Facts, Findings and Recommendations

NWSFO Sioux Falls Operational Procedures
Dissemination of Warning and Forecast Products
Service Coordination and Preparedness

Data and Guidance Available to Forecasters

FACT: Computer model data and surface and upper air observations, which are key elements of the forecasts and severe weather outlooks issued by an NWS forecast office, were available to the Sioux Falls staff in a timely manner prior to the severe weather events of May 30, 1998.

FACT: Severe Weather Outlooks, Mesoscale Convective Discussions, and Severe Thunderstorm and Tornado Watches issued by the NWS SPC in Norman, Oklahoma, provided valuable and timely guidance to NWSFO Sioux Falls, the media, and emergency officials. The SPC called the forecast office just before issuing each of the three watches affecting its CWA during the afternoon and evening of May 30. The SPC made an additional coordination call at 7:15 p.m.

FACT: During the severe weather events surrounding the Spencer tornado, the Sioux Falls WSR-88D was the primary source of data on which warnings and other products, such as Severe Weather Statements, were based. The radar was operated in Volume Coverage Pattern (VCP) 11 to provide the highest vertical resolution. The system operated without interruption, except briefly for a change to generator power at approximately 8:15 p.m. Radar imagery was available at the PUP workstation and on one "slave" monitor at the public forecaster's AFOS workstation.

FACT: WSR-88D reflectivity and velocity data exhibited supercell characteristics in the thunderstorm that would eventually produce the Spencer tornado at about the same time (7:55 p.m.) the first report of a funnel cloud was received at the Sioux Falls NWSFO. The funnel cloud was reported in northeast Davison County, about 22 miles west-northwest of Spencer. WSR-88D computer algorithms indicated a mesocyclone at 8 p.m. over extreme northwest Hanson County, about 19 miles from Spencer, and a Tornado Vortex Signature (TVS) at 8:38 p.m. near Spencer.

FACT: Valuable severe weather observations from law enforcement officials were relayed in a timely manner through NAWAS warning points at Huron, Mitchell, and Sioux Falls (Metro Communications Center). These and a few reports from meteorologists who were storm chasing were the most reliable spotter reports available. They contributed significantly to many of the Severe Thunderstorm and Tornado Warnings issued during the event.

Finding 1: There were at least 10 meteorologists from other parts of the country, including NWS forecasters, "chasing" the supercell thunderstorm which eventually produced the Spencer tornado. Two of these storm chasers provided reports to NWSFO Sioux Falls, but most were unaware of how to contact the office. One who did, the WCM from NWSO Kansas City, called his own office and asked the staff to relay his report to Sioux Falls.

Recommendation 1: The NWS Office of Meteorology should form a team of NWS forecasters and experienced storm chasers to recommend methods of improving coordination between NWS forecast offices and "visiting" meteorologists engaged in storm chasing.

Finding 2: Most of the key severe weather reports prior to the Spencer tornado originated from law enforcement officials. A small contingent of trained spotters from McCook County was activated prior to the Spencer tornado, but there is no record of their reports reaching the NWSFO at Sioux Falls. The NWSFO Sioux Falls WCM has tried on numerous occasions to enlist the aid of area amateur radio (HAM) operators to improve severe weather communications in the CWA, but progress has been slow.

Recommendation 2: Central Region should provide the Sioux Falls NWSFO with examples of proven methods of enhancing communications with amateur radio networks for severe storm reporting.

NWSFO Sioux Falls Operational Procedures

FACT: NWSFO Sioux Falls has a well organized severe weather operation which receives strong emphasis in terms of guidance and training from station managers.

FACT: Warning and forecast operations at NWSFO Sioux Falls are conducted using a combination of new and old technology, ranging from the state-of-the-art WSR-88D radar to systems, such as AFOS and tape-based NWR consoles which have been in use for two decades. The Automated Weather Information Processing System (AWIPS) is scheduled for delivery at Sioux Falls in March 1999, and the NOAA Weather Radio 2000 Console Replacement System (CRS), delivered in June 1998, will be implemented during the fall of 1998.

FACT: At NWSFO Sioux Falls, warnings and related products are generated primarily by a two-person team, consisting of a PUP operator who analyzes WSR-88D data and a warning forecaster who prepares warnings and statements at a PC. The PC is equipped with NWS developed formatting software for warnings (WISE) and locally developed formatting software for statements and Short Term Forecasts.

FACT: The NWSFO Sioux Falls forecasters conducted a thorough analysis of all meteorological data available to them prior to the development of severe storms on the afternoon of May 30 and made an accurate and timely assessment of the severe weather threat in their CWA.

