A cold front sagged south across the state during the previous night and became stationary east-west over far southern Iowa.  The airmass became very unstable during the afternoon as temperatures soared into the low to mid 90s.  Dew points pooled over southwest into west central Iowa and were in the upper 70s to low 80s across the area.  This lead to CAPE values in excess of 7000 J/kg and a lifted index of -12 C.  Needless to say, considerable moisture was available with precipitable water values in the 2 to 2.25 inch range.  Thunderstorms developed over Nebraska and moved into Iowa during the afternoon.  A strong bow echo developed and advanced east-southeast across the west central, then across the south west into the south central counties of the state.  Some of the storms produced hail, but the hail was below severe levels.  In spite of the available cape in the -10 to -30 C. layer of the atmosphere being in the 600 to 900 J/kg range, hail was suppressed once again by the high freezing levels.  Freezing levels were between 14,500 and 15,000 feet.  The LCL was a relatively low 750 to 1000 meters, however downdraft CAPE was very high, between 1200 and 1600 J/kg.  Winds dominated the event as the storms advanced rapidly eastward in a shear environment of 40 to 50 kts.  There were numerous reports of trees toppled and power line damage.  Wind gusts of 60 to 70 MPH were common.  Some of the higher gusts came from the Adair area.  Mesonet sites reported wind gusts of 66 to 71 MPH in the area.

Thunderstorm Wind in AUDUBON, IOWA
From 12-AUG-07 17:17:00 to 12-AUG-07 17:17:00 (CST-6)
Location: IMBALLTON
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in ADAIR, IOWA
From 12-AUG-07 17:38:00 to 12-AUG-07 17:38:00 (CST-6)
Location: ADAIR
Magnitude: 50.00 MG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Mesonet

Thunderstorm Wind in TAYLOR, IOWA
From 12-AUG-07 18:00:00 to 12-AUG-07 18:00:00 (CST-6)
Location: GRAVITY
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in ADAIR, IOWA
From 12-AUG-07 17:45:00 to 12-AUG-07 17:45:00 (CST-6)
Location: ADAIR
Magnitude: 57.00 MG
Property damage: 10.00K
Crop damage: 2.00K
Reported by: Mesonet

Thunderstorm Wind in WARREN, IOWA
From 12-AUG-07 18:36:00 to 12-AUG-07 18:36:00 (CST-6)
Location: NEW VIRGINIA
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Thunderstorm Wind in UNION, IOWA
From 12-AUG-07 18:18:00 to 12-AUG-07 18:18:00 (CST-6)
Location: AFTON
Magnitude: 50.00 MG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Mesonet

Thunderstorm Wind in TAYLOR, IOWA
From 12-AUG-07 18:10:00 to 12-AUG-07 18:10:00 (CST-6)
Location: BEDFORD ARPT
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Other Federal Agency

Thunderstorm Wind in AUDUBON, IOWA
From 12-AUG-07 17:10:00 to 12-AUG-07 17:10:00 (CST-6)
Location: EXIRA
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Public

Thunderstorm Wind in UNION, IOWA
From 12-AUG-07 18:08:00 to 12-AUG-07 18:08:00 (CST-6)
Location: CRESTON
Magnitude: 50.00 MG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Mesonet

Thunderstorm Wind in WARREN, IOWA
From 12-AUG-07 18:47:00 to 12-AUG-07 18:47:00 (CST-6)
Location: NORWALK
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in TAYLOR, IOWA
From 12-AUG-07 18:10:00 to 12-AUG-07 18:10:00 (CST-6)
Location: BEDFORD ARPT
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Other Federal Agency

Thunderstorm Wind in CASS, IOWA
From 12-AUG-07 17:30:00 to 12-AUG-07 17:30:00 (CST-6)
Location: FLETCHER CHAPEL
Magnitude: 54.00 MG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A trained spotter measured a 62 MPH wind gust.

Thunderstorm Wind in CLARKE, IOWA
From 12-AUG-07 18:40:00 to 12-AUG-07 18:40:00 (CST-6)
Location: LACELLE
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A trained spotter reported large tree limbs blown down by high wind.

Thunderstorm Wind in GUTHRIE, IOWA
From 12-AUG-07 17:43:00 to 12-AUG-07 17:43:00 (CST-6)
Location: ADAIR
Magnitude: 56.00 EG
Property damage: 5.00K
Crop damage: 2.00K
Reported by: Trained Spotter

A trained spotter estimated wind gusts of 60 to 70 MPH.

Thunderstorm Wind in ADAIR, IOWA
From 12-AUG-07 17:41:00 to 12-AUG-07 17:41:00 (CST-6)
Location: ADAIR
Magnitude: 62.00 MG
Property damage: 35.00K
Crop damage: 2.00K
Reported by: Mesonet