A weak cold front moved southeast through a weakly unstable airmass over the state. Temperatures were in the low to mid 70s ahead of the front with dew points in the mid 50s.
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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 moved southeast through a weakly unstable airmass over the state. Temperatures were in the low to mid 70s ahead of the front with dew points in the mid 50s. Most unstable CAPE values were in the 1000 to 1500 J/kg range with CAPE in the -10 to -30 layer of the atmosphere in the 300 to 500 J/kg range. Lifted indices fell to between -3 and -6 with effective shear rather weak at 20 to 35 kts. The freezing level was around 10,500 feet. Precipitable water values were not all that high at just over an inch. Thunderstorms pulsed ahead of the front during the afternoon. A more organized scattered line of storms developed on the front by mid afternoon. Some of the cells became severe and produced hail up to golf ball size. In Odeboldt, in Sac County, golf ball size hail covered the ground and rainfall of 1.5 inches in a short period of time caused some local flooding in town. Other storms produced penny to nickle size hail in western Iowa.
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 6, 10:52 AM CST, 3 hours 23 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 1152 AM CDT WED MAY 6 2009 .UPDATED AVIATION DISCUSSION... .SHORT TERM...TODAY AREAL COVERAGE OF RAIN AND ISO THUNDER QUICKLY FILLING IN WEST. HAVE RAISED POPS FOR THE MORNING HOURS MOST AREAS SOUTH./REV .PREVIOUS SHORT TERM...TODAY SFC WAVE CONTINUES TO IMPACT THE AREA WITH WEAK SOUTHERLY FLOW BOTH IN THE BOUNDARY LAYER AND MID LEVEL FLOW. THOUGH OBJECTIVE ANALYSIS SHOWS RATHER WEAK FLOW AT H850 AND H700...BY AFTERNOON...SOUNDINGS CONTINUE TO ADVERTISE LINEAR SHEAR OF 20 TO 25KTS THROUGH THE COLUMN WITH MUCAPE OF 2300 TO 2700 J/KG ACROSS THE AREA. WITH CURRENT PROGGED WINDS...MINIMAL ROTATION MIGHT OCCUR WITH STORMS MOST LIKELY TO PRODUCE SOME HAIL AS THEY TRACK EAST ACROSS THE REGION. UNTIL THAT TIME WE CONTINUE TO HAVE THUNDER FIRING ALONG THE WARM FRONT OVER CENTRAL TO NORTHEAST IOWA RIGHT NOW. THIS ACTIVITY WILL WEAKEN SOMEWHAT AFTER SUNRISE...BUT SOME PULSE TYPE STORMS MAY CONTINUE AT TIMES ESPECIALLY AS DAYTIME HEATING HELPS A RATHER UNCAPPED ATMOSPHERE IN THE LATE MORNING AND AFTERNOON. AS WAVE MOVES ACROSS THE FORECAST AREA THIS AFTERNOON THETAE ADVECTION WILL ONCE AGAIN INCREASE ALONG WITH WEAK VORT MAX TRACKING EAST. ALL SAID...THIS SHOULD BE ENOUGH TO FIRE AN AREA OF WEAK TO MODEST STORMS. CURRENT DAY1 CONVECTIVE OUTLOOK HAS US IN SLIGHT RISK AND THIS SEEMS REASONABLE. TMAX TODAY WILL BE SOMEWHAT VARIABLE OVER THE REGION. MOST OF THE REGION HAS A UNIFORM AIRMASS TODAY WITH THE ONLY VARIABLE BEING THE AMOUNT OF SUNSHINE DURING THE DAY. SINCE THE CLOUD DECK IS GOING TO HAVE BREAKS HERE AND THERE...MOST AREAS WILL SEE SIMILAR HIGHS IN THE LOWER TO MID 70S AND HAVE STUCK TO THAT THESIS. SFC WINDS WILL MIX TO NEAR 20 MPH AT TIMES THIS AFTERNOON BUT OVERALL...WILL NOT BE ALL THAT STRONG. .LONG TERM...TONIGHT-TUE PROGRESSIVE ZONAL FLOW WILL CONTINUE FOR AT LEAST THE NEXT 48 HOURS. WATER VAPOR IMAGERY IS REVEALING AN IMPRESSIVE LOOKING SHORT WAVE CURRENTLY OFF THE OREGON AND CALIFORNIA COAST. THIS WAVE IS MOVING EAST AT OVER 60 KTS AND IS DUE TO ARRIVE IN THE MIDWEST BY EARLY THURSDAY. A FEW LINGERING SHOWERS AND THUNDERSTORMS WILL BE LINGERING OVER THE EASTERN HALF THIS EVENING BEFORE TROUGH OF LOW PRESSURE PASSES TO THE EAST. THUNDERSTORM CHANCES BEGIN TO INCREASE OVER THE FAR SOUTHWEST AND WEST CENTRAL LATE TONIGHT IN ADVANCE OF THE APPROACHING SHORT WAVE. CHANCES WILL SPREAD OVER THE CENTRAL AND SOUTH CENTRAL AREAS ON THURSDAY. SFC FLOW WILL REMAIN WEAK DURING THE PERIOD WITH FORCING BEING DERIVED IN THE MID LEVELS AND MAINLY ABOVE 700 MB. DECENT THETA-E ADVECTION WILL MOVE ACROSS THIS REGION IN ADDITION TO THE KINEMATIC SUPPORT FROM THE SHORT WAVE AND THE LEFT EXIT REGION OF A 115 KT UPPER LEVEL JET. NOT SURE THE NAM OR THE GFS PROPERLY HAVE A HANDLE OF THIS SYSTEM AS IT WAS