Runoff from heavy rain on saturated ground caused flooding along the Cheyenne River.
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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 on saturated ground caused flooding along the Cheyenne River.
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, 4:43 PM MST, 2 hours 17 minutes earlier.
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY NATIONAL WEATHER SERVICE RAPID CITY SD 543 PM MDT SAT MAY 21 2011 .DISCUSSION...HAVE UPDATED TO RAISE POPS QUITE A BIT FOR TONIGHT ACROSS SWRN SD AS WDSPRD -SHRA ARE WRAPPING AROUND THE UPPER LOW THAT IS CENTERED OVER THE BLKHLS. && .PREV DISCUSSION... /ISSUED 243 PM MDT SAT MAY 21 2011/ DISCUSSION...CURRENT SURFACE MAP SHOWS LOW OVER EXTREME SOUTHWEST NORTH DAKOTA. UPPER LOW SPINNING ACROSS WESTERN SOUTH DAKOTA. TROWAL WRAPPED AROUND UPPER LOW BRINGING SHOWERS TO NORTHEAST WYOMING/NORTHWEST SOUTH DAKOTA...WITH SHOWERS/THUNDERSTORMS ON THE PLAINS EAST OF THE BLACK HILLS. UPPER LOW SLOWLY SPINS EASTWARD OVERNIGHT...REACHING NORTH CENTRAL SOUTH DAKOTA BY SUNDAY MORNING...THEN MOVES INTO EASTERN SOUTH DAKOTA ON SUNDAY. TROWAL ON BACK SIDE WILL CONTINUE TO BRING SHOWERS TO THE AREA...THOUGH WATER VAPOR IMAGERY SHOWS SOME DRIER MID LEVEL AIR WRAPPING INTO NORTHWEST SOUTH DAKOTA. STEEP LOW LEVEL LAPSE RATES KEEPS FROUDE NUMBER ABOVE 1.0 THROUGH SUNDAY AFTERNOON...WITH LOW LEVEL MOISTURE HIGH ENOUGH FOR UPSLOPE ENHANCEMENT OVER BEAR LODGE AND BLACK HILLS. HIGHEST PRECIPITATION TOTALS IN THAT AREA. PRESSURE GRADIENT TIGHTENS SUNDAY AS SURFACE LOW MOVES AWAY. STRONGEST WINDS WILL BE ON PLAINS NE/E OF THE BLACK HILLS. UPPER LOW PULLS EAST SUNDAY NIGHT...WITH WEAK SHORTWAVE RIDGE OVER THE AREA ON MONDAY. WITH MOIST BOUNDARY LAYER FROM RECENT RAIN...MLCAPE OF 100-500 J/KG AND MINIMAL CIN WILL RESULT IN MORE SHOWERS/THUNDERSTORMS. 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 SOUTHERN CANADA THURSDAY AND FRIDAY...BRINGING A CHANCE FOR SHOWERS AND THUNDERSTORMS. TEMPERATURES WILL GENERALLY BE NEAR OR BELOW AVERAGE THROUGH THURSDAY...THEN WARM INTO THE HOLIDAY WEEKEND. AVIATION...MVFR/IFR CONDITIONS WITH RAIN/RAIN SHOWERS CAN BE EXPECTED THROUGH SUNDAY MORNING...AS A STRONG AREA OF LOW PRESSURE CROSSES SOUTH DAKOTA. CONDITIONS SHOULD BEGIN TO IMPROVE FROM WEST TO EAST ON SUNDAY. && .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.
The national radar mosaic for the moment the first event began.
2 flood. Local standard time, as filed.
Flooding occurred along the Cheyenne River. The river gage on the Highway 34/73 bridge crested at 19.6 feet, which is 3.6 feet above flood stage.
Flooding occurred along the Cheyenne River.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in South Dakota in 2011Every state in 2011This day in weather historyWarnings in South Dakota, 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: 313868, 313874.