRONT WILL CONTINUE
TO PUSH SOUTH ACROSS THE AREA CROSSING INTERSTATE 80 AROUND 03Z
MONDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

&&

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

&&

$$

SHORT TERM...ALLEN
LONG TERM...KPL
AVIATION...ALLEN
FIRE WEATHER...ALLEN






000
FXUS65 KRIW 212204
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
304 PM MST SUN DEC 21 2014

.SHORT TERM...TONIGHT THROUGH WEDNESDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES WITH MORE VALLEY
LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX OR FROM A WET SNOW TO A
DRIER ACCUMULATING SNOW TONIGHT. AS THE STRONG WESTERLY FLOW
SWITCHES TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT THERE COULD BE
PERIODS OF GUSTY WIND MOVING INTO ARES MORE PRONE TO STRONG
NORTHWEST FLOW...SPECIFICALLY INTO THE WIND RIVER BASIN AND
BUFFALO/PINEY CREEK AREA. THERE DOES NOT APPEAR TO BE MUCH DOWNWARD
FORCING AS THE LEFT FRONT QUAD OF THE JET REMAINS IN THE
AREA...THERE ARE SOME 50 TO 60KT BARBS AT 700MB BUT THERE IS NOT
EXPECTED TO BE WIDESPREAD TRANSLATION TO THE SURFACE AS FORCING FOR
ASCENT WILL LIKELY WIN OUT. HOWEVER THERE WILL BE A FEW SPOTS
FLIRTING WITH HIGH WIND CRITERIA...ESPECIALLY NORTHWEST OF BUFFALO.
THE NORTHWEST FLOW WILL ALSO BRING DOWN A COLD POOL
ALOFT...INCREASING LOW AND MID LEVEL LAPSE RATES TO OVER 8.5DEG/KM
IN SOME CASES...ESPECIALLY ALONG AND EAST OF THE DIVIDE...AS WELL AS
IN SOME LOCATIONS WEST OF THE DIVIDE LIKE THE TETONS AND YELLOWSTONE.
COULD BE AN INTERESTING EVENING FOR SNOW BANDING. ONE BAND HAS
ALREADY MOVED ACROSS DUBOIS...DROPPING ABOUT AN INCH OF SNOW IN LESS
THAN ONE HOUR.

ON MONDAY...THE MAIN TROUGH MOVES EAST AND UNDERGOES RAPID
CYCLOGENESIS IN THE PLAINS. AROUND THE BACK OF THE TROUGH WE ARE
LOOKING AT A SHORT WAVE THAT IS SET TO MOVE THROUGH LATE TOMORROW
AFTERNOON. LOOKING AT STRICTLY THE MODEL QPF...IT WOULD APPEAR AS IF
NOT MUCH WILL COME OV IT. HOWEVER...THERE WILL STILL BE SOME DECENT
MOISTURE HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS A
SECOND COLD POOL ALOFT SETTLES IN COMBINING WITH A SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ALONG THE BIGHORNS INTO JOHNSON
COUNTY...POPS WERE ALSO INCREASED FOR POTENTIAL SNOW BANDING
ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM SHOSHONI THROUGH CASPER
AND AREAS SOUTHEAST OF THE EASTERN TIP OF THE WIND RIVER MOUNTAINS.
STAYED FAIRLY CONSERVATIVE WITH QPF AND SNOW AMOUNTS GIVEN THE
CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ON TUESDAY...HIGH PRESSURE BUILDS INTO THE WEST WITH ANOTHER SNOW
SHOWER OR TWO POSSIBLE ALONG THE I25 CORRIDOR AND IN THE BIGHORNS.
ELSEWHERE...CLEARING AND COOL WITH DECREASING WINDS. ON
WEDNESDAY...A RIDGE BUILDS IN ALOFT WHILE A LEE TROUGH DIGS AT THE
SURFACE...INCREASING WINDS FROM ROCK SPRINGS TO CASPER IN THE
AFTERNOON. OTHERWISE...INCREASING CLOUDS WITH MORE SNOW EXPECTED
ACROSS THE WEST AND NORTH LATE IN THE AFTERNOON.

.LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY

GOING INTO THE CHRISTMAS DAY FORECAST STILL BRINGS
CHALLENGES...ESPECIALLY EAST OF THE DIVIDE. ONE THING IS CERTAIN...
A COLD FRONT WILL BRING COLDER TEMPERATURES TO THE REGION BY EARLY
CHRISTMAS MORNING.

ECMWF MODEL STILL DIGS SYSTEM TO THE SOUTHWEST OF FORECAST AREA ON
CHRISTMAS MORNING. THE LOW COMES OVER THE ROCKIES AS AN OPEN WAVE.
BUT THERE SHOULD BE A LONG ENOUGH PERIOD OF UPSLOPE FLOW ON BOTH
SIDES OF THE DIVIDE FOR A FEW INCHES OF SNOW. THIS IS TYPICAL MOST
LOCATIONS EAST OF THE DIVIDE AFTER FROPA. HOWEVER...LOCALLY HIGHER
AMOUNTS WILL BE POSSIBLE ALONG FAVORED NORTHEAST MOUNTAIN SLOPES
ON CHRISTMAS. DID NOT CHANGE POPS MUCH ON THURSDAY INTO THURSDAY
NIGHT. REGARDLESS...THIS IS NOT SHAPING UP TO BE A BIG SNOW EVENT.

FLOW ALOFT THEN SUPPORTS SCATTERED SNOW SHOWERS ON FRIDAY. THINKING
IS THAT THERE WILL BE ENOUGH INSTABILITY ALOFT...ESPECIALLY OVER THE
WESTERN AND NORTHERN MOUNTAIN RANGES. BOTH THURSDAY AND FRIDAY
NIGHTS SHOULD BE QUITE COLD...ESPECIALLY WITH ANY FRESH SNOW COVER.

MOSTLY DRY W-NW FLOW THEN SETS UP OVER THE FORECAST AREA SATURDAY
INTO SUNDAY. DETAILS VARY A BIT WITH EACH MEDIUM RANGE MODEL...BUT
LOOKS LIKE TEMPERATURES WILL MODERATE NEXT WEEKEND. POSSIBLY BETTER
CHANCE FOR SNOW NORTHWEST WYOMING MOUNTAINS BY SUNDAY AFTERNOON.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE MIXING OUT. EXPECT PERIODS OF 20 TO 30KT WINDS WITH GUSTS MAINLY
IN THE 35-45KT RANGE BUT A FEW MORE WIND PRONE AREAS COULD SEE GUSTS
UP TO 55KT...BUT NOT AT ANY OF THE FORECAST TERMINALS. A STRONG NW
FLOW WILL FOLLOW THIS SYSTEM TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW
SHOWERS POSSIBLE ALONG THE FRONT ACROSS THE LOWER ELEVATIONS THIS
EVENING...ESPECIALLY VCNTY AND EAST OF INTERSTATE 25. DRIER AIR
PREVAIL NW-SE BUT GUSTY NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

STRONG MTN TOP WINDS RESULTING IN AREAS MDT-SVR TURBULENCE AND
LLWS...WILL CONTINUE THROUGH THE NIGHT. A COLD FRONT WILL CONTINUE
TO PUSH SOUTH ACROSS THE AREA CROSSING INTERSTATE 80 AROUND 03Z
MONDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

&&

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

&&

$$

SHORT TERM...ALLEN
LONG TERM...KPL
AVIATION...ALLEN
FIRE WEATHER...ALLEN





000
FXUS65 KCYS 212203
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
303 PM MST SUN DEC 21 2014

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

POWERFUL PACIFIC LOW PRESSURE SYSTEM CONTINUES TO MOVE INTO THE
AREA FROM THE WEST THIS AFTERNOON...BRINGING WIDESPREAD STRONG
WINDS AND NEAR BLIZZARD CONDITIONS ALONG PORTIONS OF INTERSTATE 80
OUT NEAR ARLINGTON. HAVE SEEN SOME REPORTS OF WIND GUSTS
APPROACHING 70MPH AND HAD AN 80MPH GUST REPORTED AT A UPR SITE UP
ON THE SOUTH LARAMIE RANGE. FORECAST CHALLENGES CONTINUE TO BE
MAINLY WINDS...BUT LATER THIS EVENING...WINTER WEATHER CONDITIONS
WILL TAKE SHAPE.

CURRENTLY...1015MB SURFACE LOW CURRENTLY OVER CENTRAL UTAH EARLY
THIS AFTERNOON. PERHAPS OUR STRONGEST GRADIENT IS YET TO COME AS
SURFACE ANALYSIS SHOWS THE STRONG PRESSURE GRADIENT STILL OVER
NORTHWESTERN COLORADO AND NORTHEASTERN UTAH. CRAIG TO CASPER
SURFACE GRADIENT RIGHT AROUND 12MBS AT 1 PM THIS AFTERNOON. LATEST
WRKHGT PRODUCTS HAS 850/700MB CRAIG TO CASPER HEIGHT GRADIENTS OF
75 AND 73MTRS RESPECTIVELY. MOSAIC RADAR SHOWING MOST OF THE SNOW
OVER NORTHWESTERN COLORADO AND UP OVER NORTHWESTERN WYOMING.

HEIGHT GRADIENTS REMAIN STRONG OVER SOUTHEAST WYOMING THROUGH THE
EVENING HOURS. WILL KEEP ALL WIND HEADLINES GOING AS THEY ARE FOR
NOW AS THE GFS SHOWS 700MB WINDS STILL AROUND 60-65KTS AT 06Z
TONIGHT. ECMWF SHOWS THE 500MB SHORTWAVE MOVING THROUGH CENTRAL
WYOMING INTO WESTERN NEBRASKA AFTER 06Z WITH WINDS SHIFTING
NORTHWEST BEHIND THE FRONT TONIGHT. AREAS WEST OF THE LARAMIE
RANGE STAY IN THE FAVORABLE LEFT FRONT QUADRANT OF A 170+ KT
JET...SO HEAVY SNOW LOOKS TO CONTINUE FOR THE SNOWY AND SIERRA
MADRE RANGES. LOWER ELEVATIONS WILL CONTINUE TO SEE STRONG
WINDS...THOUGH NOT AS STRONG AS TODAY...BUT ENOUGH TO KEEP WINTER
HEADLINES GOING OUT THERE THROUGH THE OVERNIGHT HOURS.

ATTENTION TURNS TO THE PANHANDLE FOR MONDAY. GFS 850MB WINDS
BEHIND THE FRONT OUT OVER THE PANHANDLE INCREASE SIGNIFICANTLY
OVERNIGHT. LOOKING AT 850MB WIND SPEEDS OF 40-45KTS FOR MUCH OF
THE PANHANDLE. WENT AHEAD WITH A WIND ADVISORY FOR NOW COVERING
MUCH OF THE DAY. LATER SHIFTS MAY NEED TO UPGRADE TO HIGH WIND
WARNINGS IF LATER GUIDANCE SHOWS ANYTHING STRONGER THAN WHAT I AM
SEEING NOW. HEAVY SNOW CONTINUES FOR THE SNOWY AND SIERRA MADRE
RANGES ALL DAY MONDAY.

FINALLY BEGIN TO SEE AN EASING ON THE SNOW OUT WEST MONDAY NIGHT
INTO TUESDAY AS THE UPPER LOW MOVES EAST. CURRENT WINTER STORM
WARNING FOR THE MOUNTAINS LOOKS GOOD THROUGH 12Z TUESDAY...NO
CHANGES MADE IN HEADLINES.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY EVENING THROUGH
FRIDAY DUE TO HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER
WEATHER ON CHRISTMAS DAY. MODELS ARE MAINTAINING RUN TO RUN
CONSISTENCY FOR THE POTENTIAL WINTER WEATHER ON CHRISTMAS...BUT
WITH SUCH A LARGE DISCREPANCY BETWEEN INDIVIDUAL MODEL RUNS...THE
PICTURE IS NOT LOOKING ANY CLEARER TODAY IN TERMS OF THE WEATHER.

EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY TRAVEL
PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS DOWNSLOPE FLOW
DEVELOPS...WITH HIGHS IN THE MID 30S TO MID 40S...WARMEST ALONG
THE I25 CORRIDOR DUE TO DOWNSLOPE FLOW NEAR THE SURFACE. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS INDICATE A RAPIDLY MOVING
PACIFIC UPPER LEVEL TROUGH PUSHING INTO THE AREA FROM THE
NORTHWEST UNITED STATES. A STRONG PACIFIC COLD FRONT IS FORECAST
TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME CHRISTMAS MORNING WITH
SNOW DEVELOPING BEHIND THE FRONT. THERE IS THE POTENTIAL FOR A
HIGH WIND EVENT ACROSS THE WIND PRONE AREAS OF SOUTHEAST WYOMING
AHEAD OF THIS FRONT...SO CONTINUED TO INCREASE WINDS OVER THE
ARLINGTON AND BORDEAUX AREAS. WIND IMPACTS SHOULD BE MINIMAL
HOWEVER FOR HOLIDAY TRAVELERS...DUE TO A RELATIVELY BRIEF PERIOD
OF STRONG WINDS...AND THE WINDS MAINLY AFFECTING HIGH PROFILE
VEHICLES.

FORECAST BECOMES TRICKY ON CHRISTMAS DAY IN TERMS OF SNOW
POTENTIAL AS THERE IS ONLY SLIGHTLY MORE CONFIDENCE COMPARED TO
YESTERDAY THAT A DECENT PORTION OF THE AREA WILL RECEIVE
ACCUMULATING SNOW. ALL MODELS NOW SHOW THE SYSTEM MOVING RAPIDLY
ACROSS THE AREA INTO THURSDAY NIGHT...WHICH IS IMPORTANT BECAUSE
IT GREATLY LOWERS THE CHANCE OF WINTER STORM CONDITIONS. THE 12Z
ECMWF IS SLIGHTLY FASTER AND SHOWING WIDESPREAD LIGHT TO MODERATE
SNOWFALL NEARLY EVERYWHERE ACROSS SOUTHEAST WYOMING AND WESTERN
NEBRASKA. THE 12Z GFS HAS BEEN CONSISTENTLY FURTHER NORTH WITH THE
TROUGH AXIS AND PORT MAX...AND THUS MUCH LESS SNOW DUE TO
DOWNSLOPE WINDS. THE PRIMARY DIFFERENCE BETWEEN THESE TWO
SOLUTIONS...OTHER THAN THE QPF...IS THE STORM TRACK AND JET STREAM
LOCATION. THE ECMWF HAS THE JET DIGGING FURTHER SOUTH WITH A
SURFACE LOW DEVELOPING NEAR THE WYOMING/COLORADO BORDER AND MOVING
SOUTHEAST. THE GFS ON THE OTHER HAND SHOWS THE JET STREAM OVER THE
STATE OF WYOMING WITH A SURFACE LOW MUCH FURTHER NORTH ACROSS
MONTANA AND THE DAKOTAS. THE NET RESULT IS BROAD DRY DOWNSLOPE
FLOW AND LLVL SUBSIDENCE COMPARED TO THE ECMWF WHICH SHOWS PLENTY
OF NORTHEAST UPSLOPE FLOW. THE GEM IS SOMEWHERE IN BETWEEN THESE
TWO EXTREMES BUT A LITTLE CLOSER TO THE GFS. ECMWF QPF VALUES
RANGE FROM ONE QUARTER OF AN INCH TO ABOUT A THIRD OF AN INCH.
WHICH MEANS THERE IS POTENTIAL FOR LIGHT TO MODERATE SNOW AMOUNTS.
INCREASED POP SLIGHTLY ACROSS THE I80 CORRIDOR TO AROUND 30 TO 40
PERCENT FOR NOW...WITH VALUES NEAR 80 PERCENT FOR THE MOUNTAINS
WHICH HAVE THE BEST CHANCE OF SEEING 6+ INCHES OF SNOW.
HOPEFULLY...MODELS TREND TOWARD A SIMILAR SOLUTION OVER THE NEXT
24 HOURS...BUT HAVE A FEELING THAT MAY NOT HAPPEN UNTIL TUESDAY
WHEN THE SYSTEM BEGINS TO MOVE ONSHORE. THERE IS HIGH CONFIDENCE
THAT MUCH COLDER TEMPERATURES WILL ENTER THE REGION FOR THE
REMAINDER OF THE WEEK AND INTO NEXT WEEKEND WITH HIGHS IN THE 20S
TO MID 30S...AND LOWS IN THE SINGLE DIGITS (ABOVE AND BELOW ZERO)
AND TEENS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH MONDAY AFTERNOON)

POTENT STORM SYSTEM WILL BRING A COMBINATION OF SNOW AND HIGH WINDS
TO AREAS ALONG AND WEST OF THE LARAMIE RANGE...PRODUCING PREVAILING
MVFR CONDITIONS WITH PERIODS OF LIFR CONDITIONS IN MODERATE
SNOWFALL. LIGHT RAIN AND SNOW IS POSSIBLE ACROSS THE EASTERN HIGH
PLAINS THIS EVENING...BUT THE TIMING OF THIS PRECIP WILL BE
DIFFICULT TO PREDICT...SO KEPT VCSH IN THE FORECAST FOR NOW. MVFR
CONDITIONS ARE POSSIBLE WITH THIS ACTIVITY AS IT MOVES SOUTHEAST
ACROSS THE AREA. STRONG WINDS WILL SLOWLY DIMINISH LATE THIS
EVENING.

&&

.FIRE WEATHER...
ISSUED AT 110 PM MST SUN DEC 21 2014

NO FIRE WEATHER CONCERNS THROUGH THE MIDDLE OF THE WEEK. VERY WINDY
CONDITIONS ARE EXPECTED THROUGH THIS EVENING ALONG AND WEST OF
THE LARAMIE RANGE WITH GUSTS BETWEEN 60 AND 70 MPH LIKELY.
INCREASING MOISTURE WILL KEEP THE RISK FOR RAPID FIRE GROWTH LOW.
SIGNIFICANT MOUNTAIN SNOWS WILL PERSIST OVER THE NEXT 24 TO 48
HOURS WITH TOTAL ACCUMULATIONS IN EXCESS OF 2 FEET POSSIBLE IN THE
SNOWY AND SIERRA MADRES BEFORE ALL IS SAID AND DONE.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING UNTIL MIDNIGHT MST TONIGHT FOR WYZ104>107-109-
     116>118.

     WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     WINTER WEATHER ADVISORY UNTIL 8 AM MST MONDAY FOR WYZ113-115.

     WINTER STORM WARNING UNTIL 11 AM MST MONDAY FOR WYZ110-111.

NE...WIND ADVISORY FROM 8 AM TO 5 PM MST MONDAY FOR NEZ002-003-
     019>021-054-055-095-096.

&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...GCC



000
FXUS65 KCYS 212203
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
303 PM MST SUN DEC 21 2014

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

POWERFUL PACIFIC LOW PRESSURE SYSTEM CONTINUES TO MOVE INTO THE
AREA FROM THE WEST THIS AFTERNOON...BRINGING WIDESPREAD STRONG
WINDS AND NEAR BLIZZARD CONDITIONS ALONG PORTIONS OF INTERSTATE 80
OUT NEAR ARLINGTON. HAVE SEEN SOME REPORTS OF WIND GUSTS
APPROACHING 70MPH AND HAD AN 80MPH GUST REPORTED AT A UPR SITE UP
ON THE SOUTH LARAMIE RANGE. FORECAST CHALLENGES CONTINUE TO BE
MAINLY WINDS...BUT LATER THIS EVENING...WINTER WEATHER CONDITIONS
WILL TAKE SHAPE.

CURRENTLY...1015MB SURFACE LOW CURRENTLY OVER CENTRAL UTAH EARLY
THIS AFTERNOON. PERHAPS OUR STRONGEST GRADIENT IS YET TO COME AS
SURFACE ANALYSIS SHOWS THE STRONG PRESSURE GRADIENT STILL OVER
NORTHWESTERN COLORADO AND NORTHEASTERN UTAH. CRAIG TO CASPER
SURFACE GRADIENT RIGHT AROUND 12MBS AT 1 PM THIS AFTERNOON. LATEST
WRKHGT PRODUCTS HAS 850/700MB CRAIG TO CASPER HEIGHT GRADIENTS OF
75 AND 73MTRS RESPECTIVELY. MOSAIC RADAR SHOWING MOST OF THE SNOW
OVER NORTHWESTERN COLORADO AND UP OVER NORTHWESTERN WYOMING.

HEIGHT GRADIENTS REMAIN STRONG OVER SOUTHEAST WYOMING THROUGH THE
EVENING HOURS. WILL KEEP ALL WIND HEADLINES GOING AS THEY ARE FOR
NOW AS THE GFS SHOWS 700MB WINDS STILL AROUND 60-65KTS AT 06Z
TONIGHT. ECMWF SHOWS THE 500MB SHORTWAVE MOVING THROUGH CENTRAL
WYOMING INTO WESTERN NEBRASKA AFTER 06Z WITH WINDS SHIFTING
NORTHWEST BEHIND THE FRONT TONIGHT. AREAS WEST OF THE LARAMIE
RANGE STAY IN THE FAVORABLE LEFT FRONT QUADRANT OF A 170+ KT
JET...SO HEAVY SNOW LOOKS TO CONTINUE FOR THE SNOWY AND SIERRA
MADRE RANGES. LOWER ELEVATIONS WILL CONTINUE TO SEE STRONG
WINDS...THOUGH NOT AS STRONG AS TODAY...BUT ENOUGH TO KEEP WINTER
HEADLINES GOING OUT THERE THROUGH THE OVERNIGHT HOURS.

ATTENTION TURNS TO THE PANHANDLE FOR MONDAY. GFS 850MB WINDS
BEHIND THE FRONT OUT OVER THE PANHANDLE INCREASE SIGNIFICANTLY
OVERNIGHT. LOOKING AT 850MB WIND SPEEDS OF 40-45KTS FOR MUCH OF
THE PANHANDLE. WENT AHEAD WITH A WIND ADVISORY FOR NOW COVERING
MUCH OF THE DAY. LATER SHIFTS MAY NEED TO UPGRADE TO HIGH WIND
WARNINGS IF LATER GUIDANCE SHOWS ANYTHING STRONGER THAN WHAT I AM
SEEING NOW. HEAVY SNOW CONTINUES FOR THE SNOWY AND SIERRA MADRE
RANGES ALL DAY MONDAY.

FINALLY BEGIN TO SEE AN EASING ON THE SNOW OUT WEST MONDAY NIGHT
INTO TUESDAY AS THE UPPER LOW MOVES EAST. CURRENT WINTER STORM
WARNING FOR THE MOUNTAINS LOOKS GOOD THROUGH 12Z TUESDAY...NO
CHANGES MADE IN HEADLINES.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 300 PM MST SUN DEC 21 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY EVENING THROUGH
FRIDAY DUE TO HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER
WEATHER ON CHRISTMAS DAY. MODELS ARE MAINTAINING RUN TO RUN
CONSISTENCY FOR THE POTENTIAL WINTER WEATHER ON CHRISTMAS...BUT
WITH SUCH A LARGE DISCREPANCY BETWEEN INDIVIDUAL MODEL RUNS...THE
PICTURE IS NOT LOOKING ANY CLEARER TODAY IN TERMS OF THE WEATHER.

EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY TRAVEL
PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS DOWNSLOPE FLOW
DEVELOPS...WITH HIGHS IN THE MID 30S TO MID 40S...WARMEST ALONG
THE I25 CORRIDOR DUE TO DOWNSLOPE FLOW NEAR THE SURFACE. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS INDICATE A RAPIDLY MOVING
PACIFIC UPPER LEVEL TROUGH PUSHING INTO THE AREA FROM THE
NORTHWEST UNITED STATES. A STRONG PACIFIC COLD FRONT IS FORECAST
TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME CHRISTMAS MORNING WITH
SNOW DEVELOPING BEHIND THE FRONT. THERE IS THE POTENTIAL FOR A
HIGH WIND EVENT ACROSS THE WIND PRONE AREAS OF SOUTHEAST WYOMING
AHEAD OF THIS FRONT...SO CONTINUED TO INCREASE WINDS OVER THE
ARLINGTON AND BORDEAUX AREAS. WIND IMPACTS SHOULD BE MINIMAL
HOWEVER FOR HOLIDAY TRAVELERS...DUE TO A RELATIVELY BRIEF PERIOD
OF STRONG WINDS...AND THE WINDS MAINLY AFFECTING HIGH PROFILE
VEHICLES.

FORECAST BECOMES TRICKY ON CHRISTMAS DAY IN TERMS OF SNOW
POTENTIAL AS THERE IS ONLY SLIGHTLY MORE CONFIDENCE COMPARED TO
YESTERDAY THAT A DECENT PORTION OF THE AREA WILL RECEIVE
ACCUMULATING SNOW. ALL MODELS NOW SHOW THE SYSTEM MOVING RAPIDLY
ACROSS THE AREA INTO THURSDAY NIGHT...WHICH IS IMPORTANT BECAUSE
IT GREATLY LOWERS THE CHANCE OF WINTER STORM CONDITIONS. THE 12Z
ECMWF IS SLIGHTLY FASTER AND SHOWING WIDESPREAD LIGHT TO MODERATE
SNOWFALL NEARLY EVERYWHERE ACROSS SOUTHEAST WYOMING AND WESTERN
NEBRASKA. THE 12Z GFS HAS BEEN CONSISTENTLY FURTHER NORTH WITH THE
TROUGH AXIS AND PORT MAX...AND THUS MUCH LESS SNOW DUE TO
DOWNSLOPE WINDS. THE PRIMARY DIFFERENCE BETWEEN THESE TWO
SOLUTIONS...OTHER THAN THE QPF...IS THE STORM TRACK AND JET STREAM
LOCATION. THE ECMWF HAS THE JET DIGGING FURTHER SOUTH WITH A
SURFACE LOW DEVELOPING NEAR THE WYOMING/COLORADO BORDER AND MOVING
SOUTHEAST. THE GFS ON THE OTHER HAND SHOWS THE JET STREAM OVER THE
STATE OF WYOMING WITH A SURFACE LOW MUCH FURTHER NORTH ACROSS
MONTANA AND THE DAKOTAS. THE NET RESULT IS BROAD DRY DOWNSLOPE
FLOW AND LLVL SUBSIDENCE COMPARED TO THE ECMWF WHICH SHOWS PLENTY
OF NORTHEAST UPSLOPE FLOW. THE GEM IS SOMEWHERE IN BETWEEN THESE
TWO EXTREMES BUT A LITTLE CLOSER TO THE GFS. ECMWF QPF VALUES
RANGE FROM ONE QUARTER OF AN INCH TO ABOUT A THIRD OF AN INCH.
WHICH MEANS THERE IS POTENTIAL FOR LIGHT TO MODERATE SNOW AMOUNTS.
INCREASED POP SLIGHTLY ACROSS THE I80 CORRIDOR TO AROUND 30 TO 40
PERCENT FOR NOW...WITH VALUES NEAR 80 PERCENT FOR THE MOUNTAINS
WHICH HAVE THE BEST CHANCE OF SEEING 6+ INCHES OF SNOW.
HOPEFULLY...MODELS TREND TOWARD A SIMILAR SOLUTION OVER THE NEXT
24 HOURS...BUT HAVE A FEELING THAT MAY NOT HAPPEN UNTIL TUESDAY
WHEN THE SYSTEM BEGINS TO MOVE ONSHORE. THERE IS HIGH CONFIDENCE
THAT MUCH COLDER TEMPERATURES WILL ENTER THE REGION FOR THE
REMAINDER OF THE WEEK AND INTO NEXT WEEKEND WITH HIGHS IN THE 20S
TO MID 30S...AND LOWS IN THE SINGLE DIGITS (ABOVE AND BELOW ZERO)
AND TEENS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH MONDAY AFTERNOON)

POTENT STORM SYSTEM WILL BRING A COMBINATION OF SNOW AND HIGH WINDS
TO AREAS ALONG AND WEST OF THE LARAMIE RANGE...PRODUCING PREVAILING
MVFR CONDITIONS WITH PERIODS OF LIFR CONDITIONS IN MODERATE
SNOWFALL. LIGHT RAIN AND SNOW IS POSSIBLE ACROSS THE EASTERN HIGH
PLAINS THIS EVENING...BUT THE TIMING OF THIS PRECIP WILL BE
DIFFICULT TO PREDICT...SO KEPT VCSH IN THE FORECAST FOR NOW. MVFR
CONDITIONS ARE POSSIBLE WITH THIS ACTIVITY AS IT MOVES SOUTHEAST
ACROSS THE AREA. STRONG WINDS WILL SLOWLY DIMINISH LATE THIS
EVENING.

&&

.FIRE WEATHER...
ISSUED AT 110 PM MST SUN DEC 21 2014

NO FIRE WEATHER CONCERNS THROUGH THE MIDDLE OF THE WEEK. VERY WINDY
CONDITIONS ARE EXPECTED THROUGH THIS EVENING ALONG AND WEST OF
THE LARAMIE RANGE WITH GUSTS BETWEEN 60 AND 70 MPH LIKELY.
INCREASING MOISTURE WILL KEEP THE RISK FOR RAPID FIRE GROWTH LOW.
SIGNIFICANT MOUNTAIN SNOWS WILL PERSIST OVER THE NEXT 24 TO 48
HOURS WITH TOTAL ACCUMULATIONS IN EXCESS OF 2 FEET POSSIBLE IN THE
SNOWY AND SIERRA MADRES BEFORE ALL IS SAID AND DONE.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING UNTIL MIDNIGHT MST TONIGHT FOR WYZ104>107-109-
     116>118.

     WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     WINTER WEATHER ADVISORY UNTIL 8 AM MST MONDAY FOR WYZ113-115.

     WINTER STORM WARNING UNTIL 11 AM MST MONDAY FOR WYZ110-111.

NE...WIND ADVISORY FROM 8 AM TO 5 PM MST MONDAY FOR NEZ002-003-
     019>021-054-055-095-096.

&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...GCC




000
FXUS65 KRIW 211757 AAA
AFDRIW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RIVERTON WY
1057 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN ACTIVE PERIOD ACROSS WESTERN AND CENTRAL WYOMING. SNOWFALL WILL
BE ABUNDANT ACROSS THE AREA...ESPECIALLY ACROSS THE WESTERN VALLEYS
AND MOUNTAINS WHERE SNOWFALL WILL BE HEAVY AT TIMES. SOME AREAS
SEEING HEAVIER SNOWFALL WILL ALSO SEE INCREASED WIND...CREATING A
HAZARDOUS COMBINATION OF SNOW AND BLOWING SNOW. WINTER STORM
WARNINGS ARE CURRENTLY IN EFFECT...AND WILL REMAIN THROUGH MONDAY
MORNING FOR SOME LOCATIONS. SNOW TOTALS BY MONDAY MORNING COULD BE
UP TO 2 FEET ACROSS THE WESTERN MOUNTAINS WITH 5 TO 10 INCHES
POSSIBLE ACROSS THE WESTERN VALLEYS.

AS THIS PUSH OF MOISTURE MOVES THROUGH TODAY...IT WILL BRING AN
INCREASED GRADIENT ACROSS THE FORECAST AREA. HIGH WINDS ARE
EXPECTED ACROSS THE INTERSTATE 80 CORRIDOR AND THE GREEN MOUNTAINS
AND RATTLESNAKE RANGE THIS MORNING...AND WILL CONTINUE THROUGH THE
LATE EVENING HOURS. HIGH WIND WARNINGS HAVE BEEN ISSUED FOR THESE
LOCATIONS.

THE NORTHWEST FLOW ASSOCIATED WITH THIS PATTERN IS ALSO FAVORABLE TO
CREATING STRONG WIND ACROSS THE WIND RIVER BASIN. MODEL GUIDANCE
SUGGESTS AN INCREASED PROBABILITY OF STRONGER WIND DEVELOPING LATE
TONIGHT THROUGH MONDAY MORNING...WITH A HIGH WIND WATCH ISSUED.
SIMILARLY...A HIGH WIND WATCH HAS BEEN ISSUED FOR NORTHERN JOHNSON
COUNTY THROUGH MONDAY AFTERNOON.

CONDITIONS WILL START TO IMPROVE MONDAY EVENING ACROSS THE AREA AS
HIGH PRESSURE BUILDS ACROSS THE AREA. SOME LINGERING SNOWFALL WILL
BE FOUND ACROSS THE EASTERN THIRD OF THE FORECAST AREA...BUT IS
EXPECTED TO HAVE GENERALLY MOVED OUT OF THE AREA BY TUESDAY EVENING.
SOME ADDITIONAL MOISTURE IN THE RIDGE MAY CREATE SOME LIGHT SNOWFALL
ACROSS THE WESTERN MOUNTAINS WEDNESDAY MORNING...THOUGH MODEL
VARIATION DECREASES CONFIDENCE IN THIS DEVELOPMENT FOR NOW.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY LOOKS DRY FOR MOST PLACES WITH BREEZY AREAS. SOME MOISTURE
MOVES INTO NW WY IN THE AFTERNOON FOR SOME LIGHT SNOW DEVELOPING
IN THE MOUNTAINS. THE GFS/ECMWF HAVE GONE DRIER FOR WED IN THE
WEST AND IF THIS TREND CONTINUES THEN PRECIP CHANCES WILL NEED
MORE TRIMMING. THE INCOMING WEATHER SYSTEM IMPACTS THE WEST AND
NORTH WED NIGHT. THEN THE SYSTEM MOVES THROUGH THE REST OF THE
AREA CHRISTMAS DAY. DECENT COLD FRONTAL PASSAGE WILL PUT A CHILL
IN THE AIR ALONG WITH SOME LIGHT SNOW. SNOW AMOUNTS LOOK TO BE 1
TO 4 INCHES FOR THE LOWER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. EXPECT DRIFTING SNOW IN OPEN AREAS. STILL HAVE A FEW
DAYS TO WATCH THE TRACK OF THIS WEATHER SYSTEM AND REFINE SNOWFALL
AMOUNTS. THE LIGHT SNOW ENDS LATE CHRISTMAS NIGHT IN MOST PLACES.
FRIDAY LOOKS COLD WITH MOUNTAIN LIGHT SNOW SHOWERS WITH NOT MUCH
IF ANY SNOW SHOWERS AT THE LOWER ELEVATIONS. THE GFS AND ECMWF
MODELS DIFFER WITH THE WEATHER PATTERN SATURDAY AND SUNDAY. THE
GFS BRINGS ANOTHER WEATHER SYSTEM INTO THE NORTH SATURDAY NIGHT
ALONG WITH ANOTHER COLD FRONT. THEN THIS COLD AIR BOUNDARY SAGS
SOUTH NEXT SUNDAY INTO CENTRAL WY. THE ECMWF MODEL DOES NOT SHOW
THIS WEATHER SYSTEM AT ALL SATURDAY NIGHT AND SUNDAY. THUS THE
ECMWF IS DRY SATURDAY AND SUNDAY. HAVE LEANED TOWARD THE DRIER
ECMWF MODEL BUT HAVE LEFT LOW CHANCE OF SNOW IN THE WESTERN AND
NORTHERN MOUNTAINS FOR NOW. AS FOR TEMPS...CHRISTMAS EVE WILL BE
SLIGHTLY MILDER...THEN COLDER CHRISTMAS DAY AND FRIDAY. SLIGHTLY
MILDER SATURDAY AND SUNDAY.

.AVIATION.../18Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE BEGINNING TO MIX OUT BUT UNTIL THEN...EXPECT BRIEF PERIODS OF
LLWS AT FOOTHILL AND VALLEY TERMINALS FOLLOWED BY PERIODS OF 20 TO
30KT WINDS WITH GUSTS MAINLY IN THE 35-45KT RANGE BUT A FEW MORE
WIND PRONE AREAS COULD SEE GUSTS UP TO 60KT...BUT NOT AT ANY OF
THE FORECAST TERMINALS. A STRONG NW FLOW WILL FOLLOW THIS SYSTEM
TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG
THE FRONT ACROSS THE LOWER ELEVATIONS THIS EVENING...ESPECIALLY
VCNTY AND EAST OF INTERSTATE 25. DRIER AIR PREVAIL NW-SE BUT GUSTY
NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 00Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA THIS AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING TODAY. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT...ALONG WITH A
COUPLE AREAS IN A HIGH WIND WATCH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH MONDAY
AFTERNOON WYZ010.

HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH MONDAY
MORNING WYZ016-017.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...ALLEN
FIRE WEATHER...BRANHAM






000
FXUS65 KRIW 211757 AAA
AFDRIW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RIVERTON WY
1057 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN ACTIVE PERIOD ACROSS WESTERN AND CENTRAL WYOMING. SNOWFALL WILL
BE ABUNDANT ACROSS THE AREA...ESPECIALLY ACROSS THE WESTERN VALLEYS
AND MOUNTAINS WHERE SNOWFALL WILL BE HEAVY AT TIMES. SOME AREAS
SEEING HEAVIER SNOWFALL WILL ALSO SEE INCREASED WIND...CREATING A
HAZARDOUS COMBINATION OF SNOW AND BLOWING SNOW. WINTER STORM
WARNINGS ARE CURRENTLY IN EFFECT...AND WILL REMAIN THROUGH MONDAY
MORNING FOR SOME LOCATIONS. SNOW TOTALS BY MONDAY MORNING COULD BE
UP TO 2 FEET ACROSS THE WESTERN MOUNTAINS WITH 5 TO 10 INCHES
POSSIBLE ACROSS THE WESTERN VALLEYS.

AS THIS PUSH OF MOISTURE MOVES THROUGH TODAY...IT WILL BRING AN
INCREASED GRADIENT ACROSS THE FORECAST AREA. HIGH WINDS ARE
EXPECTED ACROSS THE INTERSTATE 80 CORRIDOR AND THE GREEN MOUNTAINS
AND RATTLESNAKE RANGE THIS MORNING...AND WILL CONTINUE THROUGH THE
LATE EVENING HOURS. HIGH WIND WARNINGS HAVE BEEN ISSUED FOR THESE
LOCATIONS.

THE NORTHWEST FLOW ASSOCIATED WITH THIS PATTERN IS ALSO FAVORABLE TO
CREATING STRONG WIND ACROSS THE WIND RIVER BASIN. MODEL GUIDANCE
SUGGESTS AN INCREASED PROBABILITY OF STRONGER WIND DEVELOPING LATE
TONIGHT THROUGH MONDAY MORNING...WITH A HIGH WIND WATCH ISSUED.
SIMILARLY...A HIGH WIND WATCH HAS BEEN ISSUED FOR NORTHERN JOHNSON
COUNTY THROUGH MONDAY AFTERNOON.

CONDITIONS WILL START TO IMPROVE MONDAY EVENING ACROSS THE AREA AS
HIGH PRESSURE BUILDS ACROSS THE AREA. SOME LINGERING SNOWFALL WILL
BE FOUND ACROSS THE EASTERN THIRD OF THE FORECAST AREA...BUT IS
EXPECTED TO HAVE GENERALLY MOVED OUT OF THE AREA BY TUESDAY EVENING.
SOME ADDITIONAL MOISTURE IN THE RIDGE MAY CREATE SOME LIGHT SNOWFALL
ACROSS THE WESTERN MOUNTAINS WEDNESDAY MORNING...THOUGH MODEL
VARIATION DECREASES CONFIDENCE IN THIS DEVELOPMENT FOR NOW.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY LOOKS DRY FOR MOST PLACES WITH BREEZY AREAS. SOME MOISTURE
MOVES INTO NW WY IN THE AFTERNOON FOR SOME LIGHT SNOW DEVELOPING
IN THE MOUNTAINS. THE GFS/ECMWF HAVE GONE DRIER FOR WED IN THE
WEST AND IF THIS TREND CONTINUES THEN PRECIP CHANCES WILL NEED
MORE TRIMMING. THE INCOMING WEATHER SYSTEM IMPACTS THE WEST AND
NORTH WED NIGHT. THEN THE SYSTEM MOVES THROUGH THE REST OF THE
AREA CHRISTMAS DAY. DECENT COLD FRONTAL PASSAGE WILL PUT A CHILL
IN THE AIR ALONG WITH SOME LIGHT SNOW. SNOW AMOUNTS LOOK TO BE 1
TO 4 INCHES FOR THE LOWER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. EXPECT DRIFTING SNOW IN OPEN AREAS. STILL HAVE A FEW
DAYS TO WATCH THE TRACK OF THIS WEATHER SYSTEM AND REFINE SNOWFALL
AMOUNTS. THE LIGHT SNOW ENDS LATE CHRISTMAS NIGHT IN MOST PLACES.
FRIDAY LOOKS COLD WITH MOUNTAIN LIGHT SNOW SHOWERS WITH NOT MUCH
IF ANY SNOW SHOWERS AT THE LOWER ELEVATIONS. THE GFS AND ECMWF
MODELS DIFFER WITH THE WEATHER PATTERN SATURDAY AND SUNDAY. THE
GFS BRINGS ANOTHER WEATHER SYSTEM INTO THE NORTH SATURDAY NIGHT
ALONG WITH ANOTHER COLD FRONT. THEN THIS COLD AIR BOUNDARY SAGS
SOUTH NEXT SUNDAY INTO CENTRAL WY. THE ECMWF MODEL DOES NOT SHOW
THIS WEATHER SYSTEM AT ALL SATURDAY NIGHT AND SUNDAY. THUS THE
ECMWF IS DRY SATURDAY AND SUNDAY. HAVE LEANED TOWARD THE DRIER
ECMWF MODEL BUT HAVE LEFT LOW CHANCE OF SNOW IN THE WESTERN AND
NORTHERN MOUNTAINS FOR NOW. AS FOR TEMPS...CHRISTMAS EVE WILL BE
SLIGHTLY MILDER...THEN COLDER CHRISTMAS DAY AND FRIDAY. SLIGHTLY
MILDER SATURDAY AND SUNDAY.

.AVIATION.../18Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE BEGINNING TO MIX OUT BUT UNTIL THEN...EXPECT BRIEF PERIODS OF
LLWS AT FOOTHILL AND VALLEY TERMINALS FOLLOWED BY PERIODS OF 20 TO
30KT WINDS WITH GUSTS MAINLY IN THE 35-45KT RANGE BUT A FEW MORE
WIND PRONE AREAS COULD SEE GUSTS UP TO 60KT...BUT NOT AT ANY OF
THE FORECAST TERMINALS. A STRONG NW FLOW WILL FOLLOW THIS SYSTEM
TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG
THE FRONT ACROSS THE LOWER ELEVATIONS THIS EVENING...ESPECIALLY
VCNTY AND EAST OF INTERSTATE 25. DRIER AIR PREVAIL NW-SE BUT GUSTY
NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 00Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA THIS AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING TODAY. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT...ALONG WITH A
COUPLE AREAS IN A HIGH WIND WATCH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH MONDAY
AFTERNOON WYZ010.

HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH MONDAY
MORNING WYZ016-017.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...ALLEN
FIRE WEATHER...BRANHAM






000
FXUS65 KRIW 211757 AAA
AFDRIW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RIVERTON WY
1057 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN ACTIVE PERIOD ACROSS WESTERN AND CENTRAL WYOMING. SNOWFALL WILL
BE ABUNDANT ACROSS THE AREA...ESPECIALLY ACROSS THE WESTERN VALLEYS
AND MOUNTAINS WHERE SNOWFALL WILL BE HEAVY AT TIMES. SOME AREAS
SEEING HEAVIER SNOWFALL WILL ALSO SEE INCREASED WIND...CREATING A
HAZARDOUS COMBINATION OF SNOW AND BLOWING SNOW. WINTER STORM
WARNINGS ARE CURRENTLY IN EFFECT...AND WILL REMAIN THROUGH MONDAY
MORNING FOR SOME LOCATIONS. SNOW TOTALS BY MONDAY MORNING COULD BE
UP TO 2 FEET ACROSS THE WESTERN MOUNTAINS WITH 5 TO 10 INCHES
POSSIBLE ACROSS THE WESTERN VALLEYS.

AS THIS PUSH OF MOISTURE MOVES THROUGH TODAY...IT WILL BRING AN
INCREASED GRADIENT ACROSS THE FORECAST AREA. HIGH WINDS ARE
EXPECTED ACROSS THE INTERSTATE 80 CORRIDOR AND THE GREEN MOUNTAINS
AND RATTLESNAKE RANGE THIS MORNING...AND WILL CONTINUE THROUGH THE
LATE EVENING HOURS. HIGH WIND WARNINGS HAVE BEEN ISSUED FOR THESE
LOCATIONS.

THE NORTHWEST FLOW ASSOCIATED WITH THIS PATTERN IS ALSO FAVORABLE TO
CREATING STRONG WIND ACROSS THE WIND RIVER BASIN. MODEL GUIDANCE
SUGGESTS AN INCREASED PROBABILITY OF STRONGER WIND DEVELOPING LATE
TONIGHT THROUGH MONDAY MORNING...WITH A HIGH WIND WATCH ISSUED.
SIMILARLY...A HIGH WIND WATCH HAS BEEN ISSUED FOR NORTHERN JOHNSON
COUNTY THROUGH MONDAY AFTERNOON.

CONDITIONS WILL START TO IMPROVE MONDAY EVENING ACROSS THE AREA AS
HIGH PRESSURE BUILDS ACROSS THE AREA. SOME LINGERING SNOWFALL WILL
BE FOUND ACROSS THE EASTERN THIRD OF THE FORECAST AREA...BUT IS
EXPECTED TO HAVE GENERALLY MOVED OUT OF THE AREA BY TUESDAY EVENING.
SOME ADDITIONAL MOISTURE IN THE RIDGE MAY CREATE SOME LIGHT SNOWFALL
ACROSS THE WESTERN MOUNTAINS WEDNESDAY MORNING...THOUGH MODEL
VARIATION DECREASES CONFIDENCE IN THIS DEVELOPMENT FOR NOW.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY LOOKS DRY FOR MOST PLACES WITH BREEZY AREAS. SOME MOISTURE
MOVES INTO NW WY IN THE AFTERNOON FOR SOME LIGHT SNOW DEVELOPING
IN THE MOUNTAINS. THE GFS/ECMWF HAVE GONE DRIER FOR WED IN THE
WEST AND IF THIS TREND CONTINUES THEN PRECIP CHANCES WILL NEED
MORE TRIMMING. THE INCOMING WEATHER SYSTEM IMPACTS THE WEST AND
NORTH WED NIGHT. THEN THE SYSTEM MOVES THROUGH THE REST OF THE
AREA CHRISTMAS DAY. DECENT COLD FRONTAL PASSAGE WILL PUT A CHILL
IN THE AIR ALONG WITH SOME LIGHT SNOW. SNOW AMOUNTS LOOK TO BE 1
TO 4 INCHES FOR THE LOWER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. EXPECT DRIFTING SNOW IN OPEN AREAS. STILL HAVE A FEW
DAYS TO WATCH THE TRACK OF THIS WEATHER SYSTEM AND REFINE SNOWFALL
AMOUNTS. THE LIGHT SNOW ENDS LATE CHRISTMAS NIGHT IN MOST PLACES.
FRIDAY LOOKS COLD WITH MOUNTAIN LIGHT SNOW SHOWERS WITH NOT MUCH
IF ANY SNOW SHOWERS AT THE LOWER ELEVATIONS. THE GFS AND ECMWF
MODELS DIFFER WITH THE WEATHER PATTERN SATURDAY AND SUNDAY. THE
GFS BRINGS ANOTHER WEATHER SYSTEM INTO THE NORTH SATURDAY NIGHT
ALONG WITH ANOTHER COLD FRONT. THEN THIS COLD AIR BOUNDARY SAGS
SOUTH NEXT SUNDAY INTO CENTRAL WY. THE ECMWF MODEL DOES NOT SHOW
THIS WEATHER SYSTEM AT ALL SATURDAY NIGHT AND SUNDAY. THUS THE
ECMWF IS DRY SATURDAY AND SUNDAY. HAVE LEANED TOWARD THE DRIER
ECMWF MODEL BUT HAVE LEFT LOW CHANCE OF SNOW IN THE WESTERN AND
NORTHERN MOUNTAINS FOR NOW. AS FOR TEMPS...CHRISTMAS EVE WILL BE
SLIGHTLY MILDER...THEN COLDER CHRISTMAS DAY AND FRIDAY. SLIGHTLY
MILDER SATURDAY AND SUNDAY.

.AVIATION.../18Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE BEGINNING TO MIX OUT BUT UNTIL THEN...EXPECT BRIEF PERIODS OF
LLWS AT FOOTHILL AND VALLEY TERMINALS FOLLOWED BY PERIODS OF 20 TO
30KT WINDS WITH GUSTS MAINLY IN THE 35-45KT RANGE BUT A FEW MORE
WIND PRONE AREAS COULD SEE GUSTS UP TO 60KT...BUT NOT AT ANY OF
THE FORECAST TERMINALS. A STRONG NW FLOW WILL FOLLOW THIS SYSTEM
TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG
THE FRONT ACROSS THE LOWER ELEVATIONS THIS EVENING...ESPECIALLY
VCNTY AND EAST OF INTERSTATE 25. DRIER AIR PREVAIL NW-SE BUT GUSTY
NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 00Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA THIS AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING TODAY. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT...ALONG WITH A
COUPLE AREAS IN A HIGH WIND WATCH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH MONDAY
AFTERNOON WYZ010.

HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH MONDAY
MORNING WYZ016-017.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...ALLEN
FIRE WEATHER...BRANHAM






000
FXUS65 KRIW 211757 AAA
AFDRIW

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RIVERTON WY
1057 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN ACTIVE PERIOD ACROSS WESTERN AND CENTRAL WYOMING. SNOWFALL WILL
BE ABUNDANT ACROSS THE AREA...ESPECIALLY ACROSS THE WESTERN VALLEYS
AND MOUNTAINS WHERE SNOWFALL WILL BE HEAVY AT TIMES. SOME AREAS
SEEING HEAVIER SNOWFALL WILL ALSO SEE INCREASED WIND...CREATING A
HAZARDOUS COMBINATION OF SNOW AND BLOWING SNOW. WINTER STORM
WARNINGS ARE CURRENTLY IN EFFECT...AND WILL REMAIN THROUGH MONDAY
MORNING FOR SOME LOCATIONS. SNOW TOTALS BY MONDAY MORNING COULD BE
UP TO 2 FEET ACROSS THE WESTERN MOUNTAINS WITH 5 TO 10 INCHES
POSSIBLE ACROSS THE WESTERN VALLEYS.

AS THIS PUSH OF MOISTURE MOVES THROUGH TODAY...IT WILL BRING AN
INCREASED GRADIENT ACROSS THE FORECAST AREA. HIGH WINDS ARE
EXPECTED ACROSS THE INTERSTATE 80 CORRIDOR AND THE GREEN MOUNTAINS
AND RATTLESNAKE RANGE THIS MORNING...AND WILL CONTINUE THROUGH THE
LATE EVENING HOURS. HIGH WIND WARNINGS HAVE BEEN ISSUED FOR THESE
LOCATIONS.

THE NORTHWEST FLOW ASSOCIATED WITH THIS PATTERN IS ALSO FAVORABLE TO
CREATING STRONG WIND ACROSS THE WIND RIVER BASIN. MODEL GUIDANCE
SUGGESTS AN INCREASED PROBABILITY OF STRONGER WIND DEVELOPING LATE
TONIGHT THROUGH MONDAY MORNING...WITH A HIGH WIND WATCH ISSUED.
SIMILARLY...A HIGH WIND WATCH HAS BEEN ISSUED FOR NORTHERN JOHNSON
COUNTY THROUGH MONDAY AFTERNOON.

CONDITIONS WILL START TO IMPROVE MONDAY EVENING ACROSS THE AREA AS
HIGH PRESSURE BUILDS ACROSS THE AREA. SOME LINGERING SNOWFALL WILL
BE FOUND ACROSS THE EASTERN THIRD OF THE FORECAST AREA...BUT IS
EXPECTED TO HAVE GENERALLY MOVED OUT OF THE AREA BY TUESDAY EVENING.
SOME ADDITIONAL MOISTURE IN THE RIDGE MAY CREATE SOME LIGHT SNOWFALL
ACROSS THE WESTERN MOUNTAINS WEDNESDAY MORNING...THOUGH MODEL
VARIATION DECREASES CONFIDENCE IN THIS DEVELOPMENT FOR NOW.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY LOOKS DRY FOR MOST PLACES WITH BREEZY AREAS. SOME MOISTURE
MOVES INTO NW WY IN THE AFTERNOON FOR SOME LIGHT SNOW DEVELOPING
IN THE MOUNTAINS. THE GFS/ECMWF HAVE GONE DRIER FOR WED IN THE
WEST AND IF THIS TREND CONTINUES THEN PRECIP CHANCES WILL NEED
MORE TRIMMING. THE INCOMING WEATHER SYSTEM IMPACTS THE WEST AND
NORTH WED NIGHT. THEN THE SYSTEM MOVES THROUGH THE REST OF THE
AREA CHRISTMAS DAY. DECENT COLD FRONTAL PASSAGE WILL PUT A CHILL
IN THE AIR ALONG WITH SOME LIGHT SNOW. SNOW AMOUNTS LOOK TO BE 1
TO 4 INCHES FOR THE LOWER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. EXPECT DRIFTING SNOW IN OPEN AREAS. STILL HAVE A FEW
DAYS TO WATCH THE TRACK OF THIS WEATHER SYSTEM AND REFINE SNOWFALL
AMOUNTS. THE LIGHT SNOW ENDS LATE CHRISTMAS NIGHT IN MOST PLACES.
FRIDAY LOOKS COLD WITH MOUNTAIN LIGHT SNOW SHOWERS WITH NOT MUCH
IF ANY SNOW SHOWERS AT THE LOWER ELEVATIONS. THE GFS AND ECMWF
MODELS DIFFER WITH THE WEATHER PATTERN SATURDAY AND SUNDAY. THE
GFS BRINGS ANOTHER WEATHER SYSTEM INTO THE NORTH SATURDAY NIGHT
ALONG WITH ANOTHER COLD FRONT. THEN THIS COLD AIR BOUNDARY SAGS
SOUTH NEXT SUNDAY INTO CENTRAL WY. THE ECMWF MODEL DOES NOT SHOW
THIS WEATHER SYSTEM AT ALL SATURDAY NIGHT AND SUNDAY. THUS THE
ECMWF IS DRY SATURDAY AND SUNDAY. HAVE LEANED TOWARD THE DRIER
ECMWF MODEL BUT HAVE LEFT LOW CHANCE OF SNOW IN THE WESTERN AND
NORTHERN MOUNTAINS FOR NOW. AS FOR TEMPS...CHRISTMAS EVE WILL BE
SLIGHTLY MILDER...THEN COLDER CHRISTMAS DAY AND FRIDAY. SLIGHTLY
MILDER SATURDAY AND SUNDAY.

