Southerly winds drew moisture north into Iowa during the previous 2 to 3 days.  In addition, a moisture feed from the remnants of former Hurricane Henriette were drawn north into the state.  At the same time, a moderately strong cold front pushed in from the northwest and entered the state during the late evening and overnight hours.  In advance of the whole system, an upper level low had lifted northeast across the state during the day.  This produced considerable cloudiness.  The environment was not all that favorable for severe thunderstorms.  CAPE values were in the 2000 to 3000 J/kg range, but shear was quite weak.  There was a 30 to 40 kt shear just to the west of the Des Moines CWA, but it weakened rapidly as one headed east.  The freezing level was quite high for early September, in the 14,500 to 15,000 foot range.  This again limited hail development.  Precipitable water values were quite high, in the 1.8 to 2 inch range.  Thunderstorms developed over western Iowa initially along a pre-frontal trough.  They advanced into the state during the evening with little fanfare.  A cluster of storms formed over southwest Iowa and advanced into central Iowa.  As the low level jet intensified after sunset, heavy rain developed with rainfall rates of 1 to 2 inches per hour common.  During the late night hours, a line of thunderstorms formed along the cold front and advanced east.  One area of the line became severe with strong winds mixing down to produce a 70 MPH wind gust in Creston.  The main event was very heavy rainfall.  In Dallas and Polk Counties, 1.5 to 3 inches of rain produced considerable street flooding in Polk County, and flash flooding in Dallas County.  Water was flowing over Iowa Highway 44 just east of Dallas Center, resulting in its closure.  A swath of 2 to 4 inch rainfall stretched from southwest through central Iowa.  Another cluster of storms produced heavy rainfall in the Ottumwa area with 4.75 inches there, along with considerable urban flooding.  Some of the higher totals included 4.71 inches in Bondurant, 4.6 inches in Gilman, 4.5 inches in Windsor Heights, and 3.92 inches in Ankeny.

Heavy Rain in DALLAS, IOWA
From 06-SEP-07 21:00:00 to 07-SEP-07 00:20:00 (CST-6)
Location: DALLAS CENTER
Property damage: 20.00K
Crop damage: 10.00K
Reported by: Amateur Radio

Rainfall of 2.55 inches since 2100 CST. Street flooding was reported in town.

Thunderstorm Wind in UNION, IOWA
From 06-SEP-07 23:03:00 to 06-SEP-07 23:03:00 (CST-6)
Location: CRESTON
Magnitude: 61.00 MG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Mesonet

A KCCI TV schoolnet site at Creston high school recorded a 61 knot wind.  Small branches were reported down across town.

Heavy Rain in WAPELLO, IOWA
From 06-SEP-07 23:00:00 to 07-SEP-07 03:38:00 (CST-6)
Location: OTTUMWA
Property damage: 30.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Heavy rainfall was reported overnight from KBIZ radio.

Flash Flood in DALLAS, IOWA
From 06-SEP-07 23:10:00 to 07-SEP-07 00:55:00 (CST-6)
Location: DALLAS CENTER
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 10.00K
Reported by: Law Enforcement

Heavy Rain in POLK, IOWA
From 06-SEP-07 21:30:00 to 06-SEP-07 22:27:00 (CST-6)
Location: DES MOINES
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Reports of cars stalled in water and some places with 2 to 2.5 feet of standing water in roadways. The estimated rainfall was 1.50 to 2.00 inches.