HYDROLOGIC OUTLOOK NATIONAL WEATHER SERVICE BOISE IDAHO 1040 MDT WED APR 12 2006
...UPDATED IDAHO SPRING FLOOD OUTLOOK AND WATER SUPPLY FORECAST...
DISCUSSION...
AN ABOVE NORMAL SNOW PACK CONTINUES IN MOST OF THE IDAHO MOUNTAINS. ABOVE NORMAL PRECIPITATION IN MARCH AND ESPECIALLY DURING THE FIRST WEEK OF APRIL SIGNIFICANTLY BOOSTED HIGH ELEVATION SNOW PACK IN CENTRAL AND SOUTHERN IDAHO. FLOODING ON RIVERS AND SMALL STREAMS HAS ALREADY OCCURRED IN PORTIONS OF SOUTHERN IDAHO DUE TO RAIN AND SNOW MELT AT LOWER ELEVATIONS. RESERVOIRS ARE BEGINNING TO FILL RAPIDLY AND IT MAY BE DIFFICULT TO AVOID FLOODING BELOW SOME RESERVOIRS LATER THIS SPRING.
SNOW PACK...
SNOW PACK OBSERVATIONS ON APRIL 12TH AT NRCS SNOTEL AND SNOW COURSE LOCATIONS SHOWED THAT THE BIGGEST AMOUNTS RELATIVE TO NORMAL WERE IN THE SOUTHERN PORTION OF THE STATE AND GRADUALLY DECREASED TO NEAR NORMAL VALUES IN NORTHERN IDAHO. SNOW PACK IS IN THE RANGE OF 150 TO 170 PERCENT IN MOST TRIBUTARIES SOUTH OF THE SNAKE RIVER. BASINS OF GREATEST CONCERN INCLUDE... THE OWYHEE AT 163 PERCENT... THE BRUNEAU AT 168 PERCENT... OAKLEY AT 167 PERCENT... SALMON FALLS AT 150 PERCENT AND PORTNEUF AT 130 PERCENT. CENTRAL IDAHO HAD SNOW PACK VALUES IN THE RANGE OF 130-150 PERCENT OF NORMAL. BASINS OF GREATEST CONCERN INCLUDE...THE BIG WOOD AT 149 PERCENT...THE LITTLE WOOD AT 154 PERCENT...THE WEISER AT 148 PERCENT...THE BOISE AT 130 PERCENT AND THE PAYETTE AT 129 PERCENT. SOUTHEASTERN IDAHO AND THE UPPER SNAKE RIVER BASIN HAD VALUES BETWEEN 110 AND 125 PERCENT OF NORMAL. THE IDAHO PANHANDLE AND THE CLEARWATER RIVER BASIN HAD SNOW PACK VALUES BETWEEN 100 AND 105 PERCENT OF NORMAL.
LONG RANGE TEMPERATURE AND PRECIPITATION FORECASTS...
SEA SURFACE TEMPERATURES IN THE TROPICAL PACIFIC ARE BELOW NORMAL INDICATING LA-NINA CONDITIONS. LA-NINA PATTERNS GENERALLY RESULT IN ABOVE NORMAL WINTER SNOW PACKS IN IDAHO AND THIS YEAR IS NO EXCEPTION. THE OFFICIAL NWS CLIMATE PREDICTION CENTER FORECAST FOR THE REST OF APRIL INDICATES AN INCREASED PROBABILITY OF IDAHO EXPERIENCING COLDER THAN NORMAL TEMPERATURES AND ABOVE NORMAL PRECIPITATION. THE INFLUENCE OF LA-NINA SHOULD WANE LATER THIS SPRING SO THERE IS NO INDICATION ONE WAY OR THE OTHER ABOUT WHETHER THE COOL AND WET PATTERN WILL CONTINUE INTO MAY.
FLOOD POTENTIAL...