.AVIATION.../18Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A STRONG STORM SYSTEM CONTINUES TO MOVE ACROSS THE REGION...BASINS
ARE BEGINNING TO MIX OUT BUT UNTIL THEN...EXPECT BRIEF PERIODS OF
LLWS AT FOOTHILL AND VALLEY TERMINALS FOLLOWED BY PERIODS OF 20 TO
30KT WINDS WITH GUSTS MAINLY IN THE 35-45KT RANGE BUT A FEW MORE
WIND PRONE AREAS COULD SEE GUSTS UP TO 60KT...BUT NOT AT ANY OF
THE FORECAST TERMINALS. A STRONG NW FLOW WILL FOLLOW THIS SYSTEM
TONIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG
THE FRONT ACROSS THE LOWER ELEVATIONS THIS EVENING...ESPECIALLY
VCNTY AND EAST OF INTERSTATE 25. DRIER AIR PREVAIL NW-SE BUT GUSTY
NW SFC WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 00Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA THIS AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH THE EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING TODAY. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT...ALONG WITH A
COUPLE AREAS IN A HIGH WIND WATCH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH MONDAY
AFTERNOON WYZ010.

HIGH WIND WATCH FROM 8 PM MST THIS EVENING THROUGH MONDAY
MORNING WYZ016-017.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...ALLEN
FIRE WEATHER...BRANHAM






000
FXUS65 KCYS 211739
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1030 AM MST SUN DEC 21 2014

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 420 AM MST SUN DEC 21 2014

QUITE A CHALLENGING FORECAST FOR THE NEXT 24 HOURS WITH SNOW...WIND
AND THE POTENTIAL FOR SIGNIFICANT IMPACTS TO PRE-HOLIDAY TRAVEL IN
AND AROUND THE CWA. LATEST WATER VAPOR LOOP SHOWS A FIREHOSE OF AN
UPPER JET CRASHING INTO THE PACIFIC NORTHWEST. AMPLE MID AND HIGH
LEVEL MOISTURE CONTINUES TO STREAM INTO THE MOUNTAINS OF SOUTHEAST
WYOMING VIA STRONG WESTERLY FLOW ALOFT...SETTING THE STAGE FOR AN
INCREASE IN MOUNTAIN SNOWS SHORTLY. RADAR HAS BEEN RELATIVELY QUIET
OVER THE PAST FEW HOURS...BUT SNOW SHOULD INCREASE IN BOTH COVERAGE
AND INTENSITY AFTER SUNRISE AS LARGE SCALE ASCENT RAPIDLY INCREASES
IN THE LEFT FRONT QUADRANT OF A 150 KNOT H25 JET. THIS WILL COMBINE
WITH EXCELLENT OROGRAPHICS ON THE NORTHERN EDGE OF A BELT OF MOIST
WEST-TO-NORTHWEST FLOW TO PRODUCE SEVERAL HOURS OF HEAVY SNOW. QPF
FROM VIRTUALLY EVERY MODEL SUGGESTS UPWARDS OF 1.5 INCHES OF LIQUID
FOR OUR HIGH PEAKS...WHICH TRANSLATES TO UPWARDS OF 2 TO 3 FEET IF
WE ASSUME A 20 TO 1 RATIO. THE WINTER STORM WARNING LOOKS GOOD FOR
THOSE AREAS. WILL CONTINUE WITH A 12Z TUE EXPIRATION AS THE ARRIVAL
OF MID LEVEL DRY AIR SHOULD CUT OFF PRECIPITATION FROM WEST TO EAST
ON TUE MORNING.

WINDS ARE THE OTHER MAJOR CONCERN IN THE NEAR TERM. WILL CONTINUE A
HIGH WIND WARNING FOR THE WIND PRONE LOCATIONS INCLUDING BRX AND THE
I80 SUMMIT BETWEEN CHEYENNE AND LARAMIE. BUFORD IN THE SOUTH LARAMIE
RANGE HAS ALREADY MANAGED TO ACHIEVE 60 MPH GUSTS...SO WE MIGHT NEED
TO BUMP UP THE START TIME BEFORE THE DAY CREW ARRIVES DEPENDING ON
TRENDS. EXPECT WINDS WILL CONTINUE TO INCREASE THROUGH THE DAY AS
THE NAM H85 CAG-CPR GRADIENT CLIMBS TO 80 METERS BY 18Z. PROGGED H7
FLOW IN EXCESS OF 70 KT OVER THE WIND CORRIDOR AND GOOD LOW LEVEL
MIXING ON AFTERNOON FORECAST SOUNDINGS SUGGEST AN EXCELLENT SETUP
FOR 65 TO 75 MPH GUSTS GIVEN GOOD MID LEVEL SUBSIDENCE SEEN IN THE
OMEGA FIELDS. UPGRADED NORTHERN CARBON COUNTY / FERRIS MOUNTAINS
AND SHIRLEY BASIN / TO A HIGH WIND WARNING AS GFS H75 FLOW APPEARS
TO BE WELL IN EXCESS OF 50 KT AROUND MID DAY. FALLING AND BLOWING
SNOW IS DEFINITELY A CONCERN HERE...BUT 700-300 MILLIBAR RH PROGS
SUGGEST THE BEST MOISTURE IS TO THE SOUTH. JUST NOT CONFIDENT SNOW
AMOUNTS WILL BE HIGH ENOUGH WITHOUT GAP ENHANCEMENTS TO CAUSE
WINTER STORM WARNING TYPE IMPACTS.

NOT SO MUCH THE CASE FOR ARLINGTON THOUGH...WHICH WILL BE EXTREMELY
WINDY FOR REASONS ALREADY STATED. PERIODIC LIGHT SNOW SHOULD DEVELOP
OVER THE NORTH SNOWY RANGE FOOTHILLS BY LATE MORNING. AREA FORECAST
SOUNDINGS ARE VERY CONCERNING WITH 60+ KT FLOW JUST OFF THE SURFACE
DURING THE AFTERNOON AND EVENING. WITH COLD ADVECTION ALOFT AIDING
IN MIXING AND POTENTIAL FOR CONVECTIVE SNOW SHOWERS GIVEN SLIGHTLY
NEGATIVE LIFTED INDICES...BELIEVE BLOWING SNOW COULD EASILY BE A
MAJOR ISSUE FOR INTERSTATE TRAVEL. EVEN IF ONLY AN INCH OR TWO OF
NEW SNOW FALLS...THE COMBINATION OF 70 MPH WIND GUSTS AND FALLING
AND/OR BLOWING SNOW HAS POTENTIAL TO RESULT IN VERY LOW VISIBILITIES
AND POSSIBLY WHITEOUT CONDITIONS. WE THOUGHT A WINTER STORM WARNING
WOULD BETTER HIGHLIGHT THESE IMPACTS...SO OPTED TO CHANGE FROM NPW
TO WSW HEADLINES AT ARL. WOULD NOT BE ENTIRELY SURPRISED IF THE DAY
SHIFT NEEDS TO CONSIDER BLIZZARD HEADLINES IF THESE CONCERNS ARE
REALIZED. WE ALSO INCLUDED SOUTHWEST CARBON COUNTY ON THE WEST SIDE
OF THE SIERRA MADRE WHERE UPSLOPE ENHANCEMENTS MAY YIELD LOCAL
AMOUNTS OF 6 TO 8 INCHES AROUND DIXON AND BAGGS. SHADOWING IN THE
UPPER NORTH PLATTE RIVER VALLEY AND LARAMIE VALLEY COULD LIMIT
SNOWFALL TO LESS THAN AN INCH...BUT UPGRADED THE WINTER STORM WATCH
TO AN ADVISORY FOR DANGEROUS TRAVEL. NOT TOO CONCERNED WITH THE
SOUTH LARAMIE RANGE THE ACCUMULATING SNOW SHOULD HOLD OFF UNTIL THE
OVERNIGHT...WHEN WINDS START TO COME DOWN. DO NOT EXPECT MUCH SNOW
AT ALL EAST OF THE LARAMIE RANGE WITH DRY DOWNSLOPING WINDS. A BIT
WARMER ON THE LEE SIDE TOO...SUPPORTING MORE RAIN THAN SNOW THROUGH
THE DURATION OF THE EVENT.

HIGH WINDS WILL END AFTER 06Z AS LOW-LEVEL GRADIENTS QUICKLY DROP
OFF OVERNIGHT...BUT BREEZY CONDITIONS WILL LIKELY PERSIST WITH AREAS
OF BLOWING SNOW AND REDUCED VISIBILITIES CONTINUING THROUGH MONDAY
MORNING OR EARLY AFTERNOON. SNOW AND WIND COULD BECOME AN ISSUE OVER
THE NORTHERN PANHANDLE ON MON WITH FAST NORTH/NORTHWEST FLOW ALOFT
AND STRONG LOW LEVEL CAA. DESPITE CLOUD COVER...GFS/NAM/ECMWF EACH
DEPICT A WELL-MIXED BOUNDARY LAYER WITH 50 TO 60 KT AVAILABLE TO
MIX AROUND 18Z MON. CONTEMPLATED SOME SORT OF WATCH HEADLINE WITH
INCREASED CONFIDENCE IN A HIGHER IMPACT EVENT...BUT PLAN TO FOLLOW
LBF/S LEAD WITH AN SPS LATER THIS MORNING TO AVOID ANY CONFUSION
WITH ONGOING HAZARDS. THE MODELS REALLY WRAP UP THE MID-LEVEL
SHORTWAVE AND ASSOCIATED SURFACE LOW AFTER 00Z TUE AS IT
TRANSLATES EASTWARD INTO THE CENTRAL PLAINS. COLD AIR ALOFT
REMAINS INTACT WITH H7 TEMPS AROUND -14C...SO INSTABILITY SNOW
SHOWERS OR FLURRIES WILL STILL BE POSSIBLE ALTHOUGH CONDITIONS
SHOULD GENERALLY IMPROVE.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 330 AM MST SUN DEC 21 2014

A PRONOUNCED UPPER TROUGH OVER GREAT PLAINS WILL PROGRESS EAST
TOWARD THE ATLANTIC/GULF COASTS THURSDAY. A RETURN TO ZONAL FLOW
ALOFT WILL BE SHORT-LIVED AS THE NEXT TROUGH MOVING INTO THE
PACIFIC NORTHWEST AMPLIFIES OVER THE ROCKY MOUNTAINS ON FRIDAY.
MODEL DIFFERENCES APPEAR SATURDAY...AS THE ECMWF IS MORE PRONOUNCED
WITH THE UPPER RIDGE OVER THE PACIFIC COAST STATES AND ITS DOWNSTREAM
TROUGH AXIS EXTENDING FURTHER WEST THAN THE GFS.

MOISTURE WILL DWINDLE OVER THE SOUTHERN WY MOUNTAINS TUESDAY NIGHT
WITH A SURFACE RIDGE OF HIGH PRESSURE EXTENDING FROM WESTERN CO
WEDNESDAY. SURFACE LOW PRESSURE DEVELOPS ALONG A COLD FRONT OVER
NORTHERN ID WEDNESDAY NIGHT...THEN PUSHES SOUTHEAST ACROSS WY AND
WESTERN NE CHRISTMAS DAY. THE ECMWF IS TRENDING FASTER AND PRODUCES
MORE WIDESPREAD QPF THAN THE GFS. GENERALLY FOLLOWED THE ECMWF
SOLUTION...WITH THE PRECIPITATION DEVELOPING WEST OF THE LARAMIE
RANGE WEDNESDAY NIGHT...SPREADING EAST ACROSS THE REMAINDER OF
THE CWA CHRISTMAS DAY...AND ENDING THURSDAY NIGHT. IT/S STILL
EARLY TO PREDICT SNOW ACCUMULATIONS WITH THIS SYSTEM. A BIT OF
MOISTURE AND WEAK UPSLOPE MAY TRIGGER LIGHT SNOW FOR THE SNOWY
AND SIERRA MADRES FRIDAY...OTHERWISE IT WILL BE DRY HEADING INTO
THE HOLIDAY WEEKEND.

HIGH TEMPERATURES WEDNESDAY WILL BE NEAR OR SLIGHTLY ABOVE SEASONAL
NORMALS WITH 30S TO LOWER 40S...FALLING TO BELOW NORMAL CHRISTMAS
DAY THROUGH SATURDAY. LOW TEMPERATURES TUESDAY/WEDNESDAY NIGHTS WILL
AVERAGE IN THE TEENS AND 20S...FALLING INTO THE SINGLE DIGITS AND
LOWER TEENS THURSDAY/FRIDAY NIGHTS. NOT EXPECTING ANY STRONG WINDS
WITH BREEZY TO OCCASIONALLY WINDY PERIODS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH MONDAY MORNING) ISSUED AT 235
AM MST SUN DEC 21 2014

POTENT STORM SYSTEM WILL BRING A COMBINATION OF SNOW AND HIGH WINDS
TO AREAS ALONG AND WEST OF THE LARAMIE RANGE...PRODUCING PREVAILING
MVFR CONDITIONS WITH PERIODS OF LIFR CONDITIONS IN MODERATE
SNOWFALL. LIGHT RAIN AND SNOW IS POSSIBLE ACROSS THE EASTERN HIGH
PLAINS...BUT THE TIMING OF THIS PRECIP WILL BE DIFFICULT SO KEPT
VCSH IN THE FORECAST FOR NOW. MVFR CONDITIONS ARE POSSIBLE WITH THIS
ACTIVITY AS IT MOVES SOUTHEAST ACROSS THE AREA. WEST WINDS WILL GUST
IN EXCESS OF 45-50 KNOTS AT TIMES TODAY...MAINLY BETWEEN KRWL AND
KCYS. WINDS WILL NOT BE AS STRONG ACROSS FAR EASTERN WYOMING AND
WESTERN NEBRASKA. STRONG WINDS WILL SLOWLY DIMINISH LATE THIS
EVENING.

&&

.FIRE WEATHER...
ISSUED AT 315 AM MST SUN DEC 21 2014

NO FIRE WEATHER CONCERNS THROUGH THE MIDDLE OF THE WEEK. VERY WINDY
CONDITIONS ARE EXPECTED TODAY ALONG AND WEST OF THE LARAMIE RANGE
WITH GUSTS BETWEEN 60 AND 70 MPH LIKELY. INCREASING MOISTURE WILL
KEEP THE RISK FOR RAPID FIRE GROWTH LOW. SIGNIFICANT MOUNTAIN SNOWS
WILL PERSIST OVER THE NEXT 24 TO 48 HOURS WITH TOTAL ACCUMULATIONS
IN EXCESS OF 2 FEET POSSIBLE IN THE SNOWIES AND SIERRA MADRES BEFORE
ALL IS SAID AND DONE.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM THIS MORNING TO MIDNIGHT MST TONIGHT
     FOR WYZ104-105-109-116-117.

     WINTER STORM WARNING UNTIL 11 AM MST MONDAY FOR WYZ110-111.

     HIGH WIND WARNING UNTIL MIDNIGHT MST TONIGHT FOR WYZ106.

     WINTER WEATHER ADVISORY FROM NOON TODAY TO 8 AM MST MONDAY FOR
     WYZ113-115.

NE...NONE.
&&

$$

SHORT TERM...CLH
LONG TERM...MJ
AVIATION...MJ
FIRE WEATHER...CLH



000
FXUS65 KCYS 211739
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1030 AM MST SUN DEC 21 2014

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 420 AM MST SUN DEC 21 2014

QUITE A CHALLENGING FORECAST FOR THE NEXT 24 HOURS WITH SNOW...WIND
AND THE POTENTIAL FOR SIGNIFICANT IMPACTS TO PRE-HOLIDAY TRAVEL IN
AND AROUND THE CWA. LATEST WATER VAPOR LOOP SHOWS A FIREHOSE OF AN
UPPER JET CRASHING INTO THE PACIFIC NORTHWEST. AMPLE MID AND HIGH
LEVEL MOISTURE CONTINUES TO STREAM INTO THE MOUNTAINS OF SOUTHEAST
WYOMING VIA STRONG WESTERLY FLOW ALOFT...SETTING THE STAGE FOR AN
INCREASE IN MOUNTAIN SNOWS SHORTLY. RADAR HAS BEEN RELATIVELY QUIET
OVER THE PAST FEW HOURS...BUT SNOW SHOULD INCREASE IN BOTH COVERAGE
AND INTENSITY AFTER SUNRISE AS LARGE SCALE ASCENT RAPIDLY INCREASES
IN THE LEFT FRONT QUADRANT OF A 150 KNOT H25 JET. THIS WILL COMBINE
WITH EXCELLENT OROGRAPHICS ON THE NORTHERN EDGE OF A BELT OF MOIST
WEST-TO-NORTHWEST FLOW TO PRODUCE SEVERAL HOURS OF HEAVY SNOW. QPF
FROM VIRTUALLY EVERY MODEL SUGGESTS UPWARDS OF 1.5 INCHES OF LIQUID
FOR OUR HIGH PEAKS...WHICH TRANSLATES TO UPWARDS OF 2 TO 3 FEET IF
WE ASSUME A 20 TO 1 RATIO. THE WINTER STORM WARNING LOOKS GOOD FOR
THOSE AREAS. WILL CONTINUE WITH A 12Z TUE EXPIRATION AS THE ARRIVAL
OF MID LEVEL DRY AIR SHOULD CUT OFF PRECIPITATION FROM WEST TO EAST
ON TUE MORNING.

WINDS ARE THE OTHER MAJOR CONCERN IN THE NEAR TERM. WILL CONTINUE A
HIGH WIND WARNING FOR THE WIND PRONE LOCATIONS INCLUDING BRX AND THE
I80 SUMMIT BETWEEN CHEYENNE AND LARAMIE. BUFORD IN THE SOUTH LARAMIE
RANGE HAS ALREADY MANAGED TO ACHIEVE 60 MPH GUSTS...SO WE MIGHT NEED
TO BUMP UP THE START TIME BEFORE THE DAY CREW ARRIVES DEPENDING ON
TRENDS. EXPECT WINDS WILL CONTINUE TO INCREASE THROUGH THE DAY AS
THE NAM H85 CAG-CPR GRADIENT CLIMBS TO 80 METERS BY 18Z. PROGGED H7
FLOW IN EXCESS OF 70 KT OVER THE WIND CORRIDOR AND GOOD LOW LEVEL
MIXING ON AFTERNOON FORECAST SOUNDINGS SUGGEST AN EXCELLENT SETUP
FOR 65 TO 75 MPH GUSTS GIVEN GOOD MID LEVEL SUBSIDENCE SEEN IN THE
OMEGA FIELDS. UPGRADED NORTHERN CARBON COUNTY / FERRIS MOUNTAINS
AND SHIRLEY BASIN / TO A HIGH WIND WARNING AS GFS H75 FLOW APPEARS
TO BE WELL IN EXCESS OF 50 KT AROUND MID DAY. FALLING AND BLOWING
SNOW IS DEFINITELY A CONCERN HERE...BUT 700-300 MILLIBAR RH PROGS
SUGGEST THE BEST MOISTURE IS TO THE SOUTH. JUST NOT CONFIDENT SNOW
AMOUNTS WILL BE HIGH ENOUGH WITHOUT GAP ENHANCEMENTS TO CAUSE
WINTER STORM WARNING TYPE IMPACTS.

NOT SO MUCH THE CASE FOR ARLINGTON THOUGH...WHICH WILL BE EXTREMELY
WINDY FOR REASONS ALREADY STATED. PERIODIC LIGHT SNOW SHOULD DEVELOP
OVER THE NORTH SNOWY RANGE FOOTHILLS BY LATE MORNING. AREA FORECAST
SOUNDINGS ARE VERY CONCERNING WITH 60+ KT FLOW JUST OFF THE SURFACE
DURING THE AFTERNOON AND EVENING. WITH COLD ADVECTION ALOFT AIDING
IN MIXING AND POTENTIAL FOR CONVECTIVE SNOW SHOWERS GIVEN SLIGHTLY
NEGATIVE LIFTED INDICES...BELIEVE BLOWING SNOW COULD EASILY BE A
MAJOR ISSUE FOR INTERSTATE TRAVEL. EVEN IF ONLY AN INCH OR TWO OF
NEW SNOW FALLS...THE COMBINATION OF 70 MPH WIND GUSTS AND FALLING
AND/OR BLOWING SNOW HAS POTENTIAL TO RESULT IN VERY LOW VISIBILITIES
AND POSSIBLY WHITEOUT CONDITIONS. WE THOUGHT A WINTER STORM WARNING
WOULD BETTER HIGHLIGHT THESE IMPACTS...SO OPTED TO CHANGE FROM NPW
TO WSW HEADLINES AT ARL. WOULD NOT BE ENTIRELY SURPRISED IF THE DAY
SHIFT NEEDS TO CONSIDER BLIZZARD HEADLINES IF THESE CONCERNS ARE
REALIZED. WE ALSO INCLUDED SOUTHWEST CARBON COUNTY ON THE WEST SIDE
OF THE SIERRA MADRE WHERE UPSLOPE ENHANCEMENTS MAY YIELD LOCAL
AMOUNTS OF 6 TO 8 INCHES AROUND DIXON AND BAGGS. SHADOWING IN THE
UPPER NORTH PLATTE RIVER VALLEY AND LARAMIE VALLEY COULD LIMIT
SNOWFALL TO LESS THAN AN INCH...BUT UPGRADED THE WINTER STORM WATCH
TO AN ADVISORY FOR DANGEROUS TRAVEL. NOT TOO CONCERNED WITH THE
SOUTH LARAMIE RANGE THE ACCUMULATING SNOW SHOULD HOLD OFF UNTIL THE
OVERNIGHT...WHEN WINDS START TO COME DOWN. DO NOT EXPECT MUCH SNOW
AT ALL EAST OF THE LARAMIE RANGE WITH DRY DOWNSLOPING WINDS. A BIT
WARMER ON THE LEE SIDE TOO...SUPPORTING MORE RAIN THAN SNOW THROUGH
THE DURATION OF THE EVENT.

HIGH WINDS WILL END AFTER 06Z AS LOW-LEVEL GRADIENTS QUICKLY DROP
OFF OVERNIGHT...BUT BREEZY CONDITIONS WILL LIKELY PERSIST WITH AREAS
OF BLOWING SNOW AND REDUCED VISIBILITIES CONTINUING THROUGH MONDAY
MORNING OR EARLY AFTERNOON. SNOW AND WIND COULD BECOME AN ISSUE OVER
THE NORTHERN PANHANDLE ON MON WITH FAST NORTH/NORTHWEST FLOW ALOFT
AND STRONG LOW LEVEL CAA. DESPITE CLOUD COVER...GFS/NAM/ECMWF EACH
DEPICT A WELL-MIXED BOUNDARY LAYER WITH 50 TO 60 KT AVAILABLE TO
MIX AROUND 18Z MON. CONTEMPLATED SOME SORT OF WATCH HEADLINE WITH
INCREASED CONFIDENCE IN A HIGHER IMPACT EVENT...BUT PLAN TO FOLLOW
LBF/S LEAD WITH AN SPS LATER THIS MORNING TO AVOID ANY CONFUSION
WITH ONGOING HAZARDS. THE MODELS REALLY WRAP UP THE MID-LEVEL
SHORTWAVE AND ASSOCIATED SURFACE LOW AFTER 00Z TUE AS IT
TRANSLATES EASTWARD INTO THE CENTRAL PLAINS. COLD AIR ALOFT
REMAINS INTACT WITH H7 TEMPS AROUND -14C...SO INSTABILITY SNOW
SHOWERS OR FLURRIES WILL STILL BE POSSIBLE ALTHOUGH CONDITIONS
SHOULD GENERALLY IMPROVE.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 330 AM MST SUN DEC 21 2014

A PRONOUNCED UPPER TROUGH OVER GREAT PLAINS WILL PROGRESS EAST
TOWARD THE ATLANTIC/GULF COASTS THURSDAY. A RETURN TO ZONAL FLOW
ALOFT WILL BE SHORT-LIVED AS THE NEXT TROUGH MOVING INTO THE
PACIFIC NORTHWEST AMPLIFIES OVER THE ROCKY MOUNTAINS ON FRIDAY.
MODEL DIFFERENCES APPEAR SATURDAY...AS THE ECMWF IS MORE PRONOUNCED
WITH THE UPPER RIDGE OVER THE PACIFIC COAST STATES AND ITS DOWNSTREAM
TROUGH AXIS EXTENDING FURTHER WEST THAN THE GFS.

MOISTURE WILL DWINDLE OVER THE SOUTHERN WY MOUNTAINS TUESDAY NIGHT
WITH A SURFACE RIDGE OF HIGH PRESSURE EXTENDING FROM WESTERN CO
WEDNESDAY. SURFACE LOW PRESSURE DEVELOPS ALONG A COLD FRONT OVER
NORTHERN ID WEDNESDAY NIGHT...THEN PUSHES SOUTHEAST ACROSS WY AND
WESTERN NE CHRISTMAS DAY. THE ECMWF IS TRENDING FASTER AND PRODUCES
MORE WIDESPREAD QPF THAN THE GFS. GENERALLY FOLLOWED THE ECMWF
SOLUTION...WITH THE PRECIPITATION DEVELOPING WEST OF THE LARAMIE
RANGE WEDNESDAY NIGHT...SPREADING EAST ACROSS THE REMAINDER OF
THE CWA CHRISTMAS DAY...AND ENDING THURSDAY NIGHT. IT/S STILL
EARLY TO PREDICT SNOW ACCUMULATIONS WITH THIS SYSTEM. A BIT OF
MOISTURE AND WEAK UPSLOPE MAY TRIGGER LIGHT SNOW FOR THE SNOWY
AND SIERRA MADRES FRIDAY...OTHERWISE IT WILL BE DRY HEADING INTO
THE HOLIDAY WEEKEND.

HIGH TEMPERATURES WEDNESDAY WILL BE NEAR OR SLIGHTLY ABOVE SEASONAL
NORMALS WITH 30S TO LOWER 40S...FALLING TO BELOW NORMAL CHRISTMAS
DAY THROUGH SATURDAY. LOW TEMPERATURES TUESDAY/WEDNESDAY NIGHTS WILL
AVERAGE IN THE TEENS AND 20S...FALLING INTO THE SINGLE DIGITS AND
LOWER TEENS THURSDAY/FRIDAY NIGHTS. NOT EXPECTING ANY STRONG WINDS
WITH BREEZY TO OCCASIONALLY WINDY PERIODS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH MONDAY MORNING) ISSUED AT 235
AM MST SUN DEC 21 2014

POTENT STORM SYSTEM WILL BRING A COMBINATION OF SNOW AND HIGH WINDS
TO AREAS ALONG AND WEST OF THE LARAMIE RANGE...PRODUCING PREVAILING
MVFR CONDITIONS WITH PERIODS OF LIFR CONDITIONS IN MODERATE
SNOWFALL. LIGHT RAIN AND SNOW IS POSSIBLE ACROSS THE EASTERN HIGH
PLAINS...BUT THE TIMING OF THIS PRECIP WILL BE DIFFICULT SO KEPT
VCSH IN THE FORECAST FOR NOW. MVFR CONDITIONS ARE POSSIBLE WITH THIS
ACTIVITY AS IT MOVES SOUTHEAST ACROSS THE AREA. WEST WINDS WILL GUST
IN EXCESS OF 45-50 KNOTS AT TIMES TODAY...MAINLY BETWEEN KRWL AND
KCYS. WINDS WILL NOT BE AS STRONG ACROSS FAR EASTERN WYOMING AND
WESTERN NEBRASKA. STRONG WINDS WILL SLOWLY DIMINISH LATE THIS
EVENING.

&&

.FIRE WEATHER...
ISSUED AT 315 AM MST SUN DEC 21 2014

NO FIRE WEATHER CONCERNS THROUGH THE MIDDLE OF THE WEEK. VERY WINDY
CONDITIONS ARE EXPECTED TODAY ALONG AND WEST OF THE LARAMIE RANGE
WITH GUSTS BETWEEN 60 AND 70 MPH LIKELY. INCREASING MOISTURE WILL
KEEP THE RISK FOR RAPID FIRE GROWTH LOW. SIGNIFICANT MOUNTAIN SNOWS
WILL PERSIST OVER THE NEXT 24 TO 48 HOURS WITH TOTAL ACCUMULATIONS
IN EXCESS OF 2 FEET POSSIBLE IN THE SNOWIES AND SIERRA MADRES BEFORE
ALL IS SAID AND DONE.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM THIS MORNING TO MIDNIGHT MST TONIGHT
     FOR WYZ104-105-109-116-117.

     WINTER STORM WARNING UNTIL 11 AM MST MONDAY FOR WYZ110-111.

     HIGH WIND WARNING UNTIL MIDNIGHT MST TONIGHT FOR WYZ106.

     WINTER WEATHER ADVISORY FROM NOON TODAY TO 8 AM MST MONDAY FOR
     WYZ113-115.

NE...NONE.
&&

$$

SHORT TERM...CLH
LONG TERM...MJ
AVIATION...MJ
FIRE WEATHER...CLH




000
FXUS63 KUNR 211728
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1028 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT
ISSUED AT 255 AM MST SUN DEC 21 2014

WATER VAPOR IMAGERY AND UPPER AIR ANALYSIS SHOWS WEAK TROUGH SITTING
ACROSS THE NRN PLAINS ATTM AS A STRONG +140KT JET STREAK PUSHES INTO
THE PACIFIC NW COAST. SURFACE ANALYSIS SHOW DEEPENING LOW PRESSURE
ACROSS BRITISH COLUMBIA AND ALBERTA SLIDING SE. FORCING ASSOCIATED
WITH JET VORT MAX WILL BRING PRECIP TO THE AREA LATE THIS MRNG INTO
THE AFTN HOURS. WITH TEMPS RISING TODAY INTO THE UPPER 30S TO AROUND
50...PRECIP WILL BE RAIN.

UPPER TROUGH WILL QUICKLY DEEPEN TONIGHT AS UPPER LEVEL ENERGY DIVES
DOWN THE BACKSIDE. STRENGTHENING LOW PRESSURE WILL DROP INTO WRN ND
THIS EVNG...THEN CNTRL SD LATER TONIGHT. COLDER AIR WILL FILTER IN
FROM THE N/NW...WITH GUSTY NW WINDS DEVELOPING OVERNIGHT. RAIN
ACROSS THE AREA WILL CHANGE TO SNOW LATE TONIGHT AS THERMAL PROFILES
COOL...BUT SNOW WITH LITTLE ACCUMULATION. STEEP LOW LEVEL LAPSE
RATES AND HIGH RH WILL RESULT IN UPSLOPE PRECIP...WITH RAIN CHANGING
TO SNOW THIS EVNG. MODELS NOW SHOWING SYSTEM BECOMING A STALLED AND
STACKED UPPER LOW ON MONDAY. TIGHT PRESSURE GRADIENT ACROSS THE AREA
WILL BRING STRONG NW WINDS TO THE AREA. MODELS BEGINNING TO SHOW A
WETTER SOLUTION ACROSS THE PLAINS WITH WRAP AROUND PRECIP DEVELOPING
SOMEWHERE OVER THE WRN TO CNTRL SD PLAINS. HAVE INCREASED POPS QUITE
A BIT TO REFLECT THIS...WHICH ALSO INCREASES EXPECTED SNOW AMOUNTS
OVER THE PLAINS MONDAY. BUT IT STILL LOOKS LIKE TEMPS MAY RISE
ENOUGH TO OR ABOVE FREEZING TO HINDER SNOW ACCUMULATION. THINK
PLAINS WILL SEE AN INCH OR TWO OF SNOW DURING THE DAY. NW WINDS OF
25 TO 35 MPH ARE EXPECTED...WHICH WHEN COMBINED WITH SNOW WILL COULD
PRODUCE AREAS OF BLOWING SNOW. AT THIS TIME THINKING IS A WINTER
WEATHER ADVISORY MAY BE NEEDED...BUT THIS WOULD DEPEND ON HOW MODELS
RESOLVE SNOW AMOUNTS.

UPSLOPE SNOW WILL CONTINUE ALL DAY MONDAY AND THROUGH MONDAY NIGHT
ACROSS THE NORTHERN TO CENTRAL BLACK HILLS AND BEAR LODGE MOUNTAINS.
ATTM IT LOOKS LIKE SNOWFALL AMOUNTS OVER THE HIGHER BLACK HILLS WILL
BE IN THE 6 TO 12 INCH RANGE. WITH A MORE WESTERLY COMPONENT TO THE
WIND...HIGHEST SNOWFALL TOTALS ARE EXPECTED TO BE AROUND THE
CHEYENNE CROSSING TO ONEIL PASS INTO THE FOUR CORNERS AREA. WILL
ISSUE A WINTER STORM WATCH FOR THESE AREAS STARTING TONIGHT AND
CONTINUING UNTIL NOON TUESDAY.

.LONG TERM...TUESDAY THROUGH SATURDAY
ISSUED AT 255 AM MST SUN DEC 21 2014

AMPLIFIED PATTERN EXPECTED IN THE PERIOD AS THE EARLY WEEK LONG
WAVE TROUGH SPURS MASSIVE RIDGING INTO GREENLAND. THIS WILL FAVOR
A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A CP/MODIFIED
ARCTIC AIRMASS INTRUSION INTO THE CONUS PER WAVE TRAIN OF TROUGHS
EMANATING FROM THE NORTHERN PAC UPPER LOW. THIS COLD INTRUSION
WILL ARRIVE WITH A DECENT/STRONG SHORTWAVE EXPECTED IN THE WED
NIGHT-THUR PERIOD...WITH ANOTHER SHOT OF COLD AIR LIKELY NEXT
WEEKEND PER WESTERN NOAM RIDGING AND FRONT SIDE NORTHERN STREAM
IMPULSES. AFTER A MILD DAY WED...BELOW NORMAL TEMPS CAN BE
EXPECTED FOR THE REMAINDER OF THE PERIOD.

TUE-WED...LINGERING MORNING SNOW SHOWERS OVER THE BH AND FAR
SCENTRAL CAN BE EXPECTED AS THE EARLY WEEK SYSTEM EXITS THE REGION.
HAVE WENT WITH HIGH POPS OVER THE NORTHERN BH. CLOSED MID LEVEL
CIRCULATION WILL LIKELY SUPPORT A SLOWER EXIT OF THIS SYSTEM...WITH
SNOW LINGERING THROUGH AT LEAST MORNING. DRY WEATHER EXPECTED TUE NIGHT
THROUGH WED...WITH INCREASING CHANCES FOR PRECIP WED NIGHT INTO
THUR MORNING. COLDER CONDS EXPECTED TUE GIVEN ONGOING CAA WITH
STRONG GUSTY NW WINDS. 20 TO 30 MPH WINDS CAN BE EXPECTED TO
CONTINUE ON THE SD PLAINS FOR MUCH OF TUES.

THUR-SAT...STRONG COMPACT SPLITTING IMPULSE WILL QUICKLY MOVE INTO
THE REGION WED NIGHT SUPPORTING INCREASING CHANCES FOR SNOW. COUPLED
UPPER LEVEL JET STRUCTURE WILL LIKELY ENHANCED LIFT...FAVORING A
DECENT FGEN BANDED SNOW EVENT ACROSS A PORTION OF THE FA. CURRENT
PROGS SUGGEST MOST OF THE FA COULD SEE SNOW THUR ALTHOUGH N-S
ADJUSTMENT CAN BE EXPECTED IN SUBSEQUENT MODEL RUNS. INCREASED POPS
GIVEN RUN-RUN CONSISTENCY AND STRONG LIFT ASSOCIATED WITH THIS SYSTEM
COUPLED WITH SUFFICIENT MOISTURE. CURRENT PROGS SUGGEST 1-3 INCHES
POSSIBLE...WITH CERTAINLY HIGHER AMOUNTS IN ANY PERSISTENT BANDS.
GIVEN STRONG MERIDIONAL COMPONENT TO THE LL FLOW...HAVE CUT TEMPS
THUR-SAT...WHICH MAY NOT BE ENOUGH IF A DEEPER CENTRAL CONUS UPPER
TROUGH IS REALIZED.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY)
ISSUED AT 1025 AM MST SUN DEC 21 2014

VFR CONDITIONS ACROSS REGION AT THIS TIME. A STRONG COLD FRONT
STILL ON TRACK TO PASS THROUGH THE REGION THIS AFTERNOON AND
EVENING... BRINGING GUSTY NW WINDS... -SHRA TRANSITIONING TO
-SHSN... AND MVFR CIGS FOR MOST AREAS. THE HARDEST HIT AREAS WILL
BE THE NORTHERN BLACK HILLS AND NERN WY... WHERE MVFR/IFR
CONDITIONS WILL OCCUR THIS EVENING WITH LOCAL LIFR/VLIFR
CONDITIONS BY TOMORROW MORNING.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WATCH FROM 6 PM MST THIS EVENING THROUGH TUESDAY
     MORNING FOR SDZ024-028.

WY...WINTER STORM WATCH FROM 6 PM MST THIS EVENING THROUGH TUESDAY
     MORNING FOR WYZ057.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...SANDERS/MCKEMY






000
FXUS63 KUNR 211728
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1028 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT
ISSUED AT 255 AM MST SUN DEC 21 2014

WATER VAPOR IMAGERY AND UPPER AIR ANALYSIS SHOWS WEAK TROUGH SITTING
ACROSS THE NRN PLAINS ATTM AS A STRONG +140KT JET STREAK PUSHES INTO
THE PACIFIC NW COAST. SURFACE ANALYSIS SHOW DEEPENING LOW PRESSURE
ACROSS BRITISH COLUMBIA AND ALBERTA SLIDING SE. FORCING ASSOCIATED
WITH JET VORT MAX WILL BRING PRECIP TO THE AREA LATE THIS MRNG INTO
THE AFTN HOURS. WITH TEMPS RISING TODAY INTO THE UPPER 30S TO AROUND
50...PRECIP WILL BE RAIN.

UPPER TROUGH WILL QUICKLY DEEPEN TONIGHT AS UPPER LEVEL ENERGY DIVES
DOWN THE BACKSIDE. STRENGTHENING LOW PRESSURE WILL DROP INTO WRN ND
THIS EVNG...THEN CNTRL SD LATER TONIGHT. COLDER AIR WILL FILTER IN
FROM THE N/NW...WITH GUSTY NW WINDS DEVELOPING OVERNIGHT. RAIN
ACROSS THE AREA WILL CHANGE TO SNOW LATE TONIGHT AS THERMAL PROFILES
COOL...BUT SNOW WITH LITTLE ACCUMULATION. STEEP LOW LEVEL LAPSE
RATES AND HIGH RH WILL RESULT IN UPSLOPE PRECIP...WITH RAIN CHANGING
TO SNOW THIS EVNG. MODELS NOW SHOWING SYSTEM BECOMING A STALLED AND
STACKED UPPER LOW ON MONDAY. TIGHT PRESSURE GRADIENT ACROSS THE AREA
WILL BRING STRONG NW WINDS TO THE AREA. MODELS BEGINNING TO SHOW A
WETTER SOLUTION ACROSS THE PLAINS WITH WRAP AROUND PRECIP DEVELOPING
SOMEWHERE OVER THE WRN TO CNTRL SD PLAINS. HAVE INCREASED POPS QUITE
A BIT TO REFLECT THIS...WHICH ALSO INCREASES EXPECTED SNOW AMOUNTS
OVER THE PLAINS MONDAY. BUT IT STILL LOOKS LIKE TEMPS MAY RISE
ENOUGH TO OR ABOVE FREEZING TO HINDER SNOW ACCUMULATION. THINK
PLAINS WILL SEE AN INCH OR TWO OF SNOW DURING THE DAY. NW WINDS OF
25 TO 35 MPH ARE EXPECTED...WHICH WHEN COMBINED WITH SNOW WILL COULD
PRODUCE AREAS OF BLOWING SNOW. AT THIS TIME THINKING IS A WINTER
WEATHER ADVISORY MAY BE NEEDED...BUT THIS WOULD DEPEND ON HOW MODELS
RESOLVE SNOW AMOUNTS.

UPSLOPE SNOW WILL CONTINUE ALL DAY MONDAY AND THROUGH MONDAY NIGHT
ACROSS THE NORTHERN TO CENTRAL BLACK HILLS AND BEAR LODGE MOUNTAINS.
ATTM IT LOOKS LIKE SNOWFALL AMOUNTS OVER THE HIGHER BLACK HILLS WILL
BE IN THE 6 TO 12 INCH RANGE. WITH A MORE WESTERLY COMPONENT TO THE
WIND...HIGHEST SNOWFALL TOTALS ARE EXPECTED TO BE AROUND THE
CHEYENNE CROSSING TO ONEIL PASS INTO THE FOUR CORNERS AREA. WILL
ISSUE A WINTER STORM WATCH FOR THESE AREAS STARTING TONIGHT AND
CONTINUING UNTIL NOON TUESDAY.

.LONG TERM...TUESDAY THROUGH SATURDAY
ISSUED AT 255 AM MST SUN DEC 21 2014

AMPLIFIED PATTERN EXPECTED IN THE PERIOD AS THE EARLY WEEK LONG
WAVE TROUGH SPURS MASSIVE RIDGING INTO GREENLAND. THIS WILL FAVOR
A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A CP/MODIFIED
ARCTIC AIRMASS INTRUSION INTO THE CONUS PER WAVE TRAIN OF TROUGHS
EMANATING FROM THE NORTHERN PAC UPPER LOW. THIS COLD INTRUSION
WILL ARRIVE WITH A DECENT/STRONG SHORTWAVE EXPECTED IN THE WED
NIGHT-THUR PERIOD...WITH ANOTHER SHOT OF COLD AIR LIKELY NEXT
WEEKEND PER WESTERN NOAM RIDGING AND FRONT SIDE NORTHERN STREAM
IMPULSES. AFTER A MILD DAY WED...BELOW NORMAL TEMPS CAN BE
EXPECTED FOR THE REMAINDER OF THE PERIOD.

TUE-WED...LINGERING MORNING SNOW SHOWERS OVER THE BH AND FAR
SCENTRAL CAN BE EXPECTED AS THE EARLY WEEK SYSTEM EXITS THE REGION.
HAVE WENT WITH HIGH POPS OVER THE NORTHERN BH. CLOSED MID LEVEL
CIRCULATION WILL LIKELY SUPPORT A SLOWER EXIT OF THIS SYSTEM...WITH
SNOW LINGERING THROUGH AT LEAST MORNING. DRY WEATHER EXPECTED TUE NIGHT
THROUGH WED...WITH INCREASING CHANCES FOR PRECIP WED NIGHT INTO
THUR MORNING. COLDER CONDS EXPECTED TUE GIVEN ONGOING CAA WITH
STRONG GUSTY NW WINDS. 20 TO 30 MPH WINDS CAN BE EXPECTED TO
CONTINUE ON THE SD PLAINS FOR MUCH OF TUES.

THUR-SAT...STRONG COMPACT SPLITTING IMPULSE WILL QUICKLY MOVE INTO
THE REGION WED NIGHT SUPPORTING INCREASING CHANCES FOR SNOW. COUPLED
UPPER LEVEL JET STRUCTURE WILL LIKELY ENHANCED LIFT...FAVORING A
DECENT FGEN BANDED SNOW EVENT ACROSS A PORTION OF THE FA. CURRENT
PROGS SUGGEST MOST OF THE FA COULD SEE SNOW THUR ALTHOUGH N-S
ADJUSTMENT CAN BE EXPECTED IN SUBSEQUENT MODEL RUNS. INCREASED POPS
GIVEN RUN-RUN CONSISTENCY AND STRONG LIFT ASSOCIATED WITH THIS SYSTEM
COUPLED WITH SUFFICIENT MOISTURE. CURRENT PROGS SUGGEST 1-3 INCHES
POSSIBLE...WITH CERTAINLY HIGHER AMOUNTS IN ANY PERSISTENT BANDS.
GIVEN STRONG MERIDIONAL COMPONENT TO THE LL FLOW...HAVE CUT TEMPS
THUR-SAT...WHICH MAY NOT BE ENOUGH IF A DEEPER CENTRAL CONUS UPPER
TROUGH IS REALIZED.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY)
ISSUED AT 1025 AM MST SUN DEC 21 2014

VFR CONDITIONS ACROSS REGION AT THIS TIME. A STRONG COLD FRONT
STILL ON TRACK TO PASS THROUGH THE REGION THIS AFTERNOON AND
EVENING... BRINGING GUSTY NW WINDS... -SHRA TRANSITIONING TO
-SHSN... AND MVFR CIGS FOR MOST AREAS. THE HARDEST HIT AREAS WILL
BE THE NORTHERN BLACK HILLS AND NERN WY... WHERE MVFR/IFR
CONDITIONS WILL OCCUR THIS EVENING WITH LOCAL LIFR/VLIFR
CONDITIONS BY TOMORROW MORNING.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WATCH FROM 6 PM MST THIS EVENING THROUGH TUESDAY
     MORNING FOR SDZ024-028.

WY...WINTER STORM WATCH FROM 6 PM MST THIS EVENING THROUGH TUESDAY
     MORNING FOR WYZ057.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...SANDERS/MCKEMY







000
FXUS63 KUNR 211140
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
440 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT
ISSUED AT 255 AM MST SUN DEC 21 2014

WATER VAPOR IMAGERY AND UPPER AIR ANALYSIS SHOWS WEAK TROUGH SITTING
ACROSS THE NRN PLAINS ATTM AS A STRONG +140KT JET STREAK PUSHES INTO
THE PACIFIC NW COAST. SURFACE ANALYSIS SHOW DEEPENING LOW PRESSURE
ACROSS BRITISH COLUMBIA AND ALBERTA SLIDING SE. FORCING ASSOCIATED
WITH JET VORT MAX WILL BRING PRECIP TO THE AREA LATE THIS MRNG INTO
THE AFTN HOURS. WITH TEMPS RISING TODAY INTO THE UPPER 30S TO AROUND
50...PRECIP WILL BE RAIN.

UPPER TROUGH WILL QUICKLY DEEPEN TONIGHT AS UPPER LEVEL ENERGY DIVES
DOWN THE BACKSIDE. STRENGTHENING LOW PRESSURE WILL DROP INTO WRN ND
THIS EVNG...THEN CNTRL SD LATER TONIGHT. COLDER AIR WILL FILTER IN
FROM THE N/NW...WITH GUSTY NW WINDS DEVELOPING OVERNIGHT. RAIN
ACROSS THE AREA WILL CHANGE TO SNOW LATE TONIGHT AS THERMAL PROFILES
COOL...BUT SNOW WITH LITTLE ACCUMULATION. STEEP LOW LEVEL LAPSE
RATES AND HIGH RH WILL RESULT IN UPSLOPE PRECIP...WITH RAIN CHANGING
TO SNOW THIS EVNG. MODELS NOW SHOWING SYSTEM BECOMING A STALLED AND
STACKED UPPER LOW ON MONDAY. TIGHT PRESSURE GRADIENT ACROSS THE AREA
WILL BRING STRONG NW WINDS TO THE AREA. MODELS BEGINNING TO SHOW A
WETTER SOLUTION ACROSS THE PLAINS WITH WRAP AROUND PRECIP DEVELOPING
SOMEWHERE OVER THE WRN TO CNTRL SD PLAINS. HAVE INCREASED POPS QUITE
A BIT TO REFLECT THIS...WHICH ALSO INCREASES EXPECTED SNOW AMOUNTS
OVER THE PLAINS MONDAY. BUT IT STILL LOOKS LIKE TEMPS MAY RISE
ENOUGH TO OR ABOVE FREEZING TO HINDER SNOW ACCUMULATION. THINK
PLAINS WILL SEE AN INCH OR TWO OF SNOW DURING THE DAY. NW WINDS OF
25 TO 35 MPH ARE EXPECTED...WHICH WHEN COMBINED WITH SNOW WILL COULD
PRODUCE AREAS OF BLOWING SNOW. AT THIS TIME THINKING IS A WINTER
WEATHER ADVISORY MAY BE NEEDED...BUT THIS WOULD DEPEND ON HOW MODELS
RESOLVE SNOW AMOUNTS.

UPSLOPE SNOW WILL CONTINUE ALL DAY MONDAY AND THROUGH MONDAY NIGHT
ACROSS THE NORTHERN TO CENTRAL BLACK HILLS AND BEAR LODGE MOUNTAINS.
ATTM IT LOOKS LIKE SNOWFALL AMOUNTS OVER THE HIGHER BLACK HILLS WILL
BE IN THE 6 TO 12 INCH RANGE. WITH A MORE WESTERLY COMPONENT TO THE
WIND...HIGHEST SNOWFALL TOTALS ARE EXPECTED TO BE AROUND THE
CHEYENNE CROSSING TO ONEIL PASS INTO THE FOUR CORNERS AREA. WILL
ISSUE A WINTER STORM WATCH FOR THESE AREAS STARTING TONIGHT AND
CONTINUING UNTIL NOON TUESDAY.

.LONG TERM...TUESDAY THROUGH SATURDAY
ISSUED AT 255 AM MST SUN DEC 21 2014

AMPLIFIED PATTERN EXPECTED IN THE PERIOD AS THE EARLY WEEK LONG
WAVE TROUGH SPURS MASSIVE RIDGING INTO GREENLAND. THIS WILL FAVOR
A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A CP/MODIFIED
ARCTIC AIRMASS INTRUSION INTO THE CONUS PER WAVE TRAIN OF TROUGHS
EMANATING FROM THE NORTHERN PAC UPPER LOW. THIS COLD INTRUSION
WILL ARRIVE WITH A DECENT/STRONG SHORTWAVE EXPECTED IN THE WED
NIGHT-THUR PERIOD...WITH ANOTHER SHOT OF COLD AIR LIKELY NEXT
WEEKEND PER WESTERN NOAM RIDGING AND FRONT SIDE NORTHERN STREAM
IMPULSES. AFTER A MILD DAY WED...BELOW NORMAL TEMPS CAN BE
EXPECTED FOR THE REMAINDER OF THE PERIOD.

TUE-WED...LINGERING MORNING SNOW SHOWERS OVER THE BH AND FAR
SCENTRAL CAN BE EXPECTED AS THE EARLY WEEK SYSTEM EXITS THE REGION.
HAVE WENT WITH HIGH POPS OVER THE NORTHERN BH. CLOSED MID LEVEL
CIRCULATION WILL LIKELY SUPPORT A SLOWER EXIT OF THIS SYSTEM...WITH
SNOW LINGERING THROUGH AT LEAST MORNING. DRY WEATHER EXPECTED TUE NIGHT
THROUGH WED...WITH INCREASING CHANCES FOR PRECIP WED NIGHT INTO
THUR MORNING. COLDER CONDS EXPECTED TUE GIVEN ONGOING CAA WITH
STRONG GUSTY NW WINDS. 20 TO 30 MPH WINDS CAN BE EXPECTED TO
CONTINUE ON THE SD PLAINS FOR MUCH OF TUES.

THUR-SAT...STRONG COMPACT SPLITTING IMPULSE WILL QUICKLY MOVE INTO
THE REGION WED NIGHT SUPPORTING INCREASING CHANCES FOR SNOW. COUPLED
UPPER LEVEL JET STRUCTURE WILL LIKELY ENHANCED LIFT...FAVORING A
DECENT FGEN BANDED SNOW EVENT ACROSS A PORTION OF THE FA. CURRENT
PROGS SUGGEST MOST OF THE FA COULD SEE SNOW THUR ALTHOUGH N-S
ADJUSTMENT CAN BE EXPECTED IN SUBSEQUENT MODEL RUNS. INCREASED POPS
GIVEN RUN-RUN CONSISTENCY AND STRONG LIFT ASSOCIATED WITH THIS SYSTEM
COUPLED WITH SUFFICIENT MOISTURE. CURRENT PROGS SUGGEST 1-3 INCHES
POSSIBLE...WITH CERTAINLY HIGHER AMOUNTS IN ANY PERSISTENT BANDS.
GIVEN STRONG MERIDIONAL COMPONENT TO THE LL FLOW...HAVE CUT TEMPS
THUR-SAT...WHICH MAY NOT BE ENOUGH IF A DEEPER CENTRAL CONUS UPPER
TROUGH IS REALIZED.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 434 AM MST SUN DEC 21 2014

VFR CONDITIONS WILL CONTINUE INTO SUNDAY AFTERNOON. A STRONG
CDFNT MOVING INTO THE REGION WILL THEN BRING -SHRA AND MVFR CIGS
TO MAINLY NW PORTIONS OF THE FA. CONDITIONS WILL DETERIORATE
FURTHER SUNDAY NIGHT...ESPECIALLY OVER NERN WY AND THE NRN BLKHLS
AS SNOW DEVELOPS. LOOK FOR WIDESPREAD MVFR/IFR CONDS THERE...WITH
LOCAL LIFR/VLIFR IN THE NORTHERN AND CENTRAL BLACK HILLS BY EARLY
MONDAY MORNING. MVFR CONDS CAN ALSO BE EXPECTED ON PORTIONS OF THE
SD PLAINS BY EARLY MONDAY MORNING.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     SDZ024-028.

WY...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     WYZ057.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC






000
FXUS63 KUNR 211140
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
440 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT
ISSUED AT 255 AM MST SUN DEC 21 2014

WATER VAPOR IMAGERY AND UPPER AIR ANALYSIS SHOWS WEAK TROUGH SITTING
ACROSS THE NRN PLAINS ATTM AS A STRONG +140KT JET STREAK PUSHES INTO
THE PACIFIC NW COAST. SURFACE ANALYSIS SHOW DEEPENING LOW PRESSURE
ACROSS BRITISH COLUMBIA AND ALBERTA SLIDING SE. FORCING ASSOCIATED
WITH JET VORT MAX WILL BRING PRECIP TO THE AREA LATE THIS MRNG INTO
THE AFTN HOURS. WITH TEMPS RISING TODAY INTO THE UPPER 30S TO AROUND
50...PRECIP WILL BE RAIN.

