A cold frontal boundary, which actually is the same boundary as had been over the state for the past several days, began to move southeast across the state during the late afternoon of the 23rd.  Thunderstorms had moved across the area in the morning and left an outflow boundary that extended from southwest into east central Iowa, a ways ahead of the cold frontal boundary itself.  The airmass to the south of boundary became very unstable as highs reached the upper 80s to low 90s with dew point temperatures around 80.  CAPE reached around 3000 J/kg by the late afternoon with lifted indices in the -7 to -9 C. range.  The environment was weakly sheared with 20 to 30 kts of shear.  The airmass remained quite warm with the freezing level around 14,300 feet.  The CAPE in the -10 to -30 C. layer of the atmosphere was in the 400 to 600 J/kg range, however the warm atmosphere limited hail size in most of the storms.  Downdraft CAPE just south of the developing area was in the 1000 to 1200 J/kg range.  The LCL was lower than the past several days, and was in the 750 to 1000 meter range.  Thunderstorms fired up over southern Iowa during the late afternoon and pushed northeast across the southeast half of the state.  Storms produced high winds in the Leon area in Decatur County on the south side of the line.  A supercell moved through Marion and Mahaska Counties and produced penny size hail and high winds of up to 70 MPH.  Rainfall of 2 inches in less than an hour caused some flash flooding in the Oskaloosa area of Mahaska County.  As the storms moved east, winds of 60 MPH moved into the Ottumwa area of Wapello County.  Additional thunderstorms moved into southwest Iowa, dropping 1 to 2 inch per hour rainfall in Union and Ringgold Counties.  The event continued to unfold into a flash flood event.  Afton in Union County was one of the higher precipitation totals with 4.7 inches falling in just a couple hours time.  Many areas across southern Iowa received 2 to 5 inches of rain in just a few hours.  Flash flooding was widespread across the southern 2 to 3 tiers of Iowa Counties with reports of 2 to 4 feet of water over roads.  As the night progressed, the situation became progressively worse.  The heaviest rain, with a band of 6 to 12 inches of rain, fell across Wayne, Appanoose, and Davis Counties.  The greatest total received was from Rathbun, where 12.34 inches of rain fell in a little over 12 hours, much of it in about 9 hours.  Other high totals include 8.96 inches at Centerville, 8.17 inches at Bloomfield, 8.02 inches at Promise City, and 6.85 inches at Allerton.  Many locations had in excess of 5 inches.  The heavy rainfall was statistically a 500 year event.  An additional 6 counties were declared state flooding disaster areas.  They were Van Buren, just east of the CWA, Appanoose, Wapello, Davis, Wayne, and Mahaska.  Flooding was very widespread across southern Iowa with many roads washed out.  School was canceled for several counties due to the flooding as well.  Evacuations took place in Centerville, where 5 families were forced from their home, and in Mystic where 16 families were evacuated.  Both of these locations were in Appanoose County.  Flood waters inundated the water treatment plants at both Ottumwa and Mystic, leaving thousands of people without potable water.  County officials in several southern Iowa counties recommended no travel anywhere in the county.  Two people were stranded in Wayne County near Corydon and needed to be rescued.  As the storms were moving through central Iowa, lightning struck a condominium in West Des Moines.  It started a fire, which was brought under control within an hour.

Hail in MARION, IOWA
From 23-AUG-07 16:43:00 to 23-AUG-07 16:43:00 (CST-6)
Location: KNOXVILLE
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 5.00K
Reported by: Broadcast Media

Penny sized hail was reported by KCCI TV.

Thunderstorm Wind in DECATUR, IOWA
From 23-AUG-07 16:31:00 to 23-AUG-07 16:31:00 (CST-6)
Location: LEON
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Mesonet

Thunderstorm Wind in MAHASKA, IOWA
From 23-AUG-07 17:37:00 to 23-AUG-07 17:37:00 (CST-6)
Location: OSKALOOSA ROTH ARPT
Magnitude: 61.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

High winds downed tree limbs and knocked over furniture.

Thunderstorm Wind in MAHASKA, IOWA
From 23-AUG-07 17:37:00 to 23-AUG-07 17:37:00 (CST-6)
Location: OSKALOOSA
Magnitude: 61.00 EG
Property damage: 5.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Flash Flood in MAHASKA, IOWA
From 23-AUG-07 17:56:00 to 24-AUG-07 05:30:00 (CST-6)
Location: LEIGHTON
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Street flooding was reported in Barns City with cars stalled out in water.

Flash Flood in MAHASKA, IOWA
From 23-AUG-07 18:39:00 to 24-AUG-07 05:30:00 (CST-6)
Location: NEW SHARON ARPT
Flood cause: Heavy Rain
Property damage: 250.00K
Crop damage: 75.00K
Reported by: Emergency Manager

Numerous reports of flooding were received from throughout the county with stalled cars.  No travel advised. Highway 63 construction area was muddy and flooded.

