Thunderstorms produced hail up to quarter size and 60 mph wind gusts at several locations in northwest Iowa before daybreak in the morning of September 2nd.
Every event with a place to put it. Tap one for its entry below.
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.
Thunderstorms produced hail up to quarter size and 60 mph wind gusts at several locations in northwest Iowa before daybreak in the morning of September 2nd.
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 Sep 1, 8:07 PM CST, 5 hours 48 minutes earlier.
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA NATIONAL WEATHER SERVICE SIOUX FALLS SD 907 PM CDT THU SEP 1 2011 .DISCUSSION... FORECAST IS IN GOOD SHAPE. FRESHENED UP THE GRIDS ABOUT AN HOUR AGO BUT TRENDS ARE STILL ON TRACK. LOOKING AT A LATE NIGHT RAIN EVENT FOR OUR FORECAST AREA. CURRENTLY SOME ELEVATED CONVECTION IS MOVING NORTHEASTWARD ACROSS THE WESTERN PLAINS. SIMILAR TO LAST NIGHT...IT IS UNSTABLE IN THE MID LEVELS...BUT ALSO DRY BETWEEN 900MB AND 600MB. DEEPER BEHIND THE COLD FRONT...THE MOISTURE PROFILE BEGINS TO SATURATE UP AFTER MIDNIGHT FROM NORTH TO SOUTH LASTING THROUGH EARLY FRIDAY WHICH WILL BRING THE BEST CHANCE FOR RAINFALL IN THIS AREA. HIGHER BASED STRATUS IS CURRENTLY DEVELOPING NORTH OF OUR FORECAST AREA IN RESPONSE TO POST FRONTAL LOW LEVEL MOISTURE POOLING...AND THIS IS INDICATIVE OF WHAT WILL HAPPEN ELSEWHERE LATE TONIGHT AND EARLY FRIDAY. MINIMUM TEMPERATURES LOOK GOOD...RANGING FROM NEAR 60 AROUND CHAMBERLAIN AND HURON...TO 69 AT SIOUX CITY AND STORM LAKE. && .AVIATION... CONDITIONS SHOULD BE GENERALLY VFR THROUGH 03/06Z. POSSIBLE EXCEPTIONS WOULD BE IN THE PERIOD 02/08Z-18Z. EXPECTED SCATTERED HIGH BASED CONVECTION SEEMS UNABLE BY ITSELF TO PRODUCE ANY CEILINGS AS LOW AS 3K FEET OR VISIBILITIES OF 5SM OR LESS. IT IS POSSIBLE THAT STRENGTHENING LOW LEVEL TEMPERATURE AND PRESSURE GRADIENTS BEHIND COLD FRONT COULD PRODUCE A FEW AREAS OF CEILINGS 1-3K FEET DURING THIS TIME THOUGH THIS IS UNLIKELY TO BE WIDESPREAD. LOCATION OF ANY SUCH LOW DECKS UNCERTAIN THOUGH WITH TIME THE BEST CHANCE SHOULD BE OVER THE SOUTHEAST PART OF THE FORECAST AREA. AT THIS TIME THREAT SEEMS LOW ENOUGH NOT TO PUT ANY MVFR IN TAFS BUT WE WILL WATCH. AFTER 02/18Z ANY SHOWERS SHOULD END OR MOVE OUT AND VFR SHOULD SOLIDLY REIGN. / WILLIAMS && .PREV DISCUSSION... THE FOCUS FOR TONIGHT CONTINUES TO CENTER AROUND THE THREAT FOR SHOWERS AND THUNDERSTORMS. AN EXTENSIVE CAP IN PLACE RULES OUT ANY FRONTAL OR PRE FRONTAL ACTIVITY...BUT AS UPPER LEVEL SUPPORT SPREADS ACROSS THE ROCKIES TONIGHT EXPECT THUNDERSTORMS TO DEVELOP OVER WESTERN NEBRASKA AND SOUTHWEST SD THEN PROGRESS EASTWARD DOWN THE MID LEVEL FRONT...LIKELY NEAR 750MB TO 700MB. WHILE INSTABILITY IS NOT EXCEPTIONAL...CAPE VALUES FROM 1000 J/KG TO 1500 J/KG AND EFFECTIVE BULK SHEAR VALUES LIKELY TO BE AROUND 25 KNOTS...THE SEVERE THREAT WOULD REMAIN VERY ISOLATED. EXPECT THIS FRONT TO BECOME ORIENTED A LITTLE MORE SOUTHWEST TO NORTHEAST THROUGH THE NIGHT AS THE WAVE PEELS BY TO THE NORTH SO THE BEST CHANCES FOR RAIN AND THUNDERSTORMS WILL BE ALONG AND NORTH OF INTERSTATE 90. COOL AIR ADVECTION DOES CRANK UP OVERNIGHT AS THE FRONT PASSES SO DID INCREASE WINDS A BIT ABOVE GUIDANCE AND ALSO WENT A LITTLE BELOW GUIDANCE ON DEW POINTS AS DRIER AIR FILTERS IN LATE BEHIND THE BETTER CHANCES FOR RAINFALL. LOWS SHOULD MAINLY BE IN THE 60S. /08 THE MID LEVEL FRONT WILL BE SITUATED ACROSS OUR SOUTHEAST BY FRIDAY MORNING...AND KEPT LIKELY POPS GOING OVER THAT AREA AS A WEAK MID LEVEL SHORTWAVE SHOOTS OUT OF CENTRAL NEBRASKA DURING THE MORNING. BY AFTERNOON DYNAMICS WILL BEGIN TO WEAKEN AND SLIDE OFF TO THE SOUTHEAST...WITH DWINDLING RAIN CHANCES...THOUGH BOUNDARY REMAINS JUST CLOSE ENOUGH TO WARRANT