UPPER TROUGH WILL QUICKLY DEEPEN TONIGHT AS UPPER LEVEL ENERGY DIVES
DOWN THE BACKSIDE. STRENGTHENING LOW PRESSURE WILL DROP INTO WRN ND
THIS EVNG...THEN CNTRL SD LATER TONIGHT. COLDER AIR WILL FILTER IN
FROM THE N/NW...WITH GUSTY NW WINDS DEVELOPING OVERNIGHT. RAIN
ACROSS THE AREA WILL CHANGE TO SNOW LATE TONIGHT AS THERMAL PROFILES
COOL...BUT SNOW WITH LITTLE ACCUMULATION. STEEP LOW LEVEL LAPSE
RATES AND HIGH RH WILL RESULT IN UPSLOPE PRECIP...WITH RAIN CHANGING
TO SNOW THIS EVNG. MODELS NOW SHOWING SYSTEM BECOMING A STALLED AND
STACKED UPPER LOW ON MONDAY. TIGHT PRESSURE GRADIENT ACROSS THE AREA
WILL BRING STRONG NW WINDS TO THE AREA. MODELS BEGINNING TO SHOW A
WETTER SOLUTION ACROSS THE PLAINS WITH WRAP AROUND PRECIP DEVELOPING
SOMEWHERE OVER THE WRN TO CNTRL SD PLAINS. HAVE INCREASED POPS QUITE
A BIT TO REFLECT THIS...WHICH ALSO INCREASES EXPECTED SNOW AMOUNTS
OVER THE PLAINS MONDAY. BUT IT STILL LOOKS LIKE TEMPS MAY RISE
ENOUGH TO OR ABOVE FREEZING TO HINDER SNOW ACCUMULATION. THINK
PLAINS WILL SEE AN INCH OR TWO OF SNOW DURING THE DAY. NW WINDS OF
25 TO 35 MPH ARE EXPECTED...WHICH WHEN COMBINED WITH SNOW WILL COULD
PRODUCE AREAS OF BLOWING SNOW. AT THIS TIME THINKING IS A WINTER
WEATHER ADVISORY MAY BE NEEDED...BUT THIS WOULD DEPEND ON HOW MODELS
RESOLVE SNOW AMOUNTS.

UPSLOPE SNOW WILL CONTINUE ALL DAY MONDAY AND THROUGH MONDAY NIGHT
ACROSS THE NORTHERN TO CENTRAL BLACK HILLS AND BEAR LODGE MOUNTAINS.
ATTM IT LOOKS LIKE SNOWFALL AMOUNTS OVER THE HIGHER BLACK HILLS WILL
BE IN THE 6 TO 12 INCH RANGE. WITH A MORE WESTERLY COMPONENT TO THE
WIND...HIGHEST SNOWFALL TOTALS ARE EXPECTED TO BE AROUND THE
CHEYENNE CROSSING TO ONEIL PASS INTO THE FOUR CORNERS AREA. WILL
ISSUE A WINTER STORM WATCH FOR THESE AREAS STARTING TONIGHT AND
CONTINUING UNTIL NOON TUESDAY.

.LONG TERM...TUESDAY THROUGH SATURDAY
ISSUED AT 255 AM MST SUN DEC 21 2014

AMPLIFIED PATTERN EXPECTED IN THE PERIOD AS THE EARLY WEEK LONG
WAVE TROUGH SPURS MASSIVE RIDGING INTO GREENLAND. THIS WILL FAVOR
A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A CP/MODIFIED
ARCTIC AIRMASS INTRUSION INTO THE CONUS PER WAVE TRAIN OF TROUGHS
EMANATING FROM THE NORTHERN PAC UPPER LOW. THIS COLD INTRUSION
WILL ARRIVE WITH A DECENT/STRONG SHORTWAVE EXPECTED IN THE WED
NIGHT-THUR PERIOD...WITH ANOTHER SHOT OF COLD AIR LIKELY NEXT
WEEKEND PER WESTERN NOAM RIDGING AND FRONT SIDE NORTHERN STREAM
IMPULSES. AFTER A MILD DAY WED...BELOW NORMAL TEMPS CAN BE
EXPECTED FOR THE REMAINDER OF THE PERIOD.

TUE-WED...LINGERING MORNING SNOW SHOWERS OVER THE BH AND FAR
SCENTRAL CAN BE EXPECTED AS THE EARLY WEEK SYSTEM EXITS THE REGION.
HAVE WENT WITH HIGH POPS OVER THE NORTHERN BH. CLOSED MID LEVEL
CIRCULATION WILL LIKELY SUPPORT A SLOWER EXIT OF THIS SYSTEM...WITH
SNOW LINGERING THROUGH AT LEAST MORNING. DRY WEATHER EXPECTED TUE NIGHT
THROUGH WED...WITH INCREASING CHANCES FOR PRECIP WED NIGHT INTO
THUR MORNING. COLDER CONDS EXPECTED TUE GIVEN ONGOING CAA WITH
STRONG GUSTY NW WINDS. 20 TO 30 MPH WINDS CAN BE EXPECTED TO
CONTINUE ON THE SD PLAINS FOR MUCH OF TUES.

THUR-SAT...STRONG COMPACT SPLITTING IMPULSE WILL QUICKLY MOVE INTO
THE REGION WED NIGHT SUPPORTING INCREASING CHANCES FOR SNOW. COUPLED
UPPER LEVEL JET STRUCTURE WILL LIKELY ENHANCED LIFT...FAVORING A
DECENT FGEN BANDED SNOW EVENT ACROSS A PORTION OF THE FA. CURRENT
PROGS SUGGEST MOST OF THE FA COULD SEE SNOW THUR ALTHOUGH N-S
ADJUSTMENT CAN BE EXPECTED IN SUBSEQUENT MODEL RUNS. INCREASED POPS
GIVEN RUN-RUN CONSISTENCY AND STRONG LIFT ASSOCIATED WITH THIS SYSTEM
COUPLED WITH SUFFICIENT MOISTURE. CURRENT PROGS SUGGEST 1-3 INCHES
POSSIBLE...WITH CERTAINLY HIGHER AMOUNTS IN ANY PERSISTENT BANDS.
GIVEN STRONG MERIDIONAL COMPONENT TO THE LL FLOW...HAVE CUT TEMPS
THUR-SAT...WHICH MAY NOT BE ENOUGH IF A DEEPER CENTRAL CONUS UPPER
TROUGH IS REALIZED.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 434 AM MST SUN DEC 21 2014

VFR CONDITIONS WILL CONTINUE INTO SUNDAY AFTERNOON. A STRONG
CDFNT MOVING INTO THE REGION WILL THEN BRING -SHRA AND MVFR CIGS
TO MAINLY NW PORTIONS OF THE FA. CONDITIONS WILL DETERIORATE
FURTHER SUNDAY NIGHT...ESPECIALLY OVER NERN WY AND THE NRN BLKHLS
AS SNOW DEVELOPS. LOOK FOR WIDESPREAD MVFR/IFR CONDS THERE...WITH
LOCAL LIFR/VLIFR IN THE NORTHERN AND CENTRAL BLACK HILLS BY EARLY
MONDAY MORNING. MVFR CONDS CAN ALSO BE EXPECTED ON PORTIONS OF THE
SD PLAINS BY EARLY MONDAY MORNING.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     SDZ024-028.

WY...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     WYZ057.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC







000
FXUS65 KCYS 211124
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
424 AM MST SUN DEC 21 2014

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 420 AM MST SUN DEC 21 2014

QUITE A CHALLENGING FORECAST FOR THE NEXT 24 HOURS WITH SNOW...WIND
AND THE POTENTIAL FOR SIGNIFICANT IMPACTS TO PRE-HOLIDAY TRAVEL IN
AND AROUND THE CWA. LATEST WATER VAPOR LOOP SHOWS A FIREHOSE OF AN
UPPER JET CRASHING INTO THE PACIFIC NORTHWEST. AMPLE MID AND HIGH
LEVEL MOISTURE CONTINUES TO STREAM INTO THE MOUNTAINS OF SOUTHEAST
WYOMING VIA STRONG WESTERLY FLOW ALOFT...SETTING THE STAGE FOR AN
INCREASE IN MOUNTAIN SNOWS SHORTLY. RADAR HAS BEEN RELATIVELY QUIET
OVER THE PAST FEW HOURS...BUT SNOW SHOULD INCREASE IN BOTH COVERAGE
AND INTENSITY AFTER SUNRISE AS LARGE SCALE ASCENT RAPIDLY INCREASES
IN THE LEFT FRONT QUADRANT OF A 150 KNOT H25 JET. THIS WILL COMBINE
WITH EXCELLENT OROGRAPHICS ON THE NORTHERN EDGE OF A BELT OF MOIST
WEST-TO-NORTHWEST FLOW TO PRODUCE SEVERAL HOURS OF HEAVY SNOW. QPF
FROM VIRTUALLY EVERY MODEL SUGGESTS UPWARDS OF 1.5 INCHES OF LIQUID
FOR OUR HIGH PEAKS...WHICH TRANSLATES TO UPWARDS OF 2 TO 3 FEET IF
WE ASSUME A 20 TO 1 RATIO. THE WINTER STORM WARNING LOOKS GOOD FOR
THOSE AREAS. WILL CONTINUE WITH A 12Z TUE EXPIRATION AS THE ARRIVAL
OF MID LEVEL DRY AIR SHOULD CUT OFF PRECIPITATION FROM WEST TO EAST
ON TUE MORNING.

WINDS ARE THE OTHER MAJOR CONCERN IN THE NEAR TERM. WILL CONTINUE A
HIGH WIND WARNING FOR THE WIND PRONE LOCATIONS INCLUDING BRX AND THE
I80 SUMMIT BETWEEN CHEYENNE AND LARAMIE. BUFORD IN THE SOUTH LARAMIE
RANGE HAS ALREADY MANAGED TO ACHIEVE 60 MPH GUSTS...SO WE MIGHT NEED
TO BUMP UP THE START TIME BEFORE THE DAY CREW ARRIVES DEPENDING ON
TRENDS. EXPECT WINDS WILL CONTINUE TO INCREASE THROUGH THE DAY AS
THE NAM H85 CAG-CPR GRADIENT CLIMBS TO 80 METERS BY 18Z. PROGGED H7
FLOW IN EXCESS OF 70 KT OVER THE WIND CORRIDOR AND GOOD LOW LEVEL
MIXING ON AFTERNOON FORECAST SOUNDINGS SUGGEST AN EXCELLENT SETUP
FOR 65 TO 75 MPH GUSTS GIVEN GOOD MID LEVEL SUBSIDENCE SEEN IN THE
OMEGA FIELDS. UPGRADED NORTHERN CARBON COUNTY / FERRIS MOUNTAINS
AND SHIRLEY BASIN / TO A HIGH WIND WARNING AS GFS H75 FLOW APPEARS
TO BE WELL IN EXCESS OF 50 KT AROUND MID DAY. FALLING AND BLOWING
SNOW IS DEFINITELY A CONCERN HERE...BUT 700-300 MILLIBAR RH PROGS
SUGGEST THE BEST MOISTURE IS TO THE SOUTH. JUST NOT CONFIDENT SNOW
AMOUNTS WILL BE HIGH ENOUGH WITHOUT GAP ENHANCEMENTS TO CAUSE
WINTER STORM WARNING TYPE IMPACTS.

NOT SO MUCH THE CASE FOR ARLINGTON THOUGH...WHICH WILL BE EXTREMELY
WINDY FOR REASONS ALREADY STATED. PERIODIC LIGHT SNOW SHOULD DEVELOP
OVER THE NORTH SNOWY RANGE FOOTHILLS BY LATE MORNING. AREA FORECAST
SOUNDINGS ARE VERY CONCERNING WITH 60+ KT FLOW JUST OFF THE SURFACE
DURING THE AFTERNOON AND EVENING. WITH COLD ADVECTION ALOFT AIDING
IN MIXING AND POTENTIAL FOR CONVECTIVE SNOW SHOWERS GIVEN SLIGHTLY
NEGATIVE LIFTED INDICES...BELIEVE BLOWING SNOW COULD EASILY BE A
MAJOR ISSUE FOR INTERSTATE TRAVEL. EVEN IF ONLY AN INCH OR TWO OF
NEW SNOW FALLS...THE COMBINATION OF 70 MPH WIND GUSTS AND FALLING
AND/OR BLOWING SNOW HAS POTENTIAL TO RESULT IN VERY LOW VISIBILITIES
AND POSSIBLY WHITEOUT CONDITIONS. WE THOUGHT A WINTER STORM WARNING
WOULD BETTER HIGHLIGHT THESE IMPACTS...SO OPTED TO CHANGE FROM NPW
TO WSW HEADLINES AT ARL. WOULD NOT BE ENTIRELY SURPRISED IF THE DAY
SHIFT NEEDS TO CONSIDER BLIZZARD HEADLINES IF THESE CONCERNS ARE
REALIZED. WE ALSO INCLUDED SOUTHWEST CARBON COUNTY ON THE WEST SIDE
OF THE SIERRA MADRES WHERE UPSLOPE ENHANCEMENTS MAY YIELD LOCAL
AMOUNTS OF 6 TO 8 INCHES AROUND DIXON AND BAGGS. SHADOWING IN THE
UPPER NORTH PLATTE RIVER VALLEY AND LARAMIE VALLEY COULD LIMIT
SNOWFALL TO LESS THAN AN INCH...BUT UPGRADED THE WINTER STORM WATCH
TO AN ADVISORY FOR DANGEROUS TRAVEL. NOT TOO CONCERNED WITH THE
SOUTH LARAMIE RANGE THE ACCUMULATING SNOW SHOULD HOLD OFF UNTIL THE
OVERNIGHT...WHEN WINDS START TO COME DOWN. DO NOT EXPECT MUCH SNOW
AT ALL EAST OF THE LARAMIE RANGE WITH DRY DOWNSLOPING WINDS. A BIT
WARMER ON THE LEE SIDE TOO...SUPPORTING MORE RAIN THAN SNOW THROUGH
THE DURATION OF THE EVENT.

HIGH WINDS WILL END AFTER 06Z AS LOW-LEVEL GRADIENTS QUICKLY DROP
OFF OVERNIGHT...BUT BREEZY CONDITIONS WILL LIKELY PERSIST WITH AREAS
OF BLOWING SNOW AND REDUCED VISIBILITIES CONTINUING THROUGH MONDAY
MORNING OR EARLY AFTERNOON. SNOW AND WIND COULD BECOME AN ISSUE OVER
THE NORTHERN PANHANDLE ON MON WITH FAST NORTH/NORTHWEST FLOW ALOFT
AND STRONG LOW LEVEL CAA. DESPITE CLOUD COVER...GFS/NAM/ECMWF EACH
DEPICT A WELL-MIXED BOUNDARY LAYER WITH 50 TO 60 KT AVAILABLE TO
MIX AROUND 18Z MON. CONTEMPLATED SOME SORT OF WATCH HEADLINE WITH
INCREASED CONFIDENCE IN A HIGHER IMPACT EVENT...BUT PLAN TO FOLLOW
LBF/S LEAD WITH AN SPS LATER THIS MORNING TO AVOID ANY CONFUSION
WITH ONGOING HAZARDS. THE MODELS REALLY WRAP UP THE MID-LEVEL
SHORTWAVE AND ASSOCIATED SURFACE LOW AFTER 00Z TUE AS IT
TRANSLATES EASTWARD INTO THE CENTRAL PLAINS. COLD AIR ALOFT
REMAINS INTACT WITH H7 TEMPS AROUND -14C...SO INSTABILITY SNOW
SHOWERS OR FLURRIES WILL STILL BE POSSIBLE ALTHOUGH CONDITIONS
SHOULD GENERALLY IMPROVE.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 330 AM MST SUN DEC 21 2014

A PRONOUNCED UPPER TROUGH OVER GREAT PLAINS WILL PROGRESS EAST
TOWARD THE ATLANTIC/GULF COASTS THURSDAY. A RETURN TO ZONAL FLOW
ALOFT WILL BE SHORT-LIVED AS THE NEXT TROUGH MOVING INTO THE
PACIFIC NORTHWEST AMPLIFIES OVER THE ROCKY MOUNTAINS ON FRIDAY.
MODEL DIFFERENCES APPEAR SATURDAY...AS THE ECMWF IS MORE PRONOUNCED
WITH THE UPPER RIDGE OVER THE PACIFIC COAST STATES AND ITS DOWNSTREAM
TROUGH AXIS EXTENDING FURTHER WEST THAN THE GFS.

MOISTURE WILL DWINDLE OVER THE SOUTHERN WY MOUNTAINS TUESDAY NIGHT
WITH A SURFACE RIDGE OF HIGH PRESSURE EXTENDING FROM WESTERN CO
WEDNESDAY. SURFACE LOW PRESSURE DEVELOPS ALONG A COLD FRONT OVER
NORTHERN ID WEDNESDAY NIGHT...THEN PUSHES SOUTHEAST ACROSS WY AND
WESTERN NE CHRISTMAS DAY. THE ECMWF IS TRENDING FASTER AND PRODUCES
MORE WIDESPREAD QPF THAN THE GFS. GENERALLY FOLLOWED THE ECMWF
SOLUTION...WITH THE PRECIPITATION DEVELOPING WEST OF THE LARAMIE
RANGE WEDNESDAY NIGHT...SPREADING EAST ACROSS THE REMAINDER OF
THE CWA CHRISTMAS DAY...AND ENDING THURSDAY NIGHT. IT/S STILL
EARLY TO PREDICT SNOW ACCUMULATIONS WITH THIS SYSTEM. A BIT OF
MOISTURE AND WEAK UPSLOPE MAY TRIGGER LIGHT SNOW FOR THE SNOWY
AND SIERRA MADRES FRIDAY...OTHERWISE IT WILL BE DRY HEADING INTO
THE HOLIDAY WEEKEND.

HIGH TEMPERATURES WEDNESDAY WILL BE NEAR OR SLIGHTLY ABOVE SEASONAL
NORMALS WITH 30S TO LOWER 40S...FALLING TO BELOW NORMAL CHRISTMAS
DAY THROUGH SATURDAY. LOW TEMPERATURES TUESDAY/WEDNESDAY NIGHTS WILL
AVERAGE IN THE TEENS AND 20S...FALLING INTO THE SINGLE DIGITS AND
LOWER TEENS THURSDAY/FRIDAY NIGHTS. NOT EXPECTING ANY STRONG WINDS
WITH BREEZY TO OCCASIONALLY WINDY PERIODS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 235 AM MST SUN DEC 21 2014

POTENT STORM SYSTEM WILL BRING A COMBINATION OF SNOW AND HIGH WINDS
TO AREAS ALONG AND WEST OF THE LARAMIE RANGE...PRODUCING MVFR TO
LIFR CONDITIONS. THE MOUNTAINS WILL BE OBSCURED DURING THE PERIOD.
ELSEWHERE...SOME LIGHT RAIN WILL DEVELOP OVER THE EASTERN PLAINS
AND WESTERN NE PANHANDLE LATE THIS AFTERNOON AND CHANGE TO SNOW
THIS EVENING...RESULTING IN OCCASIONAL MVFR CONDITIONS. WEST WINDS
WILL GUST IN EXCESS OF 50 KT TODAY FOR ACROSS WIND PRONE AREAS AND
ABOVE TIMBERLINE IN THE MOUNTAINS. ELSEWHERE...GUSTS OF 25 TO 35
KT WILL BE COMMON. WINDS WILL SHIFT TO THE NORTHWEST TONIGHT AFTER
THE PASSAGE OF A COLD FRONT.

&&

.FIRE WEATHER...
ISSUED AT 315 AM MST SUN DEC 21 2014

NO FIRE WEATHER CONCERNS THROUGH THE MIDDLE OF THE WEEK. VERY WINDY
CONDITIONS ARE EXPECTED TODAY ALONG AND WEST OF THE LARAMIE RANGE
WITH GUSTS BETWEEN 60 AND 70 MPH LIKELY. INCREASING MOISTURE WILL
KEEP THE RISK FOR RAPID FIRE GROWTH LOW. SIGNIFICANT MOUNTAIN SNOWS
WILL PERSIST OVER THE NEXT 24 TO 48 HOURS WITH TOTAL ACCUMULATIONS
IN EXCESS OF 2 FEET POSSIBLE IN THE SNOWIES AND SIERRA MADRES BEFORE
ALL IS SAID AND DONE.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM THIS MORNING TO MIDNIGHT MST TONIGHT
     FOR WYZ104-105-109-116-117.

     WINTER STORM WARNING UNTIL 11 AM MST MONDAY FOR WYZ110-111.

     HIGH WIND WARNING UNTIL MIDNIGHT MST TONIGHT FOR WYZ106.

     WINTER WEATHER ADVISORY FROM NOON TODAY TO 8 AM MST MONDAY FOR
     WYZ113-115.

NE...NONE.
&&

$$

SHORT TERM...CLH
LONG TERM...MJ
AVIATION...MJ
FIRE WEATHER...CLH



000
FXUS65 KCYS 211124
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
424 AM MST SUN DEC 21 2014

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 420 AM MST SUN DEC 21 2014

QUITE A CHALLENGING FORECAST FOR THE NEXT 24 HOURS WITH SNOW...WIND
AND THE POTENTIAL FOR SIGNIFICANT IMPACTS TO PRE-HOLIDAY TRAVEL IN
AND AROUND THE CWA. LATEST WATER VAPOR LOOP SHOWS A FIREHOSE OF AN
UPPER JET CRASHING INTO THE PACIFIC NORTHWEST. AMPLE MID AND HIGH
LEVEL MOISTURE CONTINUES TO STREAM INTO THE MOUNTAINS OF SOUTHEAST
WYOMING VIA STRONG WESTERLY FLOW ALOFT...SETTING THE STAGE FOR AN
INCREASE IN MOUNTAIN SNOWS SHORTLY. RADAR HAS BEEN RELATIVELY QUIET
OVER THE PAST FEW HOURS...BUT SNOW SHOULD INCREASE IN BOTH COVERAGE
AND INTENSITY AFTER SUNRISE AS LARGE SCALE ASCENT RAPIDLY INCREASES
IN THE LEFT FRONT QUADRANT OF A 150 KNOT H25 JET. THIS WILL COMBINE
WITH EXCELLENT OROGRAPHICS ON THE NORTHERN EDGE OF A BELT OF MOIST
WEST-TO-NORTHWEST FLOW TO PRODUCE SEVERAL HOURS OF HEAVY SNOW. QPF
FROM VIRTUALLY EVERY MODEL SUGGESTS UPWARDS OF 1.5 INCHES OF LIQUID
FOR OUR HIGH PEAKS...WHICH TRANSLATES TO UPWARDS OF 2 TO 3 FEET IF
WE ASSUME A 20 TO 1 RATIO. THE WINTER STORM WARNING LOOKS GOOD FOR
THOSE AREAS. WILL CONTINUE WITH A 12Z TUE EXPIRATION AS THE ARRIVAL
OF MID LEVEL DRY AIR SHOULD CUT OFF PRECIPITATION FROM WEST TO EAST
ON TUE MORNING.

WINDS ARE THE OTHER MAJOR CONCERN IN THE NEAR TERM. WILL CONTINUE A
HIGH WIND WARNING FOR THE WIND PRONE LOCATIONS INCLUDING BRX AND THE
I80 SUMMIT BETWEEN CHEYENNE AND LARAMIE. BUFORD IN THE SOUTH LARAMIE
RANGE HAS ALREADY MANAGED TO ACHIEVE 60 MPH GUSTS...SO WE MIGHT NEED
TO BUMP UP THE START TIME BEFORE THE DAY CREW ARRIVES DEPENDING ON
TRENDS. EXPECT WINDS WILL CONTINUE TO INCREASE THROUGH THE DAY AS
THE NAM H85 CAG-CPR GRADIENT CLIMBS TO 80 METERS BY 18Z. PROGGED H7
FLOW IN EXCESS OF 70 KT OVER THE WIND CORRIDOR AND GOOD LOW LEVEL
MIXING ON AFTERNOON FORECAST SOUNDINGS SUGGEST AN EXCELLENT SETUP
FOR 65 TO 75 MPH GUSTS GIVEN GOOD MID LEVEL SUBSIDENCE SEEN IN THE
OMEGA FIELDS. UPGRADED NORTHERN CARBON COUNTY / FERRIS MOUNTAINS
AND SHIRLEY BASIN / TO A HIGH WIND WARNING AS GFS H75 FLOW APPEARS
TO BE WELL IN EXCESS OF 50 KT AROUND MID DAY. FALLING AND BLOWING
SNOW IS DEFINITELY A CONCERN HERE...BUT 700-300 MILLIBAR RH PROGS
SUGGEST THE BEST MOISTURE IS TO THE SOUTH. JUST NOT CONFIDENT SNOW
AMOUNTS WILL BE HIGH ENOUGH WITHOUT GAP ENHANCEMENTS TO CAUSE
WINTER STORM WARNING TYPE IMPACTS.

NOT SO MUCH THE CASE FOR ARLINGTON THOUGH...WHICH WILL BE EXTREMELY
WINDY FOR REASONS ALREADY STATED. PERIODIC LIGHT SNOW SHOULD DEVELOP
OVER THE NORTH SNOWY RANGE FOOTHILLS BY LATE MORNING. AREA FORECAST
SOUNDINGS ARE VERY CONCERNING WITH 60+ KT FLOW JUST OFF THE SURFACE
DURING THE AFTERNOON AND EVENING. WITH COLD ADVECTION ALOFT AIDING
IN MIXING AND POTENTIAL FOR CONVECTIVE SNOW SHOWERS GIVEN SLIGHTLY
NEGATIVE LIFTED INDICES...BELIEVE BLOWING SNOW COULD EASILY BE A
MAJOR ISSUE FOR INTERSTATE TRAVEL. EVEN IF ONLY AN INCH OR TWO OF
NEW SNOW FALLS...THE COMBINATION OF 70 MPH WIND GUSTS AND FALLING
AND/OR BLOWING SNOW HAS POTENTIAL TO RESULT IN VERY LOW VISIBILITIES
AND POSSIBLY WHITEOUT CONDITIONS. WE THOUGHT A WINTER STORM WARNING
WOULD BETTER HIGHLIGHT THESE IMPACTS...SO OPTED TO CHANGE FROM NPW
TO WSW HEADLINES AT ARL. WOULD NOT BE ENTIRELY SURPRISED IF THE DAY
SHIFT NEEDS TO CONSIDER BLIZZARD HEADLINES IF THESE CONCERNS ARE
REALIZED. WE ALSO INCLUDED SOUTHWEST CARBON COUNTY ON THE WEST SIDE
OF THE SIERRA MADRES WHERE UPSLOPE ENHANCEMENTS MAY YIELD LOCAL
AMOUNTS OF 6 TO 8 INCHES AROUND DIXON AND BAGGS. SHADOWING IN THE
UPPER NORTH PLATTE RIVER VALLEY AND LARAMIE VALLEY COULD LIMIT
SNOWFALL TO LESS THAN AN INCH...BUT UPGRADED THE WINTER STORM WATCH
TO AN ADVISORY FOR DANGEROUS TRAVEL. NOT TOO CONCERNED WITH THE
SOUTH LARAMIE RANGE THE ACCUMULATING SNOW SHOULD HOLD OFF UNTIL THE
OVERNIGHT...WHEN WINDS START TO COME DOWN. DO NOT EXPECT MUCH SNOW
AT ALL EAST OF THE LARAMIE RANGE WITH DRY DOWNSLOPING WINDS. A BIT
WARMER ON THE LEE SIDE TOO...SUPPORTING MORE RAIN THAN SNOW THROUGH
THE DURATION OF THE EVENT.

HIGH WINDS WILL END AFTER 06Z AS LOW-LEVEL GRADIENTS QUICKLY DROP
OFF OVERNIGHT...BUT BREEZY CONDITIONS WILL LIKELY PERSIST WITH AREAS
OF BLOWING SNOW AND REDUCED VISIBILITIES CONTINUING THROUGH MONDAY
MORNING OR EARLY AFTERNOON. SNOW AND WIND COULD BECOME AN ISSUE OVER
THE NORTHERN PANHANDLE ON MON WITH FAST NORTH/NORTHWEST FLOW ALOFT
AND STRONG LOW LEVEL CAA. DESPITE CLOUD COVER...GFS/NAM/ECMWF EACH
DEPICT A WELL-MIXED BOUNDARY LAYER WITH 50 TO 60 KT AVAILABLE TO
MIX AROUND 18Z MON. CONTEMPLATED SOME SORT OF WATCH HEADLINE WITH
INCREASED CONFIDENCE IN A HIGHER IMPACT EVENT...BUT PLAN TO FOLLOW
LBF/S LEAD WITH AN SPS LATER THIS MORNING TO AVOID ANY CONFUSION
WITH ONGOING HAZARDS. THE MODELS REALLY WRAP UP THE MID-LEVEL
SHORTWAVE AND ASSOCIATED SURFACE LOW AFTER 00Z TUE AS IT
TRANSLATES EASTWARD INTO THE CENTRAL PLAINS. COLD AIR ALOFT
REMAINS INTACT WITH H7 TEMPS AROUND -14C...SO INSTABILITY SNOW
SHOWERS OR FLURRIES WILL STILL BE POSSIBLE ALTHOUGH CONDITIONS
SHOULD GENERALLY IMPROVE.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 330 AM MST SUN DEC 21 2014

A PRONOUNCED UPPER TROUGH OVER GREAT PLAINS WILL PROGRESS EAST
TOWARD THE ATLANTIC/GULF COASTS THURSDAY. A RETURN TO ZONAL FLOW
ALOFT WILL BE SHORT-LIVED AS THE NEXT TROUGH MOVING INTO THE
PACIFIC NORTHWEST AMPLIFIES OVER THE ROCKY MOUNTAINS ON FRIDAY.
MODEL DIFFERENCES APPEAR SATURDAY...AS THE ECMWF IS MORE PRONOUNCED
WITH THE UPPER RIDGE OVER THE PACIFIC COAST STATES AND ITS DOWNSTREAM
TROUGH AXIS EXTENDING FURTHER WEST THAN THE GFS.

MOISTURE WILL DWINDLE OVER THE SOUTHERN WY MOUNTAINS TUESDAY NIGHT
WITH A SURFACE RIDGE OF HIGH PRESSURE EXTENDING FROM WESTERN CO
WEDNESDAY. SURFACE LOW PRESSURE DEVELOPS ALONG A COLD FRONT OVER
NORTHERN ID WEDNESDAY NIGHT...THEN PUSHES SOUTHEAST ACROSS WY AND
WESTERN NE CHRISTMAS DAY. THE ECMWF IS TRENDING FASTER AND PRODUCES
MORE WIDESPREAD QPF THAN THE GFS. GENERALLY FOLLOWED THE ECMWF
SOLUTION...WITH THE PRECIPITATION DEVELOPING WEST OF THE LARAMIE
RANGE WEDNESDAY NIGHT...SPREADING EAST ACROSS THE REMAINDER OF
THE CWA CHRISTMAS DAY...AND ENDING THURSDAY NIGHT. IT/S STILL
EARLY TO PREDICT SNOW ACCUMULATIONS WITH THIS SYSTEM. A BIT OF
MOISTURE AND WEAK UPSLOPE MAY TRIGGER LIGHT SNOW FOR THE SNOWY
AND SIERRA MADRES FRIDAY...OTHERWISE IT WILL BE DRY HEADING INTO
THE HOLIDAY WEEKEND.

HIGH TEMPERATURES WEDNESDAY WILL BE NEAR OR SLIGHTLY ABOVE SEASONAL
NORMALS WITH 30S TO LOWER 40S...FALLING TO BELOW NORMAL CHRISTMAS
DAY THROUGH SATURDAY. LOW TEMPERATURES TUESDAY/WEDNESDAY NIGHTS WILL
AVERAGE IN THE TEENS AND 20S...FALLING INTO THE SINGLE DIGITS AND
LOWER TEENS THURSDAY/FRIDAY NIGHTS. NOT EXPECTING ANY STRONG WINDS
WITH BREEZY TO OCCASIONALLY WINDY PERIODS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 235 AM MST SUN DEC 21 2014

POTENT STORM SYSTEM WILL BRING A COMBINATION OF SNOW AND HIGH WINDS
TO AREAS ALONG AND WEST OF THE LARAMIE RANGE...PRODUCING MVFR TO
LIFR CONDITIONS. THE MOUNTAINS WILL BE OBSCURED DURING THE PERIOD.
ELSEWHERE...SOME LIGHT RAIN WILL DEVELOP OVER THE EASTERN PLAINS
AND WESTERN NE PANHANDLE LATE THIS AFTERNOON AND CHANGE TO SNOW
THIS EVENING...RESULTING IN OCCASIONAL MVFR CONDITIONS. WEST WINDS
WILL GUST IN EXCESS OF 50 KT TODAY FOR ACROSS WIND PRONE AREAS AND
ABOVE TIMBERLINE IN THE MOUNTAINS. ELSEWHERE...GUSTS OF 25 TO 35
KT WILL BE COMMON. WINDS WILL SHIFT TO THE NORTHWEST TONIGHT AFTER
THE PASSAGE OF A COLD FRONT.

&&

.FIRE WEATHER...
ISSUED AT 315 AM MST SUN DEC 21 2014

NO FIRE WEATHER CONCERNS THROUGH THE MIDDLE OF THE WEEK. VERY WINDY
CONDITIONS ARE EXPECTED TODAY ALONG AND WEST OF THE LARAMIE RANGE
WITH GUSTS BETWEEN 60 AND 70 MPH LIKELY. INCREASING MOISTURE WILL
KEEP THE RISK FOR RAPID FIRE GROWTH LOW. SIGNIFICANT MOUNTAIN SNOWS
WILL PERSIST OVER THE NEXT 24 TO 48 HOURS WITH TOTAL ACCUMULATIONS
IN EXCESS OF 2 FEET POSSIBLE IN THE SNOWIES AND SIERRA MADRES BEFORE
ALL IS SAID AND DONE.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM THIS MORNING TO MIDNIGHT MST TONIGHT
     FOR WYZ104-105-109-116-117.

     WINTER STORM WARNING UNTIL 11 AM MST MONDAY FOR WYZ110-111.

     HIGH WIND WARNING UNTIL MIDNIGHT MST TONIGHT FOR WYZ106.

     WINTER WEATHER ADVISORY FROM NOON TODAY TO 8 AM MST MONDAY FOR
     WYZ113-115.

NE...NONE.
&&

$$

SHORT TERM...CLH
LONG TERM...MJ
AVIATION...MJ
FIRE WEATHER...CLH




000
FXUS65 KRIW 211010
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
310 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN ACTIVE PERIOD ACROSS WESTERN AND CENTRAL WYOMING. SNOWFALL WILL
BE ABUNDANT ACROSS THE AREA...ESPECIALLY ACROSS THE WESTERN VALLEYS
AND MOUNTAINS WHERE SNOWFALL WILL BE HEAVY AT TIMES. SOME AREAS
SEEING HEAVIER SNOWFALL WILL ALSO SEE INCREASED WIND...CREATING A
HAZARDOUS COMBINATION OF SNOW AND BLOWING SNOW. WINTER STORM
WARNINGS ARE CURRENTLY IN EFFECT...AND WILL REMAIN THROUGH MONDAY
MORNING FOR SOME LOCATIONS. SNOW TOTALS BY MONDAY MORNING COULD BE
UP TO 2 FEET ACROSS THE WESTERN MOUNTAINS WITH 5 TO 10 INCHES
POSSIBLE ACROSS THE WESTERN VALLEYS.

AS THIS PUSH OF MOISTURE MOVES THROUGH TODAY...IT WILL BRING AN
INCREASED GRADIENT ACROSS THE FORECAST AREA. HIGH WINDS ARE
EXPECTED ACROSS THE INTERSTATE 80 CORRIDOR AND THE GREEN MOUNTAINS
AND RATTLESNAKE RANGE THIS MORNING...AND WILL CONTINUE THROUGH THE
LATE EVENING HOURS. HIGH WIND WARNINGS HAVE BEEN ISSUED FOR THESE
LOCATIONS.

THE NORTHWEST FLOW ASSOCIATED WITH THIS PATTERN IS ALSO FAVORABLE TO
CREATING STRONG WIND ACROSS THE WIND RIVER BASIN. MODEL GUIDANCE
SUGGESTS AN INCREASED PROBABILITY OF STRONGER WIND DEVELOPING LATE
TONIGHT THROUGH MONDAY MORNING...WITH A HIGH WIND WATCH ISSUED.
SIMILARLY...A HIGH WIND WATCH HAS BEEN ISSUED FOR NORTHERN JOHNSON
COUNTY THROUGH MONDAY AFTERNOON.

CONDITIONS WILL START TO IMPROVE MONDAY EVENING ACROSS THE AREA AS
HIGH PRESSURE BUILDS ACROSS THE AREA. SOME LINGERING SNOWFALL WILL
BE FOUND ACROSS THE EASTERN THIRD OF THE FORECAST AREA...BUT IS
EXPECTED TO HAVE GENERALLY MOVED OUT OF THE AREA BY TUESDAY EVENING.
SOME ADDITIONAL MOISTURE IN THE RIDGE MAY CREATE SOME LIGHT SNOWFALL
ACROSS THE WESTERN MOUNTAINS WEDNESDAY MORNING...THOUGH MODEL
VARIATION DECREASES CONFIDENCE IN THIS DEVELOPMENT FOR NOW.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY LOOKS DRY FOR MOST PLACES WITH BREEZY AREAS. SOME MOISTURE
MOVES INTO NW WY IN THE AFTERNOON FOR SOME LIGHT SNOW DEVELOPING
IN THE MOUNTAINS. THE GFS/ECMWF HAVE GONE DRIER FOR WED IN THE
WEST AND IF THIS TREND CONTINUES THEN PRECIP CHANCES WILL NEED
MORE TRIMMING. THE INCOMING WEATHER SYSTEM IMPACTS THE WEST AND
NORTH WED NIGHT. THEN THE SYSTEM MOVES THROUGH THE REST OF THE
AREA CHRISTMAS DAY. DECENT COLD FRONTAL PASSAGE WILL PUT A CHILL
IN THE AIR ALONG WITH SOME LIGHT SNOW. SNOW AMOUNTS LOOK TO BE 1
TO 4 INCHES FOR THE LOWER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. EXPECT DRIFTING SNOW IN OPEN AREAS. STILL HAVE A FEW
DAYS TO WATCH THE TRACK OF THIS WEATHER SYSTEM AND REFINE SNOWFALL
AMOUNTS. THE LIGHT SNOW ENDS LATE CHRISTMAS NIGHT IN MOST PLACES.
FRIDAY LOOKS COLD WITH MOUNTAIN LIGHT SNOW SHOWERS WITH NOT MUCH
IF ANY SNOW SHOWERS AT THE LOWER ELEVATIONS. THE GFS AND ECMWF
MODELS DIFFER WITH THE WEATHER PATTERN SATURDAY AND SUNDAY. THE
GFS BRINGS ANOTHER WEATHER SYSTEM INTO THE NORTH SATURDAY NIGHT
ALONG WITH ANOTHER COLD FRONT. THEN THIS COLD AIR BOUNDARY SAGS
SOUTH NEXT SUNDAY INTO CENTRAL WY. THE ECMWF MODEL DOES NOT SHOW
THIS WEATHER SYSTEM AT ALL SATURDAY NIGHT AND SUNDAY. THUS THE
ECMWF IS DRY SATURDAY AND SUNDAY. HAVE LEANED TOWARD THE DRIER
ECMWF MODEL BUT HAVE LEFT LOW CHANCE OF SNOW IN THE WESTERN AND
NORTHERN MOUNTAINS FOR NOW. AS FOR TEMPS...CHRISTMAS EVE WILL BE
SLIGHTLY MILDER...THEN COLDER CHRISTMAS DAY AND FRIDAY. SLIGHTLY
MILDER SATURDAY AND SUNDAY.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A TROUGH OF LOW PRESSURE WILL MOVE ACROSS MONTANA ON SUNDAY AND INTO
THE NORTHERN PLAINS SUNDAY EVENING.  A STRONG JET STREAM 120-130KTS
WILL CROSS THE WYOMING DIVIDE SOUTH OF THIS SYSTEM THIS MORNING
CAUSING AREAS OF MDT-SVR TURBULENCE...LLWS OVER SHALLOW CENTRAL
BASIN INVERSIONS...AND STRONG SFC WINDS FROM VCNTY SOUTH PASS TO
VCNTY KCPR AND SOUTH ALONG THE INTERSTATE 80 CORRIDOR.  THE LEE
SLOPES ALONG THE DIVIDE AND BIGHORN RANGE WILL LIKELY REMAIN MOSTLY
OBSCURE ABOVE 9KFT.  A STRONG NW FLOW WILL FOLLOW THIS SYSTEM SUNDAY
NIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG THE FRONT
ACROSS THE LOWER ELEVATIONS SUNDAY EVENING...ESPECIALLY VCNTY AND
EAST OF INTERSTATE 25.  DRIER AIR PREVAIL NW-SE BUT GUSTY NW SFC
WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 0Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA SUNDAY AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH SUNDAY EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

&&

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING TODAY. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT...ALONG WITH A
COUPLE AREAS IN A HIGH WIND WATCH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY AFTERNOON
WYZ010.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY MORNING
WYZ016-017.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...BRANHAM








000
FXUS65 KRIW 211010
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
310 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN ACTIVE PERIOD ACROSS WESTERN AND CENTRAL WYOMING. SNOWFALL WILL
BE ABUNDANT ACROSS THE AREA...ESPECIALLY ACROSS THE WESTERN VALLEYS
AND MOUNTAINS WHERE SNOWFALL WILL BE HEAVY AT TIMES. SOME AREAS
SEEING HEAVIER SNOWFALL WILL ALSO SEE INCREASED WIND...CREATING A
HAZARDOUS COMBINATION OF SNOW AND BLOWING SNOW. WINTER STORM
WARNINGS ARE CURRENTLY IN EFFECT...AND WILL REMAIN THROUGH MONDAY
MORNING FOR SOME LOCATIONS. SNOW TOTALS BY MONDAY MORNING COULD BE
UP TO 2 FEET ACROSS THE WESTERN MOUNTAINS WITH 5 TO 10 INCHES
POSSIBLE ACROSS THE WESTERN VALLEYS.

AS THIS PUSH OF MOISTURE MOVES THROUGH TODAY...IT WILL BRING AN
INCREASED GRADIENT ACROSS THE FORECAST AREA. HIGH WINDS ARE
EXPECTED ACROSS THE INTERSTATE 80 CORRIDOR AND THE GREEN MOUNTAINS
AND RATTLESNAKE RANGE THIS MORNING...AND WILL CONTINUE THROUGH THE
LATE EVENING HOURS. HIGH WIND WARNINGS HAVE BEEN ISSUED FOR THESE
LOCATIONS.

THE NORTHWEST FLOW ASSOCIATED WITH THIS PATTERN IS ALSO FAVORABLE TO
CREATING STRONG WIND ACROSS THE WIND RIVER BASIN. MODEL GUIDANCE
SUGGESTS AN INCREASED PROBABILITY OF STRONGER WIND DEVELOPING LATE
TONIGHT THROUGH MONDAY MORNING...WITH A HIGH WIND WATCH ISSUED.
SIMILARLY...A HIGH WIND WATCH HAS BEEN ISSUED FOR NORTHERN JOHNSON
COUNTY THROUGH MONDAY AFTERNOON.

CONDITIONS WILL START TO IMPROVE MONDAY EVENING ACROSS THE AREA AS
HIGH PRESSURE BUILDS ACROSS THE AREA. SOME LINGERING SNOWFALL WILL
BE FOUND ACROSS THE EASTERN THIRD OF THE FORECAST AREA...BUT IS
EXPECTED TO HAVE GENERALLY MOVED OUT OF THE AREA BY TUESDAY EVENING.
SOME ADDITIONAL MOISTURE IN THE RIDGE MAY CREATE SOME LIGHT SNOWFALL
ACROSS THE WESTERN MOUNTAINS WEDNESDAY MORNING...THOUGH MODEL
VARIATION DECREASES CONFIDENCE IN THIS DEVELOPMENT FOR NOW.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY LOOKS DRY FOR MOST PLACES WITH BREEZY AREAS. SOME MOISTURE
MOVES INTO NW WY IN THE AFTERNOON FOR SOME LIGHT SNOW DEVELOPING
IN THE MOUNTAINS. THE GFS/ECMWF HAVE GONE DRIER FOR WED IN THE
WEST AND IF THIS TREND CONTINUES THEN PRECIP CHANCES WILL NEED
MORE TRIMMING. THE INCOMING WEATHER SYSTEM IMPACTS THE WEST AND
NORTH WED NIGHT. THEN THE SYSTEM MOVES THROUGH THE REST OF THE
AREA CHRISTMAS DAY. DECENT COLD FRONTAL PASSAGE WILL PUT A CHILL
IN THE AIR ALONG WITH SOME LIGHT SNOW. SNOW AMOUNTS LOOK TO BE 1
TO 4 INCHES FOR THE LOWER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. EXPECT DRIFTING SNOW IN OPEN AREAS. STILL HAVE A FEW
DAYS TO WATCH THE TRACK OF THIS WEATHER SYSTEM AND REFINE SNOWFALL
AMOUNTS. THE LIGHT SNOW ENDS LATE CHRISTMAS NIGHT IN MOST PLACES.
FRIDAY LOOKS COLD WITH MOUNTAIN LIGHT SNOW SHOWERS WITH NOT MUCH
IF ANY SNOW SHOWERS AT THE LOWER ELEVATIONS. THE GFS AND ECMWF
MODELS DIFFER WITH THE WEATHER PATTERN SATURDAY AND SUNDAY. THE
GFS BRINGS ANOTHER WEATHER SYSTEM INTO THE NORTH SATURDAY NIGHT
ALONG WITH ANOTHER COLD FRONT. THEN THIS COLD AIR BOUNDARY SAGS
SOUTH NEXT SUNDAY INTO CENTRAL WY. THE ECMWF MODEL DOES NOT SHOW
THIS WEATHER SYSTEM AT ALL SATURDAY NIGHT AND SUNDAY. THUS THE
ECMWF IS DRY SATURDAY AND SUNDAY. HAVE LEANED TOWARD THE DRIER
ECMWF MODEL BUT HAVE LEFT LOW CHANCE OF SNOW IN THE WESTERN AND
NORTHERN MOUNTAINS FOR NOW. AS FOR TEMPS...CHRISTMAS EVE WILL BE
SLIGHTLY MILDER...THEN COLDER CHRISTMAS DAY AND FRIDAY. SLIGHTLY
MILDER SATURDAY AND SUNDAY.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A TROUGH OF LOW PRESSURE WILL MOVE ACROSS MONTANA ON SUNDAY AND INTO
THE NORTHERN PLAINS SUNDAY EVENING.  A STRONG JET STREAM 120-130KTS
WILL CROSS THE WYOMING DIVIDE SOUTH OF THIS SYSTEM THIS MORNING
CAUSING AREAS OF MDT-SVR TURBULENCE...LLWS OVER SHALLOW CENTRAL
BASIN INVERSIONS...AND STRONG SFC WINDS FROM VCNTY SOUTH PASS TO
VCNTY KCPR AND SOUTH ALONG THE INTERSTATE 80 CORRIDOR.  THE LEE
SLOPES ALONG THE DIVIDE AND BIGHORN RANGE WILL LIKELY REMAIN MOSTLY
OBSCURE ABOVE 9KFT.  A STRONG NW FLOW WILL FOLLOW THIS SYSTEM SUNDAY
NIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG THE FRONT
ACROSS THE LOWER ELEVATIONS SUNDAY EVENING...ESPECIALLY VCNTY AND
EAST OF INTERSTATE 25.  DRIER AIR PREVAIL NW-SE BUT GUSTY NW SFC
WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 0Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA SUNDAY AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH SUNDAY EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

&&

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING TODAY. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT...ALONG WITH A
COUPLE AREAS IN A HIGH WIND WATCH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY AFTERNOON
WYZ010.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY MORNING
WYZ016-017.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...BRANHAM







000
FXUS65 KRIW 211010
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
310 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN ACTIVE PERIOD ACROSS WESTERN AND CENTRAL WYOMING. SNOWFALL WILL
BE ABUNDANT ACROSS THE AREA...ESPECIALLY ACROSS THE WESTERN VALLEYS
AND MOUNTAINS WHERE SNOWFALL WILL BE HEAVY AT TIMES. SOME AREAS
SEEING HEAVIER SNOWFALL WILL ALSO SEE INCREASED WIND...CREATING A
HAZARDOUS COMBINATION OF SNOW AND BLOWING SNOW. WINTER STORM
WARNINGS ARE CURRENTLY IN EFFECT...AND WILL REMAIN THROUGH MONDAY
MORNING FOR SOME LOCATIONS. SNOW TOTALS BY MONDAY MORNING COULD BE
UP TO 2 FEET ACROSS THE WESTERN MOUNTAINS WITH 5 TO 10 INCHES
POSSIBLE ACROSS THE WESTERN VALLEYS.

AS THIS PUSH OF MOISTURE MOVES THROUGH TODAY...IT WILL BRING AN
INCREASED GRADIENT ACROSS THE FORECAST AREA. HIGH WINDS ARE
EXPECTED ACROSS THE INTERSTATE 80 CORRIDOR AND THE GREEN MOUNTAINS
AND RATTLESNAKE RANGE THIS MORNING...AND WILL CONTINUE THROUGH THE
LATE EVENING HOURS. HIGH WIND WARNINGS HAVE BEEN ISSUED FOR THESE
LOCATIONS.

THE NORTHWEST FLOW ASSOCIATED WITH THIS PATTERN IS ALSO FAVORABLE TO
CREATING STRONG WIND ACROSS THE WIND RIVER BASIN. MODEL GUIDANCE
SUGGESTS AN INCREASED PROBABILITY OF STRONGER WIND DEVELOPING LATE
TONIGHT THROUGH MONDAY MORNING...WITH A HIGH WIND WATCH ISSUED.
SIMILARLY...A HIGH WIND WATCH HAS BEEN ISSUED FOR NORTHERN JOHNSON
COUNTY THROUGH MONDAY AFTERNOON.

CONDITIONS WILL START TO IMPROVE MONDAY EVENING ACROSS THE AREA AS
HIGH PRESSURE BUILDS ACROSS THE AREA. SOME LINGERING SNOWFALL WILL
BE FOUND ACROSS THE EASTERN THIRD OF THE FORECAST AREA...BUT IS
EXPECTED TO HAVE GENERALLY MOVED OUT OF THE AREA BY TUESDAY EVENING.
SOME ADDITIONAL MOISTURE IN THE RIDGE MAY CREATE SOME LIGHT SNOWFALL
ACROSS THE WESTERN MOUNTAINS WEDNESDAY MORNING...THOUGH MODEL
VARIATION DECREASES CONFIDENCE IN THIS DEVELOPMENT FOR NOW.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY LOOKS DRY FOR MOST PLACES WITH BREEZY AREAS. SOME MOISTURE
MOVES INTO NW WY IN THE AFTERNOON FOR SOME LIGHT SNOW DEVELOPING
IN THE MOUNTAINS. THE GFS/ECMWF HAVE GONE DRIER FOR WED IN THE
WEST AND IF THIS TREND CONTINUES THEN PRECIP CHANCES WILL NEED
MORE TRIMMING. THE INCOMING WEATHER SYSTEM IMPACTS THE WEST AND
NORTH WED NIGHT. THEN THE SYSTEM MOVES THROUGH THE REST OF THE
AREA CHRISTMAS DAY. DECENT COLD FRONTAL PASSAGE WILL PUT A CHILL
IN THE AIR ALONG WITH SOME LIGHT SNOW. SNOW AMOUNTS LOOK TO BE 1
TO 4 INCHES FOR THE LOWER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. EXPECT DRIFTING SNOW IN OPEN AREAS. STILL HAVE A FEW
DAYS TO WATCH THE TRACK OF THIS WEATHER SYSTEM AND REFINE SNOWFALL
AMOUNTS. THE LIGHT SNOW ENDS LATE CHRISTMAS NIGHT IN MOST PLACES.
FRIDAY LOOKS COLD WITH MOUNTAIN LIGHT SNOW SHOWERS WITH NOT MUCH
IF ANY SNOW SHOWERS AT THE LOWER ELEVATIONS. THE GFS AND ECMWF
MODELS DIFFER WITH THE WEATHER PATTERN SATURDAY AND SUNDAY. THE
GFS BRINGS ANOTHER WEATHER SYSTEM INTO THE NORTH SATURDAY NIGHT
ALONG WITH ANOTHER COLD FRONT. THEN THIS COLD AIR BOUNDARY SAGS
SOUTH NEXT SUNDAY INTO CENTRAL WY. THE ECMWF MODEL DOES NOT SHOW
THIS WEATHER SYSTEM AT ALL SATURDAY NIGHT AND SUNDAY. THUS THE
ECMWF IS DRY SATURDAY AND SUNDAY. HAVE LEANED TOWARD THE DRIER
ECMWF MODEL BUT HAVE LEFT LOW CHANCE OF SNOW IN THE WESTERN AND
NORTHERN MOUNTAINS FOR NOW. AS FOR TEMPS...CHRISTMAS EVE WILL BE
SLIGHTLY MILDER...THEN COLDER CHRISTMAS DAY AND FRIDAY. SLIGHTLY
MILDER SATURDAY AND SUNDAY.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A TROUGH OF LOW PRESSURE WILL MOVE ACROSS MONTANA ON SUNDAY AND INTO
THE NORTHERN PLAINS SUNDAY EVENING.  A STRONG JET STREAM 120-130KTS
WILL CROSS THE WYOMING DIVIDE SOUTH OF THIS SYSTEM THIS MORNING
CAUSING AREAS OF MDT-SVR TURBULENCE...LLWS OVER SHALLOW CENTRAL
BASIN INVERSIONS...AND STRONG SFC WINDS FROM VCNTY SOUTH PASS TO
VCNTY KCPR AND SOUTH ALONG THE INTERSTATE 80 CORRIDOR.  THE LEE
SLOPES ALONG THE DIVIDE AND BIGHORN RANGE WILL LIKELY REMAIN MOSTLY
OBSCURE ABOVE 9KFT.  A STRONG NW FLOW WILL FOLLOW THIS SYSTEM SUNDAY
NIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG THE FRONT
ACROSS THE LOWER ELEVATIONS SUNDAY EVENING...ESPECIALLY VCNTY AND
EAST OF INTERSTATE 25.  DRIER AIR PREVAIL NW-SE BUT GUSTY NW SFC
WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 0Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA SUNDAY AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH SUNDAY EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

&&

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING TODAY. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT...ALONG WITH A
COUPLE AREAS IN A HIGH WIND WATCH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY AFTERNOON
WYZ010.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY MORNING
WYZ016-017.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...BRANHAM








000
FXUS65 KRIW 211010
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
310 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT

AN ACTIVE PERIOD ACROSS WESTERN AND CENTRAL WYOMING. SNOWFALL WILL
BE ABUNDANT ACROSS THE AREA...ESPECIALLY ACROSS THE WESTERN VALLEYS
AND MOUNTAINS WHERE SNOWFALL WILL BE HEAVY AT TIMES. SOME AREAS
SEEING HEAVIER SNOWFALL WILL ALSO SEE INCREASED WIND...CREATING A
HAZARDOUS COMBINATION OF SNOW AND BLOWING SNOW. WINTER STORM
WARNINGS ARE CURRENTLY IN EFFECT...AND WILL REMAIN THROUGH MONDAY
MORNING FOR SOME LOCATIONS. SNOW TOTALS BY MONDAY MORNING COULD BE
UP TO 2 FEET ACROSS THE WESTERN MOUNTAINS WITH 5 TO 10 INCHES
POSSIBLE ACROSS THE WESTERN VALLEYS.