Flash Flood in UNION, IOWA
From 23-AUG-07 20:00:00 to 24-AUG-07 07:45:00 (CST-6)
Location: SPAULDING
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 25.00K
Reported by: Emergency Manager

Water was reported over several county roads. The water had receded but  most creeks remain out of their banks.

Flash Flood in WAYNE, IOWA
From 23-AUG-07 21:28:00 to 24-AUG-07 07:45:00 (CST-6)
Location: CORYDON
Flood cause: Heavy Rain
Property damage: 150.00K
Crop damage: 50.00K
Reported by: Emergency Manager

Three feet of water was reported running over over county J22 east of  Millerton.

Flash Flood in CLARKE, IOWA
From 23-AUG-07 21:45:00 to 24-AUG-07 08:15:00 (CST-6)
Location: MURRAY
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 20.00K
Reported by: Amateur Radio

Cars were reported stranded by high water flowing over a county road.

Flash Flood in CLARKE, IOWA
From 23-AUG-07 21:45:00 to 24-AUG-07 08:15:00 (CST-6)
Location: OSCEOLA MUNI ARPT
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 10.00K
Reported by: Amateur Radio

Cars were stranded by high water in the town of Hopeville. Several inches  of water was flowing over Highway 69 on the south edge of town.

Flash Flood in WAPELLO, IOWA
From 23-AUG-07 21:55:00 to 24-AUG-07 08:15:00 (CST-6)
Location: AGENCY
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Trained Spotter

One foot of water was reported on Lee Avenue.

Flash Flood in APPANOOSE, IOWA
From 23-AUG-07 22:34:00 to 24-AUG-07 07:45:00 (CST-6)
Location: UDELL
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 50.00K
Reported by: Law Enforcement

Old Highway 5 just west of Moravia was reported under four feet of water.

Flash Flood in APPANOOSE, IOWA
From 23-AUG-07 22:36:00 to 24-AUG-07 07:45:00 (CST-6)
Location: THIRTY
Flood cause: Heavy Rain
Property damage: 250.00K
Crop damage: 10.00K
Reported by: Law Enforcement

Homes in the area were threatened by flash flooding.

Flash Flood in WAPELLO, IOWA
From 23-AUG-07 23:09:00 to 24-AUG-07 08:15:00 (CST-6)
Location: FARSON
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 25.00K
Reported by: Fire Department/Rescue

Several small streams were in flood with water over county roads in that area.

Thunderstorm Wind in LUCAS, IOWA
From 23-AUG-07 17:15:00 to 23-AUG-07 17:15:00 (CST-6)
Location: DERBY
Magnitude: 52.00 EG
Property damage: 4.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Two large trees were blown down 1.5 miles northeast of Derby.

Thunderstorm Wind in MAHASKA, IOWA
From 23-AUG-07 17:36:00 to 23-AUG-07 17:36:00 (CST-6)
Location: OSKALOOSA
Magnitude: 50.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Winds blew down a large tree, blocking highway in town.

Thunderstorm Wind in WAPELLO, IOWA
From 23-AUG-07 18:45:00 to 23-AUG-07 18:45:00 (CST-6)
Location: ELDON
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winds estimated at 70 MPH broke 24 inch diameter tree branches.  Heavy rain was occurring at the time as well.

Thunderstorm Wind in WAPELLO, IOWA
From 23-AUG-07 17:57:00 to 23-AUG-07 17:57:00 (CST-6)
Location: OTTUMWA
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Six inch tree limbs were blown down.  Rain was falling at the rate of 2 inches per hour.

Thunderstorm Wind in WAPELLO, IOWA
From 23-AUG-07 18:05:00 to 23-AUG-07 18:05:00 (CST-6)
Location: OTTUMWA
Magnitude: 56.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Flash Flood in WAYNE, IOWA
From 24-AUG-07 05:23:00 to 24-AUG-07 07:45:00 (CST-6)
Location: HARVARD
Flood cause: Heavy Rain
Property damage: 500.00K
Crop damage: 100.00K
Reported by: Emergency Manager

Gravel roads were washed out across Wayne County with numerous bridges under water. Emergency Management asked that the public not travel on hard top or gravel roads.

Heavy Rain in WAYNE, IOWA
From 24-AUG-07 05:53:00 to 24-AUG-07 07:45:00 (CST-6)
Location: SEYMOUR
Property damage: 150.00K
Crop damage: 50.00K
Reported by: Trained Spotter

Water was reported over the roads and some were washed out.  A storm total of 6.5 inches of rain fell with rain still falling.

Heavy Rain in APPANOOSE, IOWA
From 23-AUG-07 18:30:00 to 24-AUG-07 06:30:00 (CST-6)
Location: RATHBUN
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Extreme rainfall was reported with 12.34 inches of rain, most of the rain fell in the past 12 hours.

