A very unstable atmosphere was in place over Iowa with CAPE values around 2000 J/kg and lifted indices in the -8 to -10 C range.  Precipitable water increased to around 2.25 inches along a boundary that extended from northeast into west central Iowa.  Downdraft CAPE was in the 700 to 1000 J/kg range with 400 to 800 J/kg available in the -10 to -30 C layer of the atmosphere.  The LCL was between 750 and 1000 meters.  The freezing level was very high, around 16,000 feet.  In spite of the relatively strongly sheared atmosphere, which was 35 to 45 kts, the thunderstorms had a hard time developing.  A firm cap was in place with 700 mb temperatures of 14 to 15 C by early evening, and 500 mb temperatures of -4 C.  Thunderstorms formed over northeast Iowa along the boundary.  The thunderstorms back developed along the boundary well after sunset and became very efficient rain producers.  The storms trained along the same line with a quick 2 to 3 inches of rain falling from west of Waterloo to near the Waterloo area.  The rain fell in a short period of time, one to two hours, on top of ground that had received significant rainfall during the morning hours of the 22nd.  This resulted in rapid runoff of water and flash flooding.  The thunderstorms continued through the night with total rainfall north of Waterloo in the Denver area reaching 7.11 inches by sunrise.  The line of storms back developed west across the state overnight.  Heavy rainfall of 2 to 4 inches fell in a band extending west into the areas that saw flash flooding the previous day.  Flash flooding was reported in Bremer, Webster, Wright, and Sac Counties.  General flooding took place in many areas of Hamilton County as well.  Severe weather was absent with the storms through the night.  The tropical nature of the atmosphere limited the severe threat.

Flash Flood in WEBSTER, IOWA
From 23-JUL-10 04:30:00 to 23-JUL-10 09:00:00 (CST-6)
Location: (FOD)FT DODGE MUNI A
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Two roads were inundated with water flowing over them near the airport.

Flash Flood in WRIGHT, IOWA
From 23-JUL-10 07:24:00 to 23-JUL-10 10:00:00 (CST-6)
Location: CLARION
Flood cause: Heavy Rain
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Law Enforcement

County Road R38 and a few other county roads were closed due to flooding.

Heavy Rain in BREMER, IOWA
From 23-JUL-10 04:55:00 to 23-JUL-10 04:55:00 (CST-6)
Location: DENVER
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Rainfall since 0600 CST on the 22nd was 7.11 inches.

Flash Flood in HAMILTON, IOWA
From 23-JUL-10 09:31:00 to 23-JUL-10 14:00:00 (CST-6)
Location: WEBSTER CITY
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 10.00K
Reported by: Law Enforcement

Webster City Police reported that the city campgrounds were closed and the intersection of Linn St and Oak Ave was also closed.  Additionally...Hamilton County Sheriff reported a few gravel roads were flooded in the northern part of the county.

Flash Flood in SAC, IOWA
From 23-JUL-10 07:45:00 to 23-JUL-10 10:00:00 (CST-6)
Location: SAC CITY MUNI ARPT
Flood cause: Heavy Rain
Property damage: 250.00K
Crop damage: 10.00K
Reported by: Law Enforcement

Sierra road was closed from Shasta Ave to 270th St due to flooding.  Other road closures are on 170th St north of Sac City and 350th St near Grant City.

Flash Flood in BREMER, IOWA
From 23-JUL-10 02:25:00 to 23-JUL-10 08:06:00 (CST-6)
Location: DENVER
Flood cause: Heavy Rain
Property damage: 1.00M
Crop damage: 100.00K
Reported by: Emergency Manager

Water covered most secondary roads in Bremer County, but was receding.  Numerous flooded basements across the county, but the worst hit were in the Denver and Readlyn areas.  The sewer system was threatened in Readlyn and Denver pumps were running to aid the overtaxed sewer system.