A cold front moved into Iowa from the northwest.  The airmass was quite unstable with CAPE values in the 4000-5000 J/kg range and lifted indices around -8 C.  Afternoon highs reached the upper 80s to low 90s, with dewpoints in the low to mid 70s ahead of the cold front.  Precipitable water was quite high with 1.6 to 2 inches available.  Scattered thunderstorms formed to the west of Iowa initially in a scattered line.  They coalesced into a small forward propagating MCS by the evening hours.  The airmass was moderately sheared with 40 to 45 kts of effective shear.  The freezing level was quite high, around 14,500 feet, so hail was limited.  CAPE in the -10 to -30 C layer of the atmosphere was between 700 and 1100 J/kg.  The storms produced high winds as the primary mode of severe weather.  This was not too surprising considering there was 1500 J/kg of downdraft CAPE available just ahead of the MCS.  Initially the storms did produce hail as the cells were more discrete.  Dime to quarter size hail was reported in Crawford and Audubon Counties.  The system quickly became a wind event as it raced across the southern third to half of Iowa.  Winds speeds of 60 to 70 MPH were common along its path.  The highest measured wind gust was 71 MPH northwest of Creston.  There were numerous reports of trees and power lines downed all along the path.  Damage was done to some house roofs in the town of Creston, with a tree reportedly falling onto one house in Creston.  Roof damage was also reported in Madison County with an American Legion building damaged in Macksburg.  High winds also blew a camper off of its jacks in Lucas County in Williamson.  High winds damaged outbuildings, peeling back roofs and blowing over sheds across Adair, Clarke, and Madison County.  High winds blew out a large window at a Walmart in Marion County in Knoxville.  During the early morning hours, strong thunderstorms developed over parts of northern Iowa, also along the front.  For the most part they remained below severe levels.  One of the storms produced 60 to 65 MPH winds in Franklin County at Hampton.  Numerous trees were downed and power was knocked out for much of the city.

Hail in CRAWFORD, IOWA
From 06-AUG-11 19:13:00 to 06-AUG-11 19:13:00 (CST-6)
Location: DOW CITY
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Hail in AUDUBON, IOWA
From 06-AUG-11 19:58:00 to 06-AUG-11 19:58:00 (CST-6)
Location: IMBALLTON
Magnitude: 1.00 
Property damage: 2.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Hail in AUDUBON, IOWA
From 06-AUG-11 19:49:00 to 06-AUG-11 19:54:00 (CST-6)
Location: SHARON
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 25.00K
Reported by: Trained Spotter

Trained spotter reported hail fell from 1949 to 1954 CST.  Mostly pea size hail, but then up to quarter size at the end.

Hail in AUDUBON, IOWA
From 06-AUG-11 20:01:00 to 06-AUG-11 20:08:00 (CST-6)
Location: SHARON
Magnitude: 1.00 
Property damage: 5.00K
Crop damage: 25.00K
Reported by: Trained Spotter

Trained spotter reported nickel to quarter size hail fell from 2001 to 2008 CST.

Thunderstorm Wind in UNION, IOWA
From 06-AUG-11 21:33:00 to 06-AUG-11 21:33:00 (CST-6)
Location: CRESTON
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Emergency Manager

A tree fell onto a house.

Thunderstorm Wind in MADISON, IOWA
From 06-AUG-11 21:33:00 to 06-AUG-11 21:33:00 (CST-6)
Location: MACKSBURG
Magnitude: 70.00 EG
Property damage: 25.00K
Crop damage: 20.00K
Reported by: Trained Spotter

Roof damage was reported to the American Legion Building.

Thunderstorm Wind in WARREN, IOWA
From 06-AUG-11 22:34:00 to 06-AUG-11 22:44:00 (CST-6)
Location: INDIANOLA
Magnitude: 57.00 EG
Property damage: 25.00K
Crop damage: 10.00K
Reported by: Emergency Manager

Trees and power lines down.  Winds estimated 60 to 70 MPH and blew for several minutes.

Thunderstorm Wind in ADAMS, IOWA
From 06-AUG-11 21:10:00 to 06-AUG-11 21:10:00 (CST-6)
Location: CORNING
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Tree limbs 4 to 6 inches in diameter down.

Thunderstorm Wind in WAPELLO, IOWA
From 06-AUG-11 23:20:00 to 06-AUG-11 23:20:00 (CST-6)
Location: OTTUMWA
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Police reported a power pole and lines down on the south side of Ottumwa.

Thunderstorm Wind in LUCAS, IOWA
From 06-AUG-11 22:50:00 to 06-AUG-11 22:50:00 (CST-6)
Location: WILLIAMSON
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A camper was blown off of its jacks.

