A strong south to southwest flow of moist air was on place across Iowa in advance of an approaching cold front. The cold front moved through the state during the afternoon with a line of thunderstorms forming along the front.
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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 strong south to southwest flow of moist air was on place across Iowa in advance of an approaching cold front. The cold front moved through the state during the afternoon with a line of thunderstorms forming along the front. The airmass was moderately unstable with CAPE values in the 1000 to 2000 J/kg range and lifted indices in the -4 to -6 C. range. Downdraft CAPE values were in the 600 to 800 J/kg range. There was a decent amount of shear in the atmosphere with 45 to 50 kts indicated. The freezing level was quite high, near 14,000 feet. There were reports of some pea size hail, but no significant hail was reported. Most of the storms along the line produced 30 to 40 MPH winds. A few of the storms produced severe criteria winds with spotty damage to trees and power poles reported. It appears that most of the high wind reports were associated with downbursts.
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 Sep 21, 2:04 PM CST, 2 hours 4 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 304 PM CDT FRI SEP 21 2007 .SHORT TERM /THROUGH TONIGHT/... COMPLICATED FORECAST TONIGHT. COLD FRONT IS CURRENTLY FROM A LAKE MILLS TO A SAC CITY LINE MOVING EAST AT 25 KTS OR SO. 18Z SOUNDINGS SHOWED A TREMENDOUS CAP OVER THE CWA AND THE MESOANALYSIS PAGE INDICATED SOME PRETTY STRONG CIN OVER THE CWA AS WELL. LOCAL RADARS SHOWING THINGS HAVING A TOUGH TIME GETTING STARTED BUT THINGS ARE STARTING TO PERCOLATE NOW. DEFINITELY BETTER DYNAMICS AND LIFT NE OF THE CWA AND THE FURTHER SOUTH YOU GO THE LESS THE BOUNDARY HAS GOING FOR IT. CURRENTLY LOOKING AT THE FAR NE CORNER OF THE CWA FOR POTENTIAL...AROUND THE MCW/ALO AREA BUT THIS WOULD BE FOR A LIMITED TIME THIS AFTERNOON BEFORE PUSHING INTO EASTERN IOWA WHERE THE BETTER AIRMASS IS. FOR THE GRIDS...I WILL DOWNPLAY THE THUNDER OVER THE WESTERN TWO THIRDS OF THE CWA TONIGHT WITH JUST AN ISOLATED MENTION AND KEEP THE MORE AGGRESSIVE WORDING FOR THE MCW/ALO AREA. THE FRONT SHOULD EXIT THE FAR SERN CWA BY 02Z WITH RAPIDLY CLEARING SKIES. GENERALLY WENT BELOW GUIDANCE TONIGHT...ESPECIALLY NW WHERE CAA HAS BEEN IN PLACE FOR A FEW HOURS. .LONG TERM /SATURDAY-FRIDAY/... REALLY ONLY ONE PRECIPITATION EVENT TO FOCUS ON DURING THIS PERIOD. WHILE NOT QUITE YET A SLAM DUNK...IT DOES APPEAR THAT THE BEST CHANCE OF RAIN AND THUNDERSTORMS WILL OCCUR MONDAY AND MONDAY NIGHT. TIMING DOES HINGE GREATLY ON THE ABSORPTION OF THE LARGE CUT OFF UPPER LEVEL LOW SPINNING OFF THE SRN CA COAST AT THIS TIME. EXPERIENCE HAS SHOWN THAT THESE LARGE LOWS DO NOT GET UP AND GO AS FAST AS MODELS WANT TO MAKE THEM. ON THE OTHER HAND IT IS HARD TO IGNORE THE AMAZING CONSISTENCY BETWEEN THE GFS AND NAM REGARDING THIS FEATURE. SINCE THE ECWMF/UK/ENSEMBLE PROGS ARE SHOWING A SLIGHTLY SLOWER MOVEMENT...I TRIED TO LEAN THIS FORECAST PACKAGE IN THEIR DIRECTION. THE OTHER WRINKLE WITH THIS EVENT IS THE ENTRAINING AND ABSORPTION OF THE GULF COAST TROPICAL SYSTEM EXPECTED TO GET PICKED UP BY LONG WAVE UPPER LEVEL TROUGH MOVING EAST ACROSS THE ROCKIES. MODELS APPEAR TO BE IN DECENT AGREEMENT SHOWING THESE FEATURES COMING TOGETHER IN OUR VICINITY MONDAY OR MONDAY NIGHT. SO WITH BROAD SYNOPTIC SCALE LIFT IMPINGING ON THE AREA...ALONG WITH FRONTAL FORCING AND PRECIPITABLE WATER VALUES 200 PERCENT OF NORMAL...SHOWERS AND THUNDERSTORMS ARE A GOOD BET...WITH LOCALLY HEAVY RAIN POSSIBLE. HAVE INCREASED POPS INTO LIKELY CATEGORY FOR MONDAY...AND COULD VERY WELL HAVE GONE