A very moist and unstable airmass was in place over Iowa during the late afternoon and evening of the 23rd. Surface temperatures warmed into the 90s, with dewpoint readings in the mid 70s to around 80.
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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 very moist and unstable airmass was in place over Iowa during the late afternoon and evening of the 23rd. Surface temperatures warmed into the 90s, with dewpoint readings in the mid 70s to around 80. CAPE rose to between 5000 and 7000 J/kg with a lifted index of -5 to -9 C. Monsoonal flow was in place across the state with precipitable water values around 2 inches. The freezing level remained very high, in the 15,500 to 16,000 foot range. An outflow boundary was in place across southern Iowa due to convection that had taken place during the day on the 23rd. Thunderstorms erupted during the early evening hours along the outflow boundary. Downdraft CAPE values were quite high, in the 1500 to 2000 J/kg range. The atmosphere was weakly sheared with 30 to 35 kts of shear available. There was little hail associated with the storms as the freezing level was very high. Winds of 60 MPH or more were reported with the storms with scattered tree and power line damage. A tin roof was partially torn off in Appanoose County. High winds bent corn over in Lucas County. These were two of the stronger wind gusts. Heavy rain also occurred with the storms. Three inches of rain fell in an hour east of Chariton in Lucas County.
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 Jul 23, 2:15 PM CST, 3 hours earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 315 PM CDT SAT JUL 23 2011 .SHORT TERM /TONIGHT/... A COMPLICATED WX PATTERN WITH NUMEROUS OUTFLOW BOUNDARIES AND THE MONSOONAL FLOW WELL POSITIONED OVER IA. CONVECTION DURG THE DAY KEPT A BROAD SWATH OF CNTRL IA COOL TODAY AND THAT COOL AIR WAS DRAWN NWD INTO THE NERN CONTIES. ONLY THE SRN 3 TIER WARMED INTO THE 90S THIS AFTN AND FOR THAT REASON WILL DROP HEADLINES XCP FOR THE HEAT WARNING OVR THE SRN 3 TIER. CDFNT WILL MOVE INTO NWRN IA LATER THIS EVE AND EXPECT TO SEE A LINE OF TSRA FORM WITH THAT. PUT GUSTY WINDS IN THE NWRN HALF OF THE CWA THRU THE EVE. BEST SUPPORT IS TO THE NORTHEAST OF THE CWA. AS TSRA MOVE INTO THE MOISTURE PLUME WOULD FEEL THE TSRA WILL BECOME MORE MULTI-CELLULAR IN NATURE AND REDUCE THE SVR THREAT. WOULD NOT BE SURPRISED TO SEE SOME 2+ INCH AMOUNTS IN SPOTS...BUT WITH FFG QUITE HIGH MOST OF THE CWA WITH THE EXCEPTION OF A FEW COUNTIES OVR THE NORTHEAST...AM NOT TOO CONCERNED ABOUT THAT. .LONG TERM /SUNDAY THROUGH MONDAY NIGHT/... STRONG SHORTWAVE TROUGH MOVING EAST ACROSS SOUTHERN CANADA SUNDAY MORNING IS FORECAST TO SOUTHEAST INTO THE GREAT LAKES BY 00Z TUESDAY. THE MODELS ARE IN PRETTY GOOD AGREEMENT THE THIS FEATURE. AS A RESULT...UPPER FLOW BECOMES NORTHWESTERLY SHOULD SHOULD RESULT COLD FRONT CLEARING THE STATE ON SUNDAY. 