JUST COMING INTO THE FAR WEST EDGE OF THEIR DOMAINS AT 00Z AS BOTH SOLUTIONS DILUTE THE ENERGY AS IT REACHES THE INTERMOUNTAIN REGION. CLOSER INSPECTION SUGGESTS A PORTION OF THE ENERGY IS BEING SHEARED OFF AND ASSIMILATED BY A CLOSED LOW...WHICH IS JUST TO THE NORTH OFF THE PACIFIC NORTHWEST COAST. TEMPERATURE THURSDAY WILL BE DEPENDANT ON PRECIPITATION DURATION AND CLOUD COVER. CURRENT FORECAST WILL NOT BE COOL ENOUGH IF THESE CONDITIONS PERSIST ON THURSDAY. THE CLOSED LOW WILL EJECT OUT TOWARD THE END OF THE WEEK AND MOVE INTO THE REGION LATE FRIDAY...BRINGING ONE MORE ROUND OF PRECIPITATION TO THE STATE. COOLER AIR WILL FOLLOW FOR SATURDAY AS AN CANADIAN AIR MASS DIPS SOUTH. && .AVIATION...06/18Z INITIAL DISTURBANCE AHEAD OF THE FRONT NOW EXITING CENTRAL IOWA. AS THE FRONT PUSHES INTO THE STATE SOME RECOVERY OF THE ATMOSPHERE EXPECTED AND ADDITIONAL STORMS TO DEVELOP ALONG/NEAR BOUNDARY. SOME POTENTIAL FOR AN ISOLATED WIND GUST AND ONLY SLIGHTLY BETTER RISK FOR THREE QUARTER INCH HAIL...POSSIBLY AS LARGE AS AN INCH. MOST ACTIVITY WILL DIE OFF WITH SUNSET THOUGH A FEW STORMS POSSIBLE OVER EASTERN TAF SITES KALO AND KOTM THROUGH 02Z. AREAS OF MVFR CONDITIONS EXPECTED IN AND NEAR PRECIP AREAS BUT GENERALLY VFR CIGS ELSEWHERE. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && SHORT TERM/AVIATION...FAB LONG TERM...DONAVON
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 513 AM CDT WED MAY 6 2009 IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075- 081>086-092>097-071015- 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-CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION- CLARKE-LUCAS-MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE- APPANOOSE-DAVIS- 513 AM CDT WED MAY 6 2009 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TODAY AND TONIGHT A SLIGHT RISK FOR SEVERE WEATHER EXISTS ACROSS ALL OF CENTRAL IOWA TODAY. THE SEVERE RISK IS MAINLY THIS AFTERNOON...THOUGH AN ISOLATED SEVERE STORM IS POSSIBLE THIS MORNING. HAIL UP TO THE SIZE OF HALF DOLLARS IS THE PRIMARY THREAT WITH 60 MPH WINDS A SECONDARY THREAT. A FEW THUNDERSTORMS ARE POSSIBLE THIS EVENING EAST OF INTERSTATE 35 HOWEVER THE SEVERE THREAT WILL BE QUICKLY DIMINISHING WITH SUNSET. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY SCATTERED THUNDERSTORMS ARE FORECAST FOR THURSDAY WITH AN ISOLATED SEVERE STORM POSSIBLE SOUTH OF HIGHWAY 30. ISOLATED THUNDERSTORMS ARE ALSO POSSIBLE FRIDAY AND MONDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON. DONAVON
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE DES MOINES IA 231 PM CDT WED MAY 6 2009 IAZ033-062000- SAC- 231 PM CDT WED MAY 6 2009 ...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL SAC COUNTY UNTIL 300 PM CDT... AT 230 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM 6 MILES NORTH OF ARTHUR...OR 10 MILES NORTHEAST OF IDA GROVE...MOVING EAST AT 15 MPH. NICKEL SIZE HAIL IS EXPECTED WITH THIS STORM. THIS STORM WILL BE NEAR... EARLY BY 300 PM CDT. COGIL
SPECIAL WEATHER STATEMENT NATIONAL WEATHER SERVICE DES MOINES IA 303 PM CDT WED MAY 6 2009 IAZ033-062030- SAC- 303 PM CDT WED MAY 6 2009 ...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN SAC COUNTY UNTIL 330 PM CDT... AT 300 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A STRONG THUNDERSTORM NEAR ODEBOLT...OR 11 MILES EAST OF IDA GROVE... MOVING SOUTHEAST AT 10 MPH. NICKEL SIZE HAIL IS EXPECTED WITH THIS STORM. THIS STORM WILL BE NEAR... ODEBOLT BY 315 PM CDT. WALL LAKE AND LAKE VIEW BY 330 PM CDT. COGIL
The Des Moines radar (KDMX), 142 km away, was scanning. The volume nearest the first event began at 20:16 UTC.
3 hail, 1 heavy rain. Local standard time, as filed.
Quarter to golf ball size hail covered the ground to a depth of 2 to 3 inches.
Quarter to golf ball size hail covered the ground to a depth of 2 to 3 inches.
An intersection in town was blocked for a short time due to the combination of runoff from rainfall of 1.5 inches and hail drifts.
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, May 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: 157606, 157607, 157609, 157608.