A weak cold front entered the state during night of the 2nd into the early morning hours of the 3rd. The airmass became unstable ahead of the front, though not as unstable as is typically the case in early August.
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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 weak cold front entered the state during night of the 2nd into the early morning hours of the 3rd. The airmass became unstable ahead of the front, though not as unstable as is typically the case in early August. CAPE values were in the 2000 to 4000 J/kg range with lifted indices around -6 C. Precipitable water values were generally three quarters of an inch to one inch. During the day temperatures warmed into the 80s with dew points generally in the upper 50s to mid 60s. Dew points pooled just ahead of the front and were between 65 and 70. The freezing level was quite high, between 14,500 and 15,000 feet. Thunderstorms developed over southeast South Dakota and northwest Iowa during the evening. They moved southeast and accelerated to around 50 MPH during the late night and early morning hours. Many of the storms produced hail, however hail was generally around an inch or less in diameter. One and one quarter inch diameter hail fell in Clarke County, northeast of Osceola. One of the stronger clusters of storms produced quarter to golf fall size hail in a swath from Schleswig to Denison in Crawford County. The hail stripped leaves from trees and caused extensive crop damage. Strong winds were produced as the storms moved into the northwest part of the Des Moines CWA. Considerable tree and power line damage occurred in Pocahontas, Humboldt, Webster, and Carroll Counties. Reports indicated that power was knocked out to about 10,000 homes. As the storms moved through Story County, lightning struck a house northeast of Nevada. A power pole was struck and the power line was on the house. A fire resulted causing some damage to the home.
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 Aug 2, 10:53 PM CST, 52 minutes earlier.
AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE DES MOINES IA 1153 PM CDT SUN AUG 2 2009 ...UPDATED 03/06Z AVIATION DISCUSSION... .SHORT TERM...REST OF TONIGHT...WITH ONGOING CONVECTION ACROSS SOUTHEAST SD AND SOUTHERN MN MOVING QUICKLY IN NORTHWEST IOWA...INCREASED POPS ACROSS NORTHERN CWA THROUGH 12Z MONDAY. LLJ INCREASING OVERNIGHT WITH SURFACE DEWPOINTS WELL INTO THE MIDDLE 60S TO AROUND 70 ACROSS NORTHERN IOWA. MUCAPE VALUES RANGE FROM 1500 TO 3000 J/KG IN CENTRAL TO NORTHWEST IOWA...WITH CORFIDI VECTORS DEPICTING A SOUTHERLY STORM MOTION ACROSS CENTRAL IOWA. SHEAR IS SUFFICIENT FOR DAMAGING WINDS WITH FREEZING LEVEL NEAR NEAR 14000 FEET AND SIG HAIL PARAMETERS SIGNIFICANT ENOUGH FOR LARGE HAIL. THIS IN CONJUNCTION WITH THE HISTORY OF THESE STORMS PRODUCING LARGE HAIL...NORTHERN CWA WILL LIKELY GET THE BLUNT OF THE SEVERE ACTIVITY. LIKELY WILL SEE STORMS QUICKLY PUSH INTO NORTHERN CWA BETWEEN 03-05Z...WITH THE SEVERE POTENTIAL THROUGH 10Z. PREVIOUS DISCUSSION.SHORT TERM...TONIGHT MODERATE SOUTHWEST SFC FLOW AND SUNNY SKIES HAS HELPED TEMPERATURES REBOUND QUICKLY TODAY AHEAD OF APPROACHING SYSTEM IN THE DAKOTAS. THE SYSTEM WILL SINK INTO THE STATE LATE TONIGHT AS A SHORTWAVE DIVES THROUGH THE NORTHERN MIDWEST. DYNAMICS ARE MOST FAVORABLE NORTH AND EAST OF IOWA OVERNIGHT WITH MORE LIMITED FORCING INTO THE STATE AFTER MIDNIGHT. SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS EVENING NEAR THE LOW AND ASSOCIATED BOUNDARY WHERE FORCING WL BE GREATEST. THE STRONGEST CONVECTION IS FORECAST TO REMAIN NORTH OF IOWA...HOWEVER WITH THE INSTABILITY AXIS SETTING UP OVER THE STATE TONIGHT...WL LIKELY