12Z FRONTAL POSITION SHOULD BE THROUGH CENTRAL IOWA. THE PLACEMENT OF THE FRONT WILL BE PROBLEMATIC BECAUSE OF TONIGHT/S CONVECTION. NONE THE LESS...EXPECT FRONT TO EXIT SOUTHERN IOWA SUNDAY AFTERNOON. ALOFT...MID/HIGH LEVEL MOISTURE FETCH MOVING AROUND SUBTROPICAL HIGH SHOULD BE PUSHED INTO MISSOURI AND FAR SOUTHERN IOWA BY SUNDAY AFTERNOON. IT/S BEEN UNSETTLED IN THE VICINITY OF THE TROPICAL MOISTURE BAND AND EXPECT CLOUDS AND A CHANCE OF SHOWERS AND THUNDERSTORMS SOUTHERN COUNTIES SUNDAY AFTERNOON. OF COURSE...HAVING THE FRONT MOVING THROUGH TO MAXIMIZE LOW-LEVEL CONVERGENCE DOESN/T HURT. SURFACE HIGH SHOULD PROVIDE 36 HOURS OF LOW POPS...COOLER TEMPS AND LOWER DEW POINTS WHICH WILL BE A NICE CHANGE GIVEN THE RECENT PATTERN. .EXTENDED/TUESDAY THROUGH SATURDAY/... MCS IS EXPECTED TO BE ONGOING ACROSS THE MISSOURI RIVER VALLEY AT THE START OF THE PERIOD TUESDAY MORNING. IT SHOULD DISSIPATE THROUGHOUT THE DAY IN RESPONSE TO THE LACK OF FORCING ASSOCIATED WITH THE WEAKENING LOW LEVEL JET. MEANWHILE...ANOTHER WAVE FURTHER WEST WILL BE CROSSING THE NORTHERN ROCKIES ON TUESDAY. MODELS DIFFER ON THE TIMING AND PLACEMENT...WITH THE ECMWF LESS AMPLIFIED AND THEREFORE MORE PROGRESSIVE...WHILE THE GEM...AND MORE SO GFS BEING STRONGER AND A BIT SLOWER. THE DIFFERENCE MANIFESTS ITSELF IN THE LOCATION OF THE LEE SIDE SURFACE LOW ACROSS THE HIGH PLAINS. USED A MODEL BLEND TO ACCOUNT FOR THE UNCERTAINTY...WITH BEST POPS ACROSS THE NORTH TUESDAY THROUGH WEDNESDAY. WARM MOIST BOUNDARY LAYER WILL YIELD HIGH CAPE VALUES ON WEDNESDAY...BUT H850 TEMPS OF 25+C SHOULD CAP OFF CONVECTION OVER THE MAJORITY OF THE CWA EXCEPT FOR NORTHERN TIER. SURFACE LOW THEN MOVES EASTWARD...AND TRAILING COLD FRONT BECOMES EAST/WEST ORIENTED AND STALLS OUT ACROSS THE CWA AMIDST ZONAL FLOW...BEFORE SLOWLY PUSHING SOUTH BY THE WEEKEND. MORE WIDESPREAD CONVECTION IS EXPECTED THURSDAY AFTERNOON/NIGHT WITH THE ARRIVAL OF THE AFOREMENTIONED SHORTWAVE. THEREFORE HAVE KEPT LOW POPS THROUGH FRIDAY...AND TARGETED HIGHEST CHANCE WITH THE SHORTWAVE/LLJ THURSDAY NIGHT. A FEW STRONG TO SEVERE STORMS ARE POSSIBLE DURING THIS STRETCH. DEEP LAYER SHEAR IS A MARGINAL 25-35KTS...SO CANT RULE OUT SOME LOCALIZED DAMAGING WINDS. DAILY TEMPS WILL BE GREATLY INFLUENCED BY CONVECTION...SO DIDNT STRAY TOO MUCH FROM GUIDANCE. && .AVIATION...23/18Z FCST IS COMPLICATED BY MULTIPLE OUTFLOW BOUNDARIES FROM OVERNIGHT CONVECTION. MAIN BAND IS ASSOCIATED WITH LIFTING WRMFNT EXTENDING EAST TO WAST ACRS THE STATE. WILL GO WITH CB REMARK IN TAF SITES AND EXPECT THE MAIN AREA TO BE NORTH OF KDSM AND OTM...AND SOUTH OF REMAINDER. CDFNT WILL MOVE INTO NWRN IA TNGT WITH A MORE ORGANIZED AREA OF TSRA. TRIED TO TIME THE BEST CHC FOR TSRA IN A TEMPO PD...WITH A BROAD AREA OF VCTS AS SYSTEM WILL BE QUITE DIFFUSE MOVING AS IT MOVES THRU. WOULD EXPECT TO SEE SOME MVFR CIGS MOVE INTO THE KMCW AREA SUN MORNING POST FROPA. THINKING IS THEY WILL BREAKUP BEFORE GETTING MUCH FARTHER SOUTH. && .DMX WATCHES/WARNINGS/ADVISORIES... EXCESSIVE HEAT WARNING FROM NOON TODAY TO 7 AM CDT SUNDAY FOR ADAIR-ADAMS-APPANOOSE-CASS-CLARKE-DAVIS-DECATUR-LUCAS-MADISON-MAHASKA -MARION-MONROE-RINGGOLD-TAYLOR-UNION-WAPELLO-WARREN-WAYNE. && SHORT TERM...MS JUL 11 LONG TERM...JOHNSON AVIATION...MS JUL 11 EXTENDED...BEITLICH
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 536 PM CDT SAT JUL 23 2011 IAZ004>007-015>017-023>028-033>039-044>050-057>062-242245- EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO- POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-SAC-CALHOUN- WEBSTER-HAMILTON-HARDIN-GRUNDY-BLACK HAWK-CRAWFORD-CARROLL-GREENE- BOONE-STORY-MARSHALL-TAMA-AUDUBON-GUTHRIE-DALLAS-POLK-JASPER- POWESHIEK- 536 PM CDT SAT JUL 23 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TONIGHT ISOLATED THUNDERSTORMS WILL BECOME MORE WIDESPREAD LATE THIS EVENING AND