FACT: Through detailed local analysis, forecasters at the NWSFO Sioux Falls decided to upgrade the early morning SPC Severe Weather Outlook on May 30 to a moderate risk for their CWA. The local outlook accurately specified two episodes of severe weather--one in the morning and the other in the evening.

FACT: Staffing at the peak of severe weather events on May 30 consisted of four forecasters, one hydrometeorological technician, and one meteorologist intern. Two forecasters focused on warning operations (one at the PUP and one at the PC for warning and statement generation), and the intern worked exclusively on NWR programming.

FACT: Senior forecasters at NWSFO Sioux Falls, well aware of the severe weather potential on May 30, made careful plans and adjustments to ensure adequate staffing for the severe weather events of the day. Five members of the staff worked a total of 18 hours in addition to their assigned shifts. This does not include the undocumented extra hours spent by the MIC the night of May 30 after the storm. One forecaster working the midnight shift remained on duty until noon Saturday morning, volunteered to return early that night, and was called back to duty at 9 p.m.

FACT: Between 5:30 p.m. and midnight on May 30, the NWSFO Sioux Falls staff issued 11 Severe Thunderstorm Warnings covering 15 counties, eight Tornado Warnings covering nine counties, 26 Severe Weather Statements, and five Short Term Forecasts.

FACT: The lead time on the Tornado Warning issued at 8:32 p.m. for northern McCook County was 6 minutes.

Finding 3: The NWSFO Sioux Falls staff "rose to the occasion," working the extra hours necessary to ensure adequate staffing on May 30. The only staffing shortage noted was on the day following the Spencer tornado when the NWSFO was besieged by media inquiries from around the country, and most of the office managers were engaged in initial damage surveys and on-site coordination with the media and local officials.

Recommendation 3: WSH should alert Regional Directors to advise managers of forecast offices to include in significant event staffing plans additional staff for the day or two following an event.

Finding 4: The number and types of warning and forecast products issued by NWSFO Sioux Falls during the Spencer event are consistent with that office's stage of evolution to a fully modernized NWS WFO. However, the PUP-based severe weather operation limited the availability of radar data to forecasters at other workstations. This hampered the issuance of more frequent, detailed Short Term Forecasts which could have provided an hour or two "heads up" for areas downstream of existing severe weather.

Recommendation 4: With the implementation of AWIPS, and the increased availability of radar data at workstations in forecast offices, NWS should emphasize the utility of frequent, detailed Short Term Forecasts to provide a "heads-up" for areas where severe weather is expected in a 1- to 2-hour time frame and to provide a "bridge" between watches and warnings.

Finding 5: Of the 45 warnings and statements issued by NWSFO Sioux Falls during the evening of May 30, only 13 contained spotter reports. Finding 2 addressed limited spotter reports initiated from the field; however, the PUP-based severe weather operation also limited the ability of the NWSFO staff to make probing calls into severe weather areas to obtain reports.

Recommendation 5: With the implementation of AWIPS, and the availability of radar data at all workstations, the NWS regional offices should provide direction to forecast offices on adopting a more proactive approach to obtaining spotter reports and incorporating them in their warning products.

Dissemination of Warning and Forecast Products

FACT: The Sioux Falls NWSFO operates three NWR stations which broadcast warnings and forecasts for 25 of the 45 counties in the CWA. The warning alarm on the Sioux Falls NWR (WXM-28) transmitter is activated when warnings are issued for McCook County; however, the broadcast signal is only strong enough for reliable reception in the eastern part of the county.

FACT: The NWR equipment used at the Sioux Falls NWSFO on May 30 is older technology and uses record/play decks and magnetic tapes. Hardware for the NOAA Weather Radio 2000 Console Replacement System arrived at the NWSFO in early June. The system will be implemented through the fall of 1998.

FACT: Between 7 p.m. and midnight on May 30, one of the NWSFO Sioux Falls meteorologist interns was assigned the specific task of NWR broadcasts. During the peak of the severe weather, all of his warning broadcasts were made within 2 minutes of the time the warnings were issued.

FACT: From logs which were available and from interviews with media representatives, the EAS functioned properly and was useful in the relay of critical warning information to the media.

FACT: From all accounts obtained by the Service Assessment Team, the dissemination of critical severe weather information through the commercial media was excellent. Most of those in Spencer who were aware of warnings and ongoing severe weather received information through the commercial media. Sioux Falls television stations and two commercial radio stations in Mitchell were mentioned most often by those interviewed, however, other radio stations in the area, including those in Sioux Falls and Yankton, also played valuable roles in disseminating warnings.

