A strong MCS developed over eastern Nebraska during the evening of the 2nd and moved east into Iowa. The prominent bow echo pushed into Iowa during the predawn hours and produced strong winds over west central Iowa into north central Iowa.
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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 DMX wrote it up.
A strong MCS developed over eastern Nebraska during the evening of the 2nd and moved east into Iowa. The prominent bow echo pushed into Iowa during the predawn hours and produced strong winds over west central Iowa into north central Iowa. Wind speeds were reported in the 60 to 70 MPH range. As the storms progressed east, they weakened rapidly.
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 Des Moines, IA wrote its last area forecast discussion before the first event at May 2, 11:05 PM CST, 3 hours 33 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 1205 AM CDT THU MAY 3 2012 .UPDATE... PREVIOUS THOUGHTS OF CONVECTION DEVELOPING ACROSS NORTHERN IOWA IN THE LATE AFTERNOON/EARLY EVENING HAVE NOT OCCURRED...WITH DECENT CAP STILL IN PLACE ALOFT VIA DVN 00Z SOUNDING DUE TO STRATUS/LOW CLOUD COVER LINGERING MUCH OF THE DAY. THEREFORE HAVE TAPERED POPS DOWN FOR THE EARLY EVENING HOURS AT THIS TIME. A FEW CELLS ARE TRYING TO GO UP ON SFC BOUNDARY SITUATED ACROSS ERN NE/SE SD INTO SRN MN. THESE CELLS HAVING TOUGHER TIME SUSTAINING THEMSELVES AS WELL. THEREFORE FOCUS ON THUNDERSTORM DEVELOPMENT TURNS TO LATER TONIGHT WITH MID LEVEL WAVE APPROACHES FROM THE WEST AND LLJ INCREASES AND LOW LEVEL MOISTURE TRANSPORT BECOMES ORIENTED RIGHT INTO CENTRAL IOWA. HRRR MODEL SUGGESTING STORMS PUSHING INTO CENTRAL IOWA AROUND MIDNIGHT OR LATER AT THIS TIME...SO HAVE TRENDED GREATEST POPS ACROSS THE CWA FOR THE LATE NIGHT HOURS. .SHORT TERM /TONIGHT/... SEVERAL CONCERNS OVERNIGHT AS ACTIVE WSW FLOW ALOFT CONTINUES. OUTFLOW FROM THE MORNING CONVECTION HAD CLEARED WELL SOUTH OF THE BORDER EARLIER TODAY AND THERE HAS BEEN GRADUAL RECOVER THROUGH THE AFTERNOON AS SOUTHERLY WINDS HAVE INCREASED ALONG WITH MOISTURE. CAPES HAVE STEADILY INCREASED WITH 100MB MIXED LAYER OF 2000-3000 J/KG ACROSS WESTERN AND NORTHERN IOWA. HOWEVER...18Z SOUNDING AT KOAX HAS INDICATED SOME CAPPING ALONG WITH A GENERALLY DIVERGENT SURFACE FLOW IN NORTHERN IOWA. THESE PARTICULAR FEATURES ARE LIKELY INHIBITING CONVECTION AT THIS POINT BUT THIS SHOULD CHANGE BY THIS EVENING WITH THE APPROACH OF A SHORTWAVE IN THE PLAINS. MODELS HAVE BEEN INDICATING CONVECTION IN NORTH CENTRAL AND NORTHEAST IOWA THIS EVENING WHERE LOW LEVEL JET/FLOW WILL BE DIRECTED. THIS AREA HAS VERY HIGH PWATS AND WITH THIS PERSISTENT LOW LEVEL FLOW DIRECTED IN THAT LOCATION AND FLASH FLOOD GUIDANCE VALUES OF ONE TO ONE AND A HALF INCHES...HAVE OPTED FOR A FLASH FLOOD WATCH IN FAR NORTHEAST. ELSEWHERE...CONVECTION EXPECTED IN THE NORTH THIS EVENING WHERE CAP IS WEAKEST WITH ADDITIONAL CONVECTION IN NEBRASKA HEADING TOWARD CENTRAL AND SOUTHERN IOWA LATE TONIGHT INTO EARLY THURSDAY MORNING. THIS CONVECTION WILL HAVE THE THREAT FOR SEVERE STRAIGHT LINE WINDS ALONG WITH LARGE HAIL AND A ISOLATED TORNADOES AS IT PROGRESSES RAPIDLY EASTWARD OVERNIGHT. .LONG TERM /THURSDAY THROUGH WEDNESDAY/... COMPLICATED LONG TERM FORECAST...WITH LOW CONFIDENCE. ANTICIPATE OVERNIGHT MCS TO BE LINGERING ACROSS THE NORTH AND EAST FOR BEGINNING OF TOMORROW BEFORE PUSHING OUT OF CWA. CONDITIONS WILL IMPROVE THROUGH THE DAY...BUT WITH LINGERING FRONTAL