A strong low pressure system passed to the northeast of Iowa on the 29th, with a strong cold front sweeping south across the state. The airmass was quite warm ahead of the front, with the atmosphere able to destabilize as the cooler air moved into the state.
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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 low pressure system passed to the northeast of Iowa on the 29th, with a strong cold front sweeping south across the state. The airmass was quite warm ahead of the front, with the atmosphere able to destabilize as the cooler air moved into the state. Deep mixing took place to near 700 mb, allowing the higher momentum air to mix down toward the surface. Flow in the layer around 850 mb was in the 45 to 55 kt range. A band of strong winds developed over north central Iowa during the late morning to early afternoon hours. Sustained winds were in the 30 to 40 MPH range, with wind gusting to 50 to 60 MPH. A wind gust of 59 MPH was recorded at the Mason City Airport. Damage was minor and limited to tree limb damage and spotty power outages for the most part. The winds resulted in some lodging of the corn crop as well. The fall harvest was underway. Sparks from combine activities resulted in scattered crop fires through the area. For the most part damage was limited or restricted to crop lands, though the small fires spread rapidly in the high winds. Reports of fires spreading with the wind for as long as 2 miles were received. Several homes had to be evacuated due to smoke and the threat of fire. Fires also swept into an auto junk yard in Cerro Gordo County causing some damage there.
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 Sep 29, 11:40 AM CST, 5 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 1240 PM CDT THU SEP 29 2011 ...UPDATED 18Z AVIATION DISCUSSION... .SHORT TERM /TODAY/... UPDATED ZONES FOR CLOUD COVER...MORE CLOUDS THIS MORNING BUT SHOULD STILL CLEAR THIS AFTERNOON WITH STRONG SUBSIDENCE EXPECTED. .PREVIOUS SHORT TERM /TODAY/... MAIN CONCERNS THIS PERIOD WILL BE WIND. COLD FRONT OVER CENTRAL MN AT 07Z WILL DRIVE SOUTH THIS MORNING WITH HELP OF STRONG COLD AIR ADVECTION THROUGH THE COLUMN...ESPECIALLY AT H500. AS THE COLD POOL AND INCREASING WINDS ALOFT ARRIVE...STRONG SUBSIDENCE BEHIND THE FRONT WILL MIX WINDS QUICKLY TO THE SFC. TIMING OF ADV LOOKS GOOD AS MIXING WILL BEGIN SHORTLY AFT 15Z NORTHWEST...BUT NOT REACH THE PEAK UNTIL 17Z-21Z ACROSS THE REGION. MODELS CONTINUE TO DIFFER ON DETAILS OF STRONGER WINDS ALOFT...BUT MOST ARE PUTTING THE HIGHER WINDS ROUGHLY ALONG AND EAST OF A KMCW TO KALO LINE IN THE LATE MORNING AND AFTERNOON. BEST SUBSIDENCE ARRIVES IN THE 15-18Z TIME FRAME SO WITH THE DELAY IN STRONGEST WIND FIELDS...ADVISORIES SHOULD SUFFICE. HAVING SAID THAT...WINDS MAY TOP 50 MPH ACROSS THE NORTHEAST DURING THE EARLY TO MID AFTERNOON HOURS. WITH SEASONAL INFLUENCES MIXING PROCESS WILL DIMINISH QUICKLY AFT 21Z WITH BREEZY CONDITIONS EXTENDING INTO THE EVENING HOURS AS THE BOUNDARY LAYER DECOUPLES. ONE OTHER CONCERN IS INSTABILITY NORTHEAST WITH THE UPPER LEVEL LOW AND COLD AIR ADVECTION. RAPID COOLING ALOFT FOLLOWS THE FRONT. THIS WILL ALLOW FOR CU DEVELOPMENT NORTHEAST ESPECIALLY. FOR NOW...FEEL BEST CHANCES FOR ANY SHOWERS/-TSRA WILL LIE JUST NORTHEAST OF THE FORECAST AREA. IF CONVECTIVE ELEMENTS BECOME MORE WIDESPREAD...THERE MAY BE A FEW CASES OF GUSTS EXCEEDING 50 KTS IN THE AFTERNOON HOURS NORTHEAST OR JUST NORTHEAST OF THE AREA. WILL PASS ALONG TO DAY SHIFT...THOUGH NOT EXPECTING COVERAGE TO BE WIDESPREAD ENOUGH TO GO WITH WARNING THERE. HIGHS WILL BE MILD TODAY WITH RETREATING WARM AIR. WILL MOST LIKELY WARM QUICKLY IN THE MORNING PRIOR TO