AS THIS PUSH OF MOISTURE MOVES THROUGH TODAY...IT WILL BRING AN
INCREASED GRADIENT ACROSS THE FORECAST AREA. HIGH WINDS ARE
EXPECTED ACROSS THE INTERSTATE 80 CORRIDOR AND THE GREEN MOUNTAINS
AND RATTLESNAKE RANGE THIS MORNING...AND WILL CONTINUE THROUGH THE
LATE EVENING HOURS. HIGH WIND WARNINGS HAVE BEEN ISSUED FOR THESE
LOCATIONS.

THE NORTHWEST FLOW ASSOCIATED WITH THIS PATTERN IS ALSO FAVORABLE TO
CREATING STRONG WIND ACROSS THE WIND RIVER BASIN. MODEL GUIDANCE
SUGGESTS AN INCREASED PROBABILITY OF STRONGER WIND DEVELOPING LATE
TONIGHT THROUGH MONDAY MORNING...WITH A HIGH WIND WATCH ISSUED.
SIMILARLY...A HIGH WIND WATCH HAS BEEN ISSUED FOR NORTHERN JOHNSON
COUNTY THROUGH MONDAY AFTERNOON.

CONDITIONS WILL START TO IMPROVE MONDAY EVENING ACROSS THE AREA AS
HIGH PRESSURE BUILDS ACROSS THE AREA. SOME LINGERING SNOWFALL WILL
BE FOUND ACROSS THE EASTERN THIRD OF THE FORECAST AREA...BUT IS
EXPECTED TO HAVE GENERALLY MOVED OUT OF THE AREA BY TUESDAY EVENING.
SOME ADDITIONAL MOISTURE IN THE RIDGE MAY CREATE SOME LIGHT SNOWFALL
ACROSS THE WESTERN MOUNTAINS WEDNESDAY MORNING...THOUGH MODEL
VARIATION DECREASES CONFIDENCE IN THIS DEVELOPMENT FOR NOW.

.LONG TERM...WEDNESDAY THROUGH SUNDAY

WEDNESDAY LOOKS DRY FOR MOST PLACES WITH BREEZY AREAS. SOME MOISTURE
MOVES INTO NW WY IN THE AFTERNOON FOR SOME LIGHT SNOW DEVELOPING
IN THE MOUNTAINS. THE GFS/ECMWF HAVE GONE DRIER FOR WED IN THE
WEST AND IF THIS TREND CONTINUES THEN PRECIP CHANCES WILL NEED
MORE TRIMMING. THE INCOMING WEATHER SYSTEM IMPACTS THE WEST AND
NORTH WED NIGHT. THEN THE SYSTEM MOVES THROUGH THE REST OF THE
AREA CHRISTMAS DAY. DECENT COLD FRONTAL PASSAGE WILL PUT A CHILL
IN THE AIR ALONG WITH SOME LIGHT SNOW. SNOW AMOUNTS LOOK TO BE 1
TO 4 INCHES FOR THE LOWER ELEVATIONS WITH LOCALLY HIGHER AMOUNTS
POSSIBLE. EXPECT DRIFTING SNOW IN OPEN AREAS. STILL HAVE A FEW
DAYS TO WATCH THE TRACK OF THIS WEATHER SYSTEM AND REFINE SNOWFALL
AMOUNTS. THE LIGHT SNOW ENDS LATE CHRISTMAS NIGHT IN MOST PLACES.
FRIDAY LOOKS COLD WITH MOUNTAIN LIGHT SNOW SHOWERS WITH NOT MUCH
IF ANY SNOW SHOWERS AT THE LOWER ELEVATIONS. THE GFS AND ECMWF
MODELS DIFFER WITH THE WEATHER PATTERN SATURDAY AND SUNDAY. THE
GFS BRINGS ANOTHER WEATHER SYSTEM INTO THE NORTH SATURDAY NIGHT
ALONG WITH ANOTHER COLD FRONT. THEN THIS COLD AIR BOUNDARY SAGS
SOUTH NEXT SUNDAY INTO CENTRAL WY. THE ECMWF MODEL DOES NOT SHOW
THIS WEATHER SYSTEM AT ALL SATURDAY NIGHT AND SUNDAY. THUS THE
ECMWF IS DRY SATURDAY AND SUNDAY. HAVE LEANED TOWARD THE DRIER
ECMWF MODEL BUT HAVE LEFT LOW CHANCE OF SNOW IN THE WESTERN AND
NORTHERN MOUNTAINS FOR NOW. AS FOR TEMPS...CHRISTMAS EVE WILL BE
SLIGHTLY MILDER...THEN COLDER CHRISTMAS DAY AND FRIDAY. SLIGHTLY
MILDER SATURDAY AND SUNDAY.

&&

.AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

A TROUGH OF LOW PRESSURE WILL MOVE ACROSS MONTANA ON SUNDAY AND INTO
THE NORTHERN PLAINS SUNDAY EVENING.  A STRONG JET STREAM 120-130KTS
WILL CROSS THE WYOMING DIVIDE SOUTH OF THIS SYSTEM THIS MORNING
CAUSING AREAS OF MDT-SVR TURBULENCE...LLWS OVER SHALLOW CENTRAL
BASIN INVERSIONS...AND STRONG SFC WINDS FROM VCNTY SOUTH PASS TO
VCNTY KCPR AND SOUTH ALONG THE INTERSTATE 80 CORRIDOR.  THE LEE
SLOPES ALONG THE DIVIDE AND BIGHORN RANGE WILL LIKELY REMAIN MOSTLY
OBSCURE ABOVE 9KFT.  A STRONG NW FLOW WILL FOLLOW THIS SYSTEM SUNDAY
NIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG THE FRONT
ACROSS THE LOWER ELEVATIONS SUNDAY EVENING...ESPECIALLY VCNTY AND
EAST OF INTERSTATE 25.  DRIER AIR PREVAIL NW-SE BUT GUSTY NW SFC
WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 0Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA SUNDAY AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH SUNDAY EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.

&&

.FIRE WEATHER...

ONGOING WINTRY CONDITIONS WILL KEEP SNOWFALL AND AREAS OF STRONG
WIND ACROSS WESTERN AND SOUTHERN WYOMING TODAY. WIND IS EXPECTED TO
INCREASE ACROSS CENTRAL AND NORTHEASTERN WYOMING LATER TONIGHT WITH
POTENTIALLY STRONG WIND LINGERING THROUGH MONDAY AFTERNOON. WINTER
STORM AND HIGH WIND WARNINGS ARE CURRENTLY IN EFFECT...ALONG WITH A
COUPLE AREAS IN A HIGH WIND WATCH.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING UNTIL 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING UNTIL 11 PM MST THIS EVENING WYZ019.

WINTER STORM WARNING UNTIL 11 AM MST MONDAY WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY AFTERNOON
WYZ010.

HIGH WIND WATCH FROM THIS EVENING THROUGH MONDAY MORNING
WYZ016-017.

HIGH WIND WARNING UNTIL 11 AM MST THIS MORNING WYZ003.

&&

$$

SHORT TERM...BRANHAM
LONG TERM...AR
AVIATION...AEM
FIRE WEATHER...BRANHAM







000
FXUS63 KUNR 210956
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
256 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT
ISSUED AT 255 AM MST SUN DEC 21 2014

WATER VAPOR IMAGERY AND UPPER AIR ANALYSIS SHOWS WEAK TROUGH SITTING
ACROSS THE NRN PLAINS ATTM AS A STRONG +140KT JET STREAK PUSHES INTO
THE PACIFIC NW COAST. SURFACE ANALYSIS SHOW DEEPENING LOW PRESSURE
ACROSS BRITISH COLUMBIA AND ALBERTA SLIDING SE. FORCING ASSOCIATED
WITH JET VORT MAX WILL BRING PRECIP TO THE AREA LATE THIS MRNG INTO
THE AFTN HOURS. WITH TEMPS RISING TODAY INTO THE UPPER 30S TO AROUND
50...PRECIP WILL BE RAIN.

UPPER TROUGH WILL QUICKLY DEEPEN TONIGHT AS UPPER LEVEL ENERGY DIVES
DOWN THE BACKSIDE. STRENGTHENING LOW PRESSURE WILL DROP INTO WRN ND
THIS EVNG...THEN CNTRL SD LATER TONIGHT. COLDER AIR WILL FILTER IN
FROM THE N/NW...WITH GUSTY NW WINDS DEVELOPING OVERNIGHT. RAIN
ACROSS THE AREA WILL CHANGE TO SNOW LATE TONIGHT AS THERMAL PROFILES
COOL...BUT SNOW WITH LITTLE ACCUMULATION. STEEP LOW LEVEL LAPSE
RATES AND HIGH RH WILL RESULT IN UPSLOPE PRECIP...WITH RAIN CHANGING
TO SNOW THIS EVNG. MODELS NOW SHOWING SYSTEM BECOMING A STALLED AND
STACKED UPPER LOW ON MONDAY. TIGHT PRESSURE GRADIENT ACROSS THE AREA
WILL BRING STRONG NW WINDS TO THE AREA. MODELS BEGINNING TO SHOW A
WETTER SOLUTION ACROSS THE PLAINS WITH WRAP AROUND PRECIP DEVELOPING
SOMEWHERE OVER THE WRN TO CNTRL SD PLAINS. HAVE INCREASED POPS QUITE
A BIT TO REFLECT THIS...WHICH ALSO INCREASES EXPECTED SNOW AMOUNTS
OVER THE PLAINS MONDAY. BUT IT STILL LOOKS LIKE TEMPS MAY RISE
ENOUGH TO OR ABOVE FREEZING TO HINDER SNOW ACCUMULATION. THINK
PLAINS WILL SEE AN INCH OR TWO OF SNOW DURING THE DAY. NW WINDS OF
25 TO 35 MPH ARE EXPECTED...WHICH WHEN COMBINED WITH SNOW WILL COULD
PRODUCE AREAS OF BLOWING SNOW. AT THIS TIME THINKING IS A WINTER
WEATHER ADVISORY MAY BE NEEDED...BUT THIS WOULD DEPEND ON HOW MODELS
RESOLVE SNOW AMOUNTS.

UPSLOPE SNOW WILL CONTINUE ALL DAY MONDAY AND THROUGH MONDAY NIGHT
ACROSS THE NORTHERN TO CENTRAL BLACK HILLS AND BEAR LODGE MOUNTAINS.
ATTM IT LOOKS LIKE SNOWFALL AMOUNTS OVER THE HIGHER BLACK HILLS WILL
BE IN THE 6 TO 12 INCH RANGE. WITH A MORE WESTERLY COMPONENT TO THE
WIND...HIGHEST SNOWFALL TOTALS ARE EXPECTED TO BE AROUND THE
CHEYENNE CROSSING TO ONEIL PASS INTO THE FOUR CORNERS AREA. WILL
ISSUE A WINTER STORM WATCH FOR THESE AREAS STARTING TONIGHT AND
CONTINUING UNTIL NOON TUESDAY.

.LONG TERM...TUESDAY THROUGH SATURDAY
ISSUED AT 255 AM MST SUN DEC 21 2014

AMPLIFIED PATTERN EXPECTED IN THE PERIOD AS THE EARLY WEEK LONG
WAVE TROUGH SPURS MASSIVE RIDGING INTO GREENLAND. THIS WILL FAVOR
A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A CP/MODIFIED
ARCTIC AIRMASS INTRUSION INTO THE CONUS PER WAVE TRAIN OF TROUGHS
EMANATING FROM THE NORTHERN PAC UPPER LOW. THIS COLD INTRUSION
WILL ARRIVE WITH A DECENT/STRONG SHORTWAVE EXPECTED IN THE WED
NIGHT-THUR PERIOD...WITH ANOTHER SHOT OF COLD AIR LIKELY NEXT
WEEKEND PER WESTERN NOAM RIDGING AND FRONT SIDE NORTHERN STREAM
IMPULSES. AFTER A MILD DAY WED...BELOW NORMAL TEMPS CAN BE
EXPECTED FOR THE REMAINDER OF THE PERIOD.

TUE-WED...LINGERING MORNING SNOW SHOWERS OVER THE BH AND FAR
SCENTRAL CAN BE EXPECTED AS THE EARLY WEEK SYSTEM EXITS THE REGION.
HAVE WENT WITH HIGH POPS OVER THE NORTHERN BH. CLOSED MID LEVEL
CIRCULATION WILL LIKELY SUPPORT A SLOWER EXIT OF THIS SYSTEM...WITH
SNOW LINGERING THROUGH AT LEAST MORNING. DRY WEATHER EXPECTED TUE NIGHT
THROUGH WED...WITH INCREASING CHANCES FOR PRECIP WED NIGHT INTO
THUR MORNING. COLDER CONDS EXPECTED TUE GIVEN ONGOING CAA WITH
STRONG GUSTY NW WINDS. 20 TO 30 MPH WINDS CAN BE EXPECTED TO
CONTINUE ON THE SD PLAINS FOR MUCH OF TUES.

THUR-SAT...STRONG COMPACT SPLITTING IMPULSE WILL QUICKLY MOVE INTO
THE REGION WED NIGHT SUPPORTING INCREASING CHANCES FOR SNOW. COUPLED
UPPER LEVEL JET STRUCTURE WILL LIKELY ENHANCED LIFT...FAVORING A
DECENT FGEN BANDED SNOW EVENT ACROSS A PORTION OF THE FA. CURRENT
PROGS SUGGEST MOST OF THE FA COULD SEE SNOW THUR ALTHOUGH N-S
ADJUSTMENT CAN BE EXPECTED IN SUBSEQUENT MODEL RUNS. INCREASED POPS
GIVEN RUN-RUN CONSISTENCY AND STRONG LIFT ASSOCIATED WITH THIS SYSTEM
COUPLED WITH SUFFICIENT MOISTURE. CURRENT PROGS SUGGEST 1-3 INCHES
POSSIBLE...WITH CERTAINLY HIGHER AMOUNTS IN ANY PERSISTENT BANDS.
GIVEN STRONG MERIDIONAL COMPONENT TO THE LL FLOW...HAVE CUT TEMPS
THUR-SAT...WHICH MAY NOT BE ENOUGH IF A DEEPER CENTRAL CONUS UPPER
TROUGH IS REALIZED.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING
ISSUED AT 255 AM MST SUN DEC 21 2014

VFR CONDITIONS WILL CONTINUE THROUGH 18Z ON SUNDAY. A STRONG
CDFNT MOVING INTO THE REGION SUNDAY AFTN WILL BRING SCT -SHRA AND
MVFR CIGS. CONDITIONS WILL DETERIORATE FURTHER SUNDAY
NIGHT...ESPECIALLY OVER NERN WY AND THE NRN BLKHLS AS SNOW
DEVELOPS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     SDZ024-028.

WY...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     WYZ057.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC







000
FXUS63 KUNR 210956
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
256 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT
ISSUED AT 255 AM MST SUN DEC 21 2014

WATER VAPOR IMAGERY AND UPPER AIR ANALYSIS SHOWS WEAK TROUGH SITTING
ACROSS THE NRN PLAINS ATTM AS A STRONG +140KT JET STREAK PUSHES INTO
THE PACIFIC NW COAST. SURFACE ANALYSIS SHOW DEEPENING LOW PRESSURE
ACROSS BRITISH COLUMBIA AND ALBERTA SLIDING SE. FORCING ASSOCIATED
WITH JET VORT MAX WILL BRING PRECIP TO THE AREA LATE THIS MRNG INTO
THE AFTN HOURS. WITH TEMPS RISING TODAY INTO THE UPPER 30S TO AROUND
50...PRECIP WILL BE RAIN.

UPPER TROUGH WILL QUICKLY DEEPEN TONIGHT AS UPPER LEVEL ENERGY DIVES
DOWN THE BACKSIDE. STRENGTHENING LOW PRESSURE WILL DROP INTO WRN ND
THIS EVNG...THEN CNTRL SD LATER TONIGHT. COLDER AIR WILL FILTER IN
FROM THE N/NW...WITH GUSTY NW WINDS DEVELOPING OVERNIGHT. RAIN
ACROSS THE AREA WILL CHANGE TO SNOW LATE TONIGHT AS THERMAL PROFILES
COOL...BUT SNOW WITH LITTLE ACCUMULATION. STEEP LOW LEVEL LAPSE
RATES AND HIGH RH WILL RESULT IN UPSLOPE PRECIP...WITH RAIN CHANGING
TO SNOW THIS EVNG. MODELS NOW SHOWING SYSTEM BECOMING A STALLED AND
STACKED UPPER LOW ON MONDAY. TIGHT PRESSURE GRADIENT ACROSS THE AREA
WILL BRING STRONG NW WINDS TO THE AREA. MODELS BEGINNING TO SHOW A
WETTER SOLUTION ACROSS THE PLAINS WITH WRAP AROUND PRECIP DEVELOPING
SOMEWHERE OVER THE WRN TO CNTRL SD PLAINS. HAVE INCREASED POPS QUITE
A BIT TO REFLECT THIS...WHICH ALSO INCREASES EXPECTED SNOW AMOUNTS
OVER THE PLAINS MONDAY. BUT IT STILL LOOKS LIKE TEMPS MAY RISE
ENOUGH TO OR ABOVE FREEZING TO HINDER SNOW ACCUMULATION. THINK
PLAINS WILL SEE AN INCH OR TWO OF SNOW DURING THE DAY. NW WINDS OF
25 TO 35 MPH ARE EXPECTED...WHICH WHEN COMBINED WITH SNOW WILL COULD
PRODUCE AREAS OF BLOWING SNOW. AT THIS TIME THINKING IS A WINTER
WEATHER ADVISORY MAY BE NEEDED...BUT THIS WOULD DEPEND ON HOW MODELS
RESOLVE SNOW AMOUNTS.

UPSLOPE SNOW WILL CONTINUE ALL DAY MONDAY AND THROUGH MONDAY NIGHT
ACROSS THE NORTHERN TO CENTRAL BLACK HILLS AND BEAR LODGE MOUNTAINS.
ATTM IT LOOKS LIKE SNOWFALL AMOUNTS OVER THE HIGHER BLACK HILLS WILL
BE IN THE 6 TO 12 INCH RANGE. WITH A MORE WESTERLY COMPONENT TO THE
WIND...HIGHEST SNOWFALL TOTALS ARE EXPECTED TO BE AROUND THE
CHEYENNE CROSSING TO ONEIL PASS INTO THE FOUR CORNERS AREA. WILL
ISSUE A WINTER STORM WATCH FOR THESE AREAS STARTING TONIGHT AND
CONTINUING UNTIL NOON TUESDAY.

.LONG TERM...TUESDAY THROUGH SATURDAY
ISSUED AT 255 AM MST SUN DEC 21 2014

AMPLIFIED PATTERN EXPECTED IN THE PERIOD AS THE EARLY WEEK LONG
WAVE TROUGH SPURS MASSIVE RIDGING INTO GREENLAND. THIS WILL FAVOR
A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A CP/MODIFIED
ARCTIC AIRMASS INTRUSION INTO THE CONUS PER WAVE TRAIN OF TROUGHS
EMANATING FROM THE NORTHERN PAC UPPER LOW. THIS COLD INTRUSION
WILL ARRIVE WITH A DECENT/STRONG SHORTWAVE EXPECTED IN THE WED
NIGHT-THUR PERIOD...WITH ANOTHER SHOT OF COLD AIR LIKELY NEXT
WEEKEND PER WESTERN NOAM RIDGING AND FRONT SIDE NORTHERN STREAM
IMPULSES. AFTER A MILD DAY WED...BELOW NORMAL TEMPS CAN BE
EXPECTED FOR THE REMAINDER OF THE PERIOD.

TUE-WED...LINGERING MORNING SNOW SHOWERS OVER THE BH AND FAR
SCENTRAL CAN BE EXPECTED AS THE EARLY WEEK SYSTEM EXITS THE REGION.
HAVE WENT WITH HIGH POPS OVER THE NORTHERN BH. CLOSED MID LEVEL
CIRCULATION WILL LIKELY SUPPORT A SLOWER EXIT OF THIS SYSTEM...WITH
SNOW LINGERING THROUGH AT LEAST MORNING. DRY WEATHER EXPECTED TUE NIGHT
THROUGH WED...WITH INCREASING CHANCES FOR PRECIP WED NIGHT INTO
THUR MORNING. COLDER CONDS EXPECTED TUE GIVEN ONGOING CAA WITH
STRONG GUSTY NW WINDS. 20 TO 30 MPH WINDS CAN BE EXPECTED TO
CONTINUE ON THE SD PLAINS FOR MUCH OF TUES.

THUR-SAT...STRONG COMPACT SPLITTING IMPULSE WILL QUICKLY MOVE INTO
THE REGION WED NIGHT SUPPORTING INCREASING CHANCES FOR SNOW. COUPLED
UPPER LEVEL JET STRUCTURE WILL LIKELY ENHANCED LIFT...FAVORING A
DECENT FGEN BANDED SNOW EVENT ACROSS A PORTION OF THE FA. CURRENT
PROGS SUGGEST MOST OF THE FA COULD SEE SNOW THUR ALTHOUGH N-S
ADJUSTMENT CAN BE EXPECTED IN SUBSEQUENT MODEL RUNS. INCREASED POPS
GIVEN RUN-RUN CONSISTENCY AND STRONG LIFT ASSOCIATED WITH THIS SYSTEM
COUPLED WITH SUFFICIENT MOISTURE. CURRENT PROGS SUGGEST 1-3 INCHES
POSSIBLE...WITH CERTAINLY HIGHER AMOUNTS IN ANY PERSISTENT BANDS.
GIVEN STRONG MERIDIONAL COMPONENT TO THE LL FLOW...HAVE CUT TEMPS
THUR-SAT...WHICH MAY NOT BE ENOUGH IF A DEEPER CENTRAL CONUS UPPER
TROUGH IS REALIZED.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING
ISSUED AT 255 AM MST SUN DEC 21 2014

VFR CONDITIONS WILL CONTINUE THROUGH 18Z ON SUNDAY. A STRONG
CDFNT MOVING INTO THE REGION SUNDAY AFTN WILL BRING SCT -SHRA AND
MVFR CIGS. CONDITIONS WILL DETERIORATE FURTHER SUNDAY
NIGHT...ESPECIALLY OVER NERN WY AND THE NRN BLKHLS AS SNOW
DEVELOPS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     SDZ024-028.

WY...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     WYZ057.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC







000
FXUS63 KUNR 210956
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
256 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT
ISSUED AT 255 AM MST SUN DEC 21 2014

WATER VAPOR IMAGERY AND UPPER AIR ANALYSIS SHOWS WEAK TROUGH SITTING
ACROSS THE NRN PLAINS ATTM AS A STRONG +140KT JET STREAK PUSHES INTO
THE PACIFIC NW COAST. SURFACE ANALYSIS SHOW DEEPENING LOW PRESSURE
ACROSS BRITISH COLUMBIA AND ALBERTA SLIDING SE. FORCING ASSOCIATED
WITH JET VORT MAX WILL BRING PRECIP TO THE AREA LATE THIS MRNG INTO
THE AFTN HOURS. WITH TEMPS RISING TODAY INTO THE UPPER 30S TO AROUND
50...PRECIP WILL BE RAIN.

UPPER TROUGH WILL QUICKLY DEEPEN TONIGHT AS UPPER LEVEL ENERGY DIVES
DOWN THE BACKSIDE. STRENGTHENING LOW PRESSURE WILL DROP INTO WRN ND
THIS EVNG...THEN CNTRL SD LATER TONIGHT. COLDER AIR WILL FILTER IN
FROM THE N/NW...WITH GUSTY NW WINDS DEVELOPING OVERNIGHT. RAIN
ACROSS THE AREA WILL CHANGE TO SNOW LATE TONIGHT AS THERMAL PROFILES
COOL...BUT SNOW WITH LITTLE ACCUMULATION. STEEP LOW LEVEL LAPSE
RATES AND HIGH RH WILL RESULT IN UPSLOPE PRECIP...WITH RAIN CHANGING
TO SNOW THIS EVNG. MODELS NOW SHOWING SYSTEM BECOMING A STALLED AND
STACKED UPPER LOW ON MONDAY. TIGHT PRESSURE GRADIENT ACROSS THE AREA
WILL BRING STRONG NW WINDS TO THE AREA. MODELS BEGINNING TO SHOW A
WETTER SOLUTION ACROSS THE PLAINS WITH WRAP AROUND PRECIP DEVELOPING
SOMEWHERE OVER THE WRN TO CNTRL SD PLAINS. HAVE INCREASED POPS QUITE
A BIT TO REFLECT THIS...WHICH ALSO INCREASES EXPECTED SNOW AMOUNTS
OVER THE PLAINS MONDAY. BUT IT STILL LOOKS LIKE TEMPS MAY RISE
ENOUGH TO OR ABOVE FREEZING TO HINDER SNOW ACCUMULATION. THINK
PLAINS WILL SEE AN INCH OR TWO OF SNOW DURING THE DAY. NW WINDS OF
25 TO 35 MPH ARE EXPECTED...WHICH WHEN COMBINED WITH SNOW WILL COULD
PRODUCE AREAS OF BLOWING SNOW. AT THIS TIME THINKING IS A WINTER
WEATHER ADVISORY MAY BE NEEDED...BUT THIS WOULD DEPEND ON HOW MODELS
RESOLVE SNOW AMOUNTS.

UPSLOPE SNOW WILL CONTINUE ALL DAY MONDAY AND THROUGH MONDAY NIGHT
ACROSS THE NORTHERN TO CENTRAL BLACK HILLS AND BEAR LODGE MOUNTAINS.
ATTM IT LOOKS LIKE SNOWFALL AMOUNTS OVER THE HIGHER BLACK HILLS WILL
BE IN THE 6 TO 12 INCH RANGE. WITH A MORE WESTERLY COMPONENT TO THE
WIND...HIGHEST SNOWFALL TOTALS ARE EXPECTED TO BE AROUND THE
CHEYENNE CROSSING TO ONEIL PASS INTO THE FOUR CORNERS AREA. WILL
ISSUE A WINTER STORM WATCH FOR THESE AREAS STARTING TONIGHT AND
CONTINUING UNTIL NOON TUESDAY.

.LONG TERM...TUESDAY THROUGH SATURDAY
ISSUED AT 255 AM MST SUN DEC 21 2014

AMPLIFIED PATTERN EXPECTED IN THE PERIOD AS THE EARLY WEEK LONG
WAVE TROUGH SPURS MASSIVE RIDGING INTO GREENLAND. THIS WILL FAVOR
A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A CP/MODIFIED
ARCTIC AIRMASS INTRUSION INTO THE CONUS PER WAVE TRAIN OF TROUGHS
EMANATING FROM THE NORTHERN PAC UPPER LOW. THIS COLD INTRUSION
WILL ARRIVE WITH A DECENT/STRONG SHORTWAVE EXPECTED IN THE WED
NIGHT-THUR PERIOD...WITH ANOTHER SHOT OF COLD AIR LIKELY NEXT
WEEKEND PER WESTERN NOAM RIDGING AND FRONT SIDE NORTHERN STREAM
IMPULSES. AFTER A MILD DAY WED...BELOW NORMAL TEMPS CAN BE
EXPECTED FOR THE REMAINDER OF THE PERIOD.

TUE-WED...LINGERING MORNING SNOW SHOWERS OVER THE BH AND FAR
SCENTRAL CAN BE EXPECTED AS THE EARLY WEEK SYSTEM EXITS THE REGION.
HAVE WENT WITH HIGH POPS OVER THE NORTHERN BH. CLOSED MID LEVEL
CIRCULATION WILL LIKELY SUPPORT A SLOWER EXIT OF THIS SYSTEM...WITH
SNOW LINGERING THROUGH AT LEAST MORNING. DRY WEATHER EXPECTED TUE NIGHT
THROUGH WED...WITH INCREASING CHANCES FOR PRECIP WED NIGHT INTO
THUR MORNING. COLDER CONDS EXPECTED TUE GIVEN ONGOING CAA WITH
STRONG GUSTY NW WINDS. 20 TO 30 MPH WINDS CAN BE EXPECTED TO
CONTINUE ON THE SD PLAINS FOR MUCH OF TUES.

THUR-SAT...STRONG COMPACT SPLITTING IMPULSE WILL QUICKLY MOVE INTO
THE REGION WED NIGHT SUPPORTING INCREASING CHANCES FOR SNOW. COUPLED
UPPER LEVEL JET STRUCTURE WILL LIKELY ENHANCED LIFT...FAVORING A
DECENT FGEN BANDED SNOW EVENT ACROSS A PORTION OF THE FA. CURRENT
PROGS SUGGEST MOST OF THE FA COULD SEE SNOW THUR ALTHOUGH N-S
ADJUSTMENT CAN BE EXPECTED IN SUBSEQUENT MODEL RUNS. INCREASED POPS
GIVEN RUN-RUN CONSISTENCY AND STRONG LIFT ASSOCIATED WITH THIS SYSTEM
COUPLED WITH SUFFICIENT MOISTURE. CURRENT PROGS SUGGEST 1-3 INCHES
POSSIBLE...WITH CERTAINLY HIGHER AMOUNTS IN ANY PERSISTENT BANDS.
GIVEN STRONG MERIDIONAL COMPONENT TO THE LL FLOW...HAVE CUT TEMPS
THUR-SAT...WHICH MAY NOT BE ENOUGH IF A DEEPER CENTRAL CONUS UPPER
TROUGH IS REALIZED.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING
ISSUED AT 255 AM MST SUN DEC 21 2014

VFR CONDITIONS WILL CONTINUE THROUGH 18Z ON SUNDAY. A STRONG
CDFNT MOVING INTO THE REGION SUNDAY AFTN WILL BRING SCT -SHRA AND
MVFR CIGS. CONDITIONS WILL DETERIORATE FURTHER SUNDAY
NIGHT...ESPECIALLY OVER NERN WY AND THE NRN BLKHLS AS SNOW
DEVELOPS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     SDZ024-028.

WY...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     WYZ057.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC







000
FXUS63 KUNR 210956
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
256 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT
ISSUED AT 255 AM MST SUN DEC 21 2014

WATER VAPOR IMAGERY AND UPPER AIR ANALYSIS SHOWS WEAK TROUGH SITTING
ACROSS THE NRN PLAINS ATTM AS A STRONG +140KT JET STREAK PUSHES INTO
THE PACIFIC NW COAST. SURFACE ANALYSIS SHOW DEEPENING LOW PRESSURE
ACROSS BRITISH COLUMBIA AND ALBERTA SLIDING SE. FORCING ASSOCIATED
WITH JET VORT MAX WILL BRING PRECIP TO THE AREA LATE THIS MRNG INTO
THE AFTN HOURS. WITH TEMPS RISING TODAY INTO THE UPPER 30S TO AROUND
50...PRECIP WILL BE RAIN.

UPPER TROUGH WILL QUICKLY DEEPEN TONIGHT AS UPPER LEVEL ENERGY DIVES
DOWN THE BACKSIDE. STRENGTHENING LOW PRESSURE WILL DROP INTO WRN ND
THIS EVNG...THEN CNTRL SD LATER TONIGHT. COLDER AIR WILL FILTER IN
FROM THE N/NW...WITH GUSTY NW WINDS DEVELOPING OVERNIGHT. RAIN
ACROSS THE AREA WILL CHANGE TO SNOW LATE TONIGHT AS THERMAL PROFILES
COOL...BUT SNOW WITH LITTLE ACCUMULATION. STEEP LOW LEVEL LAPSE
RATES AND HIGH RH WILL RESULT IN UPSLOPE PRECIP...WITH RAIN CHANGING
TO SNOW THIS EVNG. MODELS NOW SHOWING SYSTEM BECOMING A STALLED AND
STACKED UPPER LOW ON MONDAY. TIGHT PRESSURE GRADIENT ACROSS THE AREA
WILL BRING STRONG NW WINDS TO THE AREA. MODELS BEGINNING TO SHOW A
WETTER SOLUTION ACROSS THE PLAINS WITH WRAP AROUND PRECIP DEVELOPING
SOMEWHERE OVER THE WRN TO CNTRL SD PLAINS. HAVE INCREASED POPS QUITE
A BIT TO REFLECT THIS...WHICH ALSO INCREASES EXPECTED SNOW AMOUNTS
OVER THE PLAINS MONDAY. BUT IT STILL LOOKS LIKE TEMPS MAY RISE
ENOUGH TO OR ABOVE FREEZING TO HINDER SNOW ACCUMULATION. THINK
PLAINS WILL SEE AN INCH OR TWO OF SNOW DURING THE DAY. NW WINDS OF
25 TO 35 MPH ARE EXPECTED...WHICH WHEN COMBINED WITH SNOW WILL COULD
PRODUCE AREAS OF BLOWING SNOW. AT THIS TIME THINKING IS A WINTER
WEATHER ADVISORY MAY BE NEEDED...BUT THIS WOULD DEPEND ON HOW MODELS
RESOLVE SNOW AMOUNTS.

UPSLOPE SNOW WILL CONTINUE ALL DAY MONDAY AND THROUGH MONDAY NIGHT
ACROSS THE NORTHERN TO CENTRAL BLACK HILLS AND BEAR LODGE MOUNTAINS.
ATTM IT LOOKS LIKE SNOWFALL AMOUNTS OVER THE HIGHER BLACK HILLS WILL
BE IN THE 6 TO 12 INCH RANGE. WITH A MORE WESTERLY COMPONENT TO THE
WIND...HIGHEST SNOWFALL TOTALS ARE EXPECTED TO BE AROUND THE
CHEYENNE CROSSING TO ONEIL PASS INTO THE FOUR CORNERS AREA. WILL
ISSUE A WINTER STORM WATCH FOR THESE AREAS STARTING TONIGHT AND
CONTINUING UNTIL NOON TUESDAY.

.LONG TERM...TUESDAY THROUGH SATURDAY
ISSUED AT 255 AM MST SUN DEC 21 2014

AMPLIFIED PATTERN EXPECTED IN THE PERIOD AS THE EARLY WEEK LONG
WAVE TROUGH SPURS MASSIVE RIDGING INTO GREENLAND. THIS WILL FAVOR
A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A CP/MODIFIED
ARCTIC AIRMASS INTRUSION INTO THE CONUS PER WAVE TRAIN OF TROUGHS
EMANATING FROM THE NORTHERN PAC UPPER LOW. THIS COLD INTRUSION
WILL ARRIVE WITH A DECENT/STRONG SHORTWAVE EXPECTED IN THE WED
NIGHT-THUR PERIOD...WITH ANOTHER SHOT OF COLD AIR LIKELY NEXT
WEEKEND PER WESTERN NOAM RIDGING AND FRONT SIDE NORTHERN STREAM
IMPULSES. AFTER A MILD DAY WED...BELOW NORMAL TEMPS CAN BE
EXPECTED FOR THE REMAINDER OF THE PERIOD.

TUE-WED...LINGERING MORNING SNOW SHOWERS OVER THE BH AND FAR
SCENTRAL CAN BE EXPECTED AS THE EARLY WEEK SYSTEM EXITS THE REGION.
HAVE WENT WITH HIGH POPS OVER THE NORTHERN BH. CLOSED MID LEVEL
CIRCULATION WILL LIKELY SUPPORT A SLOWER EXIT OF THIS SYSTEM...WITH
SNOW LINGERING THROUGH AT LEAST MORNING. DRY WEATHER EXPECTED TUE NIGHT
THROUGH WED...WITH INCREASING CHANCES FOR PRECIP WED NIGHT INTO
THUR MORNING. COLDER CONDS EXPECTED TUE GIVEN ONGOING CAA WITH
STRONG GUSTY NW WINDS. 20 TO 30 MPH WINDS CAN BE EXPECTED TO
CONTINUE ON THE SD PLAINS FOR MUCH OF TUES.

THUR-SAT...STRONG COMPACT SPLITTING IMPULSE WILL QUICKLY MOVE INTO
THE REGION WED NIGHT SUPPORTING INCREASING CHANCES FOR SNOW. COUPLED
UPPER LEVEL JET STRUCTURE WILL LIKELY ENHANCED LIFT...FAVORING A
DECENT FGEN BANDED SNOW EVENT ACROSS A PORTION OF THE FA. CURRENT
PROGS SUGGEST MOST OF THE FA COULD SEE SNOW THUR ALTHOUGH N-S
ADJUSTMENT CAN BE EXPECTED IN SUBSEQUENT MODEL RUNS. INCREASED POPS
GIVEN RUN-RUN CONSISTENCY AND STRONG LIFT ASSOCIATED WITH THIS SYSTEM
COUPLED WITH SUFFICIENT MOISTURE. CURRENT PROGS SUGGEST 1-3 INCHES
POSSIBLE...WITH CERTAINLY HIGHER AMOUNTS IN ANY PERSISTENT BANDS.
GIVEN STRONG MERIDIONAL COMPONENT TO THE LL FLOW...HAVE CUT TEMPS
THUR-SAT...WHICH MAY NOT BE ENOUGH IF A DEEPER CENTRAL CONUS UPPER
TROUGH IS REALIZED.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING
ISSUED AT 255 AM MST SUN DEC 21 2014

VFR CONDITIONS WILL CONTINUE THROUGH 18Z ON SUNDAY. A STRONG
CDFNT MOVING INTO THE REGION SUNDAY AFTN WILL BRING SCT -SHRA AND
MVFR CIGS. CONDITIONS WILL DETERIORATE FURTHER SUNDAY
NIGHT...ESPECIALLY OVER NERN WY AND THE NRN BLKHLS AS SNOW
DEVELOPS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     SDZ024-028.

WY...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     WYZ057.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC







000
FXUS63 KUNR 210956
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
256 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT
ISSUED AT 255 AM MST SUN DEC 21 2014

WATER VAPOR IMAGERY AND UPPER AIR ANALYSIS SHOWS WEAK TROUGH SITTING
ACROSS THE NRN PLAINS ATTM AS A STRONG +140KT JET STREAK PUSHES INTO
THE PACIFIC NW COAST. SURFACE ANALYSIS SHOW DEEPENING LOW PRESSURE
ACROSS BRITISH COLUMBIA AND ALBERTA SLIDING SE. FORCING ASSOCIATED
WITH JET VORT MAX WILL BRING PRECIP TO THE AREA LATE THIS MRNG INTO
THE AFTN HOURS. WITH TEMPS RISING TODAY INTO THE UPPER 30S TO AROUND
50...PRECIP WILL BE RAIN.

UPPER TROUGH WILL QUICKLY DEEPEN TONIGHT AS UPPER LEVEL ENERGY DIVES
DOWN THE BACKSIDE. STRENGTHENING LOW PRESSURE WILL DROP INTO WRN ND
THIS EVNG...THEN CNTRL SD LATER TONIGHT. COLDER AIR WILL FILTER IN
FROM THE N/NW...WITH GUSTY NW WINDS DEVELOPING OVERNIGHT. RAIN
ACROSS THE AREA WILL CHANGE TO SNOW LATE TONIGHT AS THERMAL PROFILES
COOL...BUT SNOW WITH LITTLE ACCUMULATION. STEEP LOW LEVEL LAPSE
RATES AND HIGH RH WILL RESULT IN UPSLOPE PRECIP...WITH RAIN CHANGING
TO SNOW THIS EVNG. MODELS NOW SHOWING SYSTEM BECOMING A STALLED AND
STACKED UPPER LOW ON MONDAY. TIGHT PRESSURE GRADIENT ACROSS THE AREA
WILL BRING STRONG NW WINDS TO THE AREA. MODELS BEGINNING TO SHOW A
WETTER SOLUTION ACROSS THE PLAINS WITH WRAP AROUND PRECIP DEVELOPING
SOMEWHERE OVER THE WRN TO CNTRL SD PLAINS. HAVE INCREASED POPS QUITE
A BIT TO REFLECT THIS...WHICH ALSO INCREASES EXPECTED SNOW AMOUNTS
OVER THE PLAINS MONDAY. BUT IT STILL LOOKS LIKE TEMPS MAY RISE
ENOUGH TO OR ABOVE FREEZING TO HINDER SNOW ACCUMULATION. THINK
PLAINS WILL SEE AN INCH OR TWO OF SNOW DURING THE DAY. NW WINDS OF
25 TO 35 MPH ARE EXPECTED...WHICH WHEN COMBINED WITH SNOW WILL COULD
PRODUCE AREAS OF BLOWING SNOW. AT THIS TIME THINKING IS A WINTER
WEATHER ADVISORY MAY BE NEEDED...BUT THIS WOULD DEPEND ON HOW MODELS
RESOLVE SNOW AMOUNTS.

UPSLOPE SNOW WILL CONTINUE ALL DAY MONDAY AND THROUGH MONDAY NIGHT
ACROSS THE NORTHERN TO CENTRAL BLACK HILLS AND BEAR LODGE MOUNTAINS.
ATTM IT LOOKS LIKE SNOWFALL AMOUNTS OVER THE HIGHER BLACK HILLS WILL
BE IN THE 6 TO 12 INCH RANGE. WITH A MORE WESTERLY COMPONENT TO THE
WIND...HIGHEST SNOWFALL TOTALS ARE EXPECTED TO BE AROUND THE
CHEYENNE CROSSING TO ONEIL PASS INTO THE FOUR CORNERS AREA. WILL
ISSUE A WINTER STORM WATCH FOR THESE AREAS STARTING TONIGHT AND
CONTINUING UNTIL NOON TUESDAY.

.LONG TERM...TUESDAY THROUGH SATURDAY
ISSUED AT 255 AM MST SUN DEC 21 2014

AMPLIFIED PATTERN EXPECTED IN THE PERIOD AS THE EARLY WEEK LONG
WAVE TROUGH SPURS MASSIVE RIDGING INTO GREENLAND. THIS WILL FAVOR
A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A CP/MODIFIED
ARCTIC AIRMASS INTRUSION INTO THE CONUS PER WAVE TRAIN OF TROUGHS
EMANATING FROM THE NORTHERN PAC UPPER LOW. THIS COLD INTRUSION
WILL ARRIVE WITH A DECENT/STRONG SHORTWAVE EXPECTED IN THE WED
NIGHT-THUR PERIOD...WITH ANOTHER SHOT OF COLD AIR LIKELY NEXT
WEEKEND PER WESTERN NOAM RIDGING AND FRONT SIDE NORTHERN STREAM
IMPULSES. AFTER A MILD DAY WED...BELOW NORMAL TEMPS CAN BE
EXPECTED FOR THE REMAINDER OF THE PERIOD.

TUE-WED...LINGERING MORNING SNOW SHOWERS OVER THE BH AND FAR
SCENTRAL CAN BE EXPECTED AS THE EARLY WEEK SYSTEM EXITS THE REGION.
HAVE WENT WITH HIGH POPS OVER THE NORTHERN BH. CLOSED MID LEVEL
CIRCULATION WILL LIKELY SUPPORT A SLOWER EXIT OF THIS SYSTEM...WITH
SNOW LINGERING THROUGH AT LEAST MORNING. DRY WEATHER EXPECTED TUE NIGHT
THROUGH WED...WITH INCREASING CHANCES FOR PRECIP WED NIGHT INTO
THUR MORNING. COLDER CONDS EXPECTED TUE GIVEN ONGOING CAA WITH
STRONG GUSTY NW WINDS. 20 TO 30 MPH WINDS CAN BE EXPECTED TO
CONTINUE ON THE SD PLAINS FOR MUCH OF TUES.

THUR-SAT...STRONG COMPACT SPLITTING IMPULSE WILL QUICKLY MOVE INTO
THE REGION WED NIGHT SUPPORTING INCREASING CHANCES FOR SNOW. COUPLED
UPPER LEVEL JET STRUCTURE WILL LIKELY ENHANCED LIFT...FAVORING A
DECENT FGEN BANDED SNOW EVENT ACROSS A PORTION OF THE FA. CURRENT
PROGS SUGGEST MOST OF THE FA COULD SEE SNOW THUR ALTHOUGH N-S
ADJUSTMENT CAN BE EXPECTED IN SUBSEQUENT MODEL RUNS. INCREASED POPS
GIVEN RUN-RUN CONSISTENCY AND STRONG LIFT ASSOCIATED WITH THIS SYSTEM
COUPLED WITH SUFFICIENT MOISTURE. CURRENT PROGS SUGGEST 1-3 INCHES
POSSIBLE...WITH CERTAINLY HIGHER AMOUNTS IN ANY PERSISTENT BANDS.
GIVEN STRONG MERIDIONAL COMPONENT TO THE LL FLOW...HAVE CUT TEMPS
THUR-SAT...WHICH MAY NOT BE ENOUGH IF A DEEPER CENTRAL CONUS UPPER
TROUGH IS REALIZED.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING
ISSUED AT 255 AM MST SUN DEC 21 2014

VFR CONDITIONS WILL CONTINUE THROUGH 18Z ON SUNDAY. A STRONG
CDFNT MOVING INTO THE REGION SUNDAY AFTN WILL BRING SCT -SHRA AND
MVFR CIGS. CONDITIONS WILL DETERIORATE FURTHER SUNDAY
NIGHT...ESPECIALLY OVER NERN WY AND THE NRN BLKHLS AS SNOW
DEVELOPS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     SDZ024-028.

WY...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     WYZ057.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC






000
FXUS63 KUNR 210956
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
256 AM MST SUN DEC 21 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT
ISSUED AT 255 AM MST SUN DEC 21 2014

WATER VAPOR IMAGERY AND UPPER AIR ANALYSIS SHOWS WEAK TROUGH SITTING
ACROSS THE NRN PLAINS ATTM AS A STRONG +140KT JET STREAK PUSHES INTO
THE PACIFIC NW COAST. SURFACE ANALYSIS SHOW DEEPENING LOW PRESSURE
ACROSS BRITISH COLUMBIA AND ALBERTA SLIDING SE. FORCING ASSOCIATED
WITH JET VORT MAX WILL BRING PRECIP TO THE AREA LATE THIS MRNG INTO
THE AFTN HOURS. WITH TEMPS RISING TODAY INTO THE UPPER 30S TO AROUND
50...PRECIP WILL BE RAIN.

UPPER TROUGH WILL QUICKLY DEEPEN TONIGHT AS UPPER LEVEL ENERGY DIVES
DOWN THE BACKSIDE. STRENGTHENING LOW PRESSURE WILL DROP INTO WRN ND
THIS EVNG...THEN CNTRL SD LATER TONIGHT. COLDER AIR WILL FILTER IN
FROM THE N/NW...WITH GUSTY NW WINDS DEVELOPING OVERNIGHT. RAIN
ACROSS THE AREA WILL CHANGE TO SNOW LATE TONIGHT AS THERMAL PROFILES
COOL...BUT SNOW WITH LITTLE ACCUMULATION. STEEP LOW LEVEL LAPSE
RATES AND HIGH RH WILL RESULT IN UPSLOPE PRECIP...WITH RAIN CHANGING
TO SNOW THIS EVNG. MODELS NOW SHOWING SYSTEM BECOMING A STALLED AND
STACKED UPPER LOW ON MONDAY. TIGHT PRESSURE GRADIENT ACROSS THE AREA
WILL BRING STRONG NW WINDS TO THE AREA. MODELS BEGINNING TO SHOW A
WETTER SOLUTION ACROSS THE PLAINS WITH WRAP AROUND PRECIP DEVELOPING
SOMEWHERE OVER THE WRN TO CNTRL SD PLAINS. HAVE INCREASED POPS QUITE
A BIT TO REFLECT THIS...WHICH ALSO INCREASES EXPECTED SNOW AMOUNTS
OVER THE PLAINS MONDAY. BUT IT STILL LOOKS LIKE TEMPS MAY RISE
ENOUGH TO OR ABOVE FREEZING TO HINDER SNOW ACCUMULATION. THINK
PLAINS WILL SEE AN INCH OR TWO OF SNOW DURING THE DAY. NW WINDS OF
25 TO 35 MPH ARE EXPECTED...WHICH WHEN COMBINED WITH SNOW WILL COULD
PRODUCE AREAS OF BLOWING SNOW. AT THIS TIME THINKING IS A WINTER
WEATHER ADVISORY MAY BE NEEDED...BUT THIS WOULD DEPEND ON HOW MODELS
RESOLVE SNOW AMOUNTS.

UPSLOPE SNOW WILL CONTINUE ALL DAY MONDAY AND THROUGH MONDAY NIGHT
ACROSS THE NORTHERN TO CENTRAL BLACK HILLS AND BEAR LODGE MOUNTAINS.
ATTM IT LOOKS LIKE SNOWFALL AMOUNTS OVER THE HIGHER BLACK HILLS WILL
BE IN THE 6 TO 12 INCH RANGE. WITH A MORE WESTERLY COMPONENT TO THE
WIND...HIGHEST SNOWFALL TOTALS ARE EXPECTED TO BE AROUND THE
CHEYENNE CROSSING TO ONEIL PASS INTO THE FOUR CORNERS AREA. WILL
ISSUE A WINTER STORM WATCH FOR THESE AREAS STARTING TONIGHT AND
CONTINUING UNTIL NOON TUESDAY.

.LONG TERM...TUESDAY THROUGH SATURDAY
ISSUED AT 255 AM MST SUN DEC 21 2014

AMPLIFIED PATTERN EXPECTED IN THE PERIOD AS THE EARLY WEEK LONG
WAVE TROUGH SPURS MASSIVE RIDGING INTO GREENLAND. THIS WILL FAVOR
A TEMPORARY BLOCK TO THE FLOW PATTERN AND ALLOW A CP/MODIFIED
ARCTIC AIRMASS INTRUSION INTO THE CONUS PER WAVE TRAIN OF TROUGHS
EMANATING FROM THE NORTHERN PAC UPPER LOW. THIS COLD INTRUSION
WILL ARRIVE WITH A DECENT/STRONG SHORTWAVE EXPECTED IN THE WED
NIGHT-THUR PERIOD...WITH ANOTHER SHOT OF COLD AIR LIKELY NEXT
WEEKEND PER WESTERN NOAM RIDGING AND FRONT SIDE NORTHERN STREAM
IMPULSES. AFTER A MILD DAY WED...BELOW NORMAL TEMPS CAN BE
EXPECTED FOR THE REMAINDER OF THE PERIOD.

TUE-WED...LINGERING MORNING SNOW SHOWERS OVER THE BH AND FAR
SCENTRAL CAN BE EXPECTED AS THE EARLY WEEK SYSTEM EXITS THE REGION.
HAVE WENT WITH HIGH POPS OVER THE NORTHERN BH. CLOSED MID LEVEL
CIRCULATION WILL LIKELY SUPPORT A SLOWER EXIT OF THIS SYSTEM...WITH
SNOW LINGERING THROUGH AT LEAST MORNING. DRY WEATHER EXPECTED TUE NIGHT
THROUGH WED...WITH INCREASING CHANCES FOR PRECIP WED NIGHT INTO
THUR MORNING. COLDER CONDS EXPECTED TUE GIVEN ONGOING CAA WITH
STRONG GUSTY NW WINDS. 20 TO 30 MPH WINDS CAN BE EXPECTED TO
CONTINUE ON THE SD PLAINS FOR MUCH OF TUES.

THUR-SAT...STRONG COMPACT SPLITTING IMPULSE WILL QUICKLY MOVE INTO
THE REGION WED NIGHT SUPPORTING INCREASING CHANCES FOR SNOW. COUPLED
UPPER LEVEL JET STRUCTURE WILL LIKELY ENHANCED LIFT...FAVORING A
DECENT FGEN BANDED SNOW EVENT ACROSS A PORTION OF THE FA. CURRENT
PROGS SUGGEST MOST OF THE FA COULD SEE SNOW THUR ALTHOUGH N-S
ADJUSTMENT CAN BE EXPECTED IN SUBSEQUENT MODEL RUNS. INCREASED POPS
GIVEN RUN-RUN CONSISTENCY AND STRONG LIFT ASSOCIATED WITH THIS SYSTEM
COUPLED WITH SUFFICIENT MOISTURE. CURRENT PROGS SUGGEST 1-3 INCHES
POSSIBLE...WITH CERTAINLY HIGHER AMOUNTS IN ANY PERSISTENT BANDS.
GIVEN STRONG MERIDIONAL COMPONENT TO THE LL FLOW...HAVE CUT TEMPS
THUR-SAT...WHICH MAY NOT BE ENOUGH IF A DEEPER CENTRAL CONUS UPPER
TROUGH IS REALIZED.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING
ISSUED AT 255 AM MST SUN DEC 21 2014

VFR CONDITIONS WILL CONTINUE THROUGH 18Z ON SUNDAY. A STRONG
CDFNT MOVING INTO THE REGION SUNDAY AFTN WILL BRING SCT -SHRA AND
MVFR CIGS. CONDITIONS WILL DETERIORATE FURTHER SUNDAY
NIGHT...ESPECIALLY OVER NERN WY AND THE NRN BLKHLS AS SNOW
DEVELOPS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     SDZ024-028.

