Runoff from heavy rain caused minor flooding of the Little Sioux and Ocheyedan Rivers in late May. The flooding on the Little Sioux River continued to the end of the month.
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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 FSD wrote it up.
Runoff from heavy rain caused minor flooding of the Little Sioux and Ocheyedan Rivers in late May. The flooding on the Little Sioux River continued to the end of the month.
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 Sioux Falls, SD wrote its last area forecast discussion before the first event at May 28, 5:45 AM CST, 15 minutes earlier.
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA NATIONAL WEATHER SERVICE SIOUX FALLS SD 645 AM CDT MON MAY 28 2012 .DISCUSSION... SHOWERS CONTINUING OVER OUR FAR EASTERN ZONES EARLY THIS MORNING IN VICINITY OF FRONTAL BOUNDARY/UPPER LEVEL SHORTWAVE...THOUGH EXPECT THIS ACTIVITY TO PULL OUT OF OUR AREA BY SUNRISE AS THE SHORTWAVE TRACKS INTO MINNESOTA. OTHERWISE...LOOKING FOR DECREASING CLOUDS AND BREEZY CONDITIONS THROUGH THE DAY IN A COLD AIR ADVECTION REGIME...AND WILL BE A MIXY DAY WITH STEEP LOW LEVEL LAPSE RATES WITH HIGHS MUCH COOLER THAN YESTERDAY...FROM NEAR 70 IN THE NORTH TO AROUND 80 IN OUR FAR SOUTHEASTERN IOWA ZONES. MODELS WANTING TO SPIT OUT A LITTLE PRECIPITATION ALONG OUR NORTHERN BORDER EARLY IN THE DAY AS SECONDARY UPPER LEVEL SHORTWAVE DROPS OUT OF EASTERN MONTANA/WESTERN NORTH DAKOTA WITH COOLING ALOFT...THOUGH IT LOOKS LIKE MOST OF THE ENERGY WITH THIS FEATURE WILL REMAIN TO OUR NORTH DID THROW IN SLIGHT POPS OVER THAT AREA DURING THE MORNING HOURS. WINDS WILL DROP OFF TONIGHT...THOUGH REMAIN HIGH ENOUGH TO KEEP TEMPERATURES FROM COMPLETELY BOTTOMING OUT...WITH LOWS IN THE MID 40S TO LOWER 50S. MAIN UPPER LEVEL SHORTWAVE TRACKS TO OUR NORTH AND EAST ON TUESDAY PULLING EVEN COOLER AIR INTO THE REGION. WITH THE STRONG COLD AIR ADVECTION/STEEP LOW LEVEL LAPSE RATES AND RELATIVELY STOUT WINDS ALOFT IT WILL BE ANOTHER BREEZY DAY. HIGHS WILL RANGE FROM NEAR 60 NORTH TO NEAR 70 SOUTH. HIGH PRESSURE AXIS SLIDES ACROSS THE REGION ON TUESDAY NIGHT...AND WITH WINDS BECOMING NEARLY CALM IT WILL BE A COOL NIGHT WITH LOWS AROUND 40 NORTH TO MID 40S SOUTH. ANOTHER SHORTWAVE DROPS SOUTHWARD LATER ON WEDNESDAY INTO THURSDAY ON A NORTHWESTERLY UPPER LEVEL FLOW. GOOD UPPER LEVEL SUPPORT WITH THE SYSTEM WITH A 300 MB JET STREAK STREAMING FROM EASTERN SOUTH DAKOTA INTO SOUTHERN MINNESOTA...ALONG WITH DECENT MIDLEVEL FRONTOGENESIS MAXIMIZED ACROSS OUR SOUTH AND WEST. IN LIGHT OF THAT...KEPT WITH LIKELY POPS FOR WEDNESDAY AND WEDNESDAY NIGHT OVER MOST OF THE AREA...WITH SHOWER CHANCES LINGERING INTO THURSDAY. WITH CLOUDS/SHOWERS AND A NORTHEASTERLY LOW LEVEL FLOW BOTH WEDNESDAY AND THURSDAY WILL BE COOL WITH HIGHS ONLY UPPER 50S TO LOWER 60S. FARTHER OUT INTO THE EXTENDED...LOOKS LIKE A WARMING TREND AS AN UPPER LEVEL RIDGE BUILDS INTO THE REGION AND A SOUTHERLY FLOW RETURNS TO THE AREA. SHOULD BE MAINLY DRY THROUGH THE PERIOD...WITH HIGHS IN THE UPPER 60S TO LOWER 70S FOR FRIDAY...TOPPING OUT IN THE LOWER TO MID 80S BY SUNDAY. LOWS WILL