INTO THE OVERNIGHT HOURS. A LINE OF THUNDERSTORMS IS EXPECTED TO MOVE INTO NORTHERN IOWA BY SUNSET AND MOVE SOUTHEAST ACROSS THE AREA OVERNIGHT WITH LOCALLY HEAVY RAINFALL POSSIBLE. SOME STORMS MAY PRODUCE SEVERE WEATHER WITH HIGH WIND BEING MOST LIKELY. MARGINALLY SEVERE HAIL IS A SECONDARY THREAT. AN ISOLATED TORNADO IS POSSIBLE NEAR THE MINNESOTA BORDER DURING THE EARLY STAGES OF THE THUNDERSTORM LINE DEVELOPMENT. RIVER FLOOD WARNINGS REMAIN IN EFFECT FOR PORTIONS OF THE UPPER DES MOINES RIVER BASIN. PLEASE REFER TO THE NATIONAL WEATHER SERVICE WEBSITE AT WEATHER.GOV/DESMOINES FOR FURTHER DETAILS. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY THERE WILL BE SEVERAL ROUNDS OF SCATTERED THUNDERSTORMS THROUGHOUT THE PERIOD AND SOME STORMS MAY BECOME SEVERE. IT IS TOO EARLY TO PINPOINT SEVERE WEATHER THREATS OR TIMING...ESPECIALLY FOR LATER IN THE WEEK. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY NEEDED LATE TONIGHT INTO THE OVERNIGHT HOURS...AND AGAIN OFF AND ON THROUGH THE COMING WEEK...ESPECIALLY LATER IN THE WEEK. IAZ070>075-081>086-092>097-242245- CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-CLARKE-LUCAS- MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS- 536 PM CDT SAT JUL 23 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TONIGHT ISOLATED TO SCATTERED THUNDERSTORMS ARE POSSIBLE THROUGH THE EVENING HOURS...WITH THE POTENTIAL FOR SEVERE STORMS. THE MAIN THREAT WILL BE DAMAGING WINDS AND LOCALLY HEAVY RAIN...BUT CANNOT RULE OUT AN ISOLATED TORNADO. AN EXCESSIVE HEAT WARNING IS IN EFFECT FOR THE AREA UNTIL SUNDAY MORNING. PLEASE REFER TO THE NATIONAL WEATHER SERVICE WEBSITE AT WEATHER.GOV/DESMOINES FOR FURTHER DETAILS. RIVER FLOOD WARNINGS REMAIN IN EFFECT FOR PORTIONS OF THE DES MOINES RIVER BASIN. PLEASE REFER TO THE NATIONAL WEATHER SERVICE WEBSITE AT WEATHER.GOV/DESMOINES FOR FURTHER DETAILS. .DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY THERE WILL BE SEVERAL ROUNDS OF SCATTERED THUNDERSTORMS THROUGHOUT THE PERIOD AND SOME STORMS MAY BECOME SEVERE. IT IS TOO EARLY TO PINPOINT SEVERE WEATHER THREATS OR TIMING...ESPECIALLY FOR LATER IN THE WEEK. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL BE NEEDED TONIGHT...AND POSSIBLY ON AND OFF THROUGH THE COMING WEEK...ESPECIALLY LATER IN THE WEEK.
PRELIMINARY LOCAL STORM REPORT...CORRECTED
NATIONAL WEATHER SERVICE DES MOINES IA
204 PM CDT SAT JUL 23 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0637 PM TSTM WND DMG 5 N APLINGTON 42.65N 92.88W
07/22/2011 BUTLER IA EMERGENCY MNGR
CORRECTED FOR TIME... HOUSE ROOF PARTIALLY RIPPED OFF...6
OUT BUILDINGS DESTROYED WITH SIGNIFICANT TREE
DAMAGE...TIME REPORTED BY WITNESS
&&
JJOHNSONThe Des Moines radar (KDMX), 90 km away, was scanning. The volume nearest the first event began at 23:12 UTC.
7 thunderstorm wind. Local standard time, as filed.
Small limbs were blown down. Three inches of rain fell in one hour.
Corn was bent over by the high winds.
Tree limb damage.
Trees were blown down near the town of Confidence.
Power lines were downed with one power pole snapped just north of town.
Large tree limbs blown down in the town of Seymour.
Portion of a tin roof blew off of a building adjacent to a gas station in town.
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, July 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: 314653, 314652, 314655, 314656, 314657, 314658, 314659.