DRAW THE CONVECTION SOUTH INTO THE STATE. WL SEE BEST THREAT OF STORMS IN THE NORTHEAST CLOSEST TO THE STRONGEST FORCING WITH MORE ISOLATED STORMS TO THE SOUTH AND WEST. HAVE GONE WITH HIGH END OF GUIDANCE FOR LOWS GIVEN THERMAL RIDGE PLACEMENT OVER THE STATE DURING THE NIGHT AND CONTINUED MIXING...ESPECIALLY IN CENTRAL AND SOUTHERN PORTIONS OF THE STATE. .LONG TERM.../MONDAY-SUNDAY/ CHALLENGES REMAIN FOR THE BALANCE OF THE EXTENDED PERIOD...THOUGH MODELING OF OVERALL PATTERN EVOLUTION BEGINNING TO COME TOGETHER. SYSTEM APPROACHING OVERNIGHT WILL TAKE A TROUGH THROUGH THE REGION BY MIDDAY MONDAY WITH THE MAIN FRONT DROPPING INTO THE REGION MONDAY NIGHT. MODELS PICKING UP ON DUAL WINDSHIFT DURING THE DAY AND THEN NIGHT TIME HOURS WITH MAIN INSTABILITY AXIS REMAINING OVER THE SOUTH AND EAST DURING THE LATE DAY AND NIGHTTIME HOURS. AS THE SFC FRONT STALLS DURING THE OVERNIGHT HOURS...MODEST H850 WESTERLY FLOW OF 25 TO 35 KTS MAY BE ENOUGH TO CAUSE AN INCREASE IN THUNDER OVER THE FAR SOUTH NEAR THE UPPER LEVEL BOUNDARY. AS PER SPC DISCUSSION... OVERNIGHT INSTABILITY COMBINED WITH THE INCREASING SHEAR MAY BE ENOUGH TO ORGANIZE CONVECTION WITH POSSIBLE WIND AND HAIL. TIMING SUGGESTS THAT ACTIVITY WOULD MAINLY BE ELEVATED WITH THE LATE NIGHT EVENT. BEST CHANCES WILL REMAIN SOUTH OF I80 WITH THIS ACTIVITY. TUESDAY AIRMASS LOOKS TO BE LITTLE MODIFIED FROM MONDAY...OTHER THAN A MORE NORTHERLY SFC FLOW OVER THE NORTH. EURO/UKMET/GEM ALL DRIVE THE FRONT FARTHER INTO MISSOURI FOR THE MOMENT WHILE THE GFS HANGS THE BOUNDARY UP OVER SOUTHERN IA. IMPLICATIONS FOR THE FORECAST REMAIN AS THE MORE NORTHERLY SOLN WOULD FAVOR PM DEVELOPMENT OF ADDITIONAL THUNDER OVER THE AREA WITH SOME LIFT HERE. HOWEVER... WITH CONSENSUS MODEL AND SUPPORTIVE MANUAL COLLAB HAVE KEPT THE AREA DRY ON TUESDAY. THERMAL PROFILES STILL SUPPORT WARM TEMPS ACROSS THE SOUTH HALF WITH COOLER H850 TEMPS DROPPING INTO THE NORTHERN COUNTIES. ALREADY BY WEDNESDAY THE MODELS ARE REBUILDING THE HOT DOME TO THE WEST WITH INCREASING UPSTREAM THUNDER DEVELOPING IN THE STRONGER SOUTHERLY RETURN FLOW OVER THE DAKOTAS. STEERING CURRENTS WOULD ADVECT STORMS SOUTHEAST INTO THE AREA WITH FAVORED CHANCES OVER THE WEST DURING THE DAY ON WEDNESDAY AND MOST AREAS FOR WED NIGHT AND THURSDAY. TIMING OF THE RETURN OF PEAK MOISTURE AND SUBSEQUENT WIDE SPREAD RAINFALL EVENT PRIOR TO WEEKEND HEAT EPISODE THE MAIN MAJOR CHALLENGE FOR THE END OF THE WEEK. GFS SEEMS TO BE THE MOST AGGRESSIVE IN BRINGING THE RAIN IN BY THURSDAY WITH THE 00Z AND NEW 12Z EURO HOLDING THINGS OFF UNTIL FRIDAY. AT THIS TIME...INSTABILITY POINTS TOWARD EVENING SVR WEST WITH OVERNIGHT LESSENING INSTABILITY AS THE AREA EXPANDS NORTHEAST ACROSS THE REGION. THIS WILL BE THE BIG ISSUE OVER THE NEXT FEW DAYS AS WE TRANSITION INTO NEXT WEEKEND. THE MODELS KEEP US IN THE VERY WARM AIR SATURDAY WITH SOME HINT THAT THE FRONT WILL SAG INTO THE STATE ON SUNDAY AND ACT AS A FOCUS FOR ADDITIONAL THUNDERSTORM ACTIVITY... WITH VERY WARM AND HUMID CONDITIONS REMAINING. NEWEST EURO ALSO HAS H850 TEMPS INCREASING TO 24C BY 00Z SUN WHICH WOULD POINT TOWARD MID 90S FOR HIGHS NEXT SAT. SIMILAR TO THE 00Z RUN...THE EURO DROPS THE FRONT SOUTH INTO CENTRAL IA BY SUNDAY AFTERNOON AND CONTINUES TO HOLD ONTO THE FEATURE NEAR THE FORECAST AREA INTO THE FOLLOWING WEEK. IF THIS TREND CONTINUES TO DEVELOP... WE COULD BE IN FOR A PERIOD OF WARM TO HOT WX...SOMETHING NOT YET SEEN MUCH THIS SUMMER. && .AVIATION...03/06Z ONGOING CONVECTION WILL ENTER NORTHERN IOWA OVER THE NEXT 6 HOURS...MAINLY AFFECTING THE NORTHERN TAF SITES. HAVE MENTION OF MVFR CONDITIONS FOR -TSRA VIS. COULD SEE SOME STRONG GUSTS AT FOD...MCW...AND ALO BUT TIMING WAS DIFFICULT TO PINPOINT FOR MCW AND ALO. HAVE MENTION OF STRONG GUSTS IN TEMPO GROUP FOR FOD WITH STORMS MOVING INTO CWA. OTM MAY GET SOME ISO THUNDERSTORMS PAST 12Z MONDAY...ALL OTHER TAF SITES VFR CONDITIONS. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE && SHORT TERM...KLP/COGIL AVIATION...KLP LONG TERM...REV
