Little change took place in the overall weather pattern with a nearly stationary frontal boundary remaining over the state.  The morning convection moved off allowing for afternoon solar isolation to take place, destabilizing the atmosphere once again.  Temperatures over the southwest half of the state warmed into the mid to upper 80s with dew points in the low to mid 70s.  West of Iowa it warmed into the mid 90s with mid 70 dew points.  The airmass became very unstable with CAPE in the the 5000 to 8000 J/kg range from western Iowa west.  Lifted indices fell into the -10 to -14 C. range by late afternoon.  A considerable amount of shear remained in place with 40 to 55 kts present at the time of thunderstorm development.  The LCL was reasonably high however at 1000 to 1500 meters.  Thunderstorms developed in to a linear complex that showed a few bow echo elements along the leading edge.  The main weather features with this system were high winds and hail.  The available downdraft CAPE was between 1200 and 1500 J/kg and was favorable for high winds.  There was 600 to 900 J/kg of available CAPE in the -10 to -30 C. layer of the atmosphere.  In spite of the high values, hail size was limited by the high freezing levels, between 14,500 feet to over 15,500 feet.  As the storms moved into the western part of the CWA, winds were the strongest.  Reports of winds between 60  and 70 MPH were common along the leading edge of the line.  The winds diminished as the storms moved east.  Hail reports were spotty with this event.  The hail was relatively small with most of it in the three quarter to one inch diameter range.  The storms produced heavy rainfall once again with 1.6 to 1.8 inches of precipitable water available.  The heavy rain fell in areas that were affected by the past several days of rain.  Calhoun and Webster had some flash flooding, but it was relatively minor and limited to road closures caused by water flowing over the roads.

Hail in DAVIS, IOWA
From 20-AUG-07 23:00:00 to 20-AUG-07 23:00:00 (CST-6)
Location: MARK
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 5.00K
Reported by: Storm Chaser

Thunderstorm Wind in CASS, IOWA
From 20-AUG-07 19:55:00 to 20-AUG-07 19:55:00 (CST-6)
Location: ATLANTIC
Magnitude: 57.00 MG
Property damage: 10.00K
Crop damage: 5.00K
Reported by: AWOS

Thunderstorm Wind in GRUNDY, IOWA
From 20-AUG-07 22:53:00 to 20-AUG-07 22:53:00 (CST-6)
Location: GRUNDY CENTER
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in AUDUBON, IOWA
From 20-AUG-07 19:50:00 to 20-AUG-07 19:50:00 (CST-6)
Location: AUDUBON
Magnitude: 61.00 EG
Property damage: 30.00K
Crop damage: 0.00K
Reported by: Newspaper

Thunderstorm Wind in ADAMS, IOWA
From 20-AUG-07 20:23:00 to 20-AUG-07 20:23:00 (CST-6)
Location: PRESCOTT
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Flash Flood in WEBSTER, IOWA
From 20-AUG-07 21:42:00 to 20-AUG-07 23:36:00 (CST-6)
Location: TARA
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Heavy rain caused street flooding in the city.  Several roads were closed by the high water.

Thunderstorm Wind in ADAMS, IOWA
From 20-AUG-07 20:30:00 to 20-AUG-07 20:30:00 (CST-6)
Location: NODAWAY
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

High winds blew down several 6 inch diameter tree branches.

Hail in WRIGHT, IOWA
From 20-AUG-07 21:42:00 to 20-AUG-07 21:42:00 (CST-6)
Location: EAGLE GROVE
Magnitude: 1.00 
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Hail the size of quarters fell in the town of Eagle Grove.

Hail in POLK, IOWA
From 20-AUG-07 21:35:00 to 20-AUG-07 21:35:00 (CST-6)
Location: ANKENY
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Hail reported by KCCI TV on west 1st Street.

Hail in POLK, IOWA
From 20-AUG-07 21:19:00 to 20-AUG-07 21:19:00 (CST-6)
Location: DODGE FLD ARPT
Magnitude: 1.00 
Property damage: 2.00K
Crop damage: 0.00K
Reported by: NWS Employee

Quarter size hail fell at the NWS office in Johnston.

Hail in AUDUBON, IOWA
From 20-AUG-07 19:52:00 to 20-AUG-07 19:52:00 (CST-6)
Location: AUDUBON
Magnitude: 1.00 
Property damage: 5.00K
Crop damage: 50.00K
Reported by: Law Enforcement

Winds of 45 to 50 MPH also occurred with the hail.

Hail in CALHOUN, IOWA
From 20-AUG-07 21:02:00 to 20-AUG-07 21:02:00 (CST-6)
Location: MANSON
Magnitude: 1.00 
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail the size of quarters fell in Manson, with a few stones slightly larger.

Thunderstorm Wind in ADAMS, IOWA
From 20-AUG-07 20:05:00 to 20-AUG-07 20:05:00 (CST-6)
Location: IVEYVILLE
Magnitude: 52.00 EG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Very heavy rain accompanied the wind as well.

Thunderstorm Wind in TAYLOR, IOWA
From 20-AUG-07 20:30:00 to 20-AUG-07 20:30:00 (CST-6)
Location: GRAVITY
Magnitude: 56.00 EG
Property damage: 10.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Winds were estimated at 55 MPH sustained, with gusts to 65 MPH.  Visibility was reduced to zero in heavy rain.

Thunderstorm Wind in TAYLOR, IOWA
From 20-AUG-07 20:31:00 to 20-AUG-07 20:31:00 (CST-6)
Location: CLEARFIELD
Magnitude: 65.00 EG
Property damage: 75.00K
Crop damage: 10.00K
Reported by: Emergency Manager

High winds destroyed a grain bin and greenhouse at a local residence just north of town.  Several trees and power lines were downed in the town of Clearfield.

Thunderstorm Wind in RINGGOLD, IOWA
From 20-AUG-07 21:15:00 to 20-AUG-07 21:15:00 (CST-6)
Location: MT AYR
Magnitude: 57.00 EG
Property damage: 25.00K
Crop damage: 10.00K
Reported by: Law Enforcement

High winds downed numerous trees in Mt. Ayr and Kellerton.  Power lines were blown down around the county.

Thunderstorm Wind in ADAMS, IOWA
From 20-AUG-07 20:19:00 to 20-AUG-07 20:19:00 (CST-6)
Location: CORNING
Magnitude: 50.00 MG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Mesonet

High winds were measured by a KCCI Schoolnet site.

Thunderstorm Wind in UNION, IOWA
From 20-AUG-07 20:47:00 to 20-AUG-07 20:47:00 (CST-6)
Location: CRESTON
Magnitude: 53.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Mesonet

Wind speeds were measured by a KCCI Schoolnet site.

Flash Flood in CALHOUN, IOWA
From 20-AUG-07 21:48:00 to 20-AUG-07 23:06:00 (CST-6)
Location: RICHARDS
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Highway P19 was closed due to water running over road.

Thunderstorm Wind in TAYLOR, IOWA
From 20-AUG-07 20:28:00 to 20-AUG-07 20:28:00 (CST-6)
Location: GRAVITY
Magnitude: 56.00 EG
Property damage: 10.00K
Crop damage: 5.00K
Reported by: Fire Department/Rescue

Winds gusts were estimated by trained spotters.

Thunderstorm Wind in ADAMS, IOWA
From 20-AUG-07 20:31:00 to 20-AUG-07 20:31:00 (CST-6)
Location: IVEYVILLE
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Winds were estimated up to to 60 MPH.  Medium sized limbs were broken off of trees.