WY...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
     WYZ057.

&&

$$

SHORT TERM...13
LONG TERM...JC
AVIATION...JC







000
FXUS65 KRIW 210624
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1124 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESSIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../06Z ISSUANCE/

A TROUGH OF LOW PRESSURE WILL MOVE ACROSS MONTANA ON SUNDAY AND INTO
THE NORTHERN PLAINS SUNDAY EVENING.  A STRONG JET STREAM 120-130KTS
WILL CROSS THE WYOMING DIVIDE SOUTH OF THIS SYSTEM SUNDAY MORNING
CAUSING AREAS OF MDT-SVR TURBULENCE...LLWS OVER SHALLOW CENTRAL
BASIN INVERSIONS...AND STRONG SFC WINDS FROM VCNTY SOUTH PASS TO
VCNTY KCPR AND SOUTH ALONG THE INTERSTATE 80 CORRIDOR.  THE LEE
SLOPES ALONG THE DIVIDE AND BIGHORN RANGE WILL LIKELY REMAIN MOSTLY
OBSCURE ABOVE 9KFT.  A STRONG NW FLOW WILL FOLLOW THIS SYSTEM SUNDAY
NIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG THE FRONT
ACROSS THE LOWER ELEVATIONS SUNDAY EVENING...ESPECIALLY VCNTY AND
EAST OF INTERSTATE 25.  DRIER AIR PREVAIL NW-SE BUT GUSTY NW SFC
WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 0Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA SUNDAY AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH SUNDAY EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.


&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STORM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...AEM
FIRE WEATHER...C.BAKER











000
FXUS65 KRIW 210624
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1124 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESSIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../06Z ISSUANCE/

A TROUGH OF LOW PRESSURE WILL MOVE ACROSS MONTANA ON SUNDAY AND INTO
THE NORTHERN PLAINS SUNDAY EVENING.  A STRONG JET STREAM 120-130KTS
WILL CROSS THE WYOMING DIVIDE SOUTH OF THIS SYSTEM SUNDAY MORNING
CAUSING AREAS OF MDT-SVR TURBULENCE...LLWS OVER SHALLOW CENTRAL
BASIN INVERSIONS...AND STRONG SFC WINDS FROM VCNTY SOUTH PASS TO
VCNTY KCPR AND SOUTH ALONG THE INTERSTATE 80 CORRIDOR.  THE LEE
SLOPES ALONG THE DIVIDE AND BIGHORN RANGE WILL LIKELY REMAIN MOSTLY
OBSCURE ABOVE 9KFT.  A STRONG NW FLOW WILL FOLLOW THIS SYSTEM SUNDAY
NIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG THE FRONT
ACROSS THE LOWER ELEVATIONS SUNDAY EVENING...ESPECIALLY VCNTY AND
EAST OF INTERSTATE 25.  DRIER AIR PREVAIL NW-SE BUT GUSTY NW SFC
WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 0Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA SUNDAY AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH SUNDAY EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.


&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STORM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...AEM
FIRE WEATHER...C.BAKER











000
FXUS65 KRIW 210624
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1124 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESSIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../06Z ISSUANCE/

A TROUGH OF LOW PRESSURE WILL MOVE ACROSS MONTANA ON SUNDAY AND INTO
THE NORTHERN PLAINS SUNDAY EVENING.  A STRONG JET STREAM 120-130KTS
WILL CROSS THE WYOMING DIVIDE SOUTH OF THIS SYSTEM SUNDAY MORNING
CAUSING AREAS OF MDT-SVR TURBULENCE...LLWS OVER SHALLOW CENTRAL
BASIN INVERSIONS...AND STRONG SFC WINDS FROM VCNTY SOUTH PASS TO
VCNTY KCPR AND SOUTH ALONG THE INTERSTATE 80 CORRIDOR.  THE LEE
SLOPES ALONG THE DIVIDE AND BIGHORN RANGE WILL LIKELY REMAIN MOSTLY
OBSCURE ABOVE 9KFT.  A STRONG NW FLOW WILL FOLLOW THIS SYSTEM SUNDAY
NIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG THE FRONT
ACROSS THE LOWER ELEVATIONS SUNDAY EVENING...ESPECIALLY VCNTY AND
EAST OF INTERSTATE 25.  DRIER AIR PREVAIL NW-SE BUT GUSTY NW SFC
WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 0Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA SUNDAY AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH SUNDAY EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.


&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STORM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...AEM
FIRE WEATHER...C.BAKER











000
FXUS65 KRIW 210624
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1124 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESSIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../06Z ISSUANCE/

A TROUGH OF LOW PRESSURE WILL MOVE ACROSS MONTANA ON SUNDAY AND INTO
THE NORTHERN PLAINS SUNDAY EVENING.  A STRONG JET STREAM 120-130KTS
WILL CROSS THE WYOMING DIVIDE SOUTH OF THIS SYSTEM SUNDAY MORNING
CAUSING AREAS OF MDT-SVR TURBULENCE...LLWS OVER SHALLOW CENTRAL
BASIN INVERSIONS...AND STRONG SFC WINDS FROM VCNTY SOUTH PASS TO
VCNTY KCPR AND SOUTH ALONG THE INTERSTATE 80 CORRIDOR.  THE LEE
SLOPES ALONG THE DIVIDE AND BIGHORN RANGE WILL LIKELY REMAIN MOSTLY
OBSCURE ABOVE 9KFT.  A STRONG NW FLOW WILL FOLLOW THIS SYSTEM SUNDAY
NIGHT WITH ISOLD-SCT MVFR/IFR SNOW SHOWERS POSSIBLE ALONG THE FRONT
ACROSS THE LOWER ELEVATIONS SUNDAY EVENING...ESPECIALLY VCNTY AND
EAST OF INTERSTATE 25.  DRIER AIR PREVAIL NW-SE BUT GUSTY NW SFC
WINDS WILL REMAIN AFTER 06Z MONDAY.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

WIDESPREAD IFR...AREAS OF LIFR CONDITIONS IN SN/BLSN WITH MTN
OBSCURED ARE EXPECTED VCNTY AND NORTH OF A KEVW-20SM SW KLND LINE
THROUGH 0Z MONDAY.  STRONG MTN TOP WINDS WILL ALSO RESULT IN AREAS
MDT-SVR TURBULENCE AND LLWS.  A COLD FRONT WILL PUSH SOUTH ACROSS
THE AREA SUNDAY AFTERNOON...AND ACROSS INTERSTATE 80 00Z-03Z
SUNDAY.  THE FRONT WILL SPREAD NMRS MVFR/IFR -SHSN SOUTH ALONG
I-80...VCNTY KRKS...THROUGH SUNDAY EVENING.  DRIER AIR AND IMPROVING
CONDITIONS WILL PREVAIL BEHIND THE FRONT FROM NW-SE 06Z-12Z MONDAY.


&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STORM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...AEM
FIRE WEATHER...C.BAKER











000
FXUS65 KCYS 210523
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1023 PM MST SAT DEC 20 2014

.UPDATE...
ISSUED AT 913 PM MST SAT DEC 20 2014

FORECAST IS FAIRLY STRAIGHT FORWARD TONIGHT BUT THAT WILL NOT BE
THE CASE THE NEXT FEW DAYS. FOR TONIGHT SOME LIGHT SNOW WILL OCCUR
IN THE SNOWY AND SIERRA MADRE RANGES. ACCUMULATIONS WILL BE
MINIMAL WITH A FEW INCHES THROUGH THE NIGHT. SOME LIGHT SNOW WILL
ALSO OCCUR OUTSIDE OF THE MOUNTAINS OVER PORTIONS OF CARBON AND
ALBANY COUNTIES BUT ANY ACCUMULATIONS WILL GENERALLY BE LESS THAN
ONE INCH.

WINDS WILL INCREASE OVERNIGHT...ESPECIALLY OVER WIND PRONE AREAS
OF SOUTHEAST WYOMING. MODELS ARE SLIGHTLY SLOWER WITH THE ONSET OF
THE WINDS BUT SHOULD SEE ARLINGTON AND BORDEAUX APPROACHING WARNING
CRITERIA TOWARD SUNRISE WITH THE SOUTHERN LARAMIE REACHING
CRITERIA SHORTLY THEREAFTER.

THE MAIN QUESTION FOR SUNDAY INTO MONDAY IS WHAT TYPE OF HEADLINES
SHOULD BE ISSUED. THE PROBLEM IS DETERMINING IMPACTS FROM WIND AND
SNOW...AND JUST HOW MUCH SNOW WILL FALL AND HOW STRONG WITH WINDS
WILL BE. MODELS INDICATE VERY STRONG WINDS OFF THE SURFACE SUNDAY
BUT ALSO A RELATIVELY STRONG INVERSION INITIALLY. THAT INVERSION
WILL BREAK DOWN INTO SUNDAY NIGHT WITH SATURATED SOUNDINGS AND
STEEP LAPSE RATES IN THE BOUNDARY LAYER WHICH IS FAVORABLE FOR
WINDS MIXING TO THE SURFACE AND EVEN SOME CONVECTIVE TYPE WIND
GUSTS. SNOW WILL LIKELY ALSO BE FALLING AT THIS TIME. THE
QUESTION IS HOW HEAVY THE SNOW WILL BE AND HOW MUCH WILL FALL.
CERTAINLY STEEP LAPSE RATES SUGGEST THE POTENTIAL FOR AT LEAST A
SHORT PERIOD OF HEAVY SNOW. IT IS VERY POSSIBLE NEAR BLIZZARD
CONDITIONS WILL EXIST AT TIMES FOR PORTIONS OF CARBON AND ALBANY
COUNTIES LATE SUNDAY AFTERNOON THROUGH THE EVENING HOURS. AT THIS
TIME WATCHES AND WARNINGS REMAIN IN PLACE BUT LIKE
USUAL...HEADLINES WILL EVOLVE OVER THE NEXT 24 HOURS...ESPECIALLY
GIVEN THE CHALLENGES WITH THIS SYSTEM. PLEASE STAY TUNED FOR
WEATHER UPDATES WITH THE CHANGING SITUATION.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 1253 PM MST SAT DEC 20 2014

CHALLENGING FORECAST AHEAD WITH STRONG WINDS...VERY HEAVY SNOW AND
COMBINATION OF WIND AND SNOW THE FORECAST CHALLENGES TONIGHT
THROUGH MONDAY.

CURRENTLY...PRETTY TRANQUIL OUT ACROSS THE CWFA SO FAR TODAY. HIGH
PRESSURE OVER NORTHWESTERN COLORADO THIS AFTERNOON WITH PARTLY
CLOUDY SKIES EAST OF THE LARAMIE RANGE AND MOSTLY CLOUDY WEST.
PACIFIC STORM SYSTEM JUST OFFSHORE OF WASHINGTON STATE THIS
AFTERNOON CONTINUES TO MOVE SOUTHEAST TOWARDS THE COAST.

SHORT TERM GUIDANCE REALLY BEGINS TO SHOW AN UPTICK ON WINDS THIS
EVENING. GFS 700MB WINDS INCREASE TO 55KTS ACROSS CARBON AND
ALBANY COUNTIES WITH 700MB CRAIG TO CASPER HEIGHT GRADIENTS
INCREASING TO 70MTRS AT 06Z. THE NAM WRKHGT PRODUCT A LITTLE
SLOWER ON HEIGHT GRADIENTS INCREASING...SHOWING 850/700MB
GRADIENTS BOTH ABOVE 60MTRS BY 09Z. WILL KEEP THE CURRENT WIND
WARNINGS GOING AS THEY ARE FOR NOW.

BY 12Z SUNDAY...GFS 700MB WINDS REALLY BEGIN CRANKING WITH
65-70KTS WEST OF THE LARAMIE RANGE. PACIFIC LOW PRESSURE SYSTEM
MOVING INTO WESTERN WYOMING AT THAT TIME. WINDS SHOULD BEGIN TO
BECOME STRONG FAIRLY WIDESPREAD BY MID MORNING WITH THE WRKHGT
PRODUCT PEAKING OUT AT 79/74MTRS ON THE 850/700MB HEIGHT GRADIENTS
BY 00Z TOMORROW AFTERNOON. THESE STRONG GRADIENTS CONTINUE INTO
MONDAY MORNING BEFORE EASING.

INCREASING CONCERN FOR POSSIBLE WINTER WEATHER EVENT ALONG THE
I-80 CORRIDOR FROM THE I-80 SUMMIT THROUGH RAWLINS FOR LATE SUNDAY
AFTERNOON THROUGH MONDAY. ALL GUIDANCE SHOWING PRECIP BECOMING
WIDESPREAD BY NOON SUNDAY AND CONTINUING INTO MONDAY MORNING. LATEST
ECMWF AND SREF MOST WIDESPREAD AND AGGRESSIVE WITH QPF
AMOUNTS...THOUGH THE NAM DOES COME IN LINE BY 00Z. COMBINATION OF
VERY STRONG WINDS AND SNOW COULD LEAD TO VERY SERIOUS DRIVING
CONDITIONS WEST OF THE LARAMIE RANGE TOMORROW EVENING INTO MONDAY.

REPLACED THE HIGH WIND WATCHES WE HAD OUT THIS MORNING FOR THE
LOWER ELEVATIONS OF ALBANY AND CARBON COUNTIES WITH A WINTER STORM
WATCH. GRANTED...WINDS ARE GOING TO BE STRONGEST IN THE AFTERNOON
AND THIS SHOULD BE THE TIME WHEN PRECIP SHOULD BE FALLING AS
RAIN...BUT IT WONT TAKE LONG FOR THE PRECIP TO TURN OVER TO SNOW.
WILL WORD THE WATCH FOR STRONG WINDS INITIALLY...THEN A
COMBINATION OF WINDS AND SNOW LATE AFTERNOON AND OVERNIGHT.

SNOWY AND SIERRA MADRE RANGE ARE GOING TO GET POUNDED IN THIS
SETUP. WILL BE ON THE LEFT FRONT QUADRANT OF A 170KT JET THROUGH
MONDAY MORNING. LATEST HPC SNOW FORECAST SHOWING 2+ FEET OF SNOW
THROUGH MONDAY. DO BELIEVE WE COULD SEE MUCH MORE IN THIS
PERSISTENT STRONG UPSLOPE EVENT. MAYBE MORE LIKE 3 FEET BEFORE ALL
IS SAID AND DONE MONDAY NIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 253 PM MST SAT DEC 20 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY THROUGH FRIDAY DUE TO
HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER WEATHER ON CHRISTMAS
DAY. EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY
TRAVEL PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REMAIN COLDER THAN NORMAL ON TUESDAY BEHIND THE
UPPER LEVEL TROUGH FORECAST TO PUSH ACROSS THE AREA TOMORROW AND
MONDAY. HIGHS IN THE 20S TO MID 30S ARE EXPECTED WITH VERY COLD
OVERNIGHT LOWS. TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS
DOWNSLOPE FLOW DEVELOPS...WITH HIGHS IN THE 30S TO LOW 40S. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS GENERALLY INDICATE A RAPIDLY
MOVING UPPER LEVEL TROUGH PUSHING INTO THE AREA. A STRONG PACIFIC
COLD FRONT IS FORECAST TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME
CHRISTMAS MORNING WITH SNOW DEVELOPING BEHIND THE FRONT. BEFORE
THAT...THERE IS THE POTENTIAL FOR A HIGH WIND EVENT ACROSS THE
WIND PRONE AREAS OF SOUTHEAST WYOMING AHEAD OF THE FRONT...BUT
CONDITIONS WILL LIKELY NOT LAST TOO LONG AND MAINLY AFFECT
MOTORISTS WITH LARGER VEHICLES. AS FOR SNOW...THERE IS A LOW
PROBABILITY FOR WINTER STORM CONDITIONS ON CHRISTMAS DAY DUE TO
HOW PROGRESSIVE THIS SYSTEM IS. HOWEVER...THE GEM AND ECMWF DO
HINT AT A SLOWER SOLUTION AS THE STORM DIGS FURTHER TO THE SOUTH.
THE GFS ON THE OTHER HAND IS VERY PROGRESSIVE...WITH SNOW
STRUGGLING TO DEVELOP OVER MOST OF THE HIGH PLAINS MAINLY DUE TO
THE LLVL UPSLOPE FLOW DEVELOPING MUCH LATER IN THE DAY WHEN THE
EVENT IS PRACTICALLY OVER. ALTHOUGH THERE IS A POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE AREA...CONFIDENCE IS RATHER LOW AT
THIS TIME WITH THE MOST FAVORABLE LOCATIONS BEING IN THE MOUNTAINS
AND WELL NORTH OF I80 ACROSS THE HIGH PLAINS. AT THIS TIME...IT
APPEARS THE I80 CORRIDOR MAY HAVE TOO MUCH DRIER DOWNSLOPE FLOW TO
DEAL WITH TO GET ANY SUBSTANTIAL SNOW ACCUMULATIONS GOING. BUT
THIS MAY QUICKLY CHANGE OVER THE NEXT FEW DAYS. KEPT POP BETWEEN
25 TO 35 PERCENT ACROSS THE HIGH PLAINS INCLUDING THE EASTERN I80
CORRIDOR...AND CLOSER TO 50 PERCENT WEST OF THE LARAMIE RANGE.
INCREASED POP IN THE MOUNTAINS WHICH WILL HAVE THE BEST POTENTIAL
TO SEE MODERATE SNOW ACCUMULATIONS WITH THIS SYSTEM. IN EITHER
CASE...MUCH COLDER TEMPERATURES ARE EXPECTED FOR LATER NEXT WEEK.
EARLY MORNING HIGHS BETWEEN 35 TO 45 ON CHRISTMAS DAY WILL RAPIDLY
LOWER INTO THE 20S THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL
LIKELY BE BELOW FREEZING FOR FRIDAY AND SATURDAY AS NORTHERLY FLOW
ALOFT STAYS OVER THE ROCKY MOUNTAIN REGION.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1002 PM MST SAT DEC 20 2014

MANY AVIATION CONCERNS FOR AREAS ALONG AND WEST OF THE LARAMIE
RANGE SUNDAY AND MONDAY. WINDS WILL BE VERY STRONG ACROSS THIS
AREA ESPECIALLY SUNDAY INTO SUNDAY NIGHT. IN ADDITION SNOW WILL
FALL ACROSS THIS AREA WITH HEAVY SNOW ACROSS THE MOUNTAINS. THE
SNOWY AND SIERRA MADRE RANGES WILL HAVE OBSCURED MOUNTAINS WITH
MOUNTAIN TOPS OBSCURED IN THE LARAMIE RANGE AND MOUNTAINS
OBSCURED AT TIMES. EAST OF THE LARAMIE RANGE CONDITIONS WILL
MAINLY BE VFR THROUGH THE TAF PERIOD BUT LOW CLOUDS WILL INCREASE
INTO SUNDAY NIGHT.

&&

.FIRE WEATHER...
ISSUED AT 1253 PM MST SAT DEC 20 2014

NO FIRE WEATHER ISSUES EXPECTED THIS WEEKEND. BREEZY AND MAINLY DRY
CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS THIS AFTERNOON...BUT
THINGS BEGIN TO CHANGE TONIGHT THROUGH THE BEGINNING OF NEXT WEEK. STRONG
WESTERLY WINDS AND SIGNIFICANT MOUNTAIN SNOWFALL WILL RETURN
TONIGHT AND CONTINUE THROUGH MONDAY...WITH WINTER STORM WARNINGS
IN EFFECT FOR THE SNOWY AND SIERRA MADRE RANGES FOR TWO TO THREE FEET
OF SNOW. HIGH WIND WARNINGS ARE IN EFFECT FOR THE WIND PRONE AREAS
OF SOUTHEAST WYOMING FROM LATE TONIGHT THROUGH SUNDAY EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST SUNDAY NIGHT
     FOR WYZ116-117.

     WINTER STORM WATCH FROM 8 AM MST SUNDAY THROUGH MONDAY MORNING
     FOR WYZ109-111-113-115.

     HIGH WIND WARNING UNTIL MIDNIGHT MST SUNDAY NIGHT FOR WYZ106-110.

     HIGH WIND WATCH FROM 8 AM MST SUNDAY THROUGH SUNDAY EVENING FOR
     WYZ104-105.

NE...NONE.

&&

$$

UPDATE...SML
SHORT TERM...GCC
LONG TERM...TJT
AVIATION...SML
FIRE WEATHER...GCC



000
FXUS65 KCYS 210523
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1023 PM MST SAT DEC 20 2014

.UPDATE...
ISSUED AT 913 PM MST SAT DEC 20 2014

FORECAST IS FAIRLY STRAIGHT FORWARD TONIGHT BUT THAT WILL NOT BE
THE CASE THE NEXT FEW DAYS. FOR TONIGHT SOME LIGHT SNOW WILL OCCUR
IN THE SNOWY AND SIERRA MADRE RANGES. ACCUMULATIONS WILL BE
MINIMAL WITH A FEW INCHES THROUGH THE NIGHT. SOME LIGHT SNOW WILL
ALSO OCCUR OUTSIDE OF THE MOUNTAINS OVER PORTIONS OF CARBON AND
ALBANY COUNTIES BUT ANY ACCUMULATIONS WILL GENERALLY BE LESS THAN
ONE INCH.

WINDS WILL INCREASE OVERNIGHT...ESPECIALLY OVER WIND PRONE AREAS
OF SOUTHEAST WYOMING. MODELS ARE SLIGHTLY SLOWER WITH THE ONSET OF
THE WINDS BUT SHOULD SEE ARLINGTON AND BORDEAUX APPROACHING WARNING
CRITERIA TOWARD SUNRISE WITH THE SOUTHERN LARAMIE REACHING
CRITERIA SHORTLY THEREAFTER.

THE MAIN QUESTION FOR SUNDAY INTO MONDAY IS WHAT TYPE OF HEADLINES
SHOULD BE ISSUED. THE PROBLEM IS DETERMINING IMPACTS FROM WIND AND
SNOW...AND JUST HOW MUCH SNOW WILL FALL AND HOW STRONG WITH WINDS
WILL BE. MODELS INDICATE VERY STRONG WINDS OFF THE SURFACE SUNDAY
BUT ALSO A RELATIVELY STRONG INVERSION INITIALLY. THAT INVERSION
WILL BREAK DOWN INTO SUNDAY NIGHT WITH SATURATED SOUNDINGS AND
STEEP LAPSE RATES IN THE BOUNDARY LAYER WHICH IS FAVORABLE FOR
WINDS MIXING TO THE SURFACE AND EVEN SOME CONVECTIVE TYPE WIND
GUSTS. SNOW WILL LIKELY ALSO BE FALLING AT THIS TIME. THE
QUESTION IS HOW HEAVY THE SNOW WILL BE AND HOW MUCH WILL FALL.
CERTAINLY STEEP LAPSE RATES SUGGEST THE POTENTIAL FOR AT LEAST A
SHORT PERIOD OF HEAVY SNOW. IT IS VERY POSSIBLE NEAR BLIZZARD
CONDITIONS WILL EXIST AT TIMES FOR PORTIONS OF CARBON AND ALBANY
COUNTIES LATE SUNDAY AFTERNOON THROUGH THE EVENING HOURS. AT THIS
TIME WATCHES AND WARNINGS REMAIN IN PLACE BUT LIKE
USUAL...HEADLINES WILL EVOLVE OVER THE NEXT 24 HOURS...ESPECIALLY
GIVEN THE CHALLENGES WITH THIS SYSTEM. PLEASE STAY TUNED FOR
WEATHER UPDATES WITH THE CHANGING SITUATION.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 1253 PM MST SAT DEC 20 2014

CHALLENGING FORECAST AHEAD WITH STRONG WINDS...VERY HEAVY SNOW AND
COMBINATION OF WIND AND SNOW THE FORECAST CHALLENGES TONIGHT
THROUGH MONDAY.

CURRENTLY...PRETTY TRANQUIL OUT ACROSS THE CWFA SO FAR TODAY. HIGH
PRESSURE OVER NORTHWESTERN COLORADO THIS AFTERNOON WITH PARTLY
CLOUDY SKIES EAST OF THE LARAMIE RANGE AND MOSTLY CLOUDY WEST.
PACIFIC STORM SYSTEM JUST OFFSHORE OF WASHINGTON STATE THIS
AFTERNOON CONTINUES TO MOVE SOUTHEAST TOWARDS THE COAST.

SHORT TERM GUIDANCE REALLY BEGINS TO SHOW AN UPTICK ON WINDS THIS
EVENING. GFS 700MB WINDS INCREASE TO 55KTS ACROSS CARBON AND
ALBANY COUNTIES WITH 700MB CRAIG TO CASPER HEIGHT GRADIENTS
INCREASING TO 70MTRS AT 06Z. THE NAM WRKHGT PRODUCT A LITTLE
SLOWER ON HEIGHT GRADIENTS INCREASING...SHOWING 850/700MB
GRADIENTS BOTH ABOVE 60MTRS BY 09Z. WILL KEEP THE CURRENT WIND
WARNINGS GOING AS THEY ARE FOR NOW.

BY 12Z SUNDAY...GFS 700MB WINDS REALLY BEGIN CRANKING WITH
65-70KTS WEST OF THE LARAMIE RANGE. PACIFIC LOW PRESSURE SYSTEM
MOVING INTO WESTERN WYOMING AT THAT TIME. WINDS SHOULD BEGIN TO
BECOME STRONG FAIRLY WIDESPREAD BY MID MORNING WITH THE WRKHGT
PRODUCT PEAKING OUT AT 79/74MTRS ON THE 850/700MB HEIGHT GRADIENTS
BY 00Z TOMORROW AFTERNOON. THESE STRONG GRADIENTS CONTINUE INTO
MONDAY MORNING BEFORE EASING.

INCREASING CONCERN FOR POSSIBLE WINTER WEATHER EVENT ALONG THE
I-80 CORRIDOR FROM THE I-80 SUMMIT THROUGH RAWLINS FOR LATE SUNDAY
AFTERNOON THROUGH MONDAY. ALL GUIDANCE SHOWING PRECIP BECOMING
WIDESPREAD BY NOON SUNDAY AND CONTINUING INTO MONDAY MORNING. LATEST
ECMWF AND SREF MOST WIDESPREAD AND AGGRESSIVE WITH QPF
AMOUNTS...THOUGH THE NAM DOES COME IN LINE BY 00Z. COMBINATION OF
VERY STRONG WINDS AND SNOW COULD LEAD TO VERY SERIOUS DRIVING
CONDITIONS WEST OF THE LARAMIE RANGE TOMORROW EVENING INTO MONDAY.

REPLACED THE HIGH WIND WATCHES WE HAD OUT THIS MORNING FOR THE
LOWER ELEVATIONS OF ALBANY AND CARBON COUNTIES WITH A WINTER STORM
WATCH. GRANTED...WINDS ARE GOING TO BE STRONGEST IN THE AFTERNOON
AND THIS SHOULD BE THE TIME WHEN PRECIP SHOULD BE FALLING AS
RAIN...BUT IT WONT TAKE LONG FOR THE PRECIP TO TURN OVER TO SNOW.
WILL WORD THE WATCH FOR STRONG WINDS INITIALLY...THEN A
COMBINATION OF WINDS AND SNOW LATE AFTERNOON AND OVERNIGHT.

SNOWY AND SIERRA MADRE RANGE ARE GOING TO GET POUNDED IN THIS
SETUP. WILL BE ON THE LEFT FRONT QUADRANT OF A 170KT JET THROUGH
MONDAY MORNING. LATEST HPC SNOW FORECAST SHOWING 2+ FEET OF SNOW
THROUGH MONDAY. DO BELIEVE WE COULD SEE MUCH MORE IN THIS
PERSISTENT STRONG UPSLOPE EVENT. MAYBE MORE LIKE 3 FEET BEFORE ALL
IS SAID AND DONE MONDAY NIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 253 PM MST SAT DEC 20 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY THROUGH FRIDAY DUE TO
HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER WEATHER ON CHRISTMAS
DAY. EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY
TRAVEL PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REMAIN COLDER THAN NORMAL ON TUESDAY BEHIND THE
UPPER LEVEL TROUGH FORECAST TO PUSH ACROSS THE AREA TOMORROW AND
MONDAY. HIGHS IN THE 20S TO MID 30S ARE EXPECTED WITH VERY COLD
OVERNIGHT LOWS. TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS
DOWNSLOPE FLOW DEVELOPS...WITH HIGHS IN THE 30S TO LOW 40S. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS GENERALLY INDICATE A RAPIDLY
MOVING UPPER LEVEL TROUGH PUSHING INTO THE AREA. A STRONG PACIFIC
COLD FRONT IS FORECAST TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME
CHRISTMAS MORNING WITH SNOW DEVELOPING BEHIND THE FRONT. BEFORE
THAT...THERE IS THE POTENTIAL FOR A HIGH WIND EVENT ACROSS THE
WIND PRONE AREAS OF SOUTHEAST WYOMING AHEAD OF THE FRONT...BUT
CONDITIONS WILL LIKELY NOT LAST TOO LONG AND MAINLY AFFECT
MOTORISTS WITH LARGER VEHICLES. AS FOR SNOW...THERE IS A LOW
PROBABILITY FOR WINTER STORM CONDITIONS ON CHRISTMAS DAY DUE TO
HOW PROGRESSIVE THIS SYSTEM IS. HOWEVER...THE GEM AND ECMWF DO
HINT AT A SLOWER SOLUTION AS THE STORM DIGS FURTHER TO THE SOUTH.
THE GFS ON THE OTHER HAND IS VERY PROGRESSIVE...WITH SNOW
STRUGGLING TO DEVELOP OVER MOST OF THE HIGH PLAINS MAINLY DUE TO
THE LLVL UPSLOPE FLOW DEVELOPING MUCH LATER IN THE DAY WHEN THE
EVENT IS PRACTICALLY OVER. ALTHOUGH THERE IS A POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE AREA...CONFIDENCE IS RATHER LOW AT
THIS TIME WITH THE MOST FAVORABLE LOCATIONS BEING IN THE MOUNTAINS
AND WELL NORTH OF I80 ACROSS THE HIGH PLAINS. AT THIS TIME...IT
APPEARS THE I80 CORRIDOR MAY HAVE TOO MUCH DRIER DOWNSLOPE FLOW TO
DEAL WITH TO GET ANY SUBSTANTIAL SNOW ACCUMULATIONS GOING. BUT
THIS MAY QUICKLY CHANGE OVER THE NEXT FEW DAYS. KEPT POP BETWEEN
25 TO 35 PERCENT ACROSS THE HIGH PLAINS INCLUDING THE EASTERN I80
CORRIDOR...AND CLOSER TO 50 PERCENT WEST OF THE LARAMIE RANGE.
INCREASED POP IN THE MOUNTAINS WHICH WILL HAVE THE BEST POTENTIAL
TO SEE MODERATE SNOW ACCUMULATIONS WITH THIS SYSTEM. IN EITHER
CASE...MUCH COLDER TEMPERATURES ARE EXPECTED FOR LATER NEXT WEEK.
EARLY MORNING HIGHS BETWEEN 35 TO 45 ON CHRISTMAS DAY WILL RAPIDLY
LOWER INTO THE 20S THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL
LIKELY BE BELOW FREEZING FOR FRIDAY AND SATURDAY AS NORTHERLY FLOW
ALOFT STAYS OVER THE ROCKY MOUNTAIN REGION.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1002 PM MST SAT DEC 20 2014

MANY AVIATION CONCERNS FOR AREAS ALONG AND WEST OF THE LARAMIE
RANGE SUNDAY AND MONDAY. WINDS WILL BE VERY STRONG ACROSS THIS
AREA ESPECIALLY SUNDAY INTO SUNDAY NIGHT. IN ADDITION SNOW WILL
FALL ACROSS THIS AREA WITH HEAVY SNOW ACROSS THE MOUNTAINS. THE
SNOWY AND SIERRA MADRE RANGES WILL HAVE OBSCURED MOUNTAINS WITH
MOUNTAIN TOPS OBSCURED IN THE LARAMIE RANGE AND MOUNTAINS
OBSCURED AT TIMES. EAST OF THE LARAMIE RANGE CONDITIONS WILL
MAINLY BE VFR THROUGH THE TAF PERIOD BUT LOW CLOUDS WILL INCREASE
INTO SUNDAY NIGHT.

&&

.FIRE WEATHER...
ISSUED AT 1253 PM MST SAT DEC 20 2014

NO FIRE WEATHER ISSUES EXPECTED THIS WEEKEND. BREEZY AND MAINLY DRY
CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS THIS AFTERNOON...BUT
THINGS BEGIN TO CHANGE TONIGHT THROUGH THE BEGINNING OF NEXT WEEK. STRONG
WESTERLY WINDS AND SIGNIFICANT MOUNTAIN SNOWFALL WILL RETURN
TONIGHT AND CONTINUE THROUGH MONDAY...WITH WINTER STORM WARNINGS
IN EFFECT FOR THE SNOWY AND SIERRA MADRE RANGES FOR TWO TO THREE FEET
OF SNOW. HIGH WIND WARNINGS ARE IN EFFECT FOR THE WIND PRONE AREAS
OF SOUTHEAST WYOMING FROM LATE TONIGHT THROUGH SUNDAY EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST SUNDAY NIGHT
     FOR WYZ116-117.

     WINTER STORM WATCH FROM 8 AM MST SUNDAY THROUGH MONDAY MORNING
     FOR WYZ109-111-113-115.

     HIGH WIND WARNING UNTIL MIDNIGHT MST SUNDAY NIGHT FOR WYZ106-110.

     HIGH WIND WATCH FROM 8 AM MST SUNDAY THROUGH SUNDAY EVENING FOR
     WYZ104-105.

NE...NONE.

&&

$$

UPDATE...SML
SHORT TERM...GCC
LONG TERM...TJT
AVIATION...SML
FIRE WEATHER...GCC



000
FXUS65 KCYS 210523
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1023 PM MST SAT DEC 20 2014

.UPDATE...
ISSUED AT 913 PM MST SAT DEC 20 2014

FORECAST IS FAIRLY STRAIGHT FORWARD TONIGHT BUT THAT WILL NOT BE
THE CASE THE NEXT FEW DAYS. FOR TONIGHT SOME LIGHT SNOW WILL OCCUR
IN THE SNOWY AND SIERRA MADRE RANGES. ACCUMULATIONS WILL BE
MINIMAL WITH A FEW INCHES THROUGH THE NIGHT. SOME LIGHT SNOW WILL
ALSO OCCUR OUTSIDE OF THE MOUNTAINS OVER PORTIONS OF CARBON AND
ALBANY COUNTIES BUT ANY ACCUMULATIONS WILL GENERALLY BE LESS THAN
ONE INCH.

WINDS WILL INCREASE OVERNIGHT...ESPECIALLY OVER WIND PRONE AREAS
OF SOUTHEAST WYOMING. MODELS ARE SLIGHTLY SLOWER WITH THE ONSET OF
THE WINDS BUT SHOULD SEE ARLINGTON AND BORDEAUX APPROACHING WARNING
CRITERIA TOWARD SUNRISE WITH THE SOUTHERN LARAMIE REACHING
CRITERIA SHORTLY THEREAFTER.

THE MAIN QUESTION FOR SUNDAY INTO MONDAY IS WHAT TYPE OF HEADLINES
SHOULD BE ISSUED. THE PROBLEM IS DETERMINING IMPACTS FROM WIND AND
SNOW...AND JUST HOW MUCH SNOW WILL FALL AND HOW STRONG WITH WINDS
WILL BE. MODELS INDICATE VERY STRONG WINDS OFF THE SURFACE SUNDAY
BUT ALSO A RELATIVELY STRONG INVERSION INITIALLY. THAT INVERSION
WILL BREAK DOWN INTO SUNDAY NIGHT WITH SATURATED SOUNDINGS AND
STEEP LAPSE RATES IN THE BOUNDARY LAYER WHICH IS FAVORABLE FOR
WINDS MIXING TO THE SURFACE AND EVEN SOME CONVECTIVE TYPE WIND
GUSTS. SNOW WILL LIKELY ALSO BE FALLING AT THIS TIME. THE
QUESTION IS HOW HEAVY THE SNOW WILL BE AND HOW MUCH WILL FALL.
CERTAINLY STEEP LAPSE RATES SUGGEST THE POTENTIAL FOR AT LEAST A
SHORT PERIOD OF HEAVY SNOW. IT IS VERY POSSIBLE NEAR BLIZZARD
CONDITIONS WILL EXIST AT TIMES FOR PORTIONS OF CARBON AND ALBANY
COUNTIES LATE SUNDAY AFTERNOON THROUGH THE EVENING HOURS. AT THIS
TIME WATCHES AND WARNINGS REMAIN IN PLACE BUT LIKE
USUAL...HEADLINES WILL EVOLVE OVER THE NEXT 24 HOURS...ESPECIALLY
GIVEN THE CHALLENGES WITH THIS SYSTEM. PLEASE STAY TUNED FOR
WEATHER UPDATES WITH THE CHANGING SITUATION.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 1253 PM MST SAT DEC 20 2014

CHALLENGING FORECAST AHEAD WITH STRONG WINDS...VERY HEAVY SNOW AND
COMBINATION OF WIND AND SNOW THE FORECAST CHALLENGES TONIGHT
THROUGH MONDAY.

CURRENTLY...PRETTY TRANQUIL OUT ACROSS THE CWFA SO FAR TODAY. HIGH
PRESSURE OVER NORTHWESTERN COLORADO THIS AFTERNOON WITH PARTLY
CLOUDY SKIES EAST OF THE LARAMIE RANGE AND MOSTLY CLOUDY WEST.
PACIFIC STORM SYSTEM JUST OFFSHORE OF WASHINGTON STATE THIS
AFTERNOON CONTINUES TO MOVE SOUTHEAST TOWARDS THE COAST.

SHORT TERM GUIDANCE REALLY BEGINS TO SHOW AN UPTICK ON WINDS THIS
EVENING. GFS 700MB WINDS INCREASE TO 55KTS ACROSS CARBON AND
ALBANY COUNTIES WITH 700MB CRAIG TO CASPER HEIGHT GRADIENTS
INCREASING TO 70MTRS AT 06Z. THE NAM WRKHGT PRODUCT A LITTLE
SLOWER ON HEIGHT GRADIENTS INCREASING...SHOWING 850/700MB
GRADIENTS BOTH ABOVE 60MTRS BY 09Z. WILL KEEP THE CURRENT WIND
WARNINGS GOING AS THEY ARE FOR NOW.

BY 12Z SUNDAY...GFS 700MB WINDS REALLY BEGIN CRANKING WITH
65-70KTS WEST OF THE LARAMIE RANGE. PACIFIC LOW PRESSURE SYSTEM
MOVING INTO WESTERN WYOMING AT THAT TIME. WINDS SHOULD BEGIN TO
BECOME STRONG FAIRLY WIDESPREAD BY MID MORNING WITH THE WRKHGT
PRODUCT PEAKING OUT AT 79/74MTRS ON THE 850/700MB HEIGHT GRADIENTS
BY 00Z TOMORROW AFTERNOON. THESE STRONG GRADIENTS CONTINUE INTO
MONDAY MORNING BEFORE EASING.

INCREASING CONCERN FOR POSSIBLE WINTER WEATHER EVENT ALONG THE
I-80 CORRIDOR FROM THE I-80 SUMMIT THROUGH RAWLINS FOR LATE SUNDAY
AFTERNOON THROUGH MONDAY. ALL GUIDANCE SHOWING PRECIP BECOMING
WIDESPREAD BY NOON SUNDAY AND CONTINUING INTO MONDAY MORNING. LATEST
ECMWF AND SREF MOST WIDESPREAD AND AGGRESSIVE WITH QPF
AMOUNTS...THOUGH THE NAM DOES COME IN LINE BY 00Z. COMBINATION OF
VERY STRONG WINDS AND SNOW COULD LEAD TO VERY SERIOUS DRIVING
CONDITIONS WEST OF THE LARAMIE RANGE TOMORROW EVENING INTO MONDAY.

REPLACED THE HIGH WIND WATCHES WE HAD OUT THIS MORNING FOR THE
LOWER ELEVATIONS OF ALBANY AND CARBON COUNTIES WITH A WINTER STORM
WATCH. GRANTED...WINDS ARE GOING TO BE STRONGEST IN THE AFTERNOON
AND THIS SHOULD BE THE TIME WHEN PRECIP SHOULD BE FALLING AS
RAIN...BUT IT WONT TAKE LONG FOR THE PRECIP TO TURN OVER TO SNOW.
WILL WORD THE WATCH FOR STRONG WINDS INITIALLY...THEN A
COMBINATION OF WINDS AND SNOW LATE AFTERNOON AND OVERNIGHT.

SNOWY AND SIERRA MADRE RANGE ARE GOING TO GET POUNDED IN THIS
SETUP. WILL BE ON THE LEFT FRONT QUADRANT OF A 170KT JET THROUGH
MONDAY MORNING. LATEST HPC SNOW FORECAST SHOWING 2+ FEET OF SNOW
THROUGH MONDAY. DO BELIEVE WE COULD SEE MUCH MORE IN THIS
PERSISTENT STRONG UPSLOPE EVENT. MAYBE MORE LIKE 3 FEET BEFORE ALL
IS SAID AND DONE MONDAY NIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 253 PM MST SAT DEC 20 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY THROUGH FRIDAY DUE TO
HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER WEATHER ON CHRISTMAS
DAY. EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY
TRAVEL PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REMAIN COLDER THAN NORMAL ON TUESDAY BEHIND THE
UPPER LEVEL TROUGH FORECAST TO PUSH ACROSS THE AREA TOMORROW AND
MONDAY. HIGHS IN THE 20S TO MID 30S ARE EXPECTED WITH VERY COLD
OVERNIGHT LOWS. TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS
DOWNSLOPE FLOW DEVELOPS...WITH HIGHS IN THE 30S TO LOW 40S. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS GENERALLY INDICATE A RAPIDLY
MOVING UPPER LEVEL TROUGH PUSHING INTO THE AREA. A STRONG PACIFIC
COLD FRONT IS FORECAST TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME
CHRISTMAS MORNING WITH SNOW DEVELOPING BEHIND THE FRONT. BEFORE
THAT...THERE IS THE POTENTIAL FOR A HIGH WIND EVENT ACROSS THE
WIND PRONE AREAS OF SOUTHEAST WYOMING AHEAD OF THE FRONT...BUT
CONDITIONS WILL LIKELY NOT LAST TOO LONG AND MAINLY AFFECT
MOTORISTS WITH LARGER VEHICLES. AS FOR SNOW...THERE IS A LOW
PROBABILITY FOR WINTER STORM CONDITIONS ON CHRISTMAS DAY DUE TO
HOW PROGRESSIVE THIS SYSTEM IS. HOWEVER...THE GEM AND ECMWF DO
HINT AT A SLOWER SOLUTION AS THE STORM DIGS FURTHER TO THE SOUTH.
THE GFS ON THE OTHER HAND IS VERY PROGRESSIVE...WITH SNOW
STRUGGLING TO DEVELOP OVER MOST OF THE HIGH PLAINS MAINLY DUE TO
THE LLVL UPSLOPE FLOW DEVELOPING MUCH LATER IN THE DAY WHEN THE
EVENT IS PRACTICALLY OVER. ALTHOUGH THERE IS A POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE AREA...CONFIDENCE IS RATHER LOW AT
THIS TIME WITH THE MOST FAVORABLE LOCATIONS BEING IN THE MOUNTAINS
AND WELL NORTH OF I80 ACROSS THE HIGH PLAINS. AT THIS TIME...IT
APPEARS THE I80 CORRIDOR MAY HAVE TOO MUCH DRIER DOWNSLOPE FLOW TO
DEAL WITH TO GET ANY SUBSTANTIAL SNOW ACCUMULATIONS GOING. BUT
THIS MAY QUICKLY CHANGE OVER THE NEXT FEW DAYS. KEPT POP BETWEEN
25 TO 35 PERCENT ACROSS THE HIGH PLAINS INCLUDING THE EASTERN I80
CORRIDOR...AND CLOSER TO 50 PERCENT WEST OF THE LARAMIE RANGE.
INCREASED POP IN THE MOUNTAINS WHICH WILL HAVE THE BEST POTENTIAL
TO SEE MODERATE SNOW ACCUMULATIONS WITH THIS SYSTEM. IN EITHER
CASE...MUCH COLDER TEMPERATURES ARE EXPECTED FOR LATER NEXT WEEK.
EARLY MORNING HIGHS BETWEEN 35 TO 45 ON CHRISTMAS DAY WILL RAPIDLY
LOWER INTO THE 20S THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL
LIKELY BE BELOW FREEZING FOR FRIDAY AND SATURDAY AS NORTHERLY FLOW
ALOFT STAYS OVER THE ROCKY MOUNTAIN REGION.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1002 PM MST SAT DEC 20 2014

MANY AVIATION CONCERNS FOR AREAS ALONG AND WEST OF THE LARAMIE
RANGE SUNDAY AND MONDAY. WINDS WILL BE VERY STRONG ACROSS THIS
AREA ESPECIALLY SUNDAY INTO SUNDAY NIGHT. IN ADDITION SNOW WILL
FALL ACROSS THIS AREA WITH HEAVY SNOW ACROSS THE MOUNTAINS. THE
SNOWY AND SIERRA MADRE RANGES WILL HAVE OBSCURED MOUNTAINS WITH
MOUNTAIN TOPS OBSCURED IN THE LARAMIE RANGE AND MOUNTAINS
OBSCURED AT TIMES. EAST OF THE LARAMIE RANGE CONDITIONS WILL
MAINLY BE VFR THROUGH THE TAF PERIOD BUT LOW CLOUDS WILL INCREASE
INTO SUNDAY NIGHT.

&&

.FIRE WEATHER...
ISSUED AT 1253 PM MST SAT DEC 20 2014

NO FIRE WEATHER ISSUES EXPECTED THIS WEEKEND. BREEZY AND MAINLY DRY
CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS THIS AFTERNOON...BUT
THINGS BEGIN TO CHANGE TONIGHT THROUGH THE BEGINNING OF NEXT WEEK. STRONG
WESTERLY WINDS AND SIGNIFICANT MOUNTAIN SNOWFALL WILL RETURN
TONIGHT AND CONTINUE THROUGH MONDAY...WITH WINTER STORM WARNINGS
IN EFFECT FOR THE SNOWY AND SIERRA MADRE RANGES FOR TWO TO THREE FEET
OF SNOW. HIGH WIND WARNINGS ARE IN EFFECT FOR THE WIND PRONE AREAS
OF SOUTHEAST WYOMING FROM LATE TONIGHT THROUGH SUNDAY EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST SUNDAY NIGHT
     FOR WYZ116-117.

     WINTER STORM WATCH FROM 8 AM MST SUNDAY THROUGH MONDAY MORNING
     FOR WYZ109-111-113-115.

     HIGH WIND WARNING UNTIL MIDNIGHT MST SUNDAY NIGHT FOR WYZ106-110.

     HIGH WIND WATCH FROM 8 AM MST SUNDAY THROUGH SUNDAY EVENING FOR
     WYZ104-105.

NE...NONE.

&&

$$

UPDATE...SML
SHORT TERM...GCC
LONG TERM...TJT
AVIATION...SML
FIRE WEATHER...GCC



000
FXUS65 KCYS 210523
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1023 PM MST SAT DEC 20 2014

.UPDATE...
ISSUED AT 913 PM MST SAT DEC 20 2014

FORECAST IS FAIRLY STRAIGHT FORWARD TONIGHT BUT THAT WILL NOT BE
THE CASE THE NEXT FEW DAYS. FOR TONIGHT SOME LIGHT SNOW WILL OCCUR
IN THE SNOWY AND SIERRA MADRE RANGES. ACCUMULATIONS WILL BE
MINIMAL WITH A FEW INCHES THROUGH THE NIGHT. SOME LIGHT SNOW WILL
ALSO OCCUR OUTSIDE OF THE MOUNTAINS OVER PORTIONS OF CARBON AND
ALBANY COUNTIES BUT ANY ACCUMULATIONS WILL GENERALLY BE LESS THAN
ONE INCH.

WINDS WILL INCREASE OVERNIGHT...ESPECIALLY OVER WIND PRONE AREAS
OF SOUTHEAST WYOMING. MODELS ARE SLIGHTLY SLOWER WITH THE ONSET OF
THE WINDS BUT SHOULD SEE ARLINGTON AND BORDEAUX APPROACHING WARNING
CRITERIA TOWARD SUNRISE WITH THE SOUTHERN LARAMIE REACHING
CRITERIA SHORTLY THEREAFTER.

THE MAIN QUESTION FOR SUNDAY INTO MONDAY IS WHAT TYPE OF HEADLINES
SHOULD BE ISSUED. THE PROBLEM IS DETERMINING IMPACTS FROM WIND AND
SNOW...AND JUST HOW MUCH SNOW WILL FALL AND HOW STRONG WITH WINDS
WILL BE. MODELS INDICATE VERY STRONG WINDS OFF THE SURFACE SUNDAY
BUT ALSO A RELATIVELY STRONG INVERSION INITIALLY. THAT INVERSION
WILL BREAK DOWN INTO SUNDAY NIGHT WITH SATURATED SOUNDINGS AND
STEEP LAPSE RATES IN THE BOUNDARY LAYER WHICH IS FAVORABLE FOR
WINDS MIXING TO THE SURFACE AND EVEN SOME CONVECTIVE TYPE WIND
GUSTS. SNOW WILL LIKELY ALSO BE FALLING AT THIS TIME. THE
QUESTION IS HOW HEAVY THE SNOW WILL BE AND HOW MUCH WILL FALL.
CERTAINLY STEEP LAPSE RATES SUGGEST THE POTENTIAL FOR AT LEAST A
SHORT PERIOD OF HEAVY SNOW. IT IS VERY POSSIBLE NEAR BLIZZARD
CONDITIONS WILL EXIST AT TIMES FOR PORTIONS OF CARBON AND ALBANY
COUNTIES LATE SUNDAY AFTERNOON THROUGH THE EVENING HOURS. AT THIS
TIME WATCHES AND WARNINGS REMAIN IN PLACE BUT LIKE
USUAL...HEADLINES WILL EVOLVE OVER THE NEXT 24 HOURS...ESPECIALLY
GIVEN THE CHALLENGES WITH THIS SYSTEM. PLEASE STAY TUNED FOR
WEATHER UPDATES WITH THE CHANGING SITUATION.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 1253 PM MST SAT DEC 20 2014

CHALLENGING FORECAST AHEAD WITH STRONG WINDS...VERY HEAVY SNOW AND
COMBINATION OF WIND AND SNOW THE FORECAST CHALLENGES TONIGHT
THROUGH MONDAY.

CURRENTLY...PRETTY TRANQUIL OUT ACROSS THE CWFA SO FAR TODAY. HIGH
PRESSURE OVER NORTHWESTERN COLORADO THIS AFTERNOON WITH PARTLY
CLOUDY SKIES EAST OF THE LARAMIE RANGE AND MOSTLY CLOUDY WEST.
PACIFIC STORM SYSTEM JUST OFFSHORE OF WASHINGTON STATE THIS
AFTERNOON CONTINUES TO MOVE SOUTHEAST TOWARDS THE COAST.

SHORT TERM GUIDANCE REALLY BEGINS TO SHOW AN UPTICK ON WINDS THIS
EVENING. GFS 700MB WINDS INCREASE TO 55KTS ACROSS CARBON AND
ALBANY COUNTIES WITH 700MB CRAIG TO CASPER HEIGHT GRADIENTS
INCREASING TO 70MTRS AT 06Z. THE NAM WRKHGT PRODUCT A LITTLE
SLOWER ON HEIGHT GRADIENTS INCREASING...SHOWING 850/700MB
GRADIENTS BOTH ABOVE 60MTRS BY 09Z. WILL KEEP THE CURRENT WIND
WARNINGS GOING AS THEY ARE FOR NOW.

BY 12Z SUNDAY...GFS 700MB WINDS REALLY BEGIN CRANKING WITH
65-70KTS WEST OF THE LARAMIE RANGE. PACIFIC LOW PRESSURE SYSTEM
MOVING INTO WESTERN WYOMING AT THAT TIME. WINDS SHOULD BEGIN TO
BECOME STRONG FAIRLY WIDESPREAD BY MID MORNING WITH THE WRKHGT
PRODUCT PEAKING OUT AT 79/74MTRS ON THE 850/700MB HEIGHT GRADIENTS
BY 00Z TOMORROW AFTERNOON. THESE STRONG GRADIENTS CONTINUE INTO
MONDAY MORNING BEFORE EASING.

INCREASING CONCERN FOR POSSIBLE WINTER WEATHER EVENT ALONG THE
I-80 CORRIDOR FROM THE I-80 SUMMIT THROUGH RAWLINS FOR LATE SUNDAY
AFTERNOON THROUGH MONDAY. ALL GUIDANCE SHOWING PRECIP BECOMING
WIDESPREAD BY NOON SUNDAY AND CONTINUING INTO MONDAY MORNING. LATEST
ECMWF AND SREF MOST WIDESPREAD AND AGGRESSIVE WITH QPF
AMOUNTS...THOUGH THE NAM DOES COME IN LINE BY 00Z. COMBINATION OF
VERY STRONG WINDS AND SNOW COULD LEAD TO VERY SERIOUS DRIVING
CONDITIONS WEST OF THE LARAMIE RANGE TOMORROW EVENING INTO MONDAY.

REPLACED THE HIGH WIND WATCHES WE HAD OUT THIS MORNING FOR THE
LOWER ELEVATIONS OF ALBANY AND CARBON COUNTIES WITH A WINTER STORM
WATCH. GRANTED...WINDS ARE GOING TO BE STRONGEST IN THE AFTERNOON
AND THIS SHOULD BE THE TIME WHEN PRECIP SHOULD BE FALLING AS
RAIN...BUT IT WONT TAKE LONG FOR THE PRECIP TO TURN OVER TO SNOW.
WILL WORD THE WATCH FOR STRONG WINDS INITIALLY...THEN A
COMBINATION OF WINDS AND SNOW LATE AFTERNOON AND OVERNIGHT.

