Runoff from heavy rain over several days caused flooding in the Black Hills and Bear Lodge Mountains.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS UNR wrote it up.
Runoff from heavy rain over several days caused flooding in the Black Hills and Bear Lodge Mountains.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Rapid City, SD wrote its last area forecast discussion before the first event at May 21, 2:12 AM MST, 10 hours 18 minutes earlier.
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY NATIONAL WEATHER SERVICE RAPID CITY SD 312 AM MDT SAT MAY 21 2011 .DISCUSSION...08Z ANALYSIS SHOWS A BROAD AREA OF LOW PRESSURE AT THE SURFACE CENTERED OVER SOUTH DAKOTA WITH THE UPPER LOW CENTERED OVER NORTHEASTERN WYOMING. REGIONAL RADAR MOSAIC SHOWS MOSTLY DRY CONDITIONS OVER THE FORECAST AREA WITH BANDS OF RAIN ARCING AROUND THE LOW PRESSURE SYSTEM FROM NORTH CENTRAL SOUTH DAKOTA...INTO NORTH DAKOTA AND EASTERN MONTANA...THEN BACK DOWN INTO CENTRAL WYOMING. THE LOW PRESSURE SYSTEM WILL MOVE SLOWLY EASTWARD TODAY THROUGH SUNDAY WHICH WILL ALLOW THE WRAP AROUND PRECIPITATION CURRENTLY OVER CENTRAL WYOMING TO MOVE EASTWARD INTO THE FORECAST AREA. THERE WILL BE SUFFICIENT LOW LEVEL MOISTURE AND STEEP LAPSE RATES FOR SCATTERED TO NUMEROUS SHOWERS AND ISOLATED THUNDERSTORMS ACROSS MOST OF THE AREA...MAINLY IN THE AFTERNOON...WITH THE BEST CHANCE OF WIDESPREAD HEAVIER RAIN IN THE WRAP AROUND AREA OVER NORTHEASTERN WYOMING...THE NORTHERN BLACK HILLS AND NORTHWESTERN SOUTH DAKOTA. TEMPERATURES WILL BE COOLER THAN NORMAL OVER NORTHEASTERN WYOMING WHERE THE CLOUDS AND SHOWERS WILL BE MOST PERSISTANT AND WARMER THAN NORMAL OVER SOUTH CENTRAL SOUTH DAKOTA. GUSTY NORTHWEST WINDS ARE EXPECTED ACROSS THE AREA ON SUNDAY...IN THE TIGHT PRESSURE GRADIENT BEHIND THE SURFACE LOW. THE WILL BE ENOUGH INSTABILITY AND LOW LEVEL MOISTURE LINGERING FOR A LESSER CHANCE OF SHOWERS AND THUNDERSTORMS ON MONDAY. EXTENDED...ANOTHER STRONG UPPER LOW WILL CROSS THE CENTRAL ROCKIES AND CENTRAL PLAINS ON TUESDAY AND WEDNESDAY. THIS WILL BRING A CHANCE FOR SHOWERS EACH DAY...MAINLY TO SOUTHERN AND WESTERN PORTIONS OF THE CWA. ANOTHER UPPER LEVEL SYSTEM IS PROGGED TO SLIDE ACROSS THE NORTHERN PLAINS THURSDAY NIGHT AND FRIDAY...BRINGING A CHANCE FOR SHOWERS AND THUNDERSTORMS. TEMPERATURES WILL GENERALLY BE NEAR OR BELOW AVERAGE THROUGH THE EXTENDED PERIOD. && .AVIATION...AREAS OF MVFR/IFR CONDITIONS AND SHOWERS CAN BE EXPECTED THIS MORNING...MAINLY FROM NORTHEASTERN WY INTO NORTHWESTERN SD. KGCC WILL LIKELY HAVE IFR CONDITIONS THROUGH MUCH OF THE MORNING. GENERAL VFR CONDITIONS ARE EXPECTED ELSEWHERE INTO THE AFTERNOON. SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP ACROSS MUCH OF THE AREA THIS AFTERNOON AND EVENING...MOST NUMEROUS ACROSS NORTHERN AND WESTERN PORTIONS OF THE AREA. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...NONE. WY...NONE. &&
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE RAPID CITY SD 354 AM MDT SAT MAY 21 2011 SDZ001-002-012>014-024>032-041>044-046-047-049-072>074-WYZ054>058- 071-221400- BENNETT-BUTTE-CENTRAL BLACK HILLS-CUSTER CO PLAINS-FALL RIVER-HAAKON- HARDING-HERMOSA FOOT HILLS-JACKSON-MELLETTE-NORTHEASTERN CROOK- NORTHERN BLACK HILLS-NORTHERN CAMPBELL-NORTHERN FOOT HILLS- NORTHERN MEADE CO PLAINS-PENNINGTON CO PLAINS-PERKINS-RAPID CITY- SHANNON-SOUTHERN BLACK HILLS-SOUTHERN CAMPBELL-SOUTHERN FOOT HILLS- SOUTHERN MEADE CO PLAINS-STURGIS/PIEDMONT FOOT HILLS-TODD-TRIPP- WESTERN CROOK-WESTON-WYOMING BLACK HILLS-ZIEBACH- 354 AM MDT (454 AM CDT) SAT MAY 21 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN SOUTH DAKOTA AND NORTHEASTERN WYOMING. .DAY ONE...TODAY AND TONIGHT SCATTERED TO NUMEROUS RAIN SHOWERS AND ISOLATED THUNDERSTORMS WILL REDEVELOP ACROSS THE AREA TODAY. THE GREATEST RAINFALL AMOUNTS... UP TO AN INCH...ARE EXPECTED ACROSS PARTS OF NORTHEASTERN WYOMING AND THE NORTHERN BLACK HILLS THIS AFTERNOON AND TONIGHT. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY THERE IS A CHANCE OF SHOWERS AND THUNDERSTORMS OVER PARTS OF THE AREA EACH DAY FROM SUNDAY THROUGH WEDNESDAY. ALTHOUGH ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE...WIDESPREAD SEVERE WEATHER IS NOT EXPECTED. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE RAPID CITY SD
122 PM MDT SAT MAY 21 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0121 PM HEAVY RAIN 15 NNE RECLUSE 44.95N 105.64W
05/21/2011 M4.50 INCH CAMPBELL WY TRAINED SPOTTER
2 DAY TOTAL
&&
MERICKSOThe national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
Water inundated areas along the Little Missouri River and Belle Fourche River in northeastern Crook County. Several rural roads in eastern Crook County were washed out or impassable.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Wyoming in 2011Every state in 2011This day in weather historyWarnings in Wyoming, May 2011
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 313797.