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 842 PM CDT SUN AUG 2 2009 IAZ004>007-015>017-023>028-033>039-040145- EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO- POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-SAC-CALHOUN- WEBSTER-HAMILTON-HARDIN-GRUNDY-BLACK HAWK- 842 PM CDT SUN AUG 2 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TONIGHT A SLIGHT RISK OF SEVERE STORMS IS EXPECTED...GENERALLY NORTH OF HIGHWAY 20 IN NORTHERN IOWA LATE TONIGHT INTO EARLY MONDAY MORNING. THE MAIN THREAT WILL BE LARGE HAIL UP TO THE SIZE OF GOLF BALLS AND DAMAGING WINDS IN EXCESS OF 60 MPH. LOCALLY HEAVY RAIN IS ALSO POSSIBLE. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY SCATTERED THUNDERSTORMS WILL LINGER INTO THE EARLY MORNING HOURS ON MONDAY...EAST OF INTERSTATE 35 AND NORTH OF INTERSTATE 80 THROUGH SUNRISE. THE MAIN THREAT WILL BE LARGE HAIL UP TO THE SIZE OF GOLF BALLS AND DAMAGING WIND IN EXCESS OF 60 MPH. THERE WILL BE LOW CHANCES FOR SHOWERS AND THUNDERSTORMS STARTING TUESDAY NIGHT LASTING RIGHT INTO NEXT WEEKEND. THE BETTER CHANCES CURRENTLY APPEAR TO BE AREA WIDE LATE WEDNESDAY...AND THEN AGAIN THURSDAY INTO SATURDAY. THE SEVERE WEATHER POTENTIAL FOR THIS PERIOD WILL BE BETTER DETERMINED IN THE COMING DAYS. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED LATE TONIGHT THROUGH MONDAY MORNING. IAZ044>050-057>062-070>075-081>086-092>097-040145- 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- 842 PM CDT SUN AUG 2 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TONIGHT CHANCES FOR SHOWERS AND THUNDERSTORMS RETURN TO THE FORECAST TONIGHT...ESPECIALLY DURING THE LATE EVENING AND OVERNIGHT HOURS. THE SEVERE WEATHER POTENTIAL IS RATHER LOW. HOWEVER...AN ISOLATED SEVERE STORM CANNOT BE RULED OUT WITH THE MAIN THREAT OF HAIL AND BRIEF GUSTY WINDS. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY CHANCES FOR SHOWERS AND NON SEVERE THUNDERSTORMS LINGER INTO MONDAY MORNING EAST. THERE WILL BE LOW CHANCES FOR SHOWERS AND THUNDERSTORMS STARTING TUESDAY NIGHT LASTING RIGHT INTO NEXT WEEKEND. THE BETTER CHANCES CURRENTLY APPEAR TO BE AREA WIDE LATE WEDNESDAY...AND THEN AGAIN THURSDAY INTO SATURDAY. THE SEVERE WEATHER POTENTIAL FOR THIS PERIOD WILL BE BETTER DETERMINED IN THE COMING DAYS. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED BRIEFLY EARLY MONDAY MORNING. OTHERWISE SPOTTER ACTIVATION IS NOT ANTICIPATED AT THIS TIME. KLP
The Des Moines radar (KDMX), 137 km away, was scanning. The volume nearest the first event began at 05:43 UTC.
9 thunderstorm wind, 9 hail, 1 lightning. Local standard time, as filed.
Trees down in Rolfe and in Pocahontas. Twelve inch or larger tree limbs down in Rolfe. A sliding door was blown off of building that stores semi trucks.
Spotter reported a 60 MPH wind gust.
Tree branches were blown down.
Trees 2 feet in diameter were blown down.
Large trees and power lines were blown down in town.
Large trees were blown down on a house.
Large trees were blown down in town.
Hail swath of quarter to golf ball size hail.
Heavy rain, quarter size hail, and strong wind.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2009Every state in 2009This day in weather historyWarnings in Iowa, August 2009
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: 176706, 176712, 176714, 176707, 176708, 176709, 176710, 176715, 176719, 176696, 176699, 183077, 176700, 176716, 176774, 176701, 176702, 177285, 176703.