LIKELY MONDAY NIGHT TOO...BUT LEFT IN HIGH CHANCE CATEGORY FOR BETTER COLLABORATION WITH SURROUNDING OFFICES. OTHERWISE...SATURDAY WILL BE A PERFECT DAY IF YOU LIKE SUNNY AND HIGHS IN THE 70S WITH LIGHT WINDS. SOUTHERLY RETURN FLOW KICKS BACK IN LATE SATURDAY NIGHT AND SUNDAY...BOOSTING TEMPS AND HUMIDITY LEVELS. SUNDAY WILL LIKELY BE ANOTHER DAY WITH HIGHS WELL INTO THE 80S. CLOUD COVER INCREASES SUNDAY NIGHT WITH THE CHANCE OF RAIN ALSO INCEASING...SO SMALLER DIURNAL RANGE IN STORE FOR SUN NIGHT AND MONDAY. A BROAD TROUGH OR ZONAL FLOW SETS UP ACROSS THE NRN CONUS IN THE WAKE OF MONDAYS SYSTEM. THIS WILL KEEP OUR AREA DRY AND SEASONABLE THROUGH AT LEAST THURSDAY NIGHT. ANOTHER TROUGH IS EXPECTED TO DIG THROUGH THE NRN ROCKIES BY FRIDAY AND THIS MAY BRING US A CHANCE OF RAIN FRIDAY. STILL TOO EARLY TO TELL FOR SURE. .AVIATION...21/18Z TAFS WERE WRITTEN BEFORE THOSE DOING 18Z SOUNDINGS CAME OUT. THOUGHT IS PERPLEXING THAT ONLY SHOWERS WERE DEVELOPING DESPITE THE FAIR AMOUNT OF CIN...GIVEN THE SHEAR AND STRENGTH OF THE COLD FRONT. 18Z SOUNDINGS CAME OUT WITH A +16 DEGREE AREA OF WARM AIR ALOFT SO IT MAY BE THAT THUNDER MAY NOT DEVELOP...ONLY SHOWERS. TAFS HAVE THUNDERSTORMS MENTIONED IN LINE WITH 12Z DATA BUT MAY NEED A TWEAKING. CONDITIONS WILL CONTINUE TO BE MONITORED W/R/T THUNDERSTORM DEVELOPMENT. WIND GUSTS WILL BE AN ISSUE FOR ALL TAF SITES REGARDLESS. FROPA INTO EASTERN IOWA IS FORECAST TO OCCUR AROUND 00Z. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && AVIATION/SHORT TERM...FAB LONG TERM...MOYER
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 857 AM CDT FRI SEP 21 2007 IAZ005>007-016-017-023>028-033>039-044>050-057>062-070>075- 081>086-092>097-221400- KOSSUTH-WINNEBAGO-WORTH-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- 857 AM CDT FRI SEP 21 2007 THIS HAZARDOUS WEATHER OUTLOOK IS FOR MUCH OF CENTRAL IOWA. .DAY ONE...TODAY AND TONIGHT SCATTERED THUNDERSTORMS ARE EXPECTED BY THIS AFTERNOON. THE STORMS ARE EXPECTED TO FORM ALONG AN LINE THAT WILL SWEEP ACROSS CENTRAL IOWA BY EARLY THIS EVENING. SOME STORMS WILL BE SEVERE WITH DAMAGING WIND THE MAIN THREAT. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY ADDITIONAL THUNDERSTORMS ARE EXPECTED LATE SUNDAY NIGHT THROUGH EARLY TUESDAY. SOME OF THESE STORMS MAY BE SEVERE AND MAY ALSO PRODUCE LOCALLY HEAVY RAINFALL. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS LIKELY BETWEEN 1 PM AND 7 PM TODAY. SPOTTERS MAY ALSO BE NEEDED NEXT MONDAY. IAZ004-015-221400- EMMET-PALO ALTO- 857 AM CDT FRI SEP 21 2007 THIS HAZARDOUS WEATHER OUTLOOK IS FOR A SMALL PORTION OF CENTRAL IOWA. .DAY ONE...TODAY AND TONIGHT SCATTERED THUNDERSTORMS ARE EXPECTED BY NOON. AN ISOLATED SEVERE STORM WILL BE POSSIBLE WITH DAMAGING WIND THE MAIN THREAT. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY ADDITIONAL THUNDERSTORMS ARE EXPECTED LATE SUNDAY NIGHT THROUGH EARLY TUESDAY. SOME OF THESE STORMS MAY BE SEVERE AND MAY ALSO PRODUCE LOCALLY HEAVY RAINFALL. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT ANTICIPATED TODAY...HOWEVER SPOTTERS MAY BE NEEDED NEXT MONDAY. FAB
The Des Moines radar (KDMX), 152 km away, was scanning. The volume nearest the first event began at 22:07 UTC.
6 thunderstorm wind. Local standard time, as filed.
The Emergency Manager reported trees and large limbs blown down.
The Emergency Manager reported large limbs down and blocking roads.
A power pole was blown down by high winds.
A power pole was blown down in rural Warren County.
Large tree limbs were blown down in Washburn.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2007Every state in 2007This day in weather historyWarnings in Iowa, September 2007
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: 50462, 50463, 50464, 50466, 50465, 52946.