MODEST RISE IN TEMP IN THE AFTERNOON. HAVE RAISED TMAX A DEGREE OR TWO...BUT OTHERWISE PREVIOUS FCST LOOKS GOOD. .LONG TERM /TONIGHT THROUGH WEDNESDAY/... CONCERN AT BEGINNING OF PERIOD IS WITH WINDS. WINDS WILL TAPER OFF THROUGHOUT THURSDAY NIGHT...BUT WILL BE STRONG...AND HAVE LEFT GUSTS AROUND 25-30MPH THROUGH 06Z AS FRONT PUSHES FURTHER SOUTH. GUSTS COULD FADE SOONER WITH INVERSION SETTING UP OVERNIGHT...HOWEVER SURFACE WINDS WILL STILL BE BREEZY. SURFACE HIGH WILL BUILD IN OVER UPPER PLAINS AS LARGE RIDGE OVER ROCKIES DOMINATES PATTERN THROUGH MUCH OF THE EXTENDED. WITH DRY CONDITIONS...FOCUS WILL BE ON TEMPERATURES. EXPECT A WARM UP BEHIND COLD FRONT WITH GOOD WAA PUSHING IN FROM THE WEST. HAVE TRENDED A FEW DEGREES WARMER WITH TEMPERATURES LATE IN THE PERIOD. WILL LIKELY SEE A FROPA LAST IN THE PERIOD...BUT ATTM APPEARS DRY WITH LITTLE CHANGE IN WEATHER. && .AVIATION...29/18Z WINDS WILL CONTINUE TO INCREASE DURING THE EARLY AFTERNOON WITH SOME AREAS OF NORTHERN IOWA SEEING GUSTS UP TO 50 KTS. AREAS OF BLOWING DUST FROM HARVESTED FIELDS COULD GENERATE LOCALLY REDUCED VISIBILITIES ACROSS THE STATE. WINDS SHOULD THEN TAPER OFF OVERNIGHT AND REMAIN BELOW 20 KTS TOMORROW. CLOUDS ASSOCIATED WITH A DEPARTING COLD FRONT WILL PUSH OUT OF SOUTHERN IOWA BY 21Z WHILE A MID LEVEL CLOUD SHIELD OVER MINNESOTA WILL MOVE INTO EASTERN IOWA THIS AFTERNOON BUT SHOULD NOT BRING ANY PRECIPITATION. && .DMX WATCHES/WARNINGS/ADVISORIES... WIND ADVISORY UNTIL 7 PM CDT THIS EVENING FOR BLACK HAWK-BOONE- BREMER-BUTLER-CERRO GORDO-EMMET-FRANKLIN-GRUNDY-HAMILTON-HANCOCK- HARDIN-HUMBOLDT-JASPER-KOSSUTH-MAHASKA-MARION-MARSHALL-PALO ALTO- POCAHONTAS-POLK-POWESHIEK-STORY-TAMA-WAPELLO-WEBSTER-WINNEBAGO- WORTH-WRIGHT. && SHORT TERM...REV LONG TERM...AWB AVIATION...KS
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 749 AM CDT THU SEP 29 2011 IAZ033-034-044>046-057>059-070>073-081>085-092>097-301300- SAC-CALHOUN-CRAWFORD-CARROLL-GREENE-AUDUBON-GUTHRIE-DALLAS-CASS- ADAIR-MADISON-WARREN-ADAMS-UNION-CLARKE-LUCAS-MONROE-TAYLOR-RINGGOLD- DECATUR-WAYNE-APPANOOSE-DAVIS- 749 AM CDT THU SEP 29 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TODAY AND TONIGHT GUSTY NORTHWEST WINDS OF 20 TO 35 MPH WITH GUSTS OVER 40 MPH ARE POSSIBLE TODAY AND TONIGHT. THE COMBINATION OF VERY DRY AND WINDY CONDITIONS WILL RESULT IN AN ENHANCED FIRE DANGER DURING THIS HARVEST SEASON. ANY FIRE COULD QUICKLY SPREAD AND GET OUT OF CONTROL UNDER THESE CONDITIONS. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED. IAZ004>007-015>017-023>028-035>039-047>050-060>062-074-075-086- 301300- EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO- POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-WEBSTER-HAMILTON- HARDIN-GRUNDY-BLACK HAWK-BOONE-STORY-MARSHALL-TAMA-POLK-JASPER- POWESHIEK-MARION-MAHASKA-WAPELLO- 749 AM CDT THU SEP 29 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TODAY AND TONIGHT GUSTY NORTHWEST WINDS OF 25 TO 35 MPH WITH GUSTS OVER 45 MPH ARE POSSIBLE TODAY. THE COMBINATION OF VERY DRY AND WINDY CONDITIONS WILL RESULT IN AN ENHANCED FIRE DANGER DURING THIS HARVEST SEASON. ANY FIRE COULD QUICKLY SPREAD AND GET OUT OF CONTROL UNDER THESE CONDITIONS. A WIND ADVISORY IS IN EFFECT FOR THE AREA TODAY. PLEASE REFER TO THE NATIONAL WEATHER SERVICE WEBSITE AT WEATHER.GOV/DESMOINES FOR FURTHER DETAILS. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED.
The national radar mosaic for the moment the first event began.
4 high wind. Local standard time, as filed.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2011Every state in 2011This day in weather historyWarnings in Iowa, September 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: 338391, 338392, 338394, 338395.