Following the heavy rains of the previous day, thunderstorms once again developed over northern Iowa during the overnight hours of the 18th into the early morning of the 19th. A nearly stationary frontal boundary extended from southern South Dakota, southeast into east central Iowa.
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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.
Following the heavy rains of the previous day, thunderstorms once again developed over northern Iowa during the overnight hours of the 18th into the early morning of the 19th. A nearly stationary frontal boundary extended from southern South Dakota, southeast into east central Iowa. This front served as the focus for thunderstorm development north of it as the low level jet transported moisture north over the boundary. At the same time, moisture worked its way north into Iowa as the remnants of former tropical storm Erin spread north into the state. Initially, heavy rains remained to the north of Iowa. As the moisture from Erin advanced into the state, a nearly stationary line of intense thunderstorms developed from west central into northeast Iowa. The thunderstorms produced heavy rainfall of one to three inches in a band extending from south of Pocahontas, through Humboldt, into the Mason City area. Some flash flooding was reported in the Humboldt area, but was not major and mainly restricted to flooded roads in the area. As the thunderstorms moved into Cerro Gordo County, a push from the outflow of the storms to the north in Minnesota interacted with the storms. This resulted in a quick two to three inches of rain across the Mason City area. Flash flooding took place in Mason City. East Park in Mason City was evacuated. The Winnebago River flooded due to the heavy rains, flooding several roads and flooding basements on the northeast side of Town.
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 19, 2:15 AM CST, 3 hours 15 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 315 AM CDT SUN AUG 19 2007 .DISCUSSION... COMPLICATED FORECAST WITH ISSUES OF TIMING...LOCATION AND INTENSITY. MODELS HAVING INTENSITY ISSUES WITH REMNANTS OF ERIN AND AFFECT ON SCENARIO IN UPPER MIDWEST. HOWEVER MODELS CLOSER IN SOLUTIONS THAN FARTHER APART WITH USUAL PROBLEMS IN DETAILS. WITH FRONTAL BOUNDARY LOCATION NOT CERTAIN AND FEEDBACK INTO GFS THINGS BECOME UNCLEAR AND CONFIDENCE LEVEL GOES DOWN. BELIEVE WITH CURRENT PATTERN THAT WE CAN EXPECT A WET WEEK THOUGH THERE WILL BE SOME DRY DAYS DEPENDING ON LOCATION OF BOUNDARY AND TIMING OF SHORT WAVES THROUGH THE AREA. PLENTY OF LIFT IN MOST PERIODS WITH GOOD THETA ADVECTION ESPECIALLY LATER INTO THE FORECAST PERIOD (MON NGT-WED) WITH GOOD MOISTURE INTO THE AREA MAY BE LOOKING AT OFF AND ON ISSUANCE OF FFAS. BELIEVE FOR MOST PART SEVERE THREAT MINIMAL THOUGH IF CLOUDINESS BREAKS OUTLOOKS FOR DAY TWO AND THREE COULD EASILY BE REALIZED WITH THOUGH EARLY NEXT WEEK STRONG CAP AND IF CLOUDINESS PERSISTS WILL NOT REALIZE DAY TIME HEATING OR ANY GREAT INSTABILITY. AIRMASS DOES CONTAIN POTENTIAL FOR SEVERE IF FACTORS BREAK THE RIGHT WAY. TEMPERATURES ARE ANOTHER ELEMENT THAT HIGHLY DEPENDENT ON BOUNDARY POSITIONS AND CLOUDINESS. GETTING INTO SECOND HALF OF AUGUST CLOUDINESS WILL BE MORE PERSISTENT. WITH BOUNDARY SAGGING AND DECENT PRE EXISITNG FACTORS IN PLACE WILL EXTEND WATCH IN TIME AND COVERAGE UNTIL 09Z MONDAY MORNING. .AVIATION...19/06Z HAVE UPDATED TAFS TO REFLECT SLOWER TIMING OF CONVECTION IN THE NORTH. LOW STRATUS WILL ALSO BE PROBLEMATIC...ESPECIALLY IN MCW...AND WILL HAVE TO BE MONITORED FOR SOUTHWARD PROGRESS. && .DMX WATCHES/WARNINGS/ADVISORIES...FLASH FLOOD WATCH THROUGH 4 AM MONDAY IAZ004>007-IA015>017-IA023>028-IA035>039-IA049>050- && LONG TERM...FORSTER/13/9/1
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 519 AM CDT SUN AUG 19 2007 IAZ004>007-015>017-023>028-035>039-049-050-201100- EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO- POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-WEBSTER- HAMILTON-HARDIN-GRUNDY-BLACK HAWK-MARSHALL-TAMA- 519 AM CDT SUN AUG 19 2007 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TODAY AND TONIGHT NON SEVERE THUNDERSTORMS WILL BECOME MORE NUMEROUS AS THE DAY GOES ON. THESE STORMS WILL CONTAIN HEAVY RAINFALL WITH THE POTENTIAL TO PRODUCE 1 TO 2 INCHES WITH ISOLATED AMOUNTS OF 4 INCHES. A FLASH FLOOD WATCH IS IN EFFECT FOR THE AREA. PLEASE REFER TO THE NATIONAL WEATHER SERVICE WEBSITE AT WEATHER.GOV/DESMOINES. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY THERE IS A CHANCE FOR THUNDERSTORMS EACH DAY FROM MONDAY THROUGH SATURDAY...SEVERE WEATHER AND LOCALLY HEAVY RAINFALL ARE POSSIBLE. TIMING AND SPECIFIC THREAT WILL BE DEFINED IN LATER FORECASTS. .SPOTTER INFORMATION STATEMENT... SPOTTER REPORTS OF HEAVY RAINFALL WOULD BE HELPFUL. IAZ033-034-044>048-057>062-070>075-081>086-092>097-201100- SAC-CALHOUN-CRAWFORD-CARROLL-GREENE-BOONE-STORY-AUDUBON-GUTHRIE- DALLAS-POLK-JASPER-POWESHIEK-CASS-ADAIR-MADISON-WARREN-MARION- MAHASKA-ADAMS-UNION-CLARKE-LUCAS-MONROE-WAPELLO-TAYLOR-RINGGOLD- DECATUR-WAYNE-APPANOOSE-DAVIS- 519 AM CDT SUN AUG 19 2007 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TODAY AND TONIGHT NON SEVERE THUNDERSTORMS WILL BECOME MORE NUMEROUS AS THE DAY GOES ON. SOME OF THE STORMS MAY PRODUCE HEAVY RAINFALL. .DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY THERE IS A CHANCE FOR THUNDERSTORMS EACH DAY FROM MONDAY THROUGH FRIDAY...SEVERE WEATHER AND LOCALLY HEAVY RAINFALL ARE POSSIBLE. TIMING AND SPECIFIC THREAT WILL BE DEFINED IN LATER FORECASTS. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT NECESSARY AT THIS TIME. FORSTER
The Des Moines radar (KDMX), 121 km away, was scanning. The volume nearest the first event began at 11:32 UTC.
2 flash flood. Local standard time, as filed.
Heavy rains caused flooding with 1 to 2 feet of water in the streets. Evacuations were necessary in East Park.
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, August 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: 41119, 41117.