A nearly stationary frontal boundary remained draped east to west across Iowa once again.  The atmosphere became very unstable during the afternoon with highs reaching the upper 80s to low 90s and dew points in the mid 70s to the south of the front.  The environment at the beginning of the event showed a CAPE of 5000 to 6000 J/kg and lifted indices in the -9 to -12 C. range.  The LCL was a little lower than the previous couple days and was around 1000 meters.  The environment had a fair amount of shear, in the 35 to 50 kt range.  Downdraft CAPE values were quite high with 1200 to 1700 J/kg available.  Once again, the freezing level was quite high at around 15,000 feet, so in spite of the hail cape, CAPE in the -10 to -30 C. layer of the atmosphere, being 500 to 800 J/kg the hail size was restricted.  Precipitable water values were in the 1.5 to 1.75 inch range.  Thunderstorms formed in two areas.  An area of thunderstorms formed over north west into north central Iowa.  These were ahead of a line of intense thunderstorms that moved in from Nebraska during the early evening.  Initially, the storms produced high winds.  Winds of 70 to 80 MPH hit Pocahontas County in the Rolfe and Plover areas.  Outbuildings and grain bins were blown over in Humboldt  County in the Bradgate area, and a downburst occurred in the Worth County at Manley.  Downburst winds also hit south of Bode in Humboldt County.  High winds snapped off 40 utility poles in the area.  There were numerous reports of trees and power lines down in northwest and north central Iowa.  Late in the event, a small bow segment dropped southeast across Marshall County and produced a 59 MPH wind gust at the RWIS site there.  The main event was the heavy rainfall and flash flooding.  Soil conditions were extremely wet with many of the areas across northern Iowa receiving 6 to 12 inches of rain during the past week.  The additional rain on the evening of the 21st caused considerable flash flooding.  In Humboldt, for example, 5.7 inches of rain fell with the passage of the line.  This lead to the evacuation of a care center in Humboldt.  There were several reports of 2 to 4 inch rainfalls.  The hardest hit counties were Pocahontas and Humboldt with a large area of greater than 4 inches of rain covering these counties.  Following the flooding of the past few nights, the Governor Chet Culver gave a flooding disaster proclamation for 5 counties.  They were Pocahontas, Palo Alto, Webster, Humboldt, Calhoun and Boone inside of the CWA, and Cherokee just outside of the CWA.  School was canceled in many school districts for a good part of the week.

Flash Flood in POCAHONTAS, IOWA
From 21-AUG-07 20:35:00 to 22-AUG-07 01:30:00 (CST-6)
Location: PLOVER
Flood cause: Heavy Rain
Property damage: 75.00K
Crop damage: 25.00K
Reported by: Law Enforcement

Highway 3 was closed near Gilmore City by water running over the road.

Flash Flood in WEBSTER, IOWA
From 21-AUG-07 21:20:00 to 22-AUG-07 03:00:00 (CST-6)
Location: (FOD)FT DODGE MUNI A
Flood cause: Heavy Rain
Property damage: 75.00K
Crop damage: 10.00K
Reported by: Law Enforcement

Heavy rainfall of over 4 inches resulted in water flowing over roads in town.

Flash Flood in WRIGHT, IOWA
From 21-AUG-07 22:40:00 to 22-AUG-07 01:05:00 (CST-6)
Location: FLORENCE
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Water was reported in basements due to heavy rains.  Flooding was also reported in Goldfield and Eagle Grove.

Flash Flood in HUMBOLDT, IOWA
From 21-AUG-07 22:45:00 to 22-AUG-07 01:30:00 (CST-6)
Location: PIONEER
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Road were closed due to water running over them and basements flooded due to the heavy rain.

Flash Flood in WEBSTER, IOWA
From 21-AUG-07 23:10:00 to 22-AUG-07 03:00:00 (CST-6)
Location: CLARE
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Highway 169 north of Fort Dodge was closed by water running over the road. Highway 20 underpass closed by running water.

Flash Flood in WINNEBAGO, IOWA
From 21-AUG-07 23:10:00 to 21-AUG-07 23:26:00 (CST-6)
Location: FOREST CITY
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 10.00K
Reported by: Law Enforcement

Thunderstorm Wind in MARSHALL, IOWA
From 21-AUG-07 23:08:00 to 21-AUG-07 23:08:00 (CST-6)
Location: MARSHALLTOWN
Magnitude: 51.00 MG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Mesonet

Thunderstorm Wind in HUMBOLDT, IOWA
From 21-AUG-07 19:30:00 to 21-AUG-07 19:30:00 (CST-6)
Location: BODE
Magnitude: 80.00 EG
Property damage: 50.00K
Crop damage: 20.00K
Reported by: Newspaper

Flash Flood in WINNEBAGO, IOWA
From 21-AUG-07 20:14:00 to 21-AUG-07 22:36:00 (CST-6)
Location: SCARVILLE
Flood cause: Heavy Rain
Property damage: 30.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Streets were closed due to flooding at the intersection of south 10th and North Mills at the 100 block.