SNOWY AND SIERRA MADRE RANGE ARE GOING TO GET POUNDED IN THIS
SETUP. WILL BE ON THE LEFT FRONT QUADRANT OF A 170KT JET THROUGH
MONDAY MORNING. LATEST HPC SNOW FORECAST SHOWING 2+ FEET OF SNOW
THROUGH MONDAY. DO BELIEVE WE COULD SEE MUCH MORE IN THIS
PERSISTENT STRONG UPSLOPE EVENT. MAYBE MORE LIKE 3 FEET BEFORE ALL
IS SAID AND DONE MONDAY NIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 253 PM MST SAT DEC 20 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY THROUGH FRIDAY DUE TO
HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER WEATHER ON CHRISTMAS
DAY. EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY
TRAVEL PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REMAIN COLDER THAN NORMAL ON TUESDAY BEHIND THE
UPPER LEVEL TROUGH FORECAST TO PUSH ACROSS THE AREA TOMORROW AND
MONDAY. HIGHS IN THE 20S TO MID 30S ARE EXPECTED WITH VERY COLD
OVERNIGHT LOWS. TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS
DOWNSLOPE FLOW DEVELOPS...WITH HIGHS IN THE 30S TO LOW 40S. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS GENERALLY INDICATE A RAPIDLY
MOVING UPPER LEVEL TROUGH PUSHING INTO THE AREA. A STRONG PACIFIC
COLD FRONT IS FORECAST TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME
CHRISTMAS MORNING WITH SNOW DEVELOPING BEHIND THE FRONT. BEFORE
THAT...THERE IS THE POTENTIAL FOR A HIGH WIND EVENT ACROSS THE
WIND PRONE AREAS OF SOUTHEAST WYOMING AHEAD OF THE FRONT...BUT
CONDITIONS WILL LIKELY NOT LAST TOO LONG AND MAINLY AFFECT
MOTORISTS WITH LARGER VEHICLES. AS FOR SNOW...THERE IS A LOW
PROBABILITY FOR WINTER STORM CONDITIONS ON CHRISTMAS DAY DUE TO
HOW PROGRESSIVE THIS SYSTEM IS. HOWEVER...THE GEM AND ECMWF DO
HINT AT A SLOWER SOLUTION AS THE STORM DIGS FURTHER TO THE SOUTH.
THE GFS ON THE OTHER HAND IS VERY PROGRESSIVE...WITH SNOW
STRUGGLING TO DEVELOP OVER MOST OF THE HIGH PLAINS MAINLY DUE TO
THE LLVL UPSLOPE FLOW DEVELOPING MUCH LATER IN THE DAY WHEN THE
EVENT IS PRACTICALLY OVER. ALTHOUGH THERE IS A POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE AREA...CONFIDENCE IS RATHER LOW AT
THIS TIME WITH THE MOST FAVORABLE LOCATIONS BEING IN THE MOUNTAINS
AND WELL NORTH OF I80 ACROSS THE HIGH PLAINS. AT THIS TIME...IT
APPEARS THE I80 CORRIDOR MAY HAVE TOO MUCH DRIER DOWNSLOPE FLOW TO
DEAL WITH TO GET ANY SUBSTANTIAL SNOW ACCUMULATIONS GOING. BUT
THIS MAY QUICKLY CHANGE OVER THE NEXT FEW DAYS. KEPT POP BETWEEN
25 TO 35 PERCENT ACROSS THE HIGH PLAINS INCLUDING THE EASTERN I80
CORRIDOR...AND CLOSER TO 50 PERCENT WEST OF THE LARAMIE RANGE.
INCREASED POP IN THE MOUNTAINS WHICH WILL HAVE THE BEST POTENTIAL
TO SEE MODERATE SNOW ACCUMULATIONS WITH THIS SYSTEM. IN EITHER
CASE...MUCH COLDER TEMPERATURES ARE EXPECTED FOR LATER NEXT WEEK.
EARLY MORNING HIGHS BETWEEN 35 TO 45 ON CHRISTMAS DAY WILL RAPIDLY
LOWER INTO THE 20S THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL
LIKELY BE BELOW FREEZING FOR FRIDAY AND SATURDAY AS NORTHERLY FLOW
ALOFT STAYS OVER THE ROCKY MOUNTAIN REGION.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1002 PM MST SAT DEC 20 2014

MANY AVIATION CONCERNS FOR AREAS ALONG AND WEST OF THE LARAMIE
RANGE SUNDAY AND MONDAY. WINDS WILL BE VERY STRONG ACROSS THIS
AREA ESPECIALLY SUNDAY INTO SUNDAY NIGHT. IN ADDITION SNOW WILL
FALL ACROSS THIS AREA WITH HEAVY SNOW ACROSS THE MOUNTAINS. THE
SNOWY AND SIERRA MADRE RANGES WILL HAVE OBSCURED MOUNTAINS WITH
MOUNTAIN TOPS OBSCURED IN THE LARAMIE RANGE AND MOUNTAINS
OBSCURED AT TIMES. EAST OF THE LARAMIE RANGE CONDITIONS WILL
MAINLY BE VFR THROUGH THE TAF PERIOD BUT LOW CLOUDS WILL INCREASE
INTO SUNDAY NIGHT.

&&

.FIRE WEATHER...
ISSUED AT 1253 PM MST SAT DEC 20 2014

NO FIRE WEATHER ISSUES EXPECTED THIS WEEKEND. BREEZY AND MAINLY DRY
CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS THIS AFTERNOON...BUT
THINGS BEGIN TO CHANGE TONIGHT THROUGH THE BEGINNING OF NEXT WEEK. STRONG
WESTERLY WINDS AND SIGNIFICANT MOUNTAIN SNOWFALL WILL RETURN
TONIGHT AND CONTINUE THROUGH MONDAY...WITH WINTER STORM WARNINGS
IN EFFECT FOR THE SNOWY AND SIERRA MADRE RANGES FOR TWO TO THREE FEET
OF SNOW. HIGH WIND WARNINGS ARE IN EFFECT FOR THE WIND PRONE AREAS
OF SOUTHEAST WYOMING FROM LATE TONIGHT THROUGH SUNDAY EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING UNTIL 5 AM MST TUESDAY FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST SUNDAY NIGHT
     FOR WYZ116-117.

     WINTER STORM WATCH FROM 8 AM MST SUNDAY THROUGH MONDAY MORNING
     FOR WYZ109-111-113-115.

     HIGH WIND WARNING UNTIL MIDNIGHT MST SUNDAY NIGHT FOR WYZ106-110.

     HIGH WIND WATCH FROM 8 AM MST SUNDAY THROUGH SUNDAY EVENING FOR
     WYZ104-105.

NE...NONE.

&&

$$

UPDATE...SML
SHORT TERM...GCC
LONG TERM...TJT
AVIATION...SML
FIRE WEATHER...GCC



000
FXUS63 KUNR 210508
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1008 PM MST SAT DEC 20 2014

.SHORT TERM...THIS EVENING THROUGH SUNDAY NIGHT
ISSUED AT 319 PM MST SAT DEC 20 2014

CURRENT SURFACE ANALYSIS SHOWS WARM FRONT JUST TO THE EAST OF THE
FORECAST AREA. UPPER LEVEL ANALYSIS DEPICTS NEAR ZONAL FLOW ACROSS
THE REGION...WITH A STRONG STORM SYSTEM AND UPPER JET PUSHING
ACROSS THE PACIFIC NW. WATER VAPOR IMAGERY SHOWS A WEAK SHORTWAVE
HAS MOVED EAST OF THE AREA...WITH PARTLY CLOUDY SKIES BEHIND IT.
TEMPS RANGE FROM THE UPPER 30S ACROSS FAR SOUTH CENTRAL SD TO NEAR
50 IN THE RAPID CITY AREA. WINDS ARE MOSTLY ON THE LIGHT SIDE FROM
THE WEST AND NORTHWEST.

A UNSETTLED PATTERN WILL TAKE SHAPE FOR THE END OF THE WEEKEND AND
INTO EARLY NEXT WEEK AS A DEVELOPING LOW PRESSURE SYSTEM MOVES
SOUTHEAST ACROSS THE REGION. HOWEVER...IT WILL REMAIN MILD INTO
SUNDAY BEFORE THIS SYSTEM PUSHES IN. THE STORM WILL BRING AT LEAST
SOME LIGHT RAIN AND SNOW TO MOST AREAS...ALONG WITH STRONG NORTHWEST
WINDS EARLY NEXT WEEK.

FOR TONIGHT...SKIES WILL REMAIN PARTLY CLOUDY IN GENERAL AS WEST TO
SOUTHWEST WINDS DEVELOP. THE WINDS WILL BECOME BREEZY OVERNIGHT OVER
PORTIONS OF NORTHEAST WY...ESPECIALLY CAMPBELL CO. RELATIVELY MILD
TEMPS CAN BE EXPECTED...WITH LOWS IN THE 20S AND LOWER 30S...A BIT
WARMER ACROSS THE EASTERN SLOPES OF THE BLACK HILLS.

CLOUDS WILL BEGIN TO INCREASE FROM THE WEST SUNDAY MORNING...WITH
SKIES BECOMING MOSTLY CLOUDY ACROSS THE ENTIRE AREA BY MID
AFTERNOON. MILDER AIR WILL REMAIN ACROSS THE REGION THROUGH MUCH OF
THE DAY...WITH HIGHS IN THE 40S AND LOWER 50S...WARMEST AGAIN ACROSS
THE EASTERN SLOPES OF THE BLACK HILLS AND ADJACENT PLAINS.
DEVELOPING LOW PRESSURE WILL MOVE ACROSS NORTHERN MT DURING THE DAY
AND INTO ND/NORTHERN SD SUNDAY NIGHT...DRAGGING A COLD FRONT ACROSS
THE CWA DURING THE AFTERNOON AND EVENING HOURS. RAIN SHOWERS WILL
DEVELOP ALONG AND BEHIND THE COLD FRONT...MOSTLY DURING THE
AFTERNOON...AS UPPER LEVEL ENERGY ACCOMPANIES THE FRONT. THE BEST
CHANCES DURING THE AFTERNOON LOOK TO BE ACROSS FAR NORTHEAST
WY...SOUTHEAST MT...FAR NORTHWEST SD...AND EVENTUALLY THE NORTHERN
BLACK HILLS AREA. NORTHWESTERLY WINDS WILL INCREASE BEHIND THE FRONT
LATE SUNDAY AND SUNDAY NIGHT...BECOMING BREEZY TO WINDY IN MANY
AREAS OVERNIGHT.

UPPER TROF AND DEVELOPING LOW PRESSURE SYSTEM WILL TRACK FROM MT ON
SUNDAY TO SOMEWHERE OVER THE EASTERN DAKOTAS ON MONDAY MORNING.
VARIOUS MODELS CONTINUE TO BE IN SOME DISAGREEMENT ON TRACK AND
STRENGTH OF THIS SYSTEM. FOR SUNDAY NIGHT...WILL KEEP THE BEST
CHANCES FOR PCPN OVER NORTHEASTERN PORTIONS OF THE CWA...AS WELL AS
THE NORTHERN BLACK HILLS AREA. PCPN WILL GRADUALLY CHANGE OVER TO
SNOW SUNDAY NIGHT...WITH THE QUICKEST CHANGE OVER THE BLACK HILLS.
NOT EXPECTING MUCH IN THE WAY OF SNOW ACCUMULATION OVER THE PLAINS
AS MOST OF THE PCPN WILL BE OUT OF THE AREA BY THE TIME TEMPS DROP
OFF ENOUGH. HOWEVER...FORECAST SOUNDINGS AND FROUDE ANALYSIS SUGGEST
FAVORABLE CONDITIONS FOR AT LEAST OCCASIONAL SNOW OVER THE NORTHERN
BLACK HILLS SUNDAY NIGHT INTO MONDAY AS UPSLOPE NORTHWESTERLY FLOW
INCREASES. HAVE RAISED POPS OVER THESE AREAS SUNDAY NIGHT AND HAVE 1
TO 3 INCHES OF ACCUMULATION ACROSS THE HIGHER TERRAIN THROUGH EARLY
MONDAY MORNING. LOWS SUNDAY NIGHT WILL BE IN THE MID 20S TO LOWER
30S ACROSS THE FORECAST AREA.

.LONG TERM...MONDAY THROUGH SATURDAY
ISSUED AT 321 PM MST SAT DEC 20 2014

UPPER TROF WILL DIG OVER THE DAKOTAS MONDAY AND REMAIN
OVER THE UPPER MIDWEST THROUGH TUESDAY. WHILE MODELS INITIALLY HAVE
A SIMILAR PLACEMENT WITH THE TROF AXIS OVER THE EASTERN DAKOTAS
MONDAY MORNING...THEY ARE QUITE DIFFERENT WITH THE STRENGTH AS THE
GFS CLOSES A LOW OVER SOUTHEASTERN SD WITH THE NAM FARTHER NORTH AND
THE ECMWF ONLY A TROF...EVENTUALLY FORMING A CLOSED LOW BUT NOT AS
STRONG. WITH 120-140KT JET COMING OVER WEST COAST RIDGE AND
DIVING INTO THE UPPER TROF...THE STRONGER GFS WOULD BE A BETTER
SOLUTION. DEEP VERTICALLY STACKED LOW WILL HAVE A STRONG PRESSURE
GRADIENT ACROSS WESTERN SD...WITH GUSTS LIKELY TO REACH 50KT...AS
FORECAST SOUNDINGS SHOW >50KT MOMENTUM TRANSFER. PRECIPITATION WILL
SPREAD ACROSS FORECAST AREA MONDAY...COULD STILL SEE SOME RAIN/SNOW
MIX EARLY BEFORE CHANGING TO SNOW. FROUDE NUMBER INCREASES TO MORE
THAN 2 MONDAY MORNING...ALONG WITH 90-100 PERCENT RH AND STRONG
WINDS...SO UPSLOPE SNOW IS LIKELY OVER THE NORTHERN BLACK
HILLS...WHILE DOWNSLOPE WINDS WILL KEEP PRECIP TO A MINIMUM FROM
RAPID CITY TO HOT SPRINGS AND EDGEMONT. DEPENDING ON THE AMOUNT OF
PRECIPITATION...A WINTER WEATHER ADVISORY MAY BE MORE APPROPRIATE
THAN A HIGH WIND WARNING AS BLOWING SNOW WOULD HAVE THE GREATER
IMPACT. SNOW AND GUSTY WINDS MAY LINGER TUES AS A SECONDARY LOW
ROTATES AROUND MAIN STORM CENTER. BRIEF RIDGE WILL BUILD ON
WEDNESDAY BEFORE THE NEXT SYSTEM COMES ACROSS THE NORTHERN PLAINS ON
CHRISTMAS DAY. MODELS IN GOOD AGREEMENT WITH A FAST-MOVING LONGWAVE
TROF. CYCLONIC NORTHWEST FLOW REMAINS BEHIND THE TROF FRIDAY...WITH
UPPER RIDGING SLOW TO BUILD TOWARD NEXT WEEKEND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1004 PM MST SAT DEC 20 2014

VFR CONDITIONS WILL CONTINUE THROUGH 18Z ON SUNDAY. A STRONG
CDFNT MOVING INTO THE REGION SUNDAY AFTN WILL BRING SCT -SHRA
AND MVFR CIGS. CONDITIONS WILL DETERIORATE FURTHER SUNDAY
NIGHT...ESPECIALLY OVER NERN WY AND THE NRN BLKHLS AS SNOW
DEVELOPS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&

$$

SHORT TERM...26
LONG TERM...55
AVIATION...JOHNSON







000
FXUS63 KUNR 210508
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1008 PM MST SAT DEC 20 2014

.SHORT TERM...THIS EVENING THROUGH SUNDAY NIGHT
ISSUED AT 319 PM MST SAT DEC 20 2014

CURRENT SURFACE ANALYSIS SHOWS WARM FRONT JUST TO THE EAST OF THE
FORECAST AREA. UPPER LEVEL ANALYSIS DEPICTS NEAR ZONAL FLOW ACROSS
THE REGION...WITH A STRONG STORM SYSTEM AND UPPER JET PUSHING
ACROSS THE PACIFIC NW. WATER VAPOR IMAGERY SHOWS A WEAK SHORTWAVE
HAS MOVED EAST OF THE AREA...WITH PARTLY CLOUDY SKIES BEHIND IT.
TEMPS RANGE FROM THE UPPER 30S ACROSS FAR SOUTH CENTRAL SD TO NEAR
50 IN THE RAPID CITY AREA. WINDS ARE MOSTLY ON THE LIGHT SIDE FROM
THE WEST AND NORTHWEST.

A UNSETTLED PATTERN WILL TAKE SHAPE FOR THE END OF THE WEEKEND AND
INTO EARLY NEXT WEEK AS A DEVELOPING LOW PRESSURE SYSTEM MOVES
SOUTHEAST ACROSS THE REGION. HOWEVER...IT WILL REMAIN MILD INTO
SUNDAY BEFORE THIS SYSTEM PUSHES IN. THE STORM WILL BRING AT LEAST
SOME LIGHT RAIN AND SNOW TO MOST AREAS...ALONG WITH STRONG NORTHWEST
WINDS EARLY NEXT WEEK.

FOR TONIGHT...SKIES WILL REMAIN PARTLY CLOUDY IN GENERAL AS WEST TO
SOUTHWEST WINDS DEVELOP. THE WINDS WILL BECOME BREEZY OVERNIGHT OVER
PORTIONS OF NORTHEAST WY...ESPECIALLY CAMPBELL CO. RELATIVELY MILD
TEMPS CAN BE EXPECTED...WITH LOWS IN THE 20S AND LOWER 30S...A BIT
WARMER ACROSS THE EASTERN SLOPES OF THE BLACK HILLS.

CLOUDS WILL BEGIN TO INCREASE FROM THE WEST SUNDAY MORNING...WITH
SKIES BECOMING MOSTLY CLOUDY ACROSS THE ENTIRE AREA BY MID
AFTERNOON. MILDER AIR WILL REMAIN ACROSS THE REGION THROUGH MUCH OF
THE DAY...WITH HIGHS IN THE 40S AND LOWER 50S...WARMEST AGAIN ACROSS
THE EASTERN SLOPES OF THE BLACK HILLS AND ADJACENT PLAINS.
DEVELOPING LOW PRESSURE WILL MOVE ACROSS NORTHERN MT DURING THE DAY
AND INTO ND/NORTHERN SD SUNDAY NIGHT...DRAGGING A COLD FRONT ACROSS
THE CWA DURING THE AFTERNOON AND EVENING HOURS. RAIN SHOWERS WILL
DEVELOP ALONG AND BEHIND THE COLD FRONT...MOSTLY DURING THE
AFTERNOON...AS UPPER LEVEL ENERGY ACCOMPANIES THE FRONT. THE BEST
CHANCES DURING THE AFTERNOON LOOK TO BE ACROSS FAR NORTHEAST
WY...SOUTHEAST MT...FAR NORTHWEST SD...AND EVENTUALLY THE NORTHERN
BLACK HILLS AREA. NORTHWESTERLY WINDS WILL INCREASE BEHIND THE FRONT
LATE SUNDAY AND SUNDAY NIGHT...BECOMING BREEZY TO WINDY IN MANY
AREAS OVERNIGHT.

UPPER TROF AND DEVELOPING LOW PRESSURE SYSTEM WILL TRACK FROM MT ON
SUNDAY TO SOMEWHERE OVER THE EASTERN DAKOTAS ON MONDAY MORNING.
VARIOUS MODELS CONTINUE TO BE IN SOME DISAGREEMENT ON TRACK AND
STRENGTH OF THIS SYSTEM. FOR SUNDAY NIGHT...WILL KEEP THE BEST
CHANCES FOR PCPN OVER NORTHEASTERN PORTIONS OF THE CWA...AS WELL AS
THE NORTHERN BLACK HILLS AREA. PCPN WILL GRADUALLY CHANGE OVER TO
SNOW SUNDAY NIGHT...WITH THE QUICKEST CHANGE OVER THE BLACK HILLS.
NOT EXPECTING MUCH IN THE WAY OF SNOW ACCUMULATION OVER THE PLAINS
AS MOST OF THE PCPN WILL BE OUT OF THE AREA BY THE TIME TEMPS DROP
OFF ENOUGH. HOWEVER...FORECAST SOUNDINGS AND FROUDE ANALYSIS SUGGEST
FAVORABLE CONDITIONS FOR AT LEAST OCCASIONAL SNOW OVER THE NORTHERN
BLACK HILLS SUNDAY NIGHT INTO MONDAY AS UPSLOPE NORTHWESTERLY FLOW
INCREASES. HAVE RAISED POPS OVER THESE AREAS SUNDAY NIGHT AND HAVE 1
TO 3 INCHES OF ACCUMULATION ACROSS THE HIGHER TERRAIN THROUGH EARLY
MONDAY MORNING. LOWS SUNDAY NIGHT WILL BE IN THE MID 20S TO LOWER
30S ACROSS THE FORECAST AREA.

.LONG TERM...MONDAY THROUGH SATURDAY
ISSUED AT 321 PM MST SAT DEC 20 2014

UPPER TROF WILL DIG OVER THE DAKOTAS MONDAY AND REMAIN
OVER THE UPPER MIDWEST THROUGH TUESDAY. WHILE MODELS INITIALLY HAVE
A SIMILAR PLACEMENT WITH THE TROF AXIS OVER THE EASTERN DAKOTAS
MONDAY MORNING...THEY ARE QUITE DIFFERENT WITH THE STRENGTH AS THE
GFS CLOSES A LOW OVER SOUTHEASTERN SD WITH THE NAM FARTHER NORTH AND
THE ECMWF ONLY A TROF...EVENTUALLY FORMING A CLOSED LOW BUT NOT AS
STRONG. WITH 120-140KT JET COMING OVER WEST COAST RIDGE AND
DIVING INTO THE UPPER TROF...THE STRONGER GFS WOULD BE A BETTER
SOLUTION. DEEP VERTICALLY STACKED LOW WILL HAVE A STRONG PRESSURE
GRADIENT ACROSS WESTERN SD...WITH GUSTS LIKELY TO REACH 50KT...AS
FORECAST SOUNDINGS SHOW >50KT MOMENTUM TRANSFER. PRECIPITATION WILL
SPREAD ACROSS FORECAST AREA MONDAY...COULD STILL SEE SOME RAIN/SNOW
MIX EARLY BEFORE CHANGING TO SNOW. FROUDE NUMBER INCREASES TO MORE
THAN 2 MONDAY MORNING...ALONG WITH 90-100 PERCENT RH AND STRONG
WINDS...SO UPSLOPE SNOW IS LIKELY OVER THE NORTHERN BLACK
HILLS...WHILE DOWNSLOPE WINDS WILL KEEP PRECIP TO A MINIMUM FROM
RAPID CITY TO HOT SPRINGS AND EDGEMONT. DEPENDING ON THE AMOUNT OF
PRECIPITATION...A WINTER WEATHER ADVISORY MAY BE MORE APPROPRIATE
THAN A HIGH WIND WARNING AS BLOWING SNOW WOULD HAVE THE GREATER
IMPACT. SNOW AND GUSTY WINDS MAY LINGER TUES AS A SECONDARY LOW
ROTATES AROUND MAIN STORM CENTER. BRIEF RIDGE WILL BUILD ON
WEDNESDAY BEFORE THE NEXT SYSTEM COMES ACROSS THE NORTHERN PLAINS ON
CHRISTMAS DAY. MODELS IN GOOD AGREEMENT WITH A FAST-MOVING LONGWAVE
TROF. CYCLONIC NORTHWEST FLOW REMAINS BEHIND THE TROF FRIDAY...WITH
UPPER RIDGING SLOW TO BUILD TOWARD NEXT WEEKEND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 1004 PM MST SAT DEC 20 2014

VFR CONDITIONS WILL CONTINUE THROUGH 18Z ON SUNDAY. A STRONG
CDFNT MOVING INTO THE REGION SUNDAY AFTN WILL BRING SCT -SHRA
AND MVFR CIGS. CONDITIONS WILL DETERIORATE FURTHER SUNDAY
NIGHT...ESPECIALLY OVER NERN WY AND THE NRN BLKHLS AS SNOW
DEVELOPS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&

$$

SHORT TERM...26
LONG TERM...55
AVIATION...JOHNSON






000
FXUS65 KCYS 210414
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
914 PM MST SAT DEC 20 2014

.UPDATE...
ISSUED AT 913 PM MST SAT DEC 20 2014

FORECAST IS FAIRLY STRAIGHT FORWARD TONIGHT BUT THAT WILL NOT BE
THE CASE THE NEXT FEW DAYS. FOR TONIGHT SOME LIGHT SNOW WILL OCCUR
IN THE SNOWY AND SIERRA MADRE RANGES. ACCUMULATIONS WILL BE
MINIMAL WITH A FEW INCHES THROUGH THE NIGHT. SOME LIGHT SNOW WILL
ALSO OCCUR OUTSIDE OF THE MOUNTAINS OVER PORTIONS OF CARBON AND
ALBANY COUNTIES BUT ANY ACCUMULATIONS WILL GENERALLY BE LESS THAN
ONE INCH.

WINDS WILL INCREASE OVERNIGHT...ESPECIALLY OVER WIND PRONE AREAS
OF SOUTHEAST WYOMING. MODELS ARE SLIGHTLY SLOWER WITH THE ONSET OF
THE WINDS BUT SHOULD SEE ARLINGTON AND BORDEAUX APPROACHING WARNING
CRITERIA TOWARD SUNRISE WITH THE SOUTHERN LARAMIE REACHING
CRITERIA SHORTLY THEREAFTER.

THE MAIN QUESTION FOR SUNDAY INTO MONDAY IS WHAT TYPE OF HEADLINES
SHOULD BE ISSUED. THE PROBLEM IS DETERMINING IMPACTS FROM WIND AND
SNOW...AND JUST HOW MUCH SNOW WILL FALL AND HOW STRONG WITH WINDS
WILL BE. MODELS INDICATE VERY STRONG WINDS OFF THE SURFACE SUNDAY
BUT ALSO A RELATIVELY STRONG INVERSION INITIALLY. THAT INVERSION
WILL BREAK DOWN INTO SUNDAY NIGHT WITH SATURATED SOUNDINGS AND
STEEP LAPSE RATES IN THE BOUNDARY LAYER WHICH IS FAVORABLE FOR
WINDS MIXING TO THE SURFACE AND EVEN SOME CONVECTIVE TYPE WIND
GUSTS. SNOW WILL LIKELY ALSO BE FALLING AT THIS TIME. THE
QUESTION IS HOW HEAVY THE SNOW WILL BE AND HOW MUCH WILL FALL.
CERTAINLY STEEP LAPSE RATES SUGGEST THE POTENTIAL FOR AT LEAST A
SHORT PERIOD OF HEAVY SNOW. IT IS VERY POSSIBLE NEAR BLIZZARD
CONDITIONS WILL EXIST AT TIMES FOR PORTIONS OF CARBON AND ALBANY
COUNTIES LATE SUNDAY AFTERNOON THROUGH THE EVENING HOURS. AT THIS
TIME WATCHES AND WARNINGS REMAIN IN PLACE BUT LIKE
USUAL...HEADLINES WILL EVOLVE OVER THE NEXT 24 HOURS...ESPECIALLY
GIVEN THE CHALLENGES WITH THIS SYSTEM. PLEASE STAY TUNED FOR
WEATHER UPDATES WITH THE CHANGING SITUATION.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 1253 PM MST SAT DEC 20 2014

CHALLENGING FORECAST AHEAD WITH STRONG WINDS...VERY HEAVY SNOW AND
COMBINATION OF WIND AND SNOW THE FORECAST CHALLENGES TONIGHT
THROUGH MONDAY.

CURRENTLY...PRETTY TRANQUIL OUT ACROSS THE CWFA SO FAR TODAY. HIGH
PRESSURE OVER NORTHWESTERN COLORADO THIS AFTERNOON WITH PARTLY
CLOUDY SKIES EAST OF THE LARAMIE RANGE AND MOSTLY CLOUDY WEST.
PACIFIC STORM SYSTEM JUST OFFSHORE OF WASHINGTON STATE THIS
AFTERNOON CONTINUES TO MOVE SOUTHEAST TOWARDS THE COAST.

SHORT TERM GUIDANCE REALLY BEGINS TO SHOW AN UPTICK ON WINDS THIS
EVENING. GFS 700MB WINDS INCREASE TO 55KTS ACROSS CARBON AND
ALBANY COUNTIES WITH 700MB CRAIG TO CASPER HEIGHT GRADIENTS
INCREASING TO 70MTRS AT 06Z. THE NAM WRKHGT PRODUCT A LITTLE
SLOWER ON HEIGHT GRADIENTS INCREASING...SHOWING 850/700MB
GRADIENTS BOTH ABOVE 60MTRS BY 09Z. WILL KEEP THE CURRENT WIND
WARNINGS GOING AS THEY ARE FOR NOW.

BY 12Z SUNDAY...GFS 700MB WINDS REALLY BEGIN CRANKING WITH
65-70KTS WEST OF THE LARAMIE RANGE. PACIFIC LOW PRESSURE SYSTEM
MOVING INTO WESTERN WYOMING AT THAT TIME. WINDS SHOULD BEGIN TO
BECOME STRONG FAIRLY WIDESPREAD BY MID MORNING WITH THE WRKHGT
PRODUCT PEAKING OUT AT 79/74MTRS ON THE 850/700MB HEIGHT GRADIENTS
BY 00Z TOMORROW AFTERNOON. THESE STRONG GRADIENTS CONTINUE INTO
MONDAY MORNING BEFORE EASING.

INCREASING CONCERN FOR POSSIBLE WINTER WEATHER EVENT ALONG THE
I-80 CORRIDOR FROM THE I-80 SUMMIT THROUGH RAWLINS FOR LATE SUNDAY
AFTERNOON THROUGH MONDAY. ALL GUIDANCE SHOWING PRECIP BECOMING
WIDESPREAD BY NOON SUNDAY AND CONTINUING INTO MONDAY MORNING. LATEST
ECMWF AND SREF MOST WIDESPREAD AND AGGRESSIVE WITH QPF
AMOUNTS...THOUGH THE NAM DOES COME IN LINE BY 00Z. COMBINATION OF
VERY STRONG WINDS AND SNOW COULD LEAD TO VERY SERIOUS DRIVING
CONDITIONS WEST OF THE LARAMIE RANGE TOMORROW EVENING INTO MONDAY.

REPLACED THE HIGH WIND WATCHES WE HAD OUT THIS MORNING FOR THE
LOWER ELEVATIONS OF ALBANY AND CARBON COUNTIES WITH A WINTER STORM
WATCH. GRANTED...WINDS ARE GOING TO BE STRONGEST IN THE AFTERNOON
AND THIS SHOULD BE THE TIME WHEN PRECIP SHOULD BE FALLING AS
RAIN...BUT IT WONT TAKE LONG FOR THE PRECIP TO TURN OVER TO SNOW.
WILL WORD THE WATCH FOR STRONG WINDS INITIALLY...THEN A
COMBINATION OF WINDS AND SNOW LATE AFTERNOON AND OVERNIGHT.

SNOWY AND SIERRA MADRE RANGE ARE GOING TO GET POUNDED IN THIS
SETUP. WILL BE ON THE LEFT FRONT QUADRANT OF A 170KT JET THROUGH
MONDAY MORNING. LATEST HPC SNOW FORECAST SHOWING 2+ FEET OF SNOW
THROUGH MONDAY. DO BELIEVE WE COULD SEE MUCH MORE IN THIS
PERSISTENT STRONG UPSLOPE EVENT. MAYBE MORE LIKE 3 FEET BEFORE ALL
IS SAID AND DONE MONDAY NIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 253 PM MST SAT DEC 20 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY THROUGH FRIDAY DUE TO
HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER WEATHER ON CHRISTMAS
DAY. EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY
TRAVEL PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REMAIN COLDER THAN NORMAL ON TUESDAY BEHIND THE
UPPER LEVEL TROUGH FORECAST TO PUSH ACROSS THE AREA TOMORROW AND
MONDAY. HIGHS IN THE 20S TO MID 30S ARE EXPECTED WITH VERY COLD
OVERNIGHT LOWS. TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS
DOWNSLOPE FLOW DEVELOPS...WITH HIGHS IN THE 30S TO LOW 40S. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS GENERALLY INDICATE A RAPIDLY
MOVING UPPER LEVEL TROUGH PUSHING INTO THE AREA. A STRONG PACIFIC
COLD FRONT IS FORECAST TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME
CHRISTMAS MORNING WITH SNOW DEVELOPING BEHIND THE FRONT. BEFORE
THAT...THERE IS THE POTENTIAL FOR A HIGH WIND EVENT ACROSS THE
WIND PRONE AREAS OF SOUTHEAST WYOMING AHEAD OF THE FRONT...BUT
CONDITIONS WILL LIKELY NOT LAST TOO LONG AND MAINLY AFFECT
MOTORISTS WITH LARGER VEHICLES. AS FOR SNOW...THERE IS A LOW
PROBABILITY FOR WINTER STORM CONDITIONS ON CHRISTMAS DAY DUE TO
HOW PROGRESSIVE THIS SYSTEM IS. HOWEVER...THE GEM AND ECMWF DO
HINT AT A SLOWER SOLUTION AS THE STORM DIGS FURTHER TO THE SOUTH.
THE GFS ON THE OTHER HAND IS VERY PROGRESSIVE...WITH SNOW
STRUGGLING TO DEVELOP OVER MOST OF THE HIGH PLAINS MAINLY DUE TO
THE LLVL UPSLOPE FLOW DEVELOPING MUCH LATER IN THE DAY WHEN THE
EVENT IS PRACTICALLY OVER. ALTHOUGH THERE IS A POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE AREA...CONFIDENCE IS RATHER LOW AT
THIS TIME WITH THE MOST FAVORABLE LOCATIONS BEING IN THE MOUNTAINS
AND WELL NORTH OF I80 ACROSS THE HIGH PLAINS. AT THIS TIME...IT
APPEARS THE I80 CORRIDOR MAY HAVE TOO MUCH DRIER DOWNSLOPE FLOW TO
DEAL WITH TO GET ANY SUBSTANTIAL SNOW ACCUMULATIONS GOING. BUT
THIS MAY QUICKLY CHANGE OVER THE NEXT FEW DAYS. KEPT POP BETWEEN
25 TO 35 PERCENT ACROSS THE HIGH PLAINS INCLUDING THE EASTERN I80
CORRIDOR...AND CLOSER TO 50 PERCENT WEST OF THE LARAMIE RANGE.
INCREASED POP IN THE MOUNTAINS WHICH WILL HAVE THE BEST POTENTIAL
TO SEE MODERATE SNOW ACCUMULATIONS WITH THIS SYSTEM. IN EITHER
CASE...MUCH COLDER TEMPERATURES ARE EXPECTED FOR LATER NEXT WEEK.
EARLY MORNING HIGHS BETWEEN 35 TO 45 ON CHRISTMAS DAY WILL RAPIDLY
LOWER INTO THE 20S THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL
LIKELY BE BELOW FREEZING FOR FRIDAY AND SATURDAY AS NORTHERLY FLOW
ALOFT STAYS OVER THE ROCKY MOUNTAIN REGION.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH SUNDAY AFTERNOON)

VFR CONDITIONS SHOULD PREVAIL ACROSS MOST TERMINALS...WITH THE
EXCEPTION OF KRWL. MOUNTAINS WILL BE OBSCURED WITH OROGRAPHIC SNOW
CONTINUING INTO TONIGHT. PERIODS OF IFR CONDITIONS AND LIGHT SNOW
ARE EXPECTED AT KRWL EARLIER TONIGHT UNTIL 05Z. A BRIEF LULL IN THIS
ACTIVITY IS EXPECTED AFTER MIDNIGHT BEFORE MODERATE SNOW DEVELOPS
ACROSS SOUTHERN CARBON COUNTY EARLY SUNDAY MORNING.


&&

.FIRE WEATHER...
ISSUED AT 1253 PM MST SAT DEC 20 2014

NO FIRE WEATHER ISSUES EXPECTED THIS WEEKEND. BREEZY AND MAINLY DRY
CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS THIS AFTERNOON...BUT
THINGS BEGIN TO CHANGE TONIGHT THROUGH THE BEGINNING OF NEXT WEEK. STRONG
WESTERLY WINDS AND SIGNIFICANT MOUNTAIN SNOWFALL WILL RETURN
TONIGHT AND CONTINUE THROUGH MONDAY...WITH WINTER STORM WARNINGS
IN EFFECT FOR THE SNOWY AND SIERRA MADRE RANGES FOR TWO TO THREE FEET
OF SNOW. HIGH WIND WARNINGS ARE IN EFFECT FOR THE WIND PRONE AREAS
OF SOUTHEAST WYOMING FROM LATE TONIGHT THROUGH SUNDAY EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 5 AM MST TUESDAY
     FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST SUNDAY NIGHT
     FOR WYZ116-117.

     WINTER STORM WATCH FROM 8 AM MST SUNDAY THROUGH MONDAY MORNING
     FOR WYZ109-111-113-115.

     HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO MIDNIGHT MST SUNDAY
     NIGHT FOR WYZ106-110.

     HIGH WIND WATCH FROM 8 AM MST SUNDAY THROUGH SUNDAY EVENING FOR
     WYZ104-105.

NE...NONE.
&&

$$

UPDATE...SML
SHORT TERM...GCC
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...GCC




000
FXUS65 KCYS 210414
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
914 PM MST SAT DEC 20 2014

.UPDATE...
ISSUED AT 913 PM MST SAT DEC 20 2014

FORECAST IS FAIRLY STRAIGHT FORWARD TONIGHT BUT THAT WILL NOT BE
THE CASE THE NEXT FEW DAYS. FOR TONIGHT SOME LIGHT SNOW WILL OCCUR
IN THE SNOWY AND SIERRA MADRE RANGES. ACCUMULATIONS WILL BE
MINIMAL WITH A FEW INCHES THROUGH THE NIGHT. SOME LIGHT SNOW WILL
ALSO OCCUR OUTSIDE OF THE MOUNTAINS OVER PORTIONS OF CARBON AND
ALBANY COUNTIES BUT ANY ACCUMULATIONS WILL GENERALLY BE LESS THAN
ONE INCH.

WINDS WILL INCREASE OVERNIGHT...ESPECIALLY OVER WIND PRONE AREAS
OF SOUTHEAST WYOMING. MODELS ARE SLIGHTLY SLOWER WITH THE ONSET OF
THE WINDS BUT SHOULD SEE ARLINGTON AND BORDEAUX APPROACHING WARNING
CRITERIA TOWARD SUNRISE WITH THE SOUTHERN LARAMIE REACHING
CRITERIA SHORTLY THEREAFTER.

THE MAIN QUESTION FOR SUNDAY INTO MONDAY IS WHAT TYPE OF HEADLINES
SHOULD BE ISSUED. THE PROBLEM IS DETERMINING IMPACTS FROM WIND AND
SNOW...AND JUST HOW MUCH SNOW WILL FALL AND HOW STRONG WITH WINDS
WILL BE. MODELS INDICATE VERY STRONG WINDS OFF THE SURFACE SUNDAY
BUT ALSO A RELATIVELY STRONG INVERSION INITIALLY. THAT INVERSION
WILL BREAK DOWN INTO SUNDAY NIGHT WITH SATURATED SOUNDINGS AND
STEEP LAPSE RATES IN THE BOUNDARY LAYER WHICH IS FAVORABLE FOR
WINDS MIXING TO THE SURFACE AND EVEN SOME CONVECTIVE TYPE WIND
GUSTS. SNOW WILL LIKELY ALSO BE FALLING AT THIS TIME. THE
QUESTION IS HOW HEAVY THE SNOW WILL BE AND HOW MUCH WILL FALL.
CERTAINLY STEEP LAPSE RATES SUGGEST THE POTENTIAL FOR AT LEAST A
SHORT PERIOD OF HEAVY SNOW. IT IS VERY POSSIBLE NEAR BLIZZARD
CONDITIONS WILL EXIST AT TIMES FOR PORTIONS OF CARBON AND ALBANY
COUNTIES LATE SUNDAY AFTERNOON THROUGH THE EVENING HOURS. AT THIS
TIME WATCHES AND WARNINGS REMAIN IN PLACE BUT LIKE
USUAL...HEADLINES WILL EVOLVE OVER THE NEXT 24 HOURS...ESPECIALLY
GIVEN THE CHALLENGES WITH THIS SYSTEM. PLEASE STAY TUNED FOR
WEATHER UPDATES WITH THE CHANGING SITUATION.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 1253 PM MST SAT DEC 20 2014

CHALLENGING FORECAST AHEAD WITH STRONG WINDS...VERY HEAVY SNOW AND
COMBINATION OF WIND AND SNOW THE FORECAST CHALLENGES TONIGHT
THROUGH MONDAY.

CURRENTLY...PRETTY TRANQUIL OUT ACROSS THE CWFA SO FAR TODAY. HIGH
PRESSURE OVER NORTHWESTERN COLORADO THIS AFTERNOON WITH PARTLY
CLOUDY SKIES EAST OF THE LARAMIE RANGE AND MOSTLY CLOUDY WEST.
PACIFIC STORM SYSTEM JUST OFFSHORE OF WASHINGTON STATE THIS
AFTERNOON CONTINUES TO MOVE SOUTHEAST TOWARDS THE COAST.

SHORT TERM GUIDANCE REALLY BEGINS TO SHOW AN UPTICK ON WINDS THIS
EVENING. GFS 700MB WINDS INCREASE TO 55KTS ACROSS CARBON AND
ALBANY COUNTIES WITH 700MB CRAIG TO CASPER HEIGHT GRADIENTS
INCREASING TO 70MTRS AT 06Z. THE NAM WRKHGT PRODUCT A LITTLE
SLOWER ON HEIGHT GRADIENTS INCREASING...SHOWING 850/700MB
GRADIENTS BOTH ABOVE 60MTRS BY 09Z. WILL KEEP THE CURRENT WIND
WARNINGS GOING AS THEY ARE FOR NOW.

BY 12Z SUNDAY...GFS 700MB WINDS REALLY BEGIN CRANKING WITH
65-70KTS WEST OF THE LARAMIE RANGE. PACIFIC LOW PRESSURE SYSTEM
MOVING INTO WESTERN WYOMING AT THAT TIME. WINDS SHOULD BEGIN TO
BECOME STRONG FAIRLY WIDESPREAD BY MID MORNING WITH THE WRKHGT
PRODUCT PEAKING OUT AT 79/74MTRS ON THE 850/700MB HEIGHT GRADIENTS
BY 00Z TOMORROW AFTERNOON. THESE STRONG GRADIENTS CONTINUE INTO
MONDAY MORNING BEFORE EASING.

INCREASING CONCERN FOR POSSIBLE WINTER WEATHER EVENT ALONG THE
I-80 CORRIDOR FROM THE I-80 SUMMIT THROUGH RAWLINS FOR LATE SUNDAY
AFTERNOON THROUGH MONDAY. ALL GUIDANCE SHOWING PRECIP BECOMING
WIDESPREAD BY NOON SUNDAY AND CONTINUING INTO MONDAY MORNING. LATEST
ECMWF AND SREF MOST WIDESPREAD AND AGGRESSIVE WITH QPF
AMOUNTS...THOUGH THE NAM DOES COME IN LINE BY 00Z. COMBINATION OF
VERY STRONG WINDS AND SNOW COULD LEAD TO VERY SERIOUS DRIVING
CONDITIONS WEST OF THE LARAMIE RANGE TOMORROW EVENING INTO MONDAY.

REPLACED THE HIGH WIND WATCHES WE HAD OUT THIS MORNING FOR THE
LOWER ELEVATIONS OF ALBANY AND CARBON COUNTIES WITH A WINTER STORM
WATCH. GRANTED...WINDS ARE GOING TO BE STRONGEST IN THE AFTERNOON
AND THIS SHOULD BE THE TIME WHEN PRECIP SHOULD BE FALLING AS
RAIN...BUT IT WONT TAKE LONG FOR THE PRECIP TO TURN OVER TO SNOW.
WILL WORD THE WATCH FOR STRONG WINDS INITIALLY...THEN A
COMBINATION OF WINDS AND SNOW LATE AFTERNOON AND OVERNIGHT.

SNOWY AND SIERRA MADRE RANGE ARE GOING TO GET POUNDED IN THIS
SETUP. WILL BE ON THE LEFT FRONT QUADRANT OF A 170KT JET THROUGH
MONDAY MORNING. LATEST HPC SNOW FORECAST SHOWING 2+ FEET OF SNOW
THROUGH MONDAY. DO BELIEVE WE COULD SEE MUCH MORE IN THIS
PERSISTENT STRONG UPSLOPE EVENT. MAYBE MORE LIKE 3 FEET BEFORE ALL
IS SAID AND DONE MONDAY NIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 253 PM MST SAT DEC 20 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY THROUGH FRIDAY DUE TO
HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER WEATHER ON CHRISTMAS
DAY. EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY
TRAVEL PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REMAIN COLDER THAN NORMAL ON TUESDAY BEHIND THE
UPPER LEVEL TROUGH FORECAST TO PUSH ACROSS THE AREA TOMORROW AND
MONDAY. HIGHS IN THE 20S TO MID 30S ARE EXPECTED WITH VERY COLD
OVERNIGHT LOWS. TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS
DOWNSLOPE FLOW DEVELOPS...WITH HIGHS IN THE 30S TO LOW 40S. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS GENERALLY INDICATE A RAPIDLY
MOVING UPPER LEVEL TROUGH PUSHING INTO THE AREA. A STRONG PACIFIC
COLD FRONT IS FORECAST TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME
CHRISTMAS MORNING WITH SNOW DEVELOPING BEHIND THE FRONT. BEFORE
THAT...THERE IS THE POTENTIAL FOR A HIGH WIND EVENT ACROSS THE
WIND PRONE AREAS OF SOUTHEAST WYOMING AHEAD OF THE FRONT...BUT
CONDITIONS WILL LIKELY NOT LAST TOO LONG AND MAINLY AFFECT
MOTORISTS WITH LARGER VEHICLES. AS FOR SNOW...THERE IS A LOW
PROBABILITY FOR WINTER STORM CONDITIONS ON CHRISTMAS DAY DUE TO
HOW PROGRESSIVE THIS SYSTEM IS. HOWEVER...THE GEM AND ECMWF DO
HINT AT A SLOWER SOLUTION AS THE STORM DIGS FURTHER TO THE SOUTH.
THE GFS ON THE OTHER HAND IS VERY PROGRESSIVE...WITH SNOW
STRUGGLING TO DEVELOP OVER MOST OF THE HIGH PLAINS MAINLY DUE TO
THE LLVL UPSLOPE FLOW DEVELOPING MUCH LATER IN THE DAY WHEN THE
EVENT IS PRACTICALLY OVER. ALTHOUGH THERE IS A POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE AREA...CONFIDENCE IS RATHER LOW AT
THIS TIME WITH THE MOST FAVORABLE LOCATIONS BEING IN THE MOUNTAINS
AND WELL NORTH OF I80 ACROSS THE HIGH PLAINS. AT THIS TIME...IT
APPEARS THE I80 CORRIDOR MAY HAVE TOO MUCH DRIER DOWNSLOPE FLOW TO
DEAL WITH TO GET ANY SUBSTANTIAL SNOW ACCUMULATIONS GOING. BUT
THIS MAY QUICKLY CHANGE OVER THE NEXT FEW DAYS. KEPT POP BETWEEN
25 TO 35 PERCENT ACROSS THE HIGH PLAINS INCLUDING THE EASTERN I80
CORRIDOR...AND CLOSER TO 50 PERCENT WEST OF THE LARAMIE RANGE.
INCREASED POP IN THE MOUNTAINS WHICH WILL HAVE THE BEST POTENTIAL
TO SEE MODERATE SNOW ACCUMULATIONS WITH THIS SYSTEM. IN EITHER
CASE...MUCH COLDER TEMPERATURES ARE EXPECTED FOR LATER NEXT WEEK.
EARLY MORNING HIGHS BETWEEN 35 TO 45 ON CHRISTMAS DAY WILL RAPIDLY
LOWER INTO THE 20S THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL
LIKELY BE BELOW FREEZING FOR FRIDAY AND SATURDAY AS NORTHERLY FLOW
ALOFT STAYS OVER THE ROCKY MOUNTAIN REGION.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH SUNDAY AFTERNOON)

VFR CONDITIONS SHOULD PREVAIL ACROSS MOST TERMINALS...WITH THE
EXCEPTION OF KRWL. MOUNTAINS WILL BE OBSCURED WITH OROGRAPHIC SNOW
CONTINUING INTO TONIGHT. PERIODS OF IFR CONDITIONS AND LIGHT SNOW
ARE EXPECTED AT KRWL EARLIER TONIGHT UNTIL 05Z. A BRIEF LULL IN THIS
ACTIVITY IS EXPECTED AFTER MIDNIGHT BEFORE MODERATE SNOW DEVELOPS
ACROSS SOUTHERN CARBON COUNTY EARLY SUNDAY MORNING.


&&

.FIRE WEATHER...
ISSUED AT 1253 PM MST SAT DEC 20 2014

NO FIRE WEATHER ISSUES EXPECTED THIS WEEKEND. BREEZY AND MAINLY DRY
CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS THIS AFTERNOON...BUT
THINGS BEGIN TO CHANGE TONIGHT THROUGH THE BEGINNING OF NEXT WEEK. STRONG
WESTERLY WINDS AND SIGNIFICANT MOUNTAIN SNOWFALL WILL RETURN
TONIGHT AND CONTINUE THROUGH MONDAY...WITH WINTER STORM WARNINGS
IN EFFECT FOR THE SNOWY AND SIERRA MADRE RANGES FOR TWO TO THREE FEET
OF SNOW. HIGH WIND WARNINGS ARE IN EFFECT FOR THE WIND PRONE AREAS
OF SOUTHEAST WYOMING FROM LATE TONIGHT THROUGH SUNDAY EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 5 AM MST TUESDAY
     FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST SUNDAY NIGHT
     FOR WYZ116-117.

     WINTER STORM WATCH FROM 8 AM MST SUNDAY THROUGH MONDAY MORNING
     FOR WYZ109-111-113-115.

     HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO MIDNIGHT MST SUNDAY
     NIGHT FOR WYZ106-110.

     HIGH WIND WATCH FROM 8 AM MST SUNDAY THROUGH SUNDAY EVENING FOR
     WYZ104-105.

NE...NONE.
&&

$$

UPDATE...SML
SHORT TERM...GCC
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...GCC




000
FXUS65 KCYS 202345
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
448 PM MST SAT DEC 20 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 1253 PM MST SAT DEC 20 2014

CHALLENGING FORECAST AHEAD WITH STRONG WINDS...VERY HEAVY SNOW AND
COMBINATION OF WIND AND SNOW THE FORECAST CHALLENGES TONIGHT
THROUGH MONDAY.

CURRENTLY...PRETTY TRANQUIL OUT ACROSS THE CWFA SO FAR TODAY. HIGH
PRESSURE OVER NORTHWESTERN COLORADO THIS AFTERNOON WITH PARTLY
CLOUDY SKIES EAST OF THE LARAMIE RANGE AND MOSTLY CLOUDY WEST.
PACIFIC STORM SYSTEM JUST OFFSHORE OF WASHINGTON STATE THIS
AFTERNOON CONTINUES TO MOVE SOUTHEAST TOWARDS THE COAST.

SHORT TERM GUIDANCE REALLY BEGINS TO SHOW AN UPTICK ON WINDS THIS
EVENING. GFS 700MB WINDS INCREASE TO 55KTS ACROSS CARBON AND
ALBANY COUNTIES WITH 700MB CRAIG TO CASPER HEIGHT GRADIENTS
INCREASING TO 70MTRS AT 06Z. THE NAM WRKHGT PRODUCT A LITTLE
SLOWER ON HEIGHT GRADIENTS INCREASING...SHOWING 850/700MB
GRADIENTS BOTH ABOVE 60MTRS BY 09Z. WILL KEEP THE CURRENT WIND
WARNINGS GOING AS THEY ARE FOR NOW.

BY 12Z SUNDAY...GFS 700MB WINDS REALLY BEGIN CRANKING WITH
65-70KTS WEST OF THE LARAMIE RANGE. PACIFIC LOW PRESSURE SYSTEM
MOVING INTO WESTERN WYOMING AT THAT TIME. WINDS SHOULD BEGIN TO
BECOME STRONG FAIRLY WIDESPREAD BY MID MORNING WITH THE WRKHGT
PRODUCT PEAKING OUT AT 79/74MTRS ON THE 850/700MB HEIGHT GRADIENTS
BY 00Z TOMORROW AFTERNOON. THESE STRONG GRADIENTS CONTINUE INTO
MONDAY MORNING BEFORE EASING.

INCREASING CONCERN FOR POSSIBLE WINTER WEATHER EVENT ALONG THE
I-80 CORRIDOR FROM THE I-80 SUMMIT THROUGH RAWLINS FOR LATE SUNDAY
AFTERNOON THROUGH MONDAY. ALL GUIDANCE SHOWING PRECIP BECOMING
WIDESPREAD BY NOON SUNDAY AND CONTINUING INTO MONDAY MORNING. LATEST
ECMWF AND SREF MOST WIDESPREAD AND AGGRESSIVE WITH QPF
AMOUNTS...THOUGH THE NAM DOES COME IN LINE BY 00Z. COMBINATION OF
VERY STRONG WINDS AND SNOW COULD LEAD TO VERY SERIOUS DRIVING
CONDITIONS WEST OF THE LARAMIE RANGE TOMORROW EVENING INTO MONDAY.

