An unstable airmass remained in place over Iowa.  CAPE values were in the 3000 to 5000 J/kg range with lifted indices in the -5 to -10 C range.  A frontal boundary shifted south during the late afternoon and evening.  As the low level jet became more active overnight, it impinged on the frontal boundary.  As this occurred, moisture pooled along and north of the front with precipitable water values increasing to 2 to 2.5 inches.  Thunderstorms formed in the strong theta-e advection from southeast, through central, into northwest Iowa.  Initially the storms lifted northeast with the flow, but as the night progressed, they back-developed with thunderstorms moving over the same areas repeatedly.  Two to four inches of rain fell in a band extending from near Ottumwa, through Des Moines, to southwest of Fort Dodge, into the Spencer area.  Flash flooding was widespread across the area.  Some of the worst flooding took place in Mahaska County.  Flash flooding, estimated 8 feet deep, swept a car off of Highway 92 east of Oskaloosa with the car ending up in a soybean field.  There were 18 evacuations and rescues in and around the town of Oskaloosa.  There was no severe weather reported with this event.

Heavy Rain in POLK, IOWA
From 09-AUG-10 23:38:00 to 10-AUG-10 00:08:00 (CST-6)
Location: LOVINGTON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Within 30 minutes, 2.30 of rain had fallen.

Flash Flood in POLK, IOWA
From 10-AUG-10 00:26:00 to 10-AUG-10 06:00:00 (CST-6)
Location: GRIMES
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Creek just west of the intersection of James St and NW 7th Street Place is out of its banks and inundating yards and bike path at least 30 feet out of banks.

Flash Flood in POLK, IOWA
From 10-AUG-10 01:20:00 to 10-AUG-10 06:00:00 (CST-6)
Location: GRIMES
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Creek near James St and NW 7th Street Place is now 50 to 75 feet wide.

Flash Flood in POLK, IOWA
From 10-AUG-10 01:35:00 to 10-AUG-10 06:00:00 (CST-6)
Location: GRIMES
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Water from flooded creek flowing over James Road and inundating a few houses along the creek on 7th Street Place.  Creek extending to the 1800 block.

Flash Flood in DALLAS, IOWA
From 10-AUG-10 01:36:00 to 10-AUG-10 06:00:00 (CST-6)
Location: HADDEN HILL
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Department of Highways

Water over V Ave and 156th due to Walnut Creek.

Flash Flood in MAHASKA, IOWA
From 10-AUG-10 04:38:00 to 10-AUG-10 07:30:00 (CST-6)
Location: OSKALOOSA
Flood cause: Heavy Rain
Property damage: 200.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Iowa DOT and local media report Highway 92 closed east of Oskaloosa due to the flooding from Spring Creek.

Heavy Rain in MARION, IOWA
From 09-AUG-10 21:15:00 to 10-AUG-10 03:15:00 (CST-6)
Location: SWAN
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Rainfall was 4.7 inches in the past 6 hours.

Heavy Rain in MARION, IOWA
From 10-AUG-10 04:42:00 to 10-AUG-10 04:42:00 (CST-6)
Location: SWAN
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Rainfall total was 4.70 inches.

Flash Flood in MARION, IOWA
From 10-AUG-10 02:44:00 to 10-AUG-10 06:00:00 (CST-6)
Location: FIFIELD
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Water flowing over Highway 163 near mile post 36, water 5 inches deep.

Flash Flood in MAHASKA, IOWA
From 10-AUG-10 03:25:00 to 10-AUG-10 07:30:00 (CST-6)
Location: KEOMAH
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Several people were trapped and stranded in the Keomah area in eastern Oskaloosa.

Flash Flood in MAHASKA, IOWA
From 10-AUG-10 06:36:00 to 10-AUG-10 07:30:00 (CST-6)
Location: OSKALOOSA ROTH ARPT
Flood cause: Heavy Rain
Property damage: 500.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Water receding but still flooding in Oskaloosa.  Numerous houses inundated in town with 18 people rescued.

Flash Flood in MAHASKA, IOWA
From 10-AUG-10 06:36:00 to 10-AUG-10 07:30:00 (CST-6)
Location: CEDAR
Flood cause: Heavy Rain
Property damage: 250.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Several homes in Wright were flooded.

Heavy Rain in MAHASKA, IOWA
From 09-AUG-10 23:00:00 to 10-AUG-10 05:08:00 (CST-6)
Location: OSKALOOSA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Rainfall since midnight was 3.80 inches.

Heavy Rain in MAHASKA, IOWA
From 10-AUG-10 06:00:00 to 10-AUG-10 06:00:00 (CST-6)
Location: OSKALOOSA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Rainfall from overnight was 4 inches.

Flash Flood in POLK, IOWA
From 10-AUG-10 00:40:00 to 10-AUG-10 06:00:00 (CST-6)
Location: LOVINGTON
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Four feet of flowing water down the street at Aurora and 30th St.

Flash Flood in POLK, IOWA
From 10-AUG-10 02:46:00 to 10-AUG-10 06:00:00 (CST-6)
Location: AVON
Flood cause: Heavy Rain
Property damage: 75.00K
Crop damage: 0.00K
Reported by: Emergency Manager

One house had basement walls collapse due to heavy rain in the Avon Lakes area.