Flash Flood in WORTH, IOWA
From 21-AUG-07 20:14:00 to 21-AUG-07 22:36:00 (CST-6)
Location: NORTHWOOD
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Law Enforcement

The creek in town was reported out of its banks and flooding.

Flash Flood in WINNEBAGO, IOWA
From 21-AUG-07 20:14:00 to 21-AUG-07 22:36:00 (CST-6)
Location: RAKE
Flood cause: Heavy Rain
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Water was reported over Highway 9 in town.

Flash Flood in WORTH, IOWA
From 21-AUG-07 20:14:00 to 21-AUG-07 22:36:00 (CST-6)
Location: HANLONTOWN
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Street flooding was reported in town.

Flash Flood in HUMBOLDT, IOWA
From 21-AUG-07 23:32:00 to 22-AUG-07 01:30:00 (CST-6)
Location: RUTLAND
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A care center was evacuated by emergency personnel in Humboldt.

Heavy Rain in WINNEBAGO, IOWA
From 21-AUG-07 19:34:00 to 21-AUG-07 19:49:00 (CST-6)
Location: FOREST CITY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Very heavy rainfall occurred in a 15 minute period.

Heavy Rain in HUMBOLDT, IOWA
From 21-AUG-07 19:00:00 to 21-AUG-07 23:00:00 (CST-6)
Location: DAKOTA CITY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Very heavy rainfall all occurred during the evening hours.

Thunderstorm Wind in POCAHONTAS, IOWA
From 21-AUG-07 19:02:00 to 21-AUG-07 19:02:00 (CST-6)
Location: PLOVER
Magnitude: 70.00 EG
Property damage: 30.00K
Crop damage: 50.00K
Reported by: Public

High winds downed power poles down and trees between Rolfe and Plover.

Thunderstorm Wind in HUMBOLDT, IOWA
From 21-AUG-07 19:07:00 to 21-AUG-07 19:07:00 (CST-6)
Location: BRADGATE
Magnitude: 61.00 EG
Property damage: 50.00K
Crop damage: 25.00K
Reported by: Broadcast Media

High winds blew down outbuildings, grain bins, and trees.

Thunderstorm Wind in HUMBOLDT, IOWA
From 21-AUG-07 19:45:00 to 21-AUG-07 19:45:00 (CST-6)
Location: ARNOLD
Magnitude: 61.00 EG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Broadcast Media

A TV viewer reported power poles down at the intersection of Highway 169 and county road C26.

Thunderstorm Wind in WRIGHT, IOWA
From 21-AUG-07 20:10:00 to 21-AUG-07 20:10:00 (CST-6)
Location: EAGLE GROVE
Magnitude: 57.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Law Enforcement

High winds downed large trees.

Thunderstorm Wind in CERRO GORDO, IOWA
From 21-AUG-07 20:48:00 to 21-AUG-07 20:48:00 (CST-6)
Location: ROCKWELL
Magnitude: 52.00 EG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Several trees were downed by high winds.  An electrical line was smoking with a tree down on it.

Thunderstorm Wind in CERRO GORDO, IOWA
From 21-AUG-07 20:49:00 to 21-AUG-07 20:49:00 (CST-6)
Location: ROCKWELL
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

High winds blew down about a half dozen trees.

Thunderstorm Wind in POCAHONTAS, IOWA
From 21-AUG-07 18:58:00 to 21-AUG-07 18:58:00 (CST-6)
Location: PLOVER
Magnitude: 61.00 EG
Property damage: 5.00K
Crop damage: 10.00K
Reported by: Law Enforcement

Very heavy rain occurred with the storm as well.

Thunderstorm Wind in POCAHONTAS, IOWA
From 21-AUG-07 19:02:00 to 21-AUG-07 19:02:00 (CST-6)
Location: ROLFE
Magnitude: 61.00 EG
Property damage: 5.00K
Crop damage: 10.00K
Reported by: Law Enforcement

Winds were estimated to be 60 to 70 MPH along with very heavy rain.

Thunderstorm Wind in POCAHONTAS, IOWA
From 21-AUG-07 19:02:00 to 21-AUG-07 19:02:00 (CST-6)
Location: ROLFE
Magnitude: 70.00 EG
Property damage: 20.00K
Crop damage: 50.00K
Reported by: Public

Several trees were reported downed by high winds.

Thunderstorm Wind in HUMBOLDT, IOWA
From 21-AUG-07 19:45:00 to 21-AUG-07 19:45:00 (CST-6)
Location: DAKOTA CITY
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winds were still increasing at the time of this report.

Thunderstorm Wind in WORTH, IOWA
From 21-AUG-07 20:14:00 to 21-AUG-07 20:14:00 (CST-6)
Location: MANLY
Magnitude: 61.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Heavy Rain in WEBSTER, IOWA
From 21-AUG-07 20:00:00 to 22-AUG-07 01:00:00 (CST-6)
Location: GOWRIE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Rainfall of 4.90 inches occurred from 2000CST Tuesday until it ended around 0100CST Wednesday.