REPLACED THE HIGH WIND WATCHES WE HAD OUT THIS MORNING FOR THE
LOWER ELEVATIONS OF ALBANY AND CARBON COUNTIES WITH A WINTER STORM
WATCH. GRANTED...WINDS ARE GOING TO BE STRONGEST IN THE AFTERNOON
AND THIS SHOULD BE THE TIME WHEN PRECIP SHOULD BE FALLING AS
RAIN...BUT IT WONT TAKE LONG FOR THE PRECIP TO TURN OVER TO SNOW.
WILL WORD THE WATCH FOR STRONG WINDS INITIALLY...THEN A
COMBINATION OF WINDS AND SNOW LATE AFTERNOON AND OVERNIGHT.

SNOWY AND SIERRA MADRE RANGE ARE GOING TO GET POUNDED IN THIS
SETUP. WILL BE ON THE LEFT FRONT QUADRANT OF A 170KT JET THROUGH
MONDAY MORNING. LATEST HPC SNOW FORECAST SHOWING 2+ FEET OF SNOW
THROUGH MONDAY. DO BELIEVE WE COULD SEE MUCH MORE IN THIS
PERSISTENT STRONG UPSLOPE EVENT. MAYBE MORE LIKE 3 FEET BEFORE ALL
IS SAID AND DONE MONDAY NIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 253 PM MST SAT DEC 20 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY THROUGH FRIDAY DUE TO
HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER WEATHER ON CHRISTMAS
DAY. EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY
TRAVEL PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REMAIN COLDER THAN NORMAL ON TUESDAY BEHIND THE
UPPER LEVEL TROUGH FORECAST TO PUSH ACROSS THE AREA TOMORROW AND
MONDAY. HIGHS IN THE 20S TO MID 30S ARE EXPECTED WITH VERY COLD
OVERNIGHT LOWS. TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS
DOWNSLOPE FLOW DEVELOPS...WITH HIGHS IN THE 30S TO LOW 40S. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS GENERALLY INDICATE A RAPIDLY
MOVING UPPER LEVEL TROUGH PUSHING INTO THE AREA. A STRONG PACIFIC
COLD FRONT IS FORECAST TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME
CHRISTMAS MORNING WITH SNOW DEVELOPING BEHIND THE FRONT. BEFORE
THAT...THERE IS THE POTENTIAL FOR A HIGH WIND EVENT ACROSS THE
WIND PRONE AREAS OF SOUTHEAST WYOMING AHEAD OF THE FRONT...BUT
CONDITIONS WILL LIKELY NOT LAST TOO LONG AND MAINLY AFFECT
MOTORISTS WITH LARGER VEHICLES. AS FOR SNOW...THERE IS A LOW
PROBABILITY FOR WINTER STORM CONDITIONS ON CHRISTMAS DAY DUE TO
HOW PROGRESSIVE THIS SYSTEM IS. HOWEVER...THE GEM AND ECMWF DO
HINT AT A SLOWER SOLUTION AS THE STORM DIGS FURTHER TO THE SOUTH.
THE GFS ON THE OTHER HAND IS VERY PROGRESSIVE...WITH SNOW
STRUGGLING TO DEVELOP OVER MOST OF THE HIGH PLAINS MAINLY DUE TO
THE LLVL UPSLOPE FLOW DEVELOPING MUCH LATER IN THE DAY WHEN THE
EVENT IS PRACTICALLY OVER. ALTHOUGH THERE IS A POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE AREA...CONFIDENCE IS RATHER LOW AT
THIS TIME WITH THE MOST FAVORABLE LOCATIONS BEING IN THE MOUNTAINS
AND WELL NORTH OF I80 ACROSS THE HIGH PLAINS. AT THIS TIME...IT
APPEARS THE I80 CORRIDOR MAY HAVE TOO MUCH DRIER DOWNSLOPE FLOW TO
DEAL WITH TO GET ANY SUBSTANTIAL SNOW ACCUMULATIONS GOING. BUT
THIS MAY QUICKLY CHANGE OVER THE NEXT FEW DAYS. KEPT POP BETWEEN
25 TO 35 PERCENT ACROSS THE HIGH PLAINS INCLUDING THE EASTERN I80
CORRIDOR...AND CLOSER TO 50 PERCENT WEST OF THE LARAMIE RANGE.
INCREASED POP IN THE MOUNTAINS WHICH WILL HAVE THE BEST POTENTIAL
TO SEE MODERATE SNOW ACCUMULATIONS WITH THIS SYSTEM. IN EITHER
CASE...MUCH COLDER TEMPERATURES ARE EXPECTED FOR LATER NEXT WEEK.
EARLY MORNING HIGHS BETWEEN 35 TO 45 ON CHRISTMAS DAY WILL RAPIDLY
LOWER INTO THE 20S THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL
LIKELY BE BELOW FREEZING FOR FRIDAY AND SATURDAY AS NORTHERLY FLOW
ALOFT STAYS OVER THE ROCKY MOUNTAIN REGION.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH SUNDAY AFTERNOON)

VFR CONDITIONS SHOULD PREVAIL ACROSS MOST TERMINALS...WITH THE
EXCEPTION OF KRWL. MOUNTAINS WILL BE OBSCURED WITH OROGRAPHIC SNOW
CONTINUING INTO TONIGHT. PERIODS OF IFR CONDITIONS AND LIGHT SNOW
ARE EXPECTED AT KRWL EARLIER TONIGHT UNTIL 05Z. A BRIEF LULL IN THIS
ACTIVITY IS EXPECTED AFTER MIDNIGHT BEFORE MODERATE SNOW DEVELOPS
ACROSS SOUTHERN CARBON COUNTY EARLY SUNDAY MORNING.

&&

.FIRE WEATHER...
ISSUED AT 1253 PM MST SAT DEC 20 2014

NO FIRE WEATHER ISSUES EXPECTED THIS WEEKEND. BREEZY AND MAINLY DRY
CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS THIS AFTERNOON...BUT
THINGS BEGIN TO CHANGE TONIGHT THROUGH THE BEGINNING OF NEXT WEEK. STRONG
WESTERLY WINDS AND SIGNIFICANT MOUNTAIN SNOWFALL WILL RETURN
TONIGHT AND CONTINUE THROUGH MONDAY...WITH WINTER STORM WARNINGS
IN EFFECT FOR THE SNOWY AND SIERRA MADRE RANGES FOR TWO TO THREE FEET
OF SNOW. HIGH WIND WARNINGS ARE IN EFFECT FOR THE WIND PRONE AREAS
OF SOUTHEAST WYOMING FROM LATE TONIGHT THROUGH SUNDAY EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 5 AM MST TUESDAY
     FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST SUNDAY NIGHT
     FOR WYZ116-117.

     WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY MORNING
     FOR WYZ109-111-113-115.

     HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO MIDNIGHT MST SUNDAY
     NIGHT FOR WYZ106-110.

     HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING FOR
     WYZ104-105.

NE...NONE.
&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...GCC



000
FXUS65 KCYS 202345
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
448 PM MST SAT DEC 20 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 1253 PM MST SAT DEC 20 2014

CHALLENGING FORECAST AHEAD WITH STRONG WINDS...VERY HEAVY SNOW AND
COMBINATION OF WIND AND SNOW THE FORECAST CHALLENGES TONIGHT
THROUGH MONDAY.

CURRENTLY...PRETTY TRANQUIL OUT ACROSS THE CWFA SO FAR TODAY. HIGH
PRESSURE OVER NORTHWESTERN COLORADO THIS AFTERNOON WITH PARTLY
CLOUDY SKIES EAST OF THE LARAMIE RANGE AND MOSTLY CLOUDY WEST.
PACIFIC STORM SYSTEM JUST OFFSHORE OF WASHINGTON STATE THIS
AFTERNOON CONTINUES TO MOVE SOUTHEAST TOWARDS THE COAST.

SHORT TERM GUIDANCE REALLY BEGINS TO SHOW AN UPTICK ON WINDS THIS
EVENING. GFS 700MB WINDS INCREASE TO 55KTS ACROSS CARBON AND
ALBANY COUNTIES WITH 700MB CRAIG TO CASPER HEIGHT GRADIENTS
INCREASING TO 70MTRS AT 06Z. THE NAM WRKHGT PRODUCT A LITTLE
SLOWER ON HEIGHT GRADIENTS INCREASING...SHOWING 850/700MB
GRADIENTS BOTH ABOVE 60MTRS BY 09Z. WILL KEEP THE CURRENT WIND
WARNINGS GOING AS THEY ARE FOR NOW.

BY 12Z SUNDAY...GFS 700MB WINDS REALLY BEGIN CRANKING WITH
65-70KTS WEST OF THE LARAMIE RANGE. PACIFIC LOW PRESSURE SYSTEM
MOVING INTO WESTERN WYOMING AT THAT TIME. WINDS SHOULD BEGIN TO
BECOME STRONG FAIRLY WIDESPREAD BY MID MORNING WITH THE WRKHGT
PRODUCT PEAKING OUT AT 79/74MTRS ON THE 850/700MB HEIGHT GRADIENTS
BY 00Z TOMORROW AFTERNOON. THESE STRONG GRADIENTS CONTINUE INTO
MONDAY MORNING BEFORE EASING.

INCREASING CONCERN FOR POSSIBLE WINTER WEATHER EVENT ALONG THE
I-80 CORRIDOR FROM THE I-80 SUMMIT THROUGH RAWLINS FOR LATE SUNDAY
AFTERNOON THROUGH MONDAY. ALL GUIDANCE SHOWING PRECIP BECOMING
WIDESPREAD BY NOON SUNDAY AND CONTINUING INTO MONDAY MORNING. LATEST
ECMWF AND SREF MOST WIDESPREAD AND AGGRESSIVE WITH QPF
AMOUNTS...THOUGH THE NAM DOES COME IN LINE BY 00Z. COMBINATION OF
VERY STRONG WINDS AND SNOW COULD LEAD TO VERY SERIOUS DRIVING
CONDITIONS WEST OF THE LARAMIE RANGE TOMORROW EVENING INTO MONDAY.

REPLACED THE HIGH WIND WATCHES WE HAD OUT THIS MORNING FOR THE
LOWER ELEVATIONS OF ALBANY AND CARBON COUNTIES WITH A WINTER STORM
WATCH. GRANTED...WINDS ARE GOING TO BE STRONGEST IN THE AFTERNOON
AND THIS SHOULD BE THE TIME WHEN PRECIP SHOULD BE FALLING AS
RAIN...BUT IT WONT TAKE LONG FOR THE PRECIP TO TURN OVER TO SNOW.
WILL WORD THE WATCH FOR STRONG WINDS INITIALLY...THEN A
COMBINATION OF WINDS AND SNOW LATE AFTERNOON AND OVERNIGHT.

SNOWY AND SIERRA MADRE RANGE ARE GOING TO GET POUNDED IN THIS
SETUP. WILL BE ON THE LEFT FRONT QUADRANT OF A 170KT JET THROUGH
MONDAY MORNING. LATEST HPC SNOW FORECAST SHOWING 2+ FEET OF SNOW
THROUGH MONDAY. DO BELIEVE WE COULD SEE MUCH MORE IN THIS
PERSISTENT STRONG UPSLOPE EVENT. MAYBE MORE LIKE 3 FEET BEFORE ALL
IS SAID AND DONE MONDAY NIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 253 PM MST SAT DEC 20 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY THROUGH FRIDAY DUE TO
HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER WEATHER ON CHRISTMAS
DAY. EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY
TRAVEL PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REMAIN COLDER THAN NORMAL ON TUESDAY BEHIND THE
UPPER LEVEL TROUGH FORECAST TO PUSH ACROSS THE AREA TOMORROW AND
MONDAY. HIGHS IN THE 20S TO MID 30S ARE EXPECTED WITH VERY COLD
OVERNIGHT LOWS. TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS
DOWNSLOPE FLOW DEVELOPS...WITH HIGHS IN THE 30S TO LOW 40S. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS GENERALLY INDICATE A RAPIDLY
MOVING UPPER LEVEL TROUGH PUSHING INTO THE AREA. A STRONG PACIFIC
COLD FRONT IS FORECAST TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME
CHRISTMAS MORNING WITH SNOW DEVELOPING BEHIND THE FRONT. BEFORE
THAT...THERE IS THE POTENTIAL FOR A HIGH WIND EVENT ACROSS THE
WIND PRONE AREAS OF SOUTHEAST WYOMING AHEAD OF THE FRONT...BUT
CONDITIONS WILL LIKELY NOT LAST TOO LONG AND MAINLY AFFECT
MOTORISTS WITH LARGER VEHICLES. AS FOR SNOW...THERE IS A LOW
PROBABILITY FOR WINTER STORM CONDITIONS ON CHRISTMAS DAY DUE TO
HOW PROGRESSIVE THIS SYSTEM IS. HOWEVER...THE GEM AND ECMWF DO
HINT AT A SLOWER SOLUTION AS THE STORM DIGS FURTHER TO THE SOUTH.
THE GFS ON THE OTHER HAND IS VERY PROGRESSIVE...WITH SNOW
STRUGGLING TO DEVELOP OVER MOST OF THE HIGH PLAINS MAINLY DUE TO
THE LLVL UPSLOPE FLOW DEVELOPING MUCH LATER IN THE DAY WHEN THE
EVENT IS PRACTICALLY OVER. ALTHOUGH THERE IS A POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE AREA...CONFIDENCE IS RATHER LOW AT
THIS TIME WITH THE MOST FAVORABLE LOCATIONS BEING IN THE MOUNTAINS
AND WELL NORTH OF I80 ACROSS THE HIGH PLAINS. AT THIS TIME...IT
APPEARS THE I80 CORRIDOR MAY HAVE TOO MUCH DRIER DOWNSLOPE FLOW TO
DEAL WITH TO GET ANY SUBSTANTIAL SNOW ACCUMULATIONS GOING. BUT
THIS MAY QUICKLY CHANGE OVER THE NEXT FEW DAYS. KEPT POP BETWEEN
25 TO 35 PERCENT ACROSS THE HIGH PLAINS INCLUDING THE EASTERN I80
CORRIDOR...AND CLOSER TO 50 PERCENT WEST OF THE LARAMIE RANGE.
INCREASED POP IN THE MOUNTAINS WHICH WILL HAVE THE BEST POTENTIAL
TO SEE MODERATE SNOW ACCUMULATIONS WITH THIS SYSTEM. IN EITHER
CASE...MUCH COLDER TEMPERATURES ARE EXPECTED FOR LATER NEXT WEEK.
EARLY MORNING HIGHS BETWEEN 35 TO 45 ON CHRISTMAS DAY WILL RAPIDLY
LOWER INTO THE 20S THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL
LIKELY BE BELOW FREEZING FOR FRIDAY AND SATURDAY AS NORTHERLY FLOW
ALOFT STAYS OVER THE ROCKY MOUNTAIN REGION.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH SUNDAY AFTERNOON)

VFR CONDITIONS SHOULD PREVAIL ACROSS MOST TERMINALS...WITH THE
EXCEPTION OF KRWL. MOUNTAINS WILL BE OBSCURED WITH OROGRAPHIC SNOW
CONTINUING INTO TONIGHT. PERIODS OF IFR CONDITIONS AND LIGHT SNOW
ARE EXPECTED AT KRWL EARLIER TONIGHT UNTIL 05Z. A BRIEF LULL IN THIS
ACTIVITY IS EXPECTED AFTER MIDNIGHT BEFORE MODERATE SNOW DEVELOPS
ACROSS SOUTHERN CARBON COUNTY EARLY SUNDAY MORNING.

&&

.FIRE WEATHER...
ISSUED AT 1253 PM MST SAT DEC 20 2014

NO FIRE WEATHER ISSUES EXPECTED THIS WEEKEND. BREEZY AND MAINLY DRY
CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS THIS AFTERNOON...BUT
THINGS BEGIN TO CHANGE TONIGHT THROUGH THE BEGINNING OF NEXT WEEK. STRONG
WESTERLY WINDS AND SIGNIFICANT MOUNTAIN SNOWFALL WILL RETURN
TONIGHT AND CONTINUE THROUGH MONDAY...WITH WINTER STORM WARNINGS
IN EFFECT FOR THE SNOWY AND SIERRA MADRE RANGES FOR TWO TO THREE FEET
OF SNOW. HIGH WIND WARNINGS ARE IN EFFECT FOR THE WIND PRONE AREAS
OF SOUTHEAST WYOMING FROM LATE TONIGHT THROUGH SUNDAY EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 5 AM MST TUESDAY
     FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST SUNDAY NIGHT
     FOR WYZ116-117.

     WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY MORNING
     FOR WYZ109-111-113-115.

     HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO MIDNIGHT MST SUNDAY
     NIGHT FOR WYZ106-110.

     HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING FOR
     WYZ104-105.

NE...NONE.
&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...GCC



000
FXUS65 KCYS 202345
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
448 PM MST SAT DEC 20 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 1253 PM MST SAT DEC 20 2014

CHALLENGING FORECAST AHEAD WITH STRONG WINDS...VERY HEAVY SNOW AND
COMBINATION OF WIND AND SNOW THE FORECAST CHALLENGES TONIGHT
THROUGH MONDAY.

CURRENTLY...PRETTY TRANQUIL OUT ACROSS THE CWFA SO FAR TODAY. HIGH
PRESSURE OVER NORTHWESTERN COLORADO THIS AFTERNOON WITH PARTLY
CLOUDY SKIES EAST OF THE LARAMIE RANGE AND MOSTLY CLOUDY WEST.
PACIFIC STORM SYSTEM JUST OFFSHORE OF WASHINGTON STATE THIS
AFTERNOON CONTINUES TO MOVE SOUTHEAST TOWARDS THE COAST.

SHORT TERM GUIDANCE REALLY BEGINS TO SHOW AN UPTICK ON WINDS THIS
EVENING. GFS 700MB WINDS INCREASE TO 55KTS ACROSS CARBON AND
ALBANY COUNTIES WITH 700MB CRAIG TO CASPER HEIGHT GRADIENTS
INCREASING TO 70MTRS AT 06Z. THE NAM WRKHGT PRODUCT A LITTLE
SLOWER ON HEIGHT GRADIENTS INCREASING...SHOWING 850/700MB
GRADIENTS BOTH ABOVE 60MTRS BY 09Z. WILL KEEP THE CURRENT WIND
WARNINGS GOING AS THEY ARE FOR NOW.

BY 12Z SUNDAY...GFS 700MB WINDS REALLY BEGIN CRANKING WITH
65-70KTS WEST OF THE LARAMIE RANGE. PACIFIC LOW PRESSURE SYSTEM
MOVING INTO WESTERN WYOMING AT THAT TIME. WINDS SHOULD BEGIN TO
BECOME STRONG FAIRLY WIDESPREAD BY MID MORNING WITH THE WRKHGT
PRODUCT PEAKING OUT AT 79/74MTRS ON THE 850/700MB HEIGHT GRADIENTS
BY 00Z TOMORROW AFTERNOON. THESE STRONG GRADIENTS CONTINUE INTO
MONDAY MORNING BEFORE EASING.

INCREASING CONCERN FOR POSSIBLE WINTER WEATHER EVENT ALONG THE
I-80 CORRIDOR FROM THE I-80 SUMMIT THROUGH RAWLINS FOR LATE SUNDAY
AFTERNOON THROUGH MONDAY. ALL GUIDANCE SHOWING PRECIP BECOMING
WIDESPREAD BY NOON SUNDAY AND CONTINUING INTO MONDAY MORNING. LATEST
ECMWF AND SREF MOST WIDESPREAD AND AGGRESSIVE WITH QPF
AMOUNTS...THOUGH THE NAM DOES COME IN LINE BY 00Z. COMBINATION OF
VERY STRONG WINDS AND SNOW COULD LEAD TO VERY SERIOUS DRIVING
CONDITIONS WEST OF THE LARAMIE RANGE TOMORROW EVENING INTO MONDAY.

REPLACED THE HIGH WIND WATCHES WE HAD OUT THIS MORNING FOR THE
LOWER ELEVATIONS OF ALBANY AND CARBON COUNTIES WITH A WINTER STORM
WATCH. GRANTED...WINDS ARE GOING TO BE STRONGEST IN THE AFTERNOON
AND THIS SHOULD BE THE TIME WHEN PRECIP SHOULD BE FALLING AS
RAIN...BUT IT WONT TAKE LONG FOR THE PRECIP TO TURN OVER TO SNOW.
WILL WORD THE WATCH FOR STRONG WINDS INITIALLY...THEN A
COMBINATION OF WINDS AND SNOW LATE AFTERNOON AND OVERNIGHT.

SNOWY AND SIERRA MADRE RANGE ARE GOING TO GET POUNDED IN THIS
SETUP. WILL BE ON THE LEFT FRONT QUADRANT OF A 170KT JET THROUGH
MONDAY MORNING. LATEST HPC SNOW FORECAST SHOWING 2+ FEET OF SNOW
THROUGH MONDAY. DO BELIEVE WE COULD SEE MUCH MORE IN THIS
PERSISTENT STRONG UPSLOPE EVENT. MAYBE MORE LIKE 3 FEET BEFORE ALL
IS SAID AND DONE MONDAY NIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 253 PM MST SAT DEC 20 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY THROUGH FRIDAY DUE TO
HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER WEATHER ON CHRISTMAS
DAY. EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY
TRAVEL PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REMAIN COLDER THAN NORMAL ON TUESDAY BEHIND THE
UPPER LEVEL TROUGH FORECAST TO PUSH ACROSS THE AREA TOMORROW AND
MONDAY. HIGHS IN THE 20S TO MID 30S ARE EXPECTED WITH VERY COLD
OVERNIGHT LOWS. TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS
DOWNSLOPE FLOW DEVELOPS...WITH HIGHS IN THE 30S TO LOW 40S. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS GENERALLY INDICATE A RAPIDLY
MOVING UPPER LEVEL TROUGH PUSHING INTO THE AREA. A STRONG PACIFIC
COLD FRONT IS FORECAST TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME
CHRISTMAS MORNING WITH SNOW DEVELOPING BEHIND THE FRONT. BEFORE
THAT...THERE IS THE POTENTIAL FOR A HIGH WIND EVENT ACROSS THE
WIND PRONE AREAS OF SOUTHEAST WYOMING AHEAD OF THE FRONT...BUT
CONDITIONS WILL LIKELY NOT LAST TOO LONG AND MAINLY AFFECT
MOTORISTS WITH LARGER VEHICLES. AS FOR SNOW...THERE IS A LOW
PROBABILITY FOR WINTER STORM CONDITIONS ON CHRISTMAS DAY DUE TO
HOW PROGRESSIVE THIS SYSTEM IS. HOWEVER...THE GEM AND ECMWF DO
HINT AT A SLOWER SOLUTION AS THE STORM DIGS FURTHER TO THE SOUTH.
THE GFS ON THE OTHER HAND IS VERY PROGRESSIVE...WITH SNOW
STRUGGLING TO DEVELOP OVER MOST OF THE HIGH PLAINS MAINLY DUE TO
THE LLVL UPSLOPE FLOW DEVELOPING MUCH LATER IN THE DAY WHEN THE
EVENT IS PRACTICALLY OVER. ALTHOUGH THERE IS A POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE AREA...CONFIDENCE IS RATHER LOW AT
THIS TIME WITH THE MOST FAVORABLE LOCATIONS BEING IN THE MOUNTAINS
AND WELL NORTH OF I80 ACROSS THE HIGH PLAINS. AT THIS TIME...IT
APPEARS THE I80 CORRIDOR MAY HAVE TOO MUCH DRIER DOWNSLOPE FLOW TO
DEAL WITH TO GET ANY SUBSTANTIAL SNOW ACCUMULATIONS GOING. BUT
THIS MAY QUICKLY CHANGE OVER THE NEXT FEW DAYS. KEPT POP BETWEEN
25 TO 35 PERCENT ACROSS THE HIGH PLAINS INCLUDING THE EASTERN I80
CORRIDOR...AND CLOSER TO 50 PERCENT WEST OF THE LARAMIE RANGE.
INCREASED POP IN THE MOUNTAINS WHICH WILL HAVE THE BEST POTENTIAL
TO SEE MODERATE SNOW ACCUMULATIONS WITH THIS SYSTEM. IN EITHER
CASE...MUCH COLDER TEMPERATURES ARE EXPECTED FOR LATER NEXT WEEK.
EARLY MORNING HIGHS BETWEEN 35 TO 45 ON CHRISTMAS DAY WILL RAPIDLY
LOWER INTO THE 20S THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL
LIKELY BE BELOW FREEZING FOR FRIDAY AND SATURDAY AS NORTHERLY FLOW
ALOFT STAYS OVER THE ROCKY MOUNTAIN REGION.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH SUNDAY AFTERNOON)

VFR CONDITIONS SHOULD PREVAIL ACROSS MOST TERMINALS...WITH THE
EXCEPTION OF KRWL. MOUNTAINS WILL BE OBSCURED WITH OROGRAPHIC SNOW
CONTINUING INTO TONIGHT. PERIODS OF IFR CONDITIONS AND LIGHT SNOW
ARE EXPECTED AT KRWL EARLIER TONIGHT UNTIL 05Z. A BRIEF LULL IN THIS
ACTIVITY IS EXPECTED AFTER MIDNIGHT BEFORE MODERATE SNOW DEVELOPS
ACROSS SOUTHERN CARBON COUNTY EARLY SUNDAY MORNING.

&&

.FIRE WEATHER...
ISSUED AT 1253 PM MST SAT DEC 20 2014

NO FIRE WEATHER ISSUES EXPECTED THIS WEEKEND. BREEZY AND MAINLY DRY
CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS THIS AFTERNOON...BUT
THINGS BEGIN TO CHANGE TONIGHT THROUGH THE BEGINNING OF NEXT WEEK. STRONG
WESTERLY WINDS AND SIGNIFICANT MOUNTAIN SNOWFALL WILL RETURN
TONIGHT AND CONTINUE THROUGH MONDAY...WITH WINTER STORM WARNINGS
IN EFFECT FOR THE SNOWY AND SIERRA MADRE RANGES FOR TWO TO THREE FEET
OF SNOW. HIGH WIND WARNINGS ARE IN EFFECT FOR THE WIND PRONE AREAS
OF SOUTHEAST WYOMING FROM LATE TONIGHT THROUGH SUNDAY EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 5 AM MST TUESDAY
     FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST SUNDAY NIGHT
     FOR WYZ116-117.

     WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY MORNING
     FOR WYZ109-111-113-115.

     HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO MIDNIGHT MST SUNDAY
     NIGHT FOR WYZ106-110.

     HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING FOR
     WYZ104-105.

NE...NONE.
&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...GCC



000
FXUS65 KCYS 202345
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
448 PM MST SAT DEC 20 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 1253 PM MST SAT DEC 20 2014

CHALLENGING FORECAST AHEAD WITH STRONG WINDS...VERY HEAVY SNOW AND
COMBINATION OF WIND AND SNOW THE FORECAST CHALLENGES TONIGHT
THROUGH MONDAY.

CURRENTLY...PRETTY TRANQUIL OUT ACROSS THE CWFA SO FAR TODAY. HIGH
PRESSURE OVER NORTHWESTERN COLORADO THIS AFTERNOON WITH PARTLY
CLOUDY SKIES EAST OF THE LARAMIE RANGE AND MOSTLY CLOUDY WEST.
PACIFIC STORM SYSTEM JUST OFFSHORE OF WASHINGTON STATE THIS
AFTERNOON CONTINUES TO MOVE SOUTHEAST TOWARDS THE COAST.

SHORT TERM GUIDANCE REALLY BEGINS TO SHOW AN UPTICK ON WINDS THIS
EVENING. GFS 700MB WINDS INCREASE TO 55KTS ACROSS CARBON AND
ALBANY COUNTIES WITH 700MB CRAIG TO CASPER HEIGHT GRADIENTS
INCREASING TO 70MTRS AT 06Z. THE NAM WRKHGT PRODUCT A LITTLE
SLOWER ON HEIGHT GRADIENTS INCREASING...SHOWING 850/700MB
GRADIENTS BOTH ABOVE 60MTRS BY 09Z. WILL KEEP THE CURRENT WIND
WARNINGS GOING AS THEY ARE FOR NOW.

BY 12Z SUNDAY...GFS 700MB WINDS REALLY BEGIN CRANKING WITH
65-70KTS WEST OF THE LARAMIE RANGE. PACIFIC LOW PRESSURE SYSTEM
MOVING INTO WESTERN WYOMING AT THAT TIME. WINDS SHOULD BEGIN TO
BECOME STRONG FAIRLY WIDESPREAD BY MID MORNING WITH THE WRKHGT
PRODUCT PEAKING OUT AT 79/74MTRS ON THE 850/700MB HEIGHT GRADIENTS
BY 00Z TOMORROW AFTERNOON. THESE STRONG GRADIENTS CONTINUE INTO
MONDAY MORNING BEFORE EASING.

INCREASING CONCERN FOR POSSIBLE WINTER WEATHER EVENT ALONG THE
I-80 CORRIDOR FROM THE I-80 SUMMIT THROUGH RAWLINS FOR LATE SUNDAY
AFTERNOON THROUGH MONDAY. ALL GUIDANCE SHOWING PRECIP BECOMING
WIDESPREAD BY NOON SUNDAY AND CONTINUING INTO MONDAY MORNING. LATEST
ECMWF AND SREF MOST WIDESPREAD AND AGGRESSIVE WITH QPF
AMOUNTS...THOUGH THE NAM DOES COME IN LINE BY 00Z. COMBINATION OF
VERY STRONG WINDS AND SNOW COULD LEAD TO VERY SERIOUS DRIVING
CONDITIONS WEST OF THE LARAMIE RANGE TOMORROW EVENING INTO MONDAY.

REPLACED THE HIGH WIND WATCHES WE HAD OUT THIS MORNING FOR THE
LOWER ELEVATIONS OF ALBANY AND CARBON COUNTIES WITH A WINTER STORM
WATCH. GRANTED...WINDS ARE GOING TO BE STRONGEST IN THE AFTERNOON
AND THIS SHOULD BE THE TIME WHEN PRECIP SHOULD BE FALLING AS
RAIN...BUT IT WONT TAKE LONG FOR THE PRECIP TO TURN OVER TO SNOW.
WILL WORD THE WATCH FOR STRONG WINDS INITIALLY...THEN A
COMBINATION OF WINDS AND SNOW LATE AFTERNOON AND OVERNIGHT.

SNOWY AND SIERRA MADRE RANGE ARE GOING TO GET POUNDED IN THIS
SETUP. WILL BE ON THE LEFT FRONT QUADRANT OF A 170KT JET THROUGH
MONDAY MORNING. LATEST HPC SNOW FORECAST SHOWING 2+ FEET OF SNOW
THROUGH MONDAY. DO BELIEVE WE COULD SEE MUCH MORE IN THIS
PERSISTENT STRONG UPSLOPE EVENT. MAYBE MORE LIKE 3 FEET BEFORE ALL
IS SAID AND DONE MONDAY NIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 253 PM MST SAT DEC 20 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY THROUGH FRIDAY DUE TO
HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER WEATHER ON CHRISTMAS
DAY. EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY
TRAVEL PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REMAIN COLDER THAN NORMAL ON TUESDAY BEHIND THE
UPPER LEVEL TROUGH FORECAST TO PUSH ACROSS THE AREA TOMORROW AND
MONDAY. HIGHS IN THE 20S TO MID 30S ARE EXPECTED WITH VERY COLD
OVERNIGHT LOWS. TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS
DOWNSLOPE FLOW DEVELOPS...WITH HIGHS IN THE 30S TO LOW 40S. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS GENERALLY INDICATE A RAPIDLY
MOVING UPPER LEVEL TROUGH PUSHING INTO THE AREA. A STRONG PACIFIC
COLD FRONT IS FORECAST TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME
CHRISTMAS MORNING WITH SNOW DEVELOPING BEHIND THE FRONT. BEFORE
THAT...THERE IS THE POTENTIAL FOR A HIGH WIND EVENT ACROSS THE
WIND PRONE AREAS OF SOUTHEAST WYOMING AHEAD OF THE FRONT...BUT
CONDITIONS WILL LIKELY NOT LAST TOO LONG AND MAINLY AFFECT
MOTORISTS WITH LARGER VEHICLES. AS FOR SNOW...THERE IS A LOW
PROBABILITY FOR WINTER STORM CONDITIONS ON CHRISTMAS DAY DUE TO
HOW PROGRESSIVE THIS SYSTEM IS. HOWEVER...THE GEM AND ECMWF DO
HINT AT A SLOWER SOLUTION AS THE STORM DIGS FURTHER TO THE SOUTH.
THE GFS ON THE OTHER HAND IS VERY PROGRESSIVE...WITH SNOW
STRUGGLING TO DEVELOP OVER MOST OF THE HIGH PLAINS MAINLY DUE TO
THE LLVL UPSLOPE FLOW DEVELOPING MUCH LATER IN THE DAY WHEN THE
EVENT IS PRACTICALLY OVER. ALTHOUGH THERE IS A POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE AREA...CONFIDENCE IS RATHER LOW AT
THIS TIME WITH THE MOST FAVORABLE LOCATIONS BEING IN THE MOUNTAINS
AND WELL NORTH OF I80 ACROSS THE HIGH PLAINS. AT THIS TIME...IT
APPEARS THE I80 CORRIDOR MAY HAVE TOO MUCH DRIER DOWNSLOPE FLOW TO
DEAL WITH TO GET ANY SUBSTANTIAL SNOW ACCUMULATIONS GOING. BUT
THIS MAY QUICKLY CHANGE OVER THE NEXT FEW DAYS. KEPT POP BETWEEN
25 TO 35 PERCENT ACROSS THE HIGH PLAINS INCLUDING THE EASTERN I80
CORRIDOR...AND CLOSER TO 50 PERCENT WEST OF THE LARAMIE RANGE.
INCREASED POP IN THE MOUNTAINS WHICH WILL HAVE THE BEST POTENTIAL
TO SEE MODERATE SNOW ACCUMULATIONS WITH THIS SYSTEM. IN EITHER
CASE...MUCH COLDER TEMPERATURES ARE EXPECTED FOR LATER NEXT WEEK.
EARLY MORNING HIGHS BETWEEN 35 TO 45 ON CHRISTMAS DAY WILL RAPIDLY
LOWER INTO THE 20S THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL
LIKELY BE BELOW FREEZING FOR FRIDAY AND SATURDAY AS NORTHERLY FLOW
ALOFT STAYS OVER THE ROCKY MOUNTAIN REGION.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH SUNDAY AFTERNOON)

VFR CONDITIONS SHOULD PREVAIL ACROSS MOST TERMINALS...WITH THE
EXCEPTION OF KRWL. MOUNTAINS WILL BE OBSCURED WITH OROGRAPHIC SNOW
CONTINUING INTO TONIGHT. PERIODS OF IFR CONDITIONS AND LIGHT SNOW
ARE EXPECTED AT KRWL EARLIER TONIGHT UNTIL 05Z. A BRIEF LULL IN THIS
ACTIVITY IS EXPECTED AFTER MIDNIGHT BEFORE MODERATE SNOW DEVELOPS
ACROSS SOUTHERN CARBON COUNTY EARLY SUNDAY MORNING.

&&

.FIRE WEATHER...
ISSUED AT 1253 PM MST SAT DEC 20 2014

NO FIRE WEATHER ISSUES EXPECTED THIS WEEKEND. BREEZY AND MAINLY DRY
CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS THIS AFTERNOON...BUT
THINGS BEGIN TO CHANGE TONIGHT THROUGH THE BEGINNING OF NEXT WEEK. STRONG
WESTERLY WINDS AND SIGNIFICANT MOUNTAIN SNOWFALL WILL RETURN
TONIGHT AND CONTINUE THROUGH MONDAY...WITH WINTER STORM WARNINGS
IN EFFECT FOR THE SNOWY AND SIERRA MADRE RANGES FOR TWO TO THREE FEET
OF SNOW. HIGH WIND WARNINGS ARE IN EFFECT FOR THE WIND PRONE AREAS
OF SOUTHEAST WYOMING FROM LATE TONIGHT THROUGH SUNDAY EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 5 AM MST TUESDAY
     FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST SUNDAY NIGHT
     FOR WYZ116-117.

     WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY MORNING
     FOR WYZ109-111-113-115.

     HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO MIDNIGHT MST SUNDAY
     NIGHT FOR WYZ106-110.

     HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING FOR
     WYZ104-105.

NE...NONE.
&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...GCC



000
FXUS65 KRIW 202225 CCA
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
249 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 00Z MONDAY AT THE
AIRPORTS. ALONG AND EAST OF THE CONTINENTAL DIVIDE OVER THE
MOUNTAINS MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW
AND BLOWING SNOW WILL BECOME PREVAILING ABOVE 8500 FEET WITH
WIDESPREAD MOUNTAIN OBSCURATIONS BY 06Z.  STRONG WEST WINDS WILL
PRODUCE AREAS OF LOW LEVEL WIND SHEAR ALONG AND NEAR THE EAST
SLOPES OF THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW AND
BLOWING SNOW WILL BECOME PREVAILING BY 06Z WITH WIDESPREAD MOUNTAIN
OBSCURATIONS. STRONG WEST WINDS WILL PRODUCE AREAS OF LOW LEVEL
WIND SHEAR AND BLOWING SNOW ALONG AND NEAR THE SLOPES OF THE
MOUNTAINS.

&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STROM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER








000
FXUS65 KRIW 202225 CCA
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
249 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 00Z MONDAY AT THE
AIRPORTS. ALONG AND EAST OF THE CONTINENTAL DIVIDE OVER THE
MOUNTAINS MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW
AND BLOWING SNOW WILL BECOME PREVAILING ABOVE 8500 FEET WITH
WIDESPREAD MOUNTAIN OBSCURATIONS BY 06Z.  STRONG WEST WINDS WILL
PRODUCE AREAS OF LOW LEVEL WIND SHEAR ALONG AND NEAR THE EAST
SLOPES OF THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW AND
BLOWING SNOW WILL BECOME PREVAILING BY 06Z WITH WIDESPREAD MOUNTAIN
OBSCURATIONS. STRONG WEST WINDS WILL PRODUCE AREAS OF LOW LEVEL
WIND SHEAR AND BLOWING SNOW ALONG AND NEAR THE SLOPES OF THE
MOUNTAINS.

&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STROM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER








000
FXUS65 KRIW 202225 CCA
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
249 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 00Z MONDAY AT THE
AIRPORTS. ALONG AND EAST OF THE CONTINENTAL DIVIDE OVER THE
MOUNTAINS MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW
AND BLOWING SNOW WILL BECOME PREVAILING ABOVE 8500 FEET WITH
WIDESPREAD MOUNTAIN OBSCURATIONS BY 06Z.  STRONG WEST WINDS WILL
PRODUCE AREAS OF LOW LEVEL WIND SHEAR ALONG AND NEAR THE EAST
SLOPES OF THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW AND
BLOWING SNOW WILL BECOME PREVAILING BY 06Z WITH WIDESPREAD MOUNTAIN
OBSCURATIONS. STRONG WEST WINDS WILL PRODUCE AREAS OF LOW LEVEL
WIND SHEAR AND BLOWING SNOW ALONG AND NEAR THE SLOPES OF THE
MOUNTAINS.

&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STROM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER








000
FXUS65 KRIW 202225 CCA
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
249 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 00Z MONDAY AT THE
AIRPORTS. ALONG AND EAST OF THE CONTINENTAL DIVIDE OVER THE
MOUNTAINS MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW
AND BLOWING SNOW WILL BECOME PREVAILING ABOVE 8500 FEET WITH
WIDESPREAD MOUNTAIN OBSCURATIONS BY 06Z.  STRONG WEST WINDS WILL
PRODUCE AREAS OF LOW LEVEL WIND SHEAR ALONG AND NEAR THE EAST
SLOPES OF THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW AND
BLOWING SNOW WILL BECOME PREVAILING BY 06Z WITH WIDESPREAD MOUNTAIN
OBSCURATIONS. STRONG WEST WINDS WILL PRODUCE AREAS OF LOW LEVEL
WIND SHEAR AND BLOWING SNOW ALONG AND NEAR THE SLOPES OF THE
MOUNTAINS.

&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STROM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER








000
FXUS63 KUNR 202222
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
322 PM MST SAT DEC 20 2014

.SHORT TERM...THIS EVENING THROUGH SUNDAY NIGHT
ISSUED AT 319 PM MST SAT DEC 20 2014

CURRENT SURFACE ANALYSIS SHOWS WARM FRONT JUST TO THE EAST OF THE
FORECAST AREA. UPPER LEVEL ANALYSIS DEPICTS NEAR ZONAL FLOW ACROSS
THE REGION...WITH A STRONG STORM SYSTEM AND UPPER JET PUSHING
ACROSS THE PACIFIC NW. WATER VAPOR IMAGERY SHOWS A WEAK SHORTWAVE
HAS MOVED EAST OF THE AREA...WITH PARTLY CLOUDY SKIES BEHIND IT.
TEMPS RANGE FROM THE UPPER 30S ACROSS FAR SOUTH CENTRAL SD TO NEAR
50 IN THE RAPID CITY AREA. WINDS ARE MOSTLY ON THE LIGHT SIDE FROM
THE WEST AND NORTHWEST.

A UNSETTLED PATTERN WILL TAKE SHAPE FOR THE END OF THE WEEKEND AND
INTO EARLY NEXT WEEK AS A DEVELOPING LOW PRESSURE SYSTEM MOVES
SOUTHEAST ACROSS THE REGION. HOWEVER...IT WILL REMAIN MILD INTO
SUNDAY BEFORE THIS SYSTEM PUSHES IN. THE STORM WILL BRING AT LEAST
SOME LIGHT RAIN AND SNOW TO MOST AREAS...ALONG WITH STRONG NORTHWEST
WINDS EARLY NEXT WEEK.

FOR TONIGHT...SKIES WILL REMAIN PARTLY CLOUDY IN GENERAL AS WEST TO
SOUTHWEST WINDS DEVELOP. THE WINDS WILL BECOME BREEZY OVERNIGHT OVER
PORTIONS OF NORTHEAST WY...ESPECIALLY CAMPBELL CO. RELATIVELY MILD
TEMPS CAN BE EXPECTED...WITH LOWS IN THE 20S AND LOWER 30S...A BIT
WARMER ACROSS THE EASTERN SLOPES OF THE BLACK HILLS.

CLOUDS WILL BEGIN TO INCREASE FROM THE WEST SUNDAY MORNING...WITH
SKIES BECOMING MOSTLY CLOUDY ACROSS THE ENTIRE AREA BY MID
AFTERNOON. MILDER AIR WILL REMAIN ACROSS THE REGION THROUGH MUCH OF
THE DAY...WITH HIGHS IN THE 40S AND LOWER 50S...WARMEST AGAIN ACROSS
THE EASTERN SLOPES OF THE BLACK HILLS AND ADJACENT PLAINS.
DEVELOPING LOW PRESSURE WILL MOVE ACROSS NORTHERN MT DURING THE DAY
AND INTO ND/NORTHERN SD SUNDAY NIGHT...DRAGGING A COLD FRONT ACROSS
THE CWA DURING THE AFTERNOON AND EVENING HOURS. RAIN SHOWERS WILL
DEVELOP ALONG AND BEHIND THE COLD FRONT...MOSTLY DURING THE
AFTERNOON...AS UPPER LEVEL ENERGY ACCOMPANIES THE FRONT. THE BEST
CHANCES DURING THE AFTERNOON LOOK TO BE ACROSS FAR NORTHEAST
WY...SOUTHEAST MT...FAR NORTHWEST SD...AND EVENTUALLY THE NORTHERN
BLACK HILLS AREA. NORTHWESTERLY WINDS WILL INCREASE BEHIND THE FRONT
LATE SUNDAY AND SUNDAY NIGHT...BECOMING BREEZY TO WINDY IN MANY
AREAS OVERNIGHT.

UPPER TROF AND DEVELOPING LOW PRESSURE SYSTEM WILL TRACK FROM MT ON
SUNDAY TO SOMEWHERE OVER THE EASTERN DAKOTAS ON MONDAY MORNING.
VARIOUS MODELS CONTINUE TO BE IN SOME DISAGREEMENT ON TRACK AND
STRENGTH OF THIS SYSTEM. FOR SUNDAY NIGHT...WILL KEEP THE BEST
CHANCES FOR PCPN OVER NORTHEASTERN PORTIONS OF THE CWA...AS WELL AS
THE NORTHERN BLACK HILLS AREA. PCPN WILL GRADUALLY CHANGE OVER TO
SNOW SUNDAY NIGHT...WITH THE QUICKEST CHANGE OVER THE BLACK HILLS.
NOT EXPECTING MUCH IN THE WAY OF SNOW ACCUMULATION OVER THE PLAINS
AS MOST OF THE PCPN WILL BE OUT OF THE AREA BY THE TIME TEMPS DROP
OFF ENOUGH. HOWEVER...FORECAST SOUNDINGS AND FROUDE ANALYSIS SUGGEST
FAVORABLE CONDITIONS FOR AT LEAST OCCASIONAL SNOW OVER THE NORTHERN
BLACK HILLS SUNDAY NIGHT INTO MONDAY AS UPSLOPE NORTHWESTERLY FLOW
INCREASES. HAVE RAISED POPS OVER THESE AREAS SUNDAY NIGHT AND HAVE 1
TO 3 INCHES OF ACCUMULATION ACROSS THE HIGHER TERRAIN THROUGH EARLY
MONDAY MORNING. LOWS SUNDAY NIGHT WILL BE IN THE MID 20S TO LOWER
30S ACROSS THE FORECAST AREA.

.LONG TERM...MONDAY THROUGH SATURDAY
ISSUED AT 321 PM MST SAT DEC 20 2014

UPPER TROF WILL DIG OVER THE DAKOTAS MONDAY AND REMAIN
OVER THE UPPER MIDWEST THROUGH TUESDAY. WHILE MODELS INITIALLY HAVE
A SIMILAR PLACEMENT WITH THE TROF AXIS OVER THE EASTERN DAKOTAS
MONDAY MORNING...THEY ARE QUITE DIFFERENT WITH THE STRENGTH AS THE
GFS CLOSES A LOW OVER SOUTHEASTERN SD WITH THE NAM FARTHER NORTH AND
THE ECMWF ONLY A TROF...EVENTUALLY FORMING A CLOSED LOW BUT NOT AS
STRONG. WITH 120-140KT JET COMING OVER WEST COAST RIDGE AND
DIVING INTO THE UPPER TROF...THE STRONGER GFS WOULD BE A BETTER
SOLUTION. DEEP VERTICALLY STACKED LOW WILL HAVE A STRONG PRESSURE
GRADIENT ACROSS WESTERN SD...WITH GUSTS LIKELY TO REACH 50KT...AS
FORECAST SOUNDINGS SHOW >50KT MOMENTUM TRANSFER. PRECIPITATION WILL
SPREAD ACROSS FORECAST AREA MONDAY...COULD STILL SEE SOME RAIN/SNOW
MIX EARLY BEFORE CHANGING TO SNOW. FROUDE NUMBER INCREASES TO MORE
THAN 2 MONDAY MORNING...ALONG WITH 90-100 PERCENT RH AND STRONG
WINDS...SO UPSLOPE SNOW IS LIKELY OVER THE NORTHERN BLACK
HILLS...WHILE DOWNSLOPE WINDS WILL KEEP PRECIP TO A MINUMUM FROM
RAPID CITY TO HOT SPRINGS AND EDGEMONT. DEPENDING ON THE AMOUNT OF
PRECIPITATION...A WINTER WEATHER ADVISORY MAY BE MORE APPROPRIATE
THAN A HIGH WIND WARNING AS BLOWING SNOW WOULD HAVE THE GREATER
IMPACT. SNOW AND GUSTY WINDS MAY LINGER TUES AS A SECONDARY LOW
ROTATES AROUND MAIN STORM CENTER. BRIEF RIDGE WILL BUILD ON
WEDNESDAY BEFORE THE NEXT SYSTEM COMES ACROSS THE NORTHERN PLAINS ON
CHRISTMAS DAY. MODELS IN GOOD AGREEMENT WITH A FAST-MOVING LONGWAVE
TROF. CYCLONIC NORTHWEST FLOW REMAINS BEHIND THE TROF FRIDAY...WITH
UPPER RIDGING SLOW TO BUILD TOWARD NEXT WEEKEND.

&&

.AVIATION...FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING
ISSUED AT 321 PM MST SAT DEC 20 2014

CLDS CONT TO CLR BEHIND A SHORT WAVE TROF CROSSING THE
NRN PLNS...WITH HI CLDS ADVANCING FRM THE WEST. WNDS WL BE LGT THRU
THE EVEN...THEN SW WNDS WL INCRS OVR NERN WY.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&

$$

SHORT TERM...26
LONG TERM...55
AVIATION...55







000
FXUS63 KUNR 202222
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
322 PM MST SAT DEC 20 2014

.SHORT TERM...THIS EVENING THROUGH SUNDAY NIGHT
ISSUED AT 319 PM MST SAT DEC 20 2014

CURRENT SURFACE ANALYSIS SHOWS WARM FRONT JUST TO THE EAST OF THE
FORECAST AREA. UPPER LEVEL ANALYSIS DEPICTS NEAR ZONAL FLOW ACROSS
THE REGION...WITH A STRONG STORM SYSTEM AND UPPER JET PUSHING
ACROSS THE PACIFIC NW. WATER VAPOR IMAGERY SHOWS A WEAK SHORTWAVE
HAS MOVED EAST OF THE AREA...WITH PARTLY CLOUDY SKIES BEHIND IT.
TEMPS RANGE FROM THE UPPER 30S ACROSS FAR SOUTH CENTRAL SD TO NEAR
50 IN THE RAPID CITY AREA. WINDS ARE MOSTLY ON THE LIGHT SIDE FROM
THE WEST AND NORTHWEST.

A UNSETTLED PATTERN WILL TAKE SHAPE FOR THE END OF THE WEEKEND AND
INTO EARLY NEXT WEEK AS A DEVELOPING LOW PRESSURE SYSTEM MOVES
SOUTHEAST ACROSS THE REGION. HOWEVER...IT WILL REMAIN MILD INTO
SUNDAY BEFORE THIS SYSTEM PUSHES IN. THE STORM WILL BRING AT LEAST
SOME LIGHT RAIN AND SNOW TO MOST AREAS...ALONG WITH STRONG NORTHWEST
WINDS EARLY NEXT WEEK.

FOR TONIGHT...SKIES WILL REMAIN PARTLY CLOUDY IN GENERAL AS WEST TO
SOUTHWEST WINDS DEVELOP. THE WINDS WILL BECOME BREEZY OVERNIGHT OVER
PORTIONS OF NORTHEAST WY...ESPECIALLY CAMPBELL CO. RELATIVELY MILD
TEMPS CAN BE EXPECTED...WITH LOWS IN THE 20S AND LOWER 30S...A BIT
WARMER ACROSS THE EASTERN SLOPES OF THE BLACK HILLS.

CLOUDS WILL BEGIN TO INCREASE FROM THE WEST SUNDAY MORNING...WITH
SKIES BECOMING MOSTLY CLOUDY ACROSS THE ENTIRE AREA BY MID
AFTERNOON. MILDER AIR WILL REMAIN ACROSS THE REGION THROUGH MUCH OF
THE DAY...WITH HIGHS IN THE 40S AND LOWER 50S...WARMEST AGAIN ACROSS
THE EASTERN SLOPES OF THE BLACK HILLS AND ADJACENT PLAINS.
DEVELOPING LOW PRESSURE WILL MOVE ACROSS NORTHERN MT DURING THE DAY
AND INTO ND/NORTHERN SD SUNDAY NIGHT...DRAGGING A COLD FRONT ACROSS
THE CWA DURING THE AFTERNOON AND EVENING HOURS. RAIN SHOWERS WILL
DEVELOP ALONG AND BEHIND THE COLD FRONT...MOSTLY DURING THE
AFTERNOON...AS UPPER LEVEL ENERGY ACCOMPANIES THE FRONT. THE BEST
CHANCES DURING THE AFTERNOON LOOK TO BE ACROSS FAR NORTHEAST
WY...SOUTHEAST MT...FAR NORTHWEST SD...AND EVENTUALLY THE NORTHERN
BLACK HILLS AREA. NORTHWESTERLY WINDS WILL INCREASE BEHIND THE FRONT
LATE SUNDAY AND SUNDAY NIGHT...BECOMING BREEZY TO WINDY IN MANY
AREAS OVERNIGHT.

UPPER TROF AND DEVELOPING LOW PRESSURE SYSTEM WILL TRACK FROM MT ON
SUNDAY TO SOMEWHERE OVER THE EASTERN DAKOTAS ON MONDAY MORNING.
VARIOUS MODELS CONTINUE TO BE IN SOME DISAGREEMENT ON TRACK AND
STRENGTH OF THIS SYSTEM. FOR SUNDAY NIGHT...WILL KEEP THE BEST
CHANCES FOR PCPN OVER NORTHEASTERN PORTIONS OF THE CWA...AS WELL AS
THE NORTHERN BLACK HILLS AREA. PCPN WILL GRADUALLY CHANGE OVER TO
SNOW SUNDAY NIGHT...WITH THE QUICKEST CHANGE OVER THE BLACK HILLS.
NOT EXPECTING MUCH IN THE WAY OF SNOW ACCUMULATION OVER THE PLAINS
AS MOST OF THE PCPN WILL BE OUT OF THE AREA BY THE TIME TEMPS DROP
OFF ENOUGH. HOWEVER...FORECAST SOUNDINGS AND FROUDE ANALYSIS SUGGEST
FAVORABLE CONDITIONS FOR AT LEAST OCCASIONAL SNOW OVER THE NORTHERN
BLACK HILLS SUNDAY NIGHT INTO MONDAY AS UPSLOPE NORTHWESTERLY FLOW
INCREASES. HAVE RAISED POPS OVER THESE AREAS SUNDAY NIGHT AND HAVE 1
TO 3 INCHES OF ACCUMULATION ACROSS THE HIGHER TERRAIN THROUGH EARLY
MONDAY MORNING. LOWS SUNDAY NIGHT WILL BE IN THE MID 20S TO LOWER
30S ACROSS THE FORECAST AREA.