FACT: The cable television provider for Spencer has 95 subscribers in town, however, there was no cable override system for local emergency management access.

FACT: Several residents of Spencer who knew the radio frequency used by local storm spotters kept themselves informed on the approaching tornado by listening to the spotter traffic on a scanner.

Finding 6: The Tornado Warning issued at 8:01 p.m. for northeast Davison and northern Hanson Counties did not reach AFOS from the PC used to compose warning products. Consequently, the warning was not disseminated over NWWS and other distribution systems which feed the media and other users. While it is impossible to be certain, the most likely point of failure is the peripheral sharing device used to link four PCs with one AFOS communications port.

Recommendation 6: The Sioux Falls NWSFO should move the PC used to generate warnings to a dedicated AFOS port. If a dedicated port cannot be made available, alternatives should be explored to reduce the number of PCs sharing the PSD with the warning PC.

Finding 7: The NWR coverage on May 30 was not adequate to ensure reliable reception of severe weather information on standard, home-use receivers in Spencer.

Recommendation 7: The Sioux Falls NWSFO should review its NWR expansion plan, update it if necessary, and redistribute. By spring 1999, the office should identify potential partners for obtaining NWR transmitters for each site in their plan.

Finding 8: In spite of attempts by NWSFO Sioux Falls to promote use of the Emergency Management Weather Information Network (EMWIN), there are no known users of the system in the Sioux Falls CWA. This system could have been useful on May 30 for the dissemination of warning and forecast products to emergency managers, law enforcement officials, etc.

Recommendation 8: Central Region should contact the appropriate state officials responsible for the emergency management programs to encourage emergency managers in the Sioux Falls CWA to install EMWIN before the next severe weather season.


FACT: In spite of the devastation inflicted on Spencer, many residents obtained sufficient warning information through media sources or by first-hand observation and avoided death or serious injury by taking appropriate precautions. There was, however, a significant segment of the small population who remained uninformed until the destruction began. With the volunteer fire department siren not functioning and the nearest NWR station essentially out of range, the only practical, readily available sources of warning information for most Spencer residents were television and commercial radio.

FACT: The Spencer tornado occurred when many people were watching television. Viewers in Spencer who were tuned to a Sioux Falls station were provided information on the 8:12 p.m. Tornado Warning for northern Hanson County and the 8:32 p.m. Tornado Warning for northern McCook County.

FACT: Residents who heard some type of warning in time to take precautions indicated Sioux Falls television stations or commercial radio stations as their source of warning information. Several residents of the area cited two radio stations in Mitchell, which included listener reports with warnings from NWSFO Sioux Falls.

FACT: Residents who took precautions indicated they took steps to protect themselves from flying debris, taking refuge in basements, under stairways, in hallways, and in closets.

FACT: Basements in many of the homes which were completely destroyed were filled with debris. Some residents survived by taking the extra precaution of finding a secondary sturdy shelter within the basement.

FACT: The six persons killed by the Spencer tornado ranged in age from 62 to 93.

Service Coordination and Preparedness

FACT: The NWSFO Sioux Falls staff, especially the MIC and WCM, maintain very active and effective preparedness and outreach programs. Documentation for 1997 and 1998 shows a very long list of spotter training classes, presentations for service organizations, school visits, media visits and workshops, and other public activities. Spotter training was conducted in April for several of the counties affected by the May 30 severe weather outbreak. Severe weather preparedness week was conducted in South Dakota during the week of April 20. All of these efforts have no doubt raised the level of severe weather awareness and education throughout the NWSFO Sioux Falls CWA.

FACT: A long-term relationship between the staff at NWSFO Sioux Falls and local media has produced an excellent working relationship which played a major role in effective severe weather warning operations on May 30. Representatives of the media who were interviewed by members of the Service Assessment Team were very familiar with the NWS products and services and with the NWSFO Sioux Falls warning operation.

FACT: The NWSFO Sioux Falls MIC and WCM also have an excellent working relationship with the Federal, state, and local officials who have jurisdiction in their CWA.

FACT: The NWSFO Sioux Falls staff was well prepared for the events of May 30. It is obvious to members of the Service Assessment Team that severe weather operations have received a great deal of emphasis and that guidance and training for warning operations have been a high priority among the NWSFO managers.

Go to Appendices, return to Table of Contents or go back to Disaster Survey Page.