RANGE FROM THE 40S ON FRIDAY MORNING...TO THE 50S TO NEAR 60 ON SUNDAY MORNING. && .AVIATION.../FOR THE 12Z TAF ISSUANCE/ MAINLY VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD. ONLY EXCEPTION IS THAT CURRENTLY SEEING A POCKET OF LOW STRATUS CLOSE TO KSUX...SO COULD SEE A BRIEF PERIOD OF MVFR CIGS THEIR THIS MORNING. AS MIXING COMMENCES ELSEWHERE...ENOUGH LOW LEVEL MOISTURE THAT WE SHOULD SEE SOME CU FORMATION. HOWEVER ONLY SCATTERED COVERAGE EXPECTED...AND BY AFTERNOON BASES WILL BE ABOVE 3K FEET. ONLY OTHER ISSUE TODAY WILL BE AFTERNOON GUSTY WINDS UP TO 30 MPH OUT OF THE WEST NORTHWEST. /CHENARD && .FSD WATCHES/WARNINGS/ADVISORIES... IA...NONE. MN...NONE. NE...NONE. SD...NONE. &&
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE SIOUX FALLS SD 549 AM CDT MON MAY 28 2012 SDZ038>040-050-052>071-MNZ071-072-080-081-089-090-097-098- IAZ001>003-012>014-020>022-031-032-NEZ013-014-291200- AURORA-BEADLE-BON HOMME-BROOKINGS-BRULE-BUENA VISTA IA- CHARLES MIX-CHEROKEE IA-CLAY-CLAY IA-COTTONWOOD MN-DAKOTA NE- DAVISON-DICKINSON IA-DIXON NE-DOUGLAS-GREGORY-HANSON-HUTCHINSON- IDA IA-JACKSON MN-JERAULD-KINGSBURY-LAKE-LINCOLN-LINCOLN MN- LYON IA-LYON MN-MCCOOK-MINER-MINNEHAHA-MOODY-MURRAY MN-NOBLES MN- OBRIEN IA-OSCEOLA IA-PIPESTONE MN-PLYMOUTH IA-ROCK MN-SANBORN- SIOUX IA-TURNER-UNION-WOODBURY IA-YANKTON- 549 AM CDT MON MAY 28 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST SOUTH DAKOTA... SOUTHWEST MINNESOTA...NORTHWEST IOWA...AND NORTHEAST NEBRASKA. .DAY ONE...TODAY AND TONIGHT FLOODING... DUE TO RECENT HEAVY RAINS...THE OCHEYEDEN RIVER AT SPENCER...THE ROCK RIVER AT ROCK RAPIDS AND ROCK VALLEY...THE LITTLE SIOUX RIVER AT SPENCER AND LINN GROVE...AND THE BIG SIOUX RIVER AT HAWARDEN AND AKRON WILL CREST ABOVE FLOOD STAGE AT VARIOUS TIMES THROUGH WEDNESDAY. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY AND TONIGHT. && FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE AT WWW.WEATHER.GOV/SIOUXFALLS. THIS INCLUDES THE GRAPHICAL HAZARDOUS WEATHER OUTLOOK.
The national radar mosaic for the moment the first event began.
4 flood. Local standard time, as filed.
Runoff from heavy rain caused minor flooding of the Little Sioux River, with lowlands including some farmland and a few roads affected. The river crested at 1.7 feet above flood stage near Milford on May 31st.
Runoff from heavy rain caused minor flooding of the Little Sioux River, with lowlands including some farmland and a few roads affected. The river crested at 1.9 feet above flood stage at Spencer on May 31st.
Runoff from heavy rain caused minor flooding of the Little Sioux River, with a few lowlands along the river affected. The river rose to less than a half foot above flood stage at Linn Grove at the end of the month.
Runoff from heavy rain caused minor lowland flooding of the Ocheyedan River near Spencer. The river crested at less than a foot above flood stage near Spencer on May 30th.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2012Every state in 2012This day in weather historyWarnings in Iowa, May 2012
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: 384779, 384780, 384781, 384782.