A weak cold front dropped south across the state during the afternoon of the 9th. Severe parameters were relatively weak with under 20 kts of shear and CAPE around 1000 J/kg.
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The episode as NWS DMX wrote it up.
A weak cold front dropped south across the state during the afternoon of the 9th. Severe parameters were relatively weak with under 20 kts of shear and CAPE around 1000 J/kg. The downdraft CAPE was around 1200 J/kg. Scattered thunderstorms formed along the cold front. Most were not severe, however one storm became severe in central Iowa and produced damaging wind in Polk County in Polk City.
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 9, 2:20 PM CST, 2 hours 14 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 320 PM CDT MON JUL 9 2012 .SHORT TERM /TONIGHT/... SECONDARY COLD FRONT EXTENDING FROM NEAR KMLI TO JUST NORTH OF KDSM TO NORTH OF KSUX WILL DROP SOUTH THROUGH THE CWA THIS EVENING. A NARROW LINE OF SCATTERED TSRA WILL ACCOMPANY THE FRONT INTO THE EARLY EVENING HOURS AND SHOULD DISSIPATE OR BECOME ISOLATED SHOWERS TOWARD SUNSET AS OCCURRED YESTERDAY WITH THE FRONT. COOLER AIR WILL FILTER INTO THE STATE WITH TEMPS A LITTLE COOLER THAN THIS MORNING. WOULD NOT BE SURPRISED TO SEE SOME PATCHY FOG ACROSS THE NORTHERN HALF OF THE CWA UNDER THE SURFACE HIGH PRESSURE. THE HIGH IS A DIRTY HIGH AS WAS EVIDENT THIS MORNING...BUT AREAL EXTENT IS QUESTIONABLE. .LONG TERM /TUESDAY THROUGH MONDAY/... FORECAST REMAINS DRY THROUGH THE EXTENDED WITH HIGH PRESSURE DOMINATING THE AREA THROUGH THE MID RANGE. EC/GEM FLATTEN CENTRAL US RIDGE TOWARD THE WEEKEND INTO EARLY NEXT WEEK. WEAK UPPER TROUGH TO MOVE THROUGH MN/IA/WI INTO THE GREAT LAKES REGION WHICH WILL BRING A WARM FRONT THROUGH THE CWA. COULD POSSIBLY SEE SOME PRECIP WITH THIS FRONTAL PASSAGE...BUT FRONT MOVES THROUGH DURING THE DAY...WITH MOST LIKELY SCENARIO OF PRECIP TO OUR WEST FRIDAY NIGHT...AND THEN AGAIN TO OUR EAST SATURDAY NIGHT. ALSO WITH THE MAIN TROUGH MOVING THROUGH SOUTHERN CANADA...FORCING STILL QUITE WEAK ACROSS THE AREA WITH ANY ACTIVITY EXPECTED TO BE QUITE ISOLATED. THEREFORE HAVE OPTED TO REFRAIN FROM ADDING POPS INTO THE FORECAST AT THIS TIME. BROAD UPPER LEVEL TROUGH DEEPENS SOMEWHAT INTO THE NORTHERN ROCKIES AND NORTHERN PLAINS LATE SUNDAY INTO MONDAY...WITH CONTINUE WAA AND SOUTHERLY TO SOUTHWESTERLY FLOW. THIS AGAIN MAY RESULT IN SOME ISOLATED ACTIVITY TOWARD MONDAY INTO MONDAY NIGHT...BUT AGAIN WITH MAIN SYSTEM TRACKING ACROSS SOUTHERN CANADA AND GIVEN DRY PATTERN HAVE AGAIN OPTED TO KEEP THE FORECAST DRY. WILL CONTINUE TO MONITOR THESE TWO SYSTEMS OVER THE NEXT DAYS...TO FURTHER REFINE ANY PRECIP CHANCES AND POSSIBLY NEED TO INSERT SOME POPS INTO SATURDAY OR MONDAY IF EC/GEM CONTINUES CONSISTENCY WITH THE TIMING/PLACEMENT. OTHERWISE OVERALL TEMPERATURE FORECAST IS FOR GRADUAL WARMING INTO THE WEEKEND...WITH H85 TEMPS CLIMBING FROM AROUND THE MID TEENS CELSIUS TUESDAY...TO THE MID 20S C BY MONDAY. THEREFORE MAX TEMPS EXPECTED TO RETURN TO WIDESPREAD 90S BY EARLY NEXT WEEK...WITH CONTINUED WARMTH EXPECTED INTO NEXT WEEK. ALSO DRIER AIR IN PLACE OVER THE NEXT FEW DAYS MAY RESULT IN A BIT LARGER DIURNAL RANGE...AND THEREFORE HAVE GONE A BIT ABOVE GUIDANCE FOR MAX TEMPS AND SLIGHTLY COOLER AT NIGHT AND DROPPED DEWPOINTS A BIT. && .AVIATION DISCUSSION... SECONDARY COLD FRONT ACROSS NRN IA WILL MOVE SOUTH ACROSS THE TAF SITES THIS AFTERNOON. ISOLATED CONVECTIVE SHOWERS WILL ACCOMPANY THE FRONT UNTIL SUNSET. VFR CONDITIONS ARE EXPECTED TO HOLD THROUGH THE PERIOD ACROSS THE SOUTH. WITH LIGHT WINDS AND HIGH PRESSURE SETTLING OVER THE NRN SITES EXPECTED TO SEE MVFR CONDITIONS WITH FOG FOR A FEW HOURS AROUND SUNRISE. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && SHORT TERM...MS JUL 12 LONG TERM...MJB AVIATION...MS JUL 12
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 312 PM CDT MON JUL 9 2012 IAZ023-033>036-044>049-057>062-070>075-081>086-092>097-101100- POCAHONTAS-SAC-CALHOUN-WEBSTER-HAMILTON-CRAWFORD-CARROLL-GREENE- BOONE-STORY-MARSHALL-AUDUBON-GUTHRIE-DALLAS-POLK-JASPER-POWESHIEK- CASS-ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-CLARKE-LUCAS- MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS- 312 PM CDT MON JUL 9 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TONIGHT ISOLATED THUNDERSTORMS ARE POSSIBLE EARLY THIS EVENING. SEVERE WEATHER IS NOT EXPECTED. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED. IAZ004>007-015>017-024>028-037>039-050-101100- EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO-HUMBOLDT- WRIGHT-FRANKLIN-BUTLER-BREMER-HARDIN-GRUNDY-BLACK HAWK-TAMA- 312 PM CDT MON JUL 9 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TONIGHT NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED.
The Des Moines radar (KDMX), 4 km away, was scanning. The volume nearest the first event began at 22:34 UTC.
1 thunderstorm wind. Local standard time, as filed.
A large tree limb was blown down on a fence along with some other damage in the area. A transformer blew out, knocking out power.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2012Every state in 2012This day in weather historyWarnings in Iowa, July 2012
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: 381771.