BASED ON CURRENT SNOW PACK AND SOIL MOISTURE CONDITIONS... THE THREAT OF SNOW MELT RELATED FLOODING IN SPRING 2006 IS ABOVE AVERAGE IN CENTRAL AND SOUTHERN IDAHO. NEAR NORMAL SNOW PACK IN NORTHERN IDAHO AND IN THE CLEARWATER RIVER BASIN MEANS THAT THE FLOOD THREAT IS AVERAGE IN THAT AREA. ADDITIONAL HEAVY PRECIPITATION COMBINED WITH MELTING SNOW COULD CAUSE FLOOD PROBLEMS WITHOUT MUCH LEAD TIME ON UNREGULATED STREAMS SUCH AS HENRYS FORK... BIG WOOD... PORTNEUF... BRUNEAU...OWYHEE...AND WEISER RIVERS. FLOODING IS ALSO POSSIBLE ON SOME REGULATED STREAMS IF RESERVOIR INFLOWS CONTINUE TO BE HIGH WHEN THE RESERVOIRS NEAR FULL CAPACITY. COOL AND WET WEATHER THROUGH APRIL WILL ALSO REDUCE IRRIGATION DEMAND FURTHER COMPLICATING FLOOD CONTROL OPERATIONS.
PEAK SPRING FLOWS RESULTING FROM A NORMAL MELTING OF CURRENT AND PROJECTED SEASONAL SNOW PACK ARE LISTED IN THE FOLLOWING TABLE. LONG RANGE FORECASTS HAVE SOME MARGIN OF ERROR AND A REASONABLE RANGE OF POSSIBLE VALUES IS LISTED FOR PLANNING PURPOSES. FORECAST FLOWS BELOW RESERVOIRS REPRESENT NATURAL FLOW AND DO NOT ACCOUNT FOR FLOOD CONTROL OPERATIONS WHICH WOULD MITIGATE THE PEAK TO SOME DEGREE.
STREAM AND LOC. FLOOD STAGE FORECAST REASONABLE RANGE
SNAKE RIVER HEISE ID 24500 CFS 22600 CFS 16300 - 23100 CFS SHELLEY ID 25600 CFS 22700 CFS 18200 - 27200 CFS
TETON RIVER ST ANTHONY ID 4750 CFS 4300 CFS 3300 - 5300 CFS
HENRYS FORK ST ANTHONY ID 9000 CFS 8200 CFS 7100 - 9400 CFS REXBURG ID 9.5 FEET 8.8 FEET 7.6 - 10.0 FEET
PORTNEUF RIVER POCATELLO ID 1140 CFS 1200 CFS 900 - 1500 CFS
BIG WOOD RIVER HAILEY ID 4000 CFS 3400 CFS 2800 - 4000 CFS
BOISE RIVER LUCKY PEAK INFLOW NONE 19000 CFS 17100 - 20900 CFS
BRUNEAU RIVER HOT SPRINGS ID 3200 CFS 3300 CFS 2300 - 4300 CFS
PAYETTE RIVER EMMETT ID 16000 CFS 14000 CFS 12400 - 15600 CFS
WEISER RIVER WEISER ID 8900 CFS 9400 CFS 7600 - 11100 CFS
SELWAY RIVER LOWELL ID 42300 CFS 31600 CFS 27000 - 36200 CFS
CLEARWATER RIVER STITES ID 9600 CFS 6400 CFS 4600 - 8100 CFS ORIFINO ID 75000 CFS 57000 CFS 47200 - 66900 CFS
MIDDLE FORK SALMON MIDDLE FORK LODGE NONE 7.4 FEET 6.9 - 7.8 FEET
SALMON RIVER SALMON 14000 CFS 11100 CFS 9700 - 12500 CFS WHITE BIRD 99000 CFS 76000 CFS 65700 - 86400 CFS
COEUR D ALENE RIVER ENAVILLE 27000 CFS 10300 CFS 7800 - 12800 CFS CATALDO 21350 CFS 14800 CFS 12800 - 16800 CFS
ST JOE RIVER CALDER 25600 CFS 13700 CFS 10300 - 17100 CFS ST MARIES 32.5 FEET 33.4 FEET 32.9 - 33.9 FEET
VOLUME FORECASTS...
