A very humid and unstable airmass was in place over Iowa during the evening of the 11th into the morning of the 12th.  A strong push if moisture pushed precipitable water values to over 2 inches over southern Iowa by evening.  Surface dew point temperatures rose to the mid 70s to around 80.  The airmass was quite unstable with 3000 to 4000 J/kg of CAPE available and a lifted index around -8 C.  There was little shear present however and steering winds were quite light.  Thunderstorms formed initially along an east-northeast to west-northwest outflow boundary left by convection the previous morning.  This boundary was reinforced as a weak cold front  and dropped southeast into Iowa.  Thunderstorms developed along this boundary and moved very slowly, dumping heavy rainfall of 1 to 3 inches on top of already saturated ground.  Spotty heavier reports were received with unofficial totals of nearly 4 inches southeast of Des Moines in the Knoxville area.  The heavy rainfall resulted in flash flooding.  Since the rain was unable to percolate into the soil, ditches filled with water and numerous county roads were flooded.  Some state highways were flooded as well with water of 1 to 2 feet in depth flowing over the road.  Highway 92 in Mahaska County, and Highway 415 in Polk County were flooded for example.  There was little severe weather associated with this thunderstorm activity.  A 58 MPH wind gust was reported by an RWIS site near Fort Dodge however.  Lightning struck a business in Runnells.  Bakeris Roofing was struck and set on fire.  The fire took 8 fire departments two hours to put out and the business was destroyed.

Heavy Rain in STORY, IOWA
From 12-JUN-10 09:55:00 to 12-JUN-10 09:55:00 (CST-6)
Location: SLATER
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Two inches of water was flowing across a gravel road from farm field to farm field near the intersection of 310th and Y Ave along the Boone and Story County line.

Flash Flood in POLK, IOWA
From 12-JUN-10 07:19:00 to 12-JUN-10 09:43:00 (CST-6)
Location: SAYLORVILLE
Flood cause: Heavy Rain
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Department of Highways

Southbound lanes of Highway 415 closed due to water running over the road.

Thunderstorm Wind in WEBSTER, IOWA
From 12-JUN-10 05:14:00 to 12-JUN-10 05:14:00 (CST-6)
Location: ROBERTS
Magnitude: 50.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Flash Flood in MAHASKA, IOWA
From 12-JUN-10 09:00:00 to 12-JUN-10 14:00:00 (CST-6)
Location: OSKALOOSA
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Newspaper

Estimated 4-5 inches of rainfall.

Lightning in POLK, IOWA
From 12-JUN-10 09:30:00 to 12-JUN-10 09:30:00 (CST-6)
Location: DES MOINES EKMAN ARP
Property damage: 250.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Flash Flood in MARION, IOWA
From 12-JUN-10 03:00:00 to 12-JUN-10 14:00:00 (CST-6)
Location: PLEASANTVILLE
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Sheriff reports water 1 foot deep at an intersection in Pleasantville at 300 AM CST.

Flash Flood in MARION, IOWA
From 12-JUN-10 08:17:00 to 12-JUN-10 14:00:00 (CST-6)
Location: DUNREATH
Flood cause: Heavy Rain
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A foot of water was flowing over 110th and Beardsley in northern Marion County.

Flash Flood in MAHASKA, IOWA
From 12-JUN-10 08:28:00 to 12-JUN-10 14:00:00 (CST-6)
Location: OSKALOOSA
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Water flowing over the road about 6 inches deep along 4th Ave east between South 3rd and South 1st St.

Flash Flood in MAHASKA, IOWA
From 12-JUN-10 08:22:00 to 12-JUN-10 14:00:00 (CST-6)
Location: EVANS
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

At least a foot of water was flowing over the road at the intersection of Highland and 245th Street, and also at Highland and 235th Street.

Flood in POLK, IOWA
From 12-JUN-10 13:50:00 to 12-JUN-10 21:13:00 (CST-6)
Location: CAPITOL HGTS
Flood cause: Heavy Rain
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Four Mile Creek was flowing over Williams St.  Williams St. was closed between east University and Mattern Ave.

Flash Flood in MAHASKA, IOWA
From 12-JUN-10 07:50:00 to 12-JUN-10 14:00:00 (CST-6)
Location: EVANS
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Department of Highways

Water from the Muchakinock Creek was flowing over Highway 92 and the highway was closed due to flowing water.

Flash Flood in MARION, IOWA
From 12-JUN-10 11:45:00 to 12-JUN-10 14:00:00 (CST-6)
Location: PLEASANTVILLE
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Coal Creek was rising and had closed paved Highway G40.  Water from the creek was also over Highway 92, but traffic was still moving.  Numerous rural gravel roads in western Marion County were under water.