Thunderstorm Wind in RINGGOLD, IOWA
From 23-AUG-07 19:45:00 to 23-AUG-07 19:45:00 (CST-6)
Location: BEACONSFIELD
Magnitude: 57.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: County Official

Several large trees were down by high winds.

Flash Flood in CLARKE, IOWA
From 23-AUG-07 21:45:00 to 24-AUG-07 08:15:00 (CST-6)
Location: LACELLE
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 10.00K
Reported by: Amateur Radio

Several cars were stranded by high water over county roads.

Flash Flood in DECATUR, IOWA
From 23-AUG-07 22:30:00 to 24-AUG-07 08:15:00 (CST-6)
Location: HIGH PT
Flood cause: Heavy Rain
Property damage: 200.00K
Crop damage: 50.00K
Reported by: Law Enforcement

Water was reported over the road at J20 and 340th Avenue near the Wayne  County line.

Flash Flood in UNION, IOWA
From 23-AUG-07 23:30:00 to 24-AUG-07 06:45:00 (CST-6)
Location: SPAULDING
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 10.00K
Reported by: Law Enforcement

South Cherry Street was closed due to flash flooding.

Flash Flood in APPANOOSE, IOWA
From 23-AUG-07 23:45:00 to 24-AUG-07 07:45:00 (CST-6)
Location: RATHBUN
Flood cause: Heavy Rain
Property damage: 500.00K
Crop damage: 75.00K
Reported by: Law Enforcement

Several homes were evacuated due to high water in Centerville and Mystic. Water was flowing over county road T14 north of Mystic. Highway 2 just east of the Chariton River was reduced to one lane and the second lane was  nearly under water.

Flash Flood in UNION, IOWA
From 24-AUG-07 00:00:00 to 24-AUG-07 06:45:00 (CST-6)
Location: LORIMOR
Flood cause: Heavy Rain
Property damage: 75.00K
Crop damage: 50.00K
Reported by: Emergency Manager

Flash flooding was reported throughout the east and southeast portions of Union County.  The flooding was along the Thompson River and tributaries  were well out of their banks. Several gravel roads were under water with trees on the roads, carried by flood waters.

Flash Flood in DAVIS, IOWA
From 24-AUG-07 01:30:00 to 24-AUG-07 08:15:00 (CST-6)
Location: FLORIS
Flood cause: Heavy Rain
Property damage: 200.00K
Crop damage: 75.00K
Reported by: Law Enforcement

City streets were flooded up to 1 foot deep and barricaded. A storage shed floated off of its foundation. One backyard was flooded to top of fence, caused by ponding and poor drainage.

Flash Flood in CLARKE, IOWA
From 24-AUG-07 03:13:00 to 24-AUG-07 08:15:00 (CST-6)
Location: LESLIE
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 50.00K
Reported by: Law Enforcement

Washouts were reported on some county roads and some paved highways were threatened by flood waters.

Flash Flood in WAPELLO, IOWA
From 24-AUG-07 03:20:00 to 24-AUG-07 08:15:00 (CST-6)
Location: AGENCY
Flood cause: Heavy Rain
Property damage: 75.00K
Crop damage: 10.00K
Reported by: Law Enforcement

Rural roads were flooded near Eldon.

Flash Flood in DAVIS, IOWA
From 24-AUG-07 03:25:00 to 24-AUG-07 08:15:00 (CST-6)
Location: PULASKI
Flood cause: Heavy Rain
Property damage: 500.00K
Crop damage: 75.00K
Reported by: Law Enforcement

Four feet of water was reported with a car stranded on the road. Water was  backing up into basements.  Gravel roads countywide reportedly had washouts with many shoulder washouts.

Flash Flood in UNION, IOWA
From 24-AUG-07 03:50:00 to 24-AUG-07 06:45:00 (CST-6)
Location: TALMAGE
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 25.00K
Reported by: Law Enforcement

Highway P64 was completely covered in water south of Thayer.

Flash Flood in APPANOOSE, IOWA
From 24-AUG-07 03:55:00 to 24-AUG-07 07:45:00 (CST-6)
Location: STREEPY
Flood cause: Heavy Rain
Property damage: 500.00K
Crop damage: 100.00K
Reported by: Law Enforcement

Water rescues occurred southwest of Mystic.  Numerous county roads were under water throughout the county.

Flash Flood in WAYNE, IOWA
From 24-AUG-07 05:00:00 to 24-AUG-07 07:45:00 (CST-6)
Location: CAMBRIA
Flood cause: Heavy Rain
Property damage: 500.00K
Crop damage: 100.00K
Reported by: Emergency Manager

Two people were rescued from vehicles at two locations southeast of Corydon. Seven to ten inch rainfall amounts were received.  Travel was not advised on county roads.