SEASONAL VOLUME FORECASTS COORDINATED BETWEEN THE NATIONAL WEATHER SERVICE AND THE NATURAL RESOURCES CONSERVATION SERVICE ARE BASED ON PRECIPITATION AND SNOW PACK OBSERVED UP UNTIL APRIL 1ST AND ASSUME NORMAL PRECIPITATION WILL OCCUR IN THE FUTURE THE VOLUME FORECASTS AND PERCENT OF AVERAGE FOR SELECTED STREAMS AND LOCATIONS ARE LISTED BELOW. NOTE THAT THE VOLUMES ARE EXPRESSED IN THOUSANDS OF ACRE FEET.
STREAM AND LOCATION STATE PERIOD VOL %AVE
SNAKE RIVER
JACKSON LAKE INFLOW WY APR-JUL 905 111 PALISADES RES INFLOW WY APR-JUL 3710 111 HEISE ID APR-JUL 3960 111 SHELLY ID APR-JUL 5140 116 BLACKFOOT ID APR-JUL 5170 112 AMER. FALLS RES IN ID APR-JUL 3780 117 KING HILL ID APR-JUL 2520 83 MURPHY ID APR-JUL 2660 87 WEISER ID APR-JUL 7550 131 BROWNLEE RES INFLOW ID APR-JUL 8380 133 HELLS CANYON ID APR-JUL 8660 133
HENRYS FORK ASHTON ID APR-JUL 605 106 ST. ANTHONY ID APR-JUL 820 112 REXBURG ID APR-JUL 1700 109
TETON RIVER ST. ANTHONY ID APR-JUL 455 113
BIG LOST RIVER MACKAY RES INFLOW ID APR-JUL 178 125
WILLOW CREEK RIRIE RES INFLOW ID APR-JUL 110 128
PORTNEUF RIVER TOPAZ, ID ID APR-JUL 120 126
GOOSE CREEK OAKLEY RES INFLOW ID APR-JUL 52 179
BIG WOOD RIVER HAILEY ID APR-JUL 380 148 MAGIC RES INFLOW ID APR-JUL 500 172
LITTLE WOOD RIVER CAREY ID APR-JUL 134 154
BRUNEAU RIVER HOT SPRINGS ID APR-JUL 360 173
OWYHEE RIVER OWYHEE RES INFLOW OR MAR-JUL 960 157 OWYHEE RES OUTFLOW OR APR-JUL 520 240
BOISE RIVER TWIN SPRINGS ID APR-JUL 835 131 ANDERSON RNCH RES INF ID APR-JUL 770 142 BOISE ID APR-JUL 1990 141 PARMA ID APR-JUL 845 142
MALHEUR RIVER DREWSEY OR MAR-JUL 230 209 BEULAH RES INFLOW OR MAR-JUL 163 201
PAYETTE RIVER HORSESHOE BEND ID APR-JUL 2100 130 EMMETT ID APR-JUL 1770 142
N.F. PAYETTE RIVER CASCADE RES INFLOW ID APR-JUL 640 129
DEADWOOD RIVER DEADWOOD RES INFLOW ID APR-JUL 172 128
WEISER RIVER WEISER ID APR-JUL 555 142
POWDER RIVER SUMPTER OR MAR-JUL 133 190
SALMON RIVER SALMON ID APR-JUL 1070 125 WHITEBIRD ID APR-JUL 6960 119
CLEARWATER RIVER ORIFINO ID APR-JUL 4870 105 SPALDING ID APR-JUL 7670 103
N.F CLEARWATER RIVER DWORSHAK RES INFLOW ID APR-JUL 2540 96
PEND OREILLE RIVER PEND OREILLE LAKE IN ID APR-JUL 12500 98
COEUR D ALENE RIVER ENAVILLE ID APR-JUL 660 90 COEUR D ALENE LAKE IN ID APR-JUL 2320 91
ST JOE RIVER CALDER ID APR-JUL 1030 91
THE IDAHO SPRING FLOOD OUTLOOK AND WATER SUPPLY FORECAST WILL BE UPDATED ON OR BEFORE MAY 13TH 2006.
BREIDENBACH