.LONG TERM...MONDAY THROUGH SATURDAY
ISSUED AT 321 PM MST SAT DEC 20 2014

UPPER TROF WILL DIG OVER THE DAKOTAS MONDAY AND REMAIN
OVER THE UPPER MIDWEST THROUGH TUESDAY. WHILE MODELS INITIALLY HAVE
A SIMILAR PLACEMENT WITH THE TROF AXIS OVER THE EASTERN DAKOTAS
MONDAY MORNING...THEY ARE QUITE DIFFERENT WITH THE STRENGTH AS THE
GFS CLOSES A LOW OVER SOUTHEASTERN SD WITH THE NAM FARTHER NORTH AND
THE ECMWF ONLY A TROF...EVENTUALLY FORMING A CLOSED LOW BUT NOT AS
STRONG. WITH 120-140KT JET COMING OVER WEST COAST RIDGE AND
DIVING INTO THE UPPER TROF...THE STRONGER GFS WOULD BE A BETTER
SOLUTION. DEEP VERTICALLY STACKED LOW WILL HAVE A STRONG PRESSURE
GRADIENT ACROSS WESTERN SD...WITH GUSTS LIKELY TO REACH 50KT...AS
FORECAST SOUNDINGS SHOW >50KT MOMENTUM TRANSFER. PRECIPITATION WILL
SPREAD ACROSS FORECAST AREA MONDAY...COULD STILL SEE SOME RAIN/SNOW
MIX EARLY BEFORE CHANGING TO SNOW. FROUDE NUMBER INCREASES TO MORE
THAN 2 MONDAY MORNING...ALONG WITH 90-100 PERCENT RH AND STRONG
WINDS...SO UPSLOPE SNOW IS LIKELY OVER THE NORTHERN BLACK
HILLS...WHILE DOWNSLOPE WINDS WILL KEEP PRECIP TO A MINUMUM FROM
RAPID CITY TO HOT SPRINGS AND EDGEMONT. DEPENDING ON THE AMOUNT OF
PRECIPITATION...A WINTER WEATHER ADVISORY MAY BE MORE APPROPRIATE
THAN A HIGH WIND WARNING AS BLOWING SNOW WOULD HAVE THE GREATER
IMPACT. SNOW AND GUSTY WINDS MAY LINGER TUES AS A SECONDARY LOW
ROTATES AROUND MAIN STORM CENTER. BRIEF RIDGE WILL BUILD ON
WEDNESDAY BEFORE THE NEXT SYSTEM COMES ACROSS THE NORTHERN PLAINS ON
CHRISTMAS DAY. MODELS IN GOOD AGREEMENT WITH A FAST-MOVING LONGWAVE
TROF. CYCLONIC NORTHWEST FLOW REMAINS BEHIND THE TROF FRIDAY...WITH
UPPER RIDGING SLOW TO BUILD TOWARD NEXT WEEKEND.

&&

.AVIATION...FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING
ISSUED AT 321 PM MST SAT DEC 20 2014

CLDS CONT TO CLR BEHIND A SHORT WAVE TROF CROSSING THE
NRN PLNS...WITH HI CLDS ADVANCING FRM THE WEST. WNDS WL BE LGT THRU
THE EVEN...THEN SW WNDS WL INCRS OVR NERN WY.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&

$$

SHORT TERM...26
LONG TERM...55
AVIATION...55








000
FXUS65 KRIW 202149
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
249 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 00Z MONDAY AT THE
AIRPORTS. ALONG AND EAST OF THE CONTINENTAL DIVIDE OVER THE
MOUNTAINS MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW
AND BLOWING SNOW WILL BECOME PREVAILING ABOVE 8500 FEET WITH
WIDESPREAD MOUNTAIN OBSCURATIONS BY 06Z.  STRONG WEST WINDS WILL
PRODUCE AREAS OF LOW LEVEL WIND SHEAR ALONG AND NEAR THE EAST
SLOPES OF THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW AND
BLOWING SNOW WILL BECOME PREVAILING BY 06Z WITH WIDESPREAD MOUNTAIN
OBSCURATIONS. STRONG WEST WINDS WILL PRODUCE AREAS OF LOW LEVEL
WIND SHEAR AND BLOWING SNOW ALONG AND NEAR THE SLOPES OF THE
MOUNTAINS.

&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STROM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER






000
FXUS65 KRIW 202149
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
249 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 00Z MONDAY AT THE
AIRPORTS. ALONG AND EAST OF THE CONTINENTAL DIVIDE OVER THE
MOUNTAINS MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW
AND BLOWING SNOW WILL BECOME PREVAILING ABOVE 8500 FEET WITH
WIDESPREAD MOUNTAIN OBSCURATIONS BY 06Z.  STRONG WEST WINDS WILL
PRODUCE AREAS OF LOW LEVEL WIND SHEAR ALONG AND NEAR THE EAST
SLOPES OF THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW AND
BLOWING SNOW WILL BECOME PREVAILING BY 06Z WITH WIDESPREAD MOUNTAIN
OBSCURATIONS. STRONG WEST WINDS WILL PRODUCE AREAS OF LOW LEVEL
WIND SHEAR AND BLOWING SNOW ALONG AND NEAR THE SLOPES OF THE
MOUNTAINS.

&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STROM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER






000
FXUS65 KRIW 202149
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
249 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 00Z MONDAY AT THE
AIRPORTS. ALONG AND EAST OF THE CONTINENTAL DIVIDE OVER THE
MOUNTAINS MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW
AND BLOWING SNOW WILL BECOME PREVAILING ABOVE 8500 FEET WITH
WIDESPREAD MOUNTAIN OBSCURATIONS BY 06Z.  STRONG WEST WINDS WILL
PRODUCE AREAS OF LOW LEVEL WIND SHEAR ALONG AND NEAR THE EAST
SLOPES OF THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW AND
BLOWING SNOW WILL BECOME PREVAILING BY 06Z WITH WIDESPREAD MOUNTAIN
OBSCURATIONS. STRONG WEST WINDS WILL PRODUCE AREAS OF LOW LEVEL
WIND SHEAR AND BLOWING SNOW ALONG AND NEAR THE SLOPES OF THE
MOUNTAINS.

&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STROM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER






000
FXUS65 KRIW 202149
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
249 PM MST SAT DEC 20 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

UPGRADED HIGH WIND AND WINTER STORM WATCHES TO WARNINGS. INCLUDED
SOUTHERN LINCOLN COUNTY IN HIGH WINDS WARNING AND STARTED THE HIGH
WIND WARNING ACROSS THE SOUTH AT 5 AM MST. OVERALL TREND WAS FOR
MORE SNOW IN THE WEST WITH LITTLE IF ANY IN THE BASINS EAST OF THE
CONTINENTAL DIVIDE. IMPRESIVE MOISTURE PLUME EXTENDING TO NEAR THE
DATELINE ALREADY SPREADING SNOW ACROSS THE WEST WITH THE SOUTHWEST
GETTING SOME SHOWWERS AS WELL. TEMPERATURES WARMER TONIGHT AND SUNDAY
WITH BETTER MIXING...CLOUD COVER. LOWER ELEVATIONS WILL LIKELY SEE SOME
RAIN AT TIMES BELOW 7300 FEET.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

SNOW ACROSS THE WESTERN MOUNTAINS CONTINUES INTO SUNDAY NIGHT WITH
MORE VALLEY LOCATIONS CHANGING OVER FROM A RAIN/SNOW MIX TO ALL SNOW
SUNDAY NIGHT. THE STRONG WESTERLY FLOW OPEN TO THE PACIFIC WILL
BEGIN TO SWITCH TO MORE OF A NORTHWESTERLY FLOW OVERNIGHT ON SUNDAY
WITH PERIODS OF GUSTY WIND SHIFTING TO BUFFALO...POWELL AND COWLEY
AREAS AND THEN DOWN INTO THE UPPER WIND RIVER BASIN. AS THE FLOW
SHIFTS NORTHWEST...THE LEFT EXIT REGION OF AN INCOMING 170 KNOT JET
BEGINS TO INFLUENCE THE REGION. IF YOU LOOK STRICTLY AT MODEL QPF
DURING THE DAY ON MONDAY...IT WOULD LOOK LIKE NOT A WHOLE LOT IS
GOING TO HAPPEN. HOWEVER...THERE WILL STILL BE SOME DECENT MOISTURE
HANGING AROUND ALONG WITH INCREASING LAPSE RATES AS THE COLD POOL
ALOFT SETTLES IN COMBINING WITH A POTENTIAL SHORT WAVE OR
TWO...THERE COULD BE SOME SURPRISING ACCUMULATIONS OF SNOW ALONG AND
EAST OF THE DIVIDE...AS IS COMMON IN STRONGLY FORCED UNSTABLE
NORTHWEST FLOW EVENTS. EXACTLY WHERE IS HARD TO PIN POINT BUT POPS
WERE INCREASED MORE THAN THEY WOULD IN AN EVENT WITH LESS FORCING
AND MORE PREDICTABLE FEATURES IN PLACES LIKE THE NORTHERN BIGHORN
BASIN AND CODY FOOTHILLS...ESPECIALLY AROUND 18Z MONDAY WHERE THE
MODELS TRY TO PLACE A STRONG DEFORMATION BAND WITH A SECONDARY BAND
ALONG THE BIGHORNS INTO JOHNSON COUNTY...POPS WERE ALSO INCREASED
FOR POTENTIAL SNOW BANDING ACTIVITY ALONG THE SOUTHERN BIGHORNS FROM
SHOSHONI THROUGH CASPER AND AREAS SOUTHEAST OF THE EASTERN TIP OF
THE WIND RIVER MOUNTAINS. STAYED FAIRLY CONSERVATIVE WITH QPF AND
SNOW AMOUNTS GIVEN THE CHAOTIC NATURE OF A SYSTEM LIKE THIS.

ONCE THIS STORM CLEARS THE AREA ON TUESDAY THE NEXT STORM OF
INTEREST WILL ARRIVE ON CHRISTMAS DAY...POTENTIALLY AS EARLY AS LATE
CHRISTMAS EVE ACROSS THE WEST. THIS LOOKS LIKE A VERY FAVORABLE
PATTERN FOR SNOW ON BOTH SIDES OF THE DIVIDE CHRISTMAS DAY AND THE
MODELS APPEAR TO BE IN DECENT AGREEMENT ON THE TIMING AND PLACEMENT
OF FEATURES THIS RUN. HOWEVER...BASED ON THE PREVIOUS RUNS THEY HAVE
NOT ALWAYS BEEN IN AGREEMENT ON EVERYTHING. RELIED HEAVILY ON THE
PREVIOUS FORECAST BUT ALLOWED POPS TO GO INTO THE HIGH CHANCE TO
LIKELY CATEGORY IN FAVORED UPSLOPE LOCATIONS EAST OF THE DIVIDE AS
WELL AS IN THE MOUNTAINS FOR CHRISTMAS DAY GIVEN THE FAVORABLE
PATTERN ADVERTISED BY THE CURRENT MODEL RUNS.

THE FRESH SNOW COVER SHOULD MAKE FOR A CHILLY DAY ON FRIDAY
ESPECIALLY WITH HIGH PRESSURE BUILDING IN BEHIND THE EXITING
SYSTEM...SO ALLOWED A FEW BASIN AND VALLEY TEMPERATURES TO DROP
BELOW ZERO OVERNIGHT. LOOKS LIKE ANOTHER POTENTIALLY WINDY DAY NEXT
SATURDAY AS ANOTHER STORM SYSTEM APPROACHES...THIS SHOULD HELP MIX
OUT THE BASINS AND COULD LEAD TO BORDERLINE TO STRONG WIND IN THE
FOOTHILL LOCATIONS AGAIN. MORE SNOW WILL BE POSSIBLE LATE SATURDAY
NIGHT.

&&

.AVIATION.../00Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH 00Z MONDAY AT THE
AIRPORTS. ALONG AND EAST OF THE CONTINENTAL DIVIDE OVER THE
MOUNTAINS MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW
AND BLOWING SNOW WILL BECOME PREVAILING ABOVE 8500 FEET WITH
WIDESPREAD MOUNTAIN OBSCURATIONS BY 06Z.  STRONG WEST WINDS WILL
PRODUCE AREAS OF LOW LEVEL WIND SHEAR ALONG AND NEAR THE EAST
SLOPES OF THE MOUNTAINS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

MVFR TO IFR CEILINGS WITH VISIBILITIES REDUCED IN SNOW AND
BLOWING SNOW WILL BECOME PREVAILING BY 06Z WITH WIDESPREAD MOUNTAIN
OBSCURATIONS. STRONG WEST WINDS WILL PRODUCE AREAS OF LOW LEVEL
WIND SHEAR AND BLOWING SNOW ALONG AND NEAR THE SLOPES OF THE
MOUNTAINS.

&&

.FIRE WEATHER...

PERIODS OF HEAVY SNOW FOR THE WEST AND STRONG WINDS EAST TONIGHT
AND SUNDAY. VARIOUS WINTER STROM WARNINGS AND HIGH WIND WARNINGS
HAVE BEN POSTED. PLEASE REFER TO THEM FOR MORE DETAILS.  OVERALL
LOW MIXING HEIGHTS WILL RESULT IN POOR SMOKE DISPERSAL.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING FROM 5 AM SUNDAY TO 2 AM MST MONDAY WYZ027>030.

HIGH WIND WARNING FROM 5 AM TO 11 PM MST SUNDAY WYZ019.

WINTER STORM WARNING FROM 11 PM THIS EVENING TO 11 AM MST MONDAY
WYZ002-014-015-025.

WINTER STORM WARNING UNTIL 8 AM MST MONDAY
WYZ001-012-013-023-024.

HIGH WIND WARNING FROM 8 PM THIS EVENING TO 11 AM MST SUNDAY
WYZ003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...ALLEN
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER






000
FXUS65 KCYS 202148
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
248 PM MST SAT DEC 20 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 1253 PM MST SAT DEC 20 2014

CHALLENGING FORECAST AHEAD WITH STRONG WINDS...VERY HEAVY SNOW AND
COMBINATION OF WIND AND SNOW THE FORECAST CHALLENGES TONIGHT
THROUGH MONDAY.

CURRENTLY...PRETTY TRANQUIL OUT ACROSS THE CWFA SO FAR TODAY. HIGH
PRESSURE OVER NORTHWESTERN COLORADO THIS AFTERNOON WITH PARTLY
CLOUDY SKIES EAST OF THE LARAMIE RANGE AND MOSTLY CLOUDY WEST.
PACIFIC STORM SYSTEM JUST OFFSHORE OF WASHINGTON STATE THIS
AFTERNOON CONTINUES TO MOVE SOUTHEAST TOWARDS THE COAST.

SHORT TERM GUIDANCE REALLY BEGINS TO SHOW AN UPTICK ON WINDS THIS
EVENING. GFS 700MB WINDS INCREASE TO 55KTS ACROSS CARBON AND
ALBANY COUNTIES WITH 700MB CRAIG TO CASPER HEIGHT GRADIENTS
INCREASING TO 70MTRS AT 06Z. THE NAM WRKHGT PRODUCT A LITTLE
SLOWER ON HEIGHT GRADIENTS INCREASING...SHOWING 850/700MB
GRADIENTS BOTH ABOVE 60MTRS BY 09Z. WILL KEEP THE CURRENT WIND
WARNINGS GOING AS THEY ARE FOR NOW.

BY 12Z SUNDAY...GFS 700MB WINDS REALLY BEGIN CRANKING WITH
65-70KTS WEST OF THE LARAMIE RANGE. PACIFIC LOW PRESSURE SYSTEM
MOVING INTO WESTERN WYOMING AT THAT TIME. WINDS SHOULD BEGIN TO
BECOME STRONG FAIRLY WIDESPREAD BY MID MORNING WITH THE WRKHGT
PRODUCT PEAKING OUT AT 79/74MTRS ON THE 850/700MB HEIGHT GRADIENTS
BY 00Z TOMORROW AFTERNOON. THESE STRONG GRADIENTS CONTINUE INTO
MONDAY MORNING BEFORE EASING.

INCREASING CONCERN FOR POSSIBLE WINTER WEATHER EVENT ALONG THE
I-80 CORRIDOR FROM THE I-80 SUMMIT THROUGH RAWLINS FOR LATE SUNDAY
AFTERNOON THROUGH MONDAY. ALL GUIDANCE SHOWING PRECIP BECOMING
WIDESPREAD BY NOON SUNDAY AND CONTINUING INTO MONDAY MORNING. LATEST
ECMWF AND SREF MOST WIDESPREAD AND AGGRESSIVE WITH QPF
AMOUNTS...THOUGH THE NAM DOES COME IN LINE BY 00Z. COMBINATION OF
VERY STRONG WINDS AND SNOW COULD LEAD TO VERY SERIOUS DRIVING
CONDITIONS WEST OF THE LARAMIE RANGE TOMORROW EVENING INTO MONDAY.

REPLACED THE HIGH WIND WATCHES WE HAD OUT THIS MORNING FOR THE
LOWER ELEVATIONS OF ALBANY AND CARBON COUNTIES WITH A WINTER STORM
WATCH. GRANTED...WINDS ARE GOING TO BE STRONGEST IN THE AFTERNOON
AND THIS SHOULD BE THE TIME WHEN PRECIP SHOULD BE FALLING AS
RAIN...BUT IT WONT TAKE LONG FOR THE PRECIP TO TURN OVER TO SNOW.
WILL WORD THE WATCH FOR STRONG WINDS INITIALLY...THEN A
COMBINATION OF WINDS AND SNOW LATE AFTERNOON AND OVERNIGHT.

SNOWY AND SIERRA MADRE RANGE ARE GOING TO GET POUNDED IN THIS
SETUP. WILL BE ON THE LEFT FRONT QUADRANT OF A 170KT JET THROUGH
MONDAY MORNING. LATEST HPC SNOW FORECAST SHOWING 2+ FEET OF SNOW
THROUGH MONDAY. DO BELIEVE WE COULD SEE MUCH MORE IN THIS
PERSISTENT STRONG UPSLOPE EVENT. MAYBE MORE LIKE 3 FEET BEFORE ALL
IS SAID AND DONE MONDAY NIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 253 PM MST SAT DEC 20 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY THROUGH FRIDAY DUE TO
HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER WEATHER ON CHRISTMAS
DAY. EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY
TRAVEL PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REMAIN COLDER THAN NORMAL ON TUESDAY BEHIND THE
UPPER LEVEL TROUGH FORECAST TO PUSH ACROSS THE AREA TOMORROW AND
MONDAY. HIGHS IN THE 20S TO MID 30S ARE EXPECTED WITH VERY COLD
OVERNIGHT LOWS. TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS
DOWNSLOPE FLOW DEVELOPS...WITH HIGHS IN THE 30S TO LOW 40S. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS GENERALLY INDICATE A RAPIDLY
MOVING UPPER LEVEL TROUGH PUSHING INTO THE AREA. A STRONG PACIFIC
COLD FRONT IS FORECAST TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME
CHRISTMAS MORNING WITH SNOW DEVELOPING BEHIND THE FRONT. BEFORE
THAT...THERE IS THE POTENTIAL FOR A HIGH WIND EVENT ACROSS THE
WIND PRONE AREAS OF SOUTHEAST WYOMING AHEAD OF THE FRONT...BUT
CONDITIONS WILL LIKELY NOT LAST TOO LONG AND MAINLY AFFECT
MOTORISTS WITH LARGER VEHICLES. AS FOR SNOW...THERE IS A LOW
PROBABILITY FOR WINTER STORM CONDITIONS ON CHRISTMAS DAY DUE TO
HOW PROGRESSIVE THIS SYSTEM IS. HOWEVER...THE GEM AND ECMWF DO
HINT AT A SLOWER SOLUTION AS THE STORM DIGS FURTHER TO THE SOUTH.
THE GFS ON THE OTHER HAND IS VERY PROGRESSIVE...WITH SNOW
STRUGGLING TO DEVELOP OVER MOST OF THE HIGH PLAINS MAINLY DUE TO
THE LLVL UPSLOPE FLOW DEVELOPING MUCH LATER IN THE DAY WHEN THE
EVENT IS PRACTICALLY OVER. ALTHOUGH THERE IS A POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE AREA...CONFIDENCE IS RATHER LOW AT
THIS TIME WITH THE MOST FAVORABLE LOCATIONS BEING IN THE MOUNTAINS
AND WELL NORTH OF I80 ACROSS THE HIGH PLAINS. AT THIS TIME...IT
APPEARS THE I80 CORRIDOR MAY HAVE TOO MUCH DRIER DOWNSLOPE FLOW TO
DEAL WITH TO GET ANY SUBSTANTIAL SNOW ACCUMULATIONS GOING. BUT
THIS MAY QUICKLY CHANGE OVER THE NEXT FEW DAYS. KEPT POP BETWEEN
25 TO 35 PERCENT ACROSS THE HIGH PLAINS INCLUDING THE EASTERN I80
CORRIDOR...AND CLOSER TO 50 PERCENT WEST OF THE LARAMIE RANGE.
INCREASED POP IN THE MOUNTAINS WHICH WILL HAVE THE BEST POTENTIAL
TO SEE MODERATE SNOW ACCUMULATIONS WITH THIS SYSTEM. IN EITHER
CASE...MUCH COLDER TEMPERATURES ARE EXPECTED FOR LATER NEXT WEEK.
EARLY MORNING HIGHS BETWEEN 35 TO 45 ON CHRISTMAS DAY WILL RAPIDLY
LOWER INTO THE 20S THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL
LIKELY BE BELOW FREEZING FOR FRIDAY AND SATURDAY AS NORTHERLY FLOW
ALOFT STAYS OVER THE ROCKY MOUNTAIN REGION.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1035 AM MST SAT DEC 20 2014

VFR CONDITIONS SHOULD PREVAIL ACROSS MOST TERMINALS...WITH THE
EXCEPTION OF KRWL. MOUNTAINS WILL BE OBSCURED WITH OROGRAPHIC SNOW
DEVELOPING THIS AFTERNOON. LOW MVFR CIGS AT KRWL WILL PREVAIL
TODAY...LOWERING TO IFR AFTER 21Z SAT WITH INCREASING MOISTURE.
ELSEWHERE...MID LEVEL CIGS AROUND 7K TO 10K FEET AGL ARE EXPECTED.

&&

.FIRE WEATHER...
ISSUED AT 1253 PM MST SAT DEC 20 2014

NO FIRE WEATHER ISSUES EXPECTED THIS WEEKEND. BREEZY AND MAINLY DRY
CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS THIS AFTERNOON...BUT
THINGS BEGIN TO CHANGE TONIGHT THROUGH THE BEGINNING OF NEXT WEEK. STRONG
WESTERLY WINDS AND SIGNIFICANT MOUNTAIN SNOWFALL WILL RETURN
TONIGHT AND CONTINUE THROUGH MONDAY...WITH WINTER STORM WARNINGS
IN EFFECT FOR THE SNOWY AND SIERRA MADRE RANGES FOR TWO TO THREE FEET
OF SNOW. HIGH WIND WARNINGS ARE IN EFFECT FOR THE WIND PRONE AREAS
OF SOUTHEAST WYOMING FROM LATE TONIGHT THROUGH SUNDAY EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 5 AM MST TUESDAY
     FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST SUNDAY NIGHT
     FOR WYZ116-117.

     WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY MORNING
     FOR WYZ109-111-113-115.

     HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO MIDNIGHT MST SUNDAY
     NIGHT FOR WYZ106-110.

     HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING FOR
     WYZ104-105.

NE...NONE.
&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...GCC




000
FXUS65 KCYS 202148
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
248 PM MST SAT DEC 20 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 1253 PM MST SAT DEC 20 2014

CHALLENGING FORECAST AHEAD WITH STRONG WINDS...VERY HEAVY SNOW AND
COMBINATION OF WIND AND SNOW THE FORECAST CHALLENGES TONIGHT
THROUGH MONDAY.

CURRENTLY...PRETTY TRANQUIL OUT ACROSS THE CWFA SO FAR TODAY. HIGH
PRESSURE OVER NORTHWESTERN COLORADO THIS AFTERNOON WITH PARTLY
CLOUDY SKIES EAST OF THE LARAMIE RANGE AND MOSTLY CLOUDY WEST.
PACIFIC STORM SYSTEM JUST OFFSHORE OF WASHINGTON STATE THIS
AFTERNOON CONTINUES TO MOVE SOUTHEAST TOWARDS THE COAST.

SHORT TERM GUIDANCE REALLY BEGINS TO SHOW AN UPTICK ON WINDS THIS
EVENING. GFS 700MB WINDS INCREASE TO 55KTS ACROSS CARBON AND
ALBANY COUNTIES WITH 700MB CRAIG TO CASPER HEIGHT GRADIENTS
INCREASING TO 70MTRS AT 06Z. THE NAM WRKHGT PRODUCT A LITTLE
SLOWER ON HEIGHT GRADIENTS INCREASING...SHOWING 850/700MB
GRADIENTS BOTH ABOVE 60MTRS BY 09Z. WILL KEEP THE CURRENT WIND
WARNINGS GOING AS THEY ARE FOR NOW.

BY 12Z SUNDAY...GFS 700MB WINDS REALLY BEGIN CRANKING WITH
65-70KTS WEST OF THE LARAMIE RANGE. PACIFIC LOW PRESSURE SYSTEM
MOVING INTO WESTERN WYOMING AT THAT TIME. WINDS SHOULD BEGIN TO
BECOME STRONG FAIRLY WIDESPREAD BY MID MORNING WITH THE WRKHGT
PRODUCT PEAKING OUT AT 79/74MTRS ON THE 850/700MB HEIGHT GRADIENTS
BY 00Z TOMORROW AFTERNOON. THESE STRONG GRADIENTS CONTINUE INTO
MONDAY MORNING BEFORE EASING.

INCREASING CONCERN FOR POSSIBLE WINTER WEATHER EVENT ALONG THE
I-80 CORRIDOR FROM THE I-80 SUMMIT THROUGH RAWLINS FOR LATE SUNDAY
AFTERNOON THROUGH MONDAY. ALL GUIDANCE SHOWING PRECIP BECOMING
WIDESPREAD BY NOON SUNDAY AND CONTINUING INTO MONDAY MORNING. LATEST
ECMWF AND SREF MOST WIDESPREAD AND AGGRESSIVE WITH QPF
AMOUNTS...THOUGH THE NAM DOES COME IN LINE BY 00Z. COMBINATION OF
VERY STRONG WINDS AND SNOW COULD LEAD TO VERY SERIOUS DRIVING
CONDITIONS WEST OF THE LARAMIE RANGE TOMORROW EVENING INTO MONDAY.

REPLACED THE HIGH WIND WATCHES WE HAD OUT THIS MORNING FOR THE
LOWER ELEVATIONS OF ALBANY AND CARBON COUNTIES WITH A WINTER STORM
WATCH. GRANTED...WINDS ARE GOING TO BE STRONGEST IN THE AFTERNOON
AND THIS SHOULD BE THE TIME WHEN PRECIP SHOULD BE FALLING AS
RAIN...BUT IT WONT TAKE LONG FOR THE PRECIP TO TURN OVER TO SNOW.
WILL WORD THE WATCH FOR STRONG WINDS INITIALLY...THEN A
COMBINATION OF WINDS AND SNOW LATE AFTERNOON AND OVERNIGHT.

SNOWY AND SIERRA MADRE RANGE ARE GOING TO GET POUNDED IN THIS
SETUP. WILL BE ON THE LEFT FRONT QUADRANT OF A 170KT JET THROUGH
MONDAY MORNING. LATEST HPC SNOW FORECAST SHOWING 2+ FEET OF SNOW
THROUGH MONDAY. DO BELIEVE WE COULD SEE MUCH MORE IN THIS
PERSISTENT STRONG UPSLOPE EVENT. MAYBE MORE LIKE 3 FEET BEFORE ALL
IS SAID AND DONE MONDAY NIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 253 PM MST SAT DEC 20 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY THROUGH FRIDAY DUE TO
HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER WEATHER ON CHRISTMAS
DAY. EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY
TRAVEL PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REMAIN COLDER THAN NORMAL ON TUESDAY BEHIND THE
UPPER LEVEL TROUGH FORECAST TO PUSH ACROSS THE AREA TOMORROW AND
MONDAY. HIGHS IN THE 20S TO MID 30S ARE EXPECTED WITH VERY COLD
OVERNIGHT LOWS. TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS
DOWNSLOPE FLOW DEVELOPS...WITH HIGHS IN THE 30S TO LOW 40S. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS GENERALLY INDICATE A RAPIDLY
MOVING UPPER LEVEL TROUGH PUSHING INTO THE AREA. A STRONG PACIFIC
COLD FRONT IS FORECAST TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME
CHRISTMAS MORNING WITH SNOW DEVELOPING BEHIND THE FRONT. BEFORE
THAT...THERE IS THE POTENTIAL FOR A HIGH WIND EVENT ACROSS THE
WIND PRONE AREAS OF SOUTHEAST WYOMING AHEAD OF THE FRONT...BUT
CONDITIONS WILL LIKELY NOT LAST TOO LONG AND MAINLY AFFECT
MOTORISTS WITH LARGER VEHICLES. AS FOR SNOW...THERE IS A LOW
PROBABILITY FOR WINTER STORM CONDITIONS ON CHRISTMAS DAY DUE TO
HOW PROGRESSIVE THIS SYSTEM IS. HOWEVER...THE GEM AND ECMWF DO
HINT AT A SLOWER SOLUTION AS THE STORM DIGS FURTHER TO THE SOUTH.
THE GFS ON THE OTHER HAND IS VERY PROGRESSIVE...WITH SNOW
STRUGGLING TO DEVELOP OVER MOST OF THE HIGH PLAINS MAINLY DUE TO
THE LLVL UPSLOPE FLOW DEVELOPING MUCH LATER IN THE DAY WHEN THE
EVENT IS PRACTICALLY OVER. ALTHOUGH THERE IS A POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE AREA...CONFIDENCE IS RATHER LOW AT
THIS TIME WITH THE MOST FAVORABLE LOCATIONS BEING IN THE MOUNTAINS
AND WELL NORTH OF I80 ACROSS THE HIGH PLAINS. AT THIS TIME...IT
APPEARS THE I80 CORRIDOR MAY HAVE TOO MUCH DRIER DOWNSLOPE FLOW TO
DEAL WITH TO GET ANY SUBSTANTIAL SNOW ACCUMULATIONS GOING. BUT
THIS MAY QUICKLY CHANGE OVER THE NEXT FEW DAYS. KEPT POP BETWEEN
25 TO 35 PERCENT ACROSS THE HIGH PLAINS INCLUDING THE EASTERN I80
CORRIDOR...AND CLOSER TO 50 PERCENT WEST OF THE LARAMIE RANGE.
INCREASED POP IN THE MOUNTAINS WHICH WILL HAVE THE BEST POTENTIAL
TO SEE MODERATE SNOW ACCUMULATIONS WITH THIS SYSTEM. IN EITHER
CASE...MUCH COLDER TEMPERATURES ARE EXPECTED FOR LATER NEXT WEEK.
EARLY MORNING HIGHS BETWEEN 35 TO 45 ON CHRISTMAS DAY WILL RAPIDLY
LOWER INTO THE 20S THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL
LIKELY BE BELOW FREEZING FOR FRIDAY AND SATURDAY AS NORTHERLY FLOW
ALOFT STAYS OVER THE ROCKY MOUNTAIN REGION.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1035 AM MST SAT DEC 20 2014

VFR CONDITIONS SHOULD PREVAIL ACROSS MOST TERMINALS...WITH THE
EXCEPTION OF KRWL. MOUNTAINS WILL BE OBSCURED WITH OROGRAPHIC SNOW
DEVELOPING THIS AFTERNOON. LOW MVFR CIGS AT KRWL WILL PREVAIL
TODAY...LOWERING TO IFR AFTER 21Z SAT WITH INCREASING MOISTURE.
ELSEWHERE...MID LEVEL CIGS AROUND 7K TO 10K FEET AGL ARE EXPECTED.

&&

.FIRE WEATHER...
ISSUED AT 1253 PM MST SAT DEC 20 2014

NO FIRE WEATHER ISSUES EXPECTED THIS WEEKEND. BREEZY AND MAINLY DRY
CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS THIS AFTERNOON...BUT
THINGS BEGIN TO CHANGE TONIGHT THROUGH THE BEGINNING OF NEXT WEEK. STRONG
WESTERLY WINDS AND SIGNIFICANT MOUNTAIN SNOWFALL WILL RETURN
TONIGHT AND CONTINUE THROUGH MONDAY...WITH WINTER STORM WARNINGS
IN EFFECT FOR THE SNOWY AND SIERRA MADRE RANGES FOR TWO TO THREE FEET
OF SNOW. HIGH WIND WARNINGS ARE IN EFFECT FOR THE WIND PRONE AREAS
OF SOUTHEAST WYOMING FROM LATE TONIGHT THROUGH SUNDAY EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 5 AM MST TUESDAY
     FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST SUNDAY NIGHT
     FOR WYZ116-117.

     WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY MORNING
     FOR WYZ109-111-113-115.

     HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO MIDNIGHT MST SUNDAY
     NIGHT FOR WYZ106-110.

     HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING FOR
     WYZ104-105.

NE...NONE.
&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...GCC




000
FXUS65 KCYS 202148
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
248 PM MST SAT DEC 20 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 1253 PM MST SAT DEC 20 2014

CHALLENGING FORECAST AHEAD WITH STRONG WINDS...VERY HEAVY SNOW AND
COMBINATION OF WIND AND SNOW THE FORECAST CHALLENGES TONIGHT
THROUGH MONDAY.

CURRENTLY...PRETTY TRANQUIL OUT ACROSS THE CWFA SO FAR TODAY. HIGH
PRESSURE OVER NORTHWESTERN COLORADO THIS AFTERNOON WITH PARTLY
CLOUDY SKIES EAST OF THE LARAMIE RANGE AND MOSTLY CLOUDY WEST.
PACIFIC STORM SYSTEM JUST OFFSHORE OF WASHINGTON STATE THIS
AFTERNOON CONTINUES TO MOVE SOUTHEAST TOWARDS THE COAST.

SHORT TERM GUIDANCE REALLY BEGINS TO SHOW AN UPTICK ON WINDS THIS
EVENING. GFS 700MB WINDS INCREASE TO 55KTS ACROSS CARBON AND
ALBANY COUNTIES WITH 700MB CRAIG TO CASPER HEIGHT GRADIENTS
INCREASING TO 70MTRS AT 06Z. THE NAM WRKHGT PRODUCT A LITTLE
SLOWER ON HEIGHT GRADIENTS INCREASING...SHOWING 850/700MB
GRADIENTS BOTH ABOVE 60MTRS BY 09Z. WILL KEEP THE CURRENT WIND
WARNINGS GOING AS THEY ARE FOR NOW.

BY 12Z SUNDAY...GFS 700MB WINDS REALLY BEGIN CRANKING WITH
65-70KTS WEST OF THE LARAMIE RANGE. PACIFIC LOW PRESSURE SYSTEM
MOVING INTO WESTERN WYOMING AT THAT TIME. WINDS SHOULD BEGIN TO
BECOME STRONG FAIRLY WIDESPREAD BY MID MORNING WITH THE WRKHGT
PRODUCT PEAKING OUT AT 79/74MTRS ON THE 850/700MB HEIGHT GRADIENTS
BY 00Z TOMORROW AFTERNOON. THESE STRONG GRADIENTS CONTINUE INTO
MONDAY MORNING BEFORE EASING.

INCREASING CONCERN FOR POSSIBLE WINTER WEATHER EVENT ALONG THE
I-80 CORRIDOR FROM THE I-80 SUMMIT THROUGH RAWLINS FOR LATE SUNDAY
AFTERNOON THROUGH MONDAY. ALL GUIDANCE SHOWING PRECIP BECOMING
WIDESPREAD BY NOON SUNDAY AND CONTINUING INTO MONDAY MORNING. LATEST
ECMWF AND SREF MOST WIDESPREAD AND AGGRESSIVE WITH QPF
AMOUNTS...THOUGH THE NAM DOES COME IN LINE BY 00Z. COMBINATION OF
VERY STRONG WINDS AND SNOW COULD LEAD TO VERY SERIOUS DRIVING
CONDITIONS WEST OF THE LARAMIE RANGE TOMORROW EVENING INTO MONDAY.

REPLACED THE HIGH WIND WATCHES WE HAD OUT THIS MORNING FOR THE
LOWER ELEVATIONS OF ALBANY AND CARBON COUNTIES WITH A WINTER STORM
WATCH. GRANTED...WINDS ARE GOING TO BE STRONGEST IN THE AFTERNOON
AND THIS SHOULD BE THE TIME WHEN PRECIP SHOULD BE FALLING AS
RAIN...BUT IT WONT TAKE LONG FOR THE PRECIP TO TURN OVER TO SNOW.
WILL WORD THE WATCH FOR STRONG WINDS INITIALLY...THEN A
COMBINATION OF WINDS AND SNOW LATE AFTERNOON AND OVERNIGHT.

SNOWY AND SIERRA MADRE RANGE ARE GOING TO GET POUNDED IN THIS
SETUP. WILL BE ON THE LEFT FRONT QUADRANT OF A 170KT JET THROUGH
MONDAY MORNING. LATEST HPC SNOW FORECAST SHOWING 2+ FEET OF SNOW
THROUGH MONDAY. DO BELIEVE WE COULD SEE MUCH MORE IN THIS
PERSISTENT STRONG UPSLOPE EVENT. MAYBE MORE LIKE 3 FEET BEFORE ALL
IS SAID AND DONE MONDAY NIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 253 PM MST SAT DEC 20 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY THROUGH FRIDAY DUE TO
HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER WEATHER ON CHRISTMAS
DAY. EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY
TRAVEL PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REMAIN COLDER THAN NORMAL ON TUESDAY BEHIND THE
UPPER LEVEL TROUGH FORECAST TO PUSH ACROSS THE AREA TOMORROW AND
MONDAY. HIGHS IN THE 20S TO MID 30S ARE EXPECTED WITH VERY COLD
OVERNIGHT LOWS. TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS
DOWNSLOPE FLOW DEVELOPS...WITH HIGHS IN THE 30S TO LOW 40S. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS GENERALLY INDICATE A RAPIDLY
MOVING UPPER LEVEL TROUGH PUSHING INTO THE AREA. A STRONG PACIFIC
COLD FRONT IS FORECAST TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME
CHRISTMAS MORNING WITH SNOW DEVELOPING BEHIND THE FRONT. BEFORE
THAT...THERE IS THE POTENTIAL FOR A HIGH WIND EVENT ACROSS THE
WIND PRONE AREAS OF SOUTHEAST WYOMING AHEAD OF THE FRONT...BUT
CONDITIONS WILL LIKELY NOT LAST TOO LONG AND MAINLY AFFECT
MOTORISTS WITH LARGER VEHICLES. AS FOR SNOW...THERE IS A LOW
PROBABILITY FOR WINTER STORM CONDITIONS ON CHRISTMAS DAY DUE TO
HOW PROGRESSIVE THIS SYSTEM IS. HOWEVER...THE GEM AND ECMWF DO
HINT AT A SLOWER SOLUTION AS THE STORM DIGS FURTHER TO THE SOUTH.
THE GFS ON THE OTHER HAND IS VERY PROGRESSIVE...WITH SNOW
STRUGGLING TO DEVELOP OVER MOST OF THE HIGH PLAINS MAINLY DUE TO
THE LLVL UPSLOPE FLOW DEVELOPING MUCH LATER IN THE DAY WHEN THE
EVENT IS PRACTICALLY OVER. ALTHOUGH THERE IS A POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE AREA...CONFIDENCE IS RATHER LOW AT
THIS TIME WITH THE MOST FAVORABLE LOCATIONS BEING IN THE MOUNTAINS
AND WELL NORTH OF I80 ACROSS THE HIGH PLAINS. AT THIS TIME...IT
APPEARS THE I80 CORRIDOR MAY HAVE TOO MUCH DRIER DOWNSLOPE FLOW TO
DEAL WITH TO GET ANY SUBSTANTIAL SNOW ACCUMULATIONS GOING. BUT
THIS MAY QUICKLY CHANGE OVER THE NEXT FEW DAYS. KEPT POP BETWEEN
25 TO 35 PERCENT ACROSS THE HIGH PLAINS INCLUDING THE EASTERN I80
CORRIDOR...AND CLOSER TO 50 PERCENT WEST OF THE LARAMIE RANGE.
INCREASED POP IN THE MOUNTAINS WHICH WILL HAVE THE BEST POTENTIAL
TO SEE MODERATE SNOW ACCUMULATIONS WITH THIS SYSTEM. IN EITHER
CASE...MUCH COLDER TEMPERATURES ARE EXPECTED FOR LATER NEXT WEEK.
EARLY MORNING HIGHS BETWEEN 35 TO 45 ON CHRISTMAS DAY WILL RAPIDLY
LOWER INTO THE 20S THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL
LIKELY BE BELOW FREEZING FOR FRIDAY AND SATURDAY AS NORTHERLY FLOW
ALOFT STAYS OVER THE ROCKY MOUNTAIN REGION.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1035 AM MST SAT DEC 20 2014

VFR CONDITIONS SHOULD PREVAIL ACROSS MOST TERMINALS...WITH THE
EXCEPTION OF KRWL. MOUNTAINS WILL BE OBSCURED WITH OROGRAPHIC SNOW
DEVELOPING THIS AFTERNOON. LOW MVFR CIGS AT KRWL WILL PREVAIL
TODAY...LOWERING TO IFR AFTER 21Z SAT WITH INCREASING MOISTURE.
ELSEWHERE...MID LEVEL CIGS AROUND 7K TO 10K FEET AGL ARE EXPECTED.

&&

.FIRE WEATHER...
ISSUED AT 1253 PM MST SAT DEC 20 2014

NO FIRE WEATHER ISSUES EXPECTED THIS WEEKEND. BREEZY AND MAINLY DRY
CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS THIS AFTERNOON...BUT
THINGS BEGIN TO CHANGE TONIGHT THROUGH THE BEGINNING OF NEXT WEEK. STRONG
WESTERLY WINDS AND SIGNIFICANT MOUNTAIN SNOWFALL WILL RETURN
TONIGHT AND CONTINUE THROUGH MONDAY...WITH WINTER STORM WARNINGS
IN EFFECT FOR THE SNOWY AND SIERRA MADRE RANGES FOR TWO TO THREE FEET
OF SNOW. HIGH WIND WARNINGS ARE IN EFFECT FOR THE WIND PRONE AREAS
OF SOUTHEAST WYOMING FROM LATE TONIGHT THROUGH SUNDAY EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 5 AM MST TUESDAY
     FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST SUNDAY NIGHT
     FOR WYZ116-117.

     WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY MORNING
     FOR WYZ109-111-113-115.

     HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO MIDNIGHT MST SUNDAY
     NIGHT FOR WYZ106-110.

     HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING FOR
     WYZ104-105.

NE...NONE.
&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...GCC




000
FXUS65 KCYS 202148
AFDCYS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
248 PM MST SAT DEC 20 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 1253 PM MST SAT DEC 20 2014

CHALLENGING FORECAST AHEAD WITH STRONG WINDS...VERY HEAVY SNOW AND
COMBINATION OF WIND AND SNOW THE FORECAST CHALLENGES TONIGHT
THROUGH MONDAY.

CURRENTLY...PRETTY TRANQUIL OUT ACROSS THE CWFA SO FAR TODAY. HIGH
PRESSURE OVER NORTHWESTERN COLORADO THIS AFTERNOON WITH PARTLY
CLOUDY SKIES EAST OF THE LARAMIE RANGE AND MOSTLY CLOUDY WEST.
PACIFIC STORM SYSTEM JUST OFFSHORE OF WASHINGTON STATE THIS
AFTERNOON CONTINUES TO MOVE SOUTHEAST TOWARDS THE COAST.

SHORT TERM GUIDANCE REALLY BEGINS TO SHOW AN UPTICK ON WINDS THIS
EVENING. GFS 700MB WINDS INCREASE TO 55KTS ACROSS CARBON AND
ALBANY COUNTIES WITH 700MB CRAIG TO CASPER HEIGHT GRADIENTS
INCREASING TO 70MTRS AT 06Z. THE NAM WRKHGT PRODUCT A LITTLE
SLOWER ON HEIGHT GRADIENTS INCREASING...SHOWING 850/700MB
GRADIENTS BOTH ABOVE 60MTRS BY 09Z. WILL KEEP THE CURRENT WIND
WARNINGS GOING AS THEY ARE FOR NOW.

BY 12Z SUNDAY...GFS 700MB WINDS REALLY BEGIN CRANKING WITH
65-70KTS WEST OF THE LARAMIE RANGE. PACIFIC LOW PRESSURE SYSTEM
MOVING INTO WESTERN WYOMING AT THAT TIME. WINDS SHOULD BEGIN TO
BECOME STRONG FAIRLY WIDESPREAD BY MID MORNING WITH THE WRKHGT
PRODUCT PEAKING OUT AT 79/74MTRS ON THE 850/700MB HEIGHT GRADIENTS
BY 00Z TOMORROW AFTERNOON. THESE STRONG GRADIENTS CONTINUE INTO
MONDAY MORNING BEFORE EASING.

INCREASING CONCERN FOR POSSIBLE WINTER WEATHER EVENT ALONG THE
I-80 CORRIDOR FROM THE I-80 SUMMIT THROUGH RAWLINS FOR LATE SUNDAY
AFTERNOON THROUGH MONDAY. ALL GUIDANCE SHOWING PRECIP BECOMING
WIDESPREAD BY NOON SUNDAY AND CONTINUING INTO MONDAY MORNING. LATEST
ECMWF AND SREF MOST WIDESPREAD AND AGGRESSIVE WITH QPF
AMOUNTS...THOUGH THE NAM DOES COME IN LINE BY 00Z. COMBINATION OF
VERY STRONG WINDS AND SNOW COULD LEAD TO VERY SERIOUS DRIVING
CONDITIONS WEST OF THE LARAMIE RANGE TOMORROW EVENING INTO MONDAY.

REPLACED THE HIGH WIND WATCHES WE HAD OUT THIS MORNING FOR THE
LOWER ELEVATIONS OF ALBANY AND CARBON COUNTIES WITH A WINTER STORM
WATCH. GRANTED...WINDS ARE GOING TO BE STRONGEST IN THE AFTERNOON
AND THIS SHOULD BE THE TIME WHEN PRECIP SHOULD BE FALLING AS
RAIN...BUT IT WONT TAKE LONG FOR THE PRECIP TO TURN OVER TO SNOW.
WILL WORD THE WATCH FOR STRONG WINDS INITIALLY...THEN A
COMBINATION OF WINDS AND SNOW LATE AFTERNOON AND OVERNIGHT.

SNOWY AND SIERRA MADRE RANGE ARE GOING TO GET POUNDED IN THIS
SETUP. WILL BE ON THE LEFT FRONT QUADRANT OF A 170KT JET THROUGH
MONDAY MORNING. LATEST HPC SNOW FORECAST SHOWING 2+ FEET OF SNOW
THROUGH MONDAY. DO BELIEVE WE COULD SEE MUCH MORE IN THIS
PERSISTENT STRONG UPSLOPE EVENT. MAYBE MORE LIKE 3 FEET BEFORE ALL
IS SAID AND DONE MONDAY NIGHT.

.LONG TERM...(TUESDAY THROUGH SATURDAY)
ISSUED AT 253 PM MST SAT DEC 20 2014

MAIN FOCUS IN THE LONG TERM WILL BE TUESDAY THROUGH FRIDAY DUE TO
HOLIDAY TRAVEL...AND THE POTENTIAL FOR WINTER WEATHER ON CHRISTMAS
DAY. EARLIER IN THE WEEK...THE BEGINNING OF THE PEAK HOLIDAY
TRAVEL PERIOD APPEARS TO BE QUIET AND LOW IMPACT...WITH ALL MODELS
SHOWING A RIDGE OF HIGH PRESSURE QUICKLY MOVING ACROSS THE
NORTHERN ROCKY MOUNTAINS AND INTO THE HIGH PLAINS BY WEDNESDAY.
TEMPERATURES WILL REMAIN COLDER THAN NORMAL ON TUESDAY BEHIND THE
UPPER LEVEL TROUGH FORECAST TO PUSH ACROSS THE AREA TOMORROW AND
MONDAY. HIGHS IN THE 20S TO MID 30S ARE EXPECTED WITH VERY COLD
OVERNIGHT LOWS. TEMPERATURES WILL REBOUND SLIGHTLY ON WEDNESDAY AS
DOWNSLOPE FLOW DEVELOPS...WITH HIGHS IN THE 30S TO LOW 40S. THIS
SLIGHT WARMING TREND WILL BE SHORT LIVED HOWEVER.

BY EARLY CHRISTMAS MORNING...MODELS GENERALLY INDICATE A RAPIDLY
MOVING UPPER LEVEL TROUGH PUSHING INTO THE AREA. A STRONG PACIFIC
COLD FRONT IS FORECAST TO PUSH THROUGH SOUTHEAST WYOMING SOMETIME
CHRISTMAS MORNING WITH SNOW DEVELOPING BEHIND THE FRONT. BEFORE
THAT...THERE IS THE POTENTIAL FOR A HIGH WIND EVENT ACROSS THE
WIND PRONE AREAS OF SOUTHEAST WYOMING AHEAD OF THE FRONT...BUT
CONDITIONS WILL LIKELY NOT LAST TOO LONG AND MAINLY AFFECT
MOTORISTS WITH LARGER VEHICLES. AS FOR SNOW...THERE IS A LOW
PROBABILITY FOR WINTER STORM CONDITIONS ON CHRISTMAS DAY DUE TO
HOW PROGRESSIVE THIS SYSTEM IS. HOWEVER...THE GEM AND ECMWF DO
HINT AT A SLOWER SOLUTION AS THE STORM DIGS FURTHER TO THE SOUTH.
THE GFS ON THE OTHER HAND IS VERY PROGRESSIVE...WITH SNOW
STRUGGLING TO DEVELOP OVER MOST OF THE HIGH PLAINS MAINLY DUE TO
THE LLVL UPSLOPE FLOW DEVELOPING MUCH LATER IN THE DAY WHEN THE
EVENT IS PRACTICALLY OVER. ALTHOUGH THERE IS A POTENTIAL FOR
ACCUMULATING SNOW ACROSS THE AREA...CONFIDENCE IS RATHER LOW AT
THIS TIME WITH THE MOST FAVORABLE LOCATIONS BEING IN THE MOUNTAINS
AND WELL NORTH OF I80 ACROSS THE HIGH PLAINS. AT THIS TIME...IT
APPEARS THE I80 CORRIDOR MAY HAVE TOO MUCH DRIER DOWNSLOPE FLOW TO
DEAL WITH TO GET ANY SUBSTANTIAL SNOW ACCUMULATIONS GOING. BUT
THIS MAY QUICKLY CHANGE OVER THE NEXT FEW DAYS. KEPT POP BETWEEN
25 TO 35 PERCENT ACROSS THE HIGH PLAINS INCLUDING THE EASTERN I80
CORRIDOR...AND CLOSER TO 50 PERCENT WEST OF THE LARAMIE RANGE.
INCREASED POP IN THE MOUNTAINS WHICH WILL HAVE THE BEST POTENTIAL
TO SEE MODERATE SNOW ACCUMULATIONS WITH THIS SYSTEM. IN EITHER
CASE...MUCH COLDER TEMPERATURES ARE EXPECTED FOR LATER NEXT WEEK.
EARLY MORNING HIGHS BETWEEN 35 TO 45 ON CHRISTMAS DAY WILL RAPIDLY
LOWER INTO THE 20S THROUGH THE AFTERNOON. HIGH TEMPERATURES WILL
LIKELY BE BELOW FREEZING FOR FRIDAY AND SATURDAY AS NORTHERLY FLOW
ALOFT STAYS OVER THE ROCKY MOUNTAIN REGION.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1035 AM MST SAT DEC 20 2014

VFR CONDITIONS SHOULD PREVAIL ACROSS MOST TERMINALS...WITH THE
EXCEPTION OF KRWL. MOUNTAINS WILL BE OBSCURED WITH OROGRAPHIC SNOW
DEVELOPING THIS AFTERNOON. LOW MVFR CIGS AT KRWL WILL PREVAIL
TODAY...LOWERING TO IFR AFTER 21Z SAT WITH INCREASING MOISTURE.
ELSEWHERE...MID LEVEL CIGS AROUND 7K TO 10K FEET AGL ARE EXPECTED.

&&

.FIRE WEATHER...
ISSUED AT 1253 PM MST SAT DEC 20 2014

NO FIRE WEATHER ISSUES EXPECTED THIS WEEKEND. BREEZY AND MAINLY DRY
CONDITIONS WILL CONTINUE ACROSS THE DISTRICTS THIS AFTERNOON...BUT
THINGS BEGIN TO CHANGE TONIGHT THROUGH THE BEGINNING OF NEXT WEEK. STRONG
WESTERLY WINDS AND SIGNIFICANT MOUNTAIN SNOWFALL WILL RETURN
TONIGHT AND CONTINUE THROUGH MONDAY...WITH WINTER STORM WARNINGS
IN EFFECT FOR THE SNOWY AND SIERRA MADRE RANGES FOR TWO TO THREE FEET
OF SNOW. HIGH WIND WARNINGS ARE IN EFFECT FOR THE WIND PRONE AREAS
OF SOUTHEAST WYOMING FROM LATE TONIGHT THROUGH SUNDAY EVENING.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 5 AM MST TUESDAY
     FOR WYZ112-114.

     HIGH WIND WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST SUNDAY NIGHT
     FOR WYZ116-117.

     WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY MORNING
     FOR WYZ109-111-113-115.

     HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO MIDNIGHT MST SUNDAY
     NIGHT FOR WYZ106-110.

     HIGH WIND WATCH FROM SUNDAY MORNING THROUGH SUNDAY EVENING FOR
     WYZ104-105.

NE...NONE.
&&

$$

SHORT TERM...GCC
LONG TERM...TJT
AVIATION...TJT
FIRE WEATHER...GCC




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