LEAVING SLIGHT POPS OVER OUR FAR SOUTHEAST INTO THE EVENING. WITH THE COLD AIR ADVECTION...IT WILL BE A COOLER DAY...IN THE MID TO UPPER 70S FOR HIGHS. THE NEXT COLD FRONT TO AFFECT OUR AREA SLIDES THROUGH THE REGION ON SATURDAY...AND UPPED POPS JUST A BIT WITH MOISTURE LOOKING TO BE A LITTLE BETTER THAN BEFORE...THOUGH DYNAMICS WITH THE SYSTEM STILL LOOK TO BE PRETTY WEAK. MAY SEE A BIT OF A WARM UP OUT AHEAD OF THE SYSTEM WITH HIGHS CLIMBING TO NEAR 80 OVER NORTHWESTERN IOWA...WHILE BEHIND THE FRONT...HIGHS WILL BE IN THE LOWER 70S IN OUR NORTH AND FAR WEST. CLEARING SKIES ON SATURDAY NIGHT WILL LEAD TO THE COOLEST NIGHT YET OF THE SEASON...WITH LOWS IN THE UPPER 40S TO AROUND 50. WITH HIGH PRESSURE BUILDING INTO THE REGION ON SUNDAY...IT WILL BE DRY WITH TEMPERATURES WELL BELOW NORMAL...IN THE UPPER 60S TO LOWER 70S IN THE AFTERNOON...THEN MID 40S IN THE EAST ON SUNDAY NIGHT. IN THE EXTENDED...MONDAY THROUGH THURSDAY...OUR AREA LOOKS TO BE DOMINATED BY A NORTHWESTERLY UPPER LEVEL FLOW. THIS WILL RESULT IN A PERIOD OF BELOW TO NEAR NORMAL TEMPERATURES AND MAINLY DRY CONDITIONS THROUGH THE PERIOD. /JM && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. &&
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE SIOUX FALLS SD 1247 PM CDT THU SEP 01 2011 SDZ038>040-050-052>071-MNZ071-072-080-081-089-090-097-098- IAZ001>003-012>014-020>022-031-032-NEZ013-014-021200- 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- 1247 PM CDT THU SEP 01 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST SOUTH DAKOTA... SOUTHWEST MINNESOTA...NORTHWEST IOWA...AND NORTHEAST NEBRASKA. .DAY ONE...TODAY AND TONIGHT THUNDERSTORMS... THUNDERSTORMS ARE EXPECTED TO DEVELOP OVER THE WESTERN HIGH PLAINS THIS EVENING...THEN WORK EASTWARD OVERNIGHT. WHILE A FEW OF THESE STORMS COULD APPROACH SEVERE LIMITS THEY SHOULD BE LIMITED TO THE POTENTIAL FOR HAIL TO THE SIZE OF NICKELS AND WIND GUSTS TO 50 MPH. THE BEST CHANCE FOR THIS WILL BE FROM ABOUT 1100 PM CDT THROUGH 500 AM CDT. FLOODING... MINOR TO MODERATE FLOODING ON PARTS OF THE JAMES RIVER WILL CONTINUE OVER THE NEXT COUPLE OF WEEKS...BUT RIVER LEVELS WILL SEE A SLOW BUT STEADY DROP. BARRING HEAVY RAINS...THE JAMES RIVER IS EXPECTED TO BE LARGELY BELOW FLOOD STAGE ON THE SOUTH END DURING THE FIRST HALF OF SEPTEMBER...FOLLOWED BY THE MID JAMES VALLEY LATER IN THE MONTH. FLOODING WILL CONTINUE ALONG THE MISSOURI RIVER BETWEEN FORT RANDALL DAM AND NEAR PONCA NEBRASKA...WITH RIVER LEVELS CONTINUING TO DROP VERY SLOWLY. EXCESSIVE TEMPERATURES... THE HEAT INDEX IS EXPECTED TO BRIEFLY CLIMB TO BETWEEN 100 AND 105 LATE THIS AFTERNOON ALONG AND EAST OF THE JAMES RIVER VALLEY. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL REMAIN POSSIBLE ON FRIDAY...WITH THE BETTER CHANCES ALONG AND SOUTH OF INTERSTATE 90 IN THE MORNING THEN MAINLY NORTHWEST IOWA IN THE AFTERNOON. .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 Sioux Falls radar (KFSD), 94 km away, was scanning. The volume nearest the first event began at 07:55 UTC.
4 thunderstorm wind, 3 hail. Local standard time, as filed.
Thunderstorm winds caused tree damage. The winds were accompanied by quarter size hail.
Quarter size hail was accompanied by 60 mph wind gusts.
Thunderstorm winds, accompanied by heavy rain, caused minor tree and shingle damage.
Thunderstorm winds caused tree damage, including several small branches blown down. The winds were accompanied by quarter size hail.
Large hail was accompanied by 60 mph wind gusts.
Thunderstorm winds caused tree damage, including small branches blown down. The winds also caused corn to lean. The winds were accompanied by small hail.
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: 347682, 347683, 347684, 347688, 347689, 347690, 347691.