BOUNDARY ACROSS SOUTHERN IOWA BY THURSDAY AFTERNOON...EXPECT TO SEE AFTERNOON DEVELOPMENT. BUT AGAIN ANTICIPATE BEST CHANCES FOR PRECIPITATION TO BE ANOTHER ROUND OF OVERNIGHT MCS CONVECTION...FOCUSED ACROSS SOUTHERN IOWA. PWAT VALUES ARE HIGH...WITH PLENTY OF MOISTURE AVAILABLE COULD SEE POTENTIAL FOR LOCALIZED AREAS OF HEAVY RAIN AGAIN OVERNIGHT THURSDAY NIGHT...AGAIN HIGHEST LIKELIHOOD APPEARS TO BE ACROSS SOUTHERN IOWA. OVERNIGHT PRECIPITATION COULD LINGER INTO EARLY FRIDAY BEFORE AGAIN QUICKLY PUSHING OUT OF THE CWA. HAVE LEFT SLIGHT CHANCE POPS FOR FRIDAY AFTERNOON WITH POTENTIAL FOR AFTERNOON DEVELOPMENT WITH ANOTHER APPROACHING FRONTAL SYSTEM...BUT AGAIN APPEARS MAIN PRECIP CHANCES WILL BE OVERNIGHT. TEMPERATURES BECOME A BIT TRICKY FOR FRIDAY AND SATURDAY. WAA AHEAD OF APPROACHING FRONTAL SYSTEM IS STRONG FOR FRIDAY WITH GOOD MIXING POSSIBLE FRIDAY. IF MIXING IS FULLY REALIZED...OR SKIES CLEAR FOR LONG ENOUGH COULD EASILY SEE TEMPERATURES POP UP INTO THE UPPER 80S FOR MUCH OF THE CENTRAL AND SOUTHERN PORTIONS OF THE CWA. HAVE INCREASED TEMPERATURES FOR FRIDAY AND SATURDAY...BUT MAY STILL HAVE BEEN TOO COOL...ESPECIALLY FOR FRIDAY. TIMING OF FRONTAL BOUNDARY WILL HAVE IMPACT ON TEMPS FOR SATURDAY...WITH LITTLE MODEL AGREEMENT ON PLACING OF FRONT HAVE TRENDED UPWARDS WITH TEMPS. ACTIVE PATTERN CONTINUES FOR REMAINDER OF EXTENDED WITH AREA OF LOW PRESSURE EXPECTED TO PUSH ACROSS THE NORTHERN PLAINS/SOUTHERN CANADA FOR THE END OF EXTENDED. ASSOCIATED FRONTAL BOUNDARYS WILL BRING CHANCES FOR PRECIPITATION THROUGH THE WEEKEND...WITH LINGERING PRECIPITATION INTO EARLY NEXT WEEK. && .AVIATION...03/06Z THUNDERSTORM ACTIVITY CONTINUES TO BE MOSTLY NON-EXISTENT ACROSS THE CWA...WITH A FEW CELLS PUSHING THROUGH EXTREME NORTHERN CWA. FORCING FOR THUNDERSTORMS REMAINS STRONGER TO THE WEST OF THE CWA...AND STILL MAY GET SOME MOVING THROUGH THE AREA LATE TONIGHT TOWARD SUNRISE OR A LITTLE BEFORE. THEREFORE HAVE GONE MORE PESSIMISTIC WITH THE TAFS AND ONLY MENTIONED VCSH FOR KDSM AND KOTM WHERE THE BETTER CHANCES WILL BE VERSUS THE NORTHERN CWA AT THIS TIME. && .DMX WATCHES/WARNINGS/ADVISORIES... FLASH FLOOD WATCH FROM 7 PM CDT THIS EVENING THROUGH THURSDAY MORNING FOR BLACK HAWK-BREMER-BUTLER-CERRO GORDO-FRANKLIN-GRUNDY- HARDIN. && SHORT TERM...COGIL LONG TERM...AWB AVIATION...MJB
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 351 PM CDT WED MAY 2 2012 IAZ004>007-015-016-023>025-033>036-044>050-057>062-070>075-081>086- 092>097-031100- EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-POCAHONTAS-HUMBOLDT- WRIGHT-SAC-CALHOUN-WEBSTER-HAMILTON-CRAWFORD-CARROLL-GREENE-BOONE- STORY-MARSHALL-TAMA-AUDUBON-GUTHRIE-DALLAS-POLK-JASPER-POWESHIEK- CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-CLARKE-LUCAS- MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS- 351 PM CDT WED MAY 2 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TONIGHT THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS ALL OF CENTRAL IOWA WITH A SMALL AREA OF MODERATE RISK IN WEST CENTRAL IOWA. TIMING WILL BE THIS EVENING INTO TONIGHT WITH DAMAGING WINDS...LARGE HAIL AND ISOLATED TORNADOES ALL POSSIBLE. HEAVY RAINS AND LOCALIZED FLASH FLOODING MAY OCCUR AS WELL. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY CHANCES FOR THUNDERSTORMS WILL CONTINUE OFF AND ON RIGHT THROUGH EARLY NEXT WEEK. THE BEST POTENTIAL FOR SEVERE WEATHER IN THIS PERIOD APPEARS TO BE LATE THURSDAY AFTERNOON AND THURSDAY EVENING FROM CENTRAL INTO SOUTHERN IOWA WHERE A SLIGHT RISK OF SEVERE WEATHER CONTINUES. DAMAGING WINDS...LARGE HAIL...LOCALLY HEAVY RAINS AND ISOLATED TORNADOES ALL REMAIN POSSIBLE. DETAILS REGARDING THE SEVERE WEATHER POTENTIAL IN THE LATER PERIODS WILL BE BETTER DEFINED IN THE COMING DAYS. .SPOTTER INFORMATION STATEMENT... SEVERAL EPISODES OF SPOTTER ACTIVATION MAY BE NEEDED THIS EVENING AND TONIGHT...AS WELL AS LATE THURSDAY. IAZ017-026>028-037>039-031100- CERRO GORDO-FRANKLIN-BUTLER-BREMER-HARDIN-GRUNDY-BLACK HAWK- 351 PM CDT WED MAY 2 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TONIGHT THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE AREA THIS EVENING INTO TONIGHT. DAMAGING WINDS...LARGE HAIL AND ISOLATED TORNADOES ARE ALL POSSIBLE. HEAVY RAIN IS ALSO EXPECTED TONIGHT WHICH MAY LEAD TO FLASH FLOODING. A FLASH FLOOD WATCH IS IN EFFECT FOR THE AREA TONIGHT. PLEASE REFER TO THE NATIONAL WEATHER SERVICE WEBSITE AT WEATHER.GOV/DESMOINES FOR FURTHER DETAIL. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY CHANCES FOR THUNDERSTORMS WILL CONTINUE OFF AND ON RIGHT THROUGH EARLY NEXT WEEK. THE BEST POTENTIAL FOR SEVERE WEATHER IN THIS PERIOD APPEARS TO BE LATE THURSDAY AFTERNOON AND THURSDAY EVENING FROM CENTRAL INTO SOUTHERN IOWA WHERE A SLIGHT RISK OF SEVERE WEATHER CONTINUES. DAMAGING WINDS...LARGE HAIL...LOCALLY HEAVY RAINS AND ISOLATED TORNADOES ALL REMAIN POSSIBLE. DETAILS REGARDING THE SEVERE WEATHER POTENTIAL IN THE LATER PERIODS WILL BE BETTER DEFINED IN THE COMING DAYS. .SPOTTER INFORMATION STATEMENT... SEVERAL EPISODES OF SPOTTER ACTIVATION MAY BE NEEDED THIS EVENING INTO TONIGHT...AS WELL AS LATE THURSDAY.
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE DES MOINES IA 237 AM CDT THU MAY 3 2012 IAZ023-033-034-044>046-057-058-070-071-081-082-092-093-031100- POCAHONTAS-SAC-CALHOUN-CRAWFORD-CARROLL-GREENE-AUDUBON-GUTHRIE- CASS-ADAIR-ADAMS-UNION-TAYLOR-RINGGOLD- INCLUDING THE CITIES OF...POCAHONTAS...SAC CITY...ROCKWELL CITY... DENISON...CARROLL...JEFFERSON...AUDUBON...GUTHRIE CENTER... ATLANTIC...GREENFIELD...CORNING...CRESTON...BEDFORD...MOUNT AYR 237 AM CDT THU MAY 3 2012 ...STRONG TO SEVERE THUNDERSTORMS MOVING INTO WEST CENTRAL IOWA THROUGH THE EARLY MORNING HOURS... A LINE OF STRONG TO SEVERE THUNDERSTORMS WILL CONTINUE TO MOVE EAST INTO PORTIONS OF SAC COUNTY SOUTHWARD THROUGH CRAWFORD COUNTY...AND INTO TAYLOR AND ADAMS COUNTIES THROUGH 4 AM CDT...AND THEN FURTHER EAST THROUGH AROUND 5 AM CDT. LARGE HAIL AND DAMAGING WINDS ARE LIKELY TO BE THE MAIN THREAT WITH LOCALLY HEAVY RAIN ALSO POSSIBLE. RAINFALL RATES IN EXCESS OF 1 TO 1.5 INCHES PER HOUR CAN BE EXPECTED. A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL 5 AM CDT. KLP
The Des Moines radar (KDMX), 113 km away, was scanning. The volume nearest the first event began at 08:39 UTC.
7 thunderstorm wind. Local standard time, as filed.
Large healthy Maple trees were blown down in the yard. They were roughly 3 feet in diameter.
Measured at the Iowa Department of Transportation Road Weather Information Site.
Measured at the Farnhamville Schoolnet site.
Several trees and large limbs down across Humboldt. One tree fell onto a house.
A tourist building was damaged in town from the gusty winds.
Measured at the Clarion Airport.
Measured at the Iowa Department of Transportation Road Weather Information Site southwest of Mason City on Interstate 35.
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: 368827, 368830, 368829, 368863, 379210, 368833, 368832.