Thunderstorm Wind in MONROE, IOWA
From 06-AUG-11 22:55:00 to 06-AUG-11 22:55:00 (CST-6)
Location: ALBIA
Magnitude: 61.00 EG
Property damage: 25.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Post event survey indicated numerous large tree limbs were down, portions of whole trees, and even a few large trees taken down along with power lines.

Thunderstorm Wind in CASS, IOWA
From 06-AUG-11 20:30:00 to 06-AUG-11 20:30:00 (CST-6)
Location: ANITA
Magnitude: 50.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Adair Iowa Department of Transportation RWIS site recorded gust.

Thunderstorm Wind in AUDUBON, IOWA
From 06-AUG-11 19:58:00 to 06-AUG-11 19:58:00 (CST-6)
Location: IMBALLTON
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Estimated wind gust of 60 MPH with small limbs down.

Thunderstorm Wind in ADAIR, IOWA
From 06-AUG-11 21:39:00 to 06-AUG-11 21:39:00 (CST-6)
Location: ORIENT
Magnitude: 56.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Torrential rains and very limited visibility.

Thunderstorm Wind in UNION, IOWA
From 06-AUG-11 21:39:00 to 06-AUG-11 21:39:00 (CST-6)
Location: AFTON
Magnitude: 50.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Measured by a KCCI schoolnet site.

Thunderstorm Wind in UNION, IOWA
From 06-AUG-11 21:40:00 to 06-AUG-11 21:40:00 (CST-6)
Location: CRESTON
Magnitude: 58.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Recorded from an Iowa Department of Transportation RWIS site.

Thunderstorm Wind in UNION, IOWA
From 06-AUG-11 21:31:00 to 06-AUG-11 21:31:00 (CST-6)
Location: CRESTON
Magnitude: 62.00 MG
Property damage: 50.00K
Crop damage: 25.00K
Reported by: Trained Spotter

Trained spotter reports a measured wind gust of 71 MPH.  Trees were uprooted on the west side of Creston with some roof damage.

Thunderstorm Wind in MADISON, IOWA
From 06-AUG-11 21:56:00 to 06-AUG-11 21:56:00 (CST-6)
Location: WINTERSET ARPT
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter estimated 60 MPH winds.

Thunderstorm Wind in CLARKE, IOWA
From 06-AUG-11 21:42:00 to 06-AUG-11 21:52:00 (CST-6)
Location: MURRAY
Magnitude: 61.00 EG
Property damage: 75.00K
Crop damage: 25.00K
Reported by: Trained Spotter

Trained spotter reports wind gusts around 70 MPH lasting quite some time.  Multiple large trees down, some on houses.  Dime to nickel size hail also fell.

Thunderstorm Wind in CLARKE, IOWA
From 06-AUG-11 21:42:00 to 06-AUG-11 21:42:00 (CST-6)
Location: MURRAY
Magnitude: 61.00 EG
Property damage: 25.00K
Crop damage: 5.00K
Reported by: Trained Spotter

A 6 foot diameter tree was sheared off near the base, a 25 foot flag pole snapped, and a few signs mangled.  Numerous 2 to 4 inch tree limbs down around town.

Thunderstorm Wind in MARION, IOWA
From 06-AUG-11 22:49:00 to 06-AUG-11 22:49:00 (CST-6)
Location: KNOXVILLE
Magnitude: 65.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Walmart Supercenter had a large window blown out by high winds.

Thunderstorm Wind in DECATUR, IOWA
From 06-AUG-11 22:02:00 to 06-AUG-11 22:02:00 (CST-6)
Location: (30I)LAMONI MUNI ARP
Magnitude: 53.00 MG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: ASOS

Thunderstorm Wind in CLARKE, IOWA
From 06-AUG-11 22:01:00 to 06-AUG-11 22:01:00 (CST-6)
Location: OSCEOLA
Magnitude: 59.00 EG
Property damage: 20.00K
Crop damage: 5.00K
Reported by: Trained Spotter

A spotter estimated wind gusts of 68 MPH.

Thunderstorm Wind in MONROE, IOWA
From 06-AUG-11 23:04:00 to 06-AUG-11 23:04:00 (CST-6)
Location: ALBIA
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A trained spotter estimated 60 MPH wind gusts.

Thunderstorm Wind in WAPELLO, IOWA
From 06-AUG-11 23:22:00 to 06-AUG-11 23:22:00 (CST-6)
Location: (OTM)OTTUMWA INDSTRL
Magnitude: 51.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Thunderstorm Wind in WAPELLO, IOWA
From 06-AUG-11 23:55:00 to 06-AUG-11 23:55:00 (CST-6)
Location: OTTUMWA
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Large trees down.

Thunderstorm Wind in CASS, IOWA
From 06-AUG-11 20:50:00 to 06-AUG-11 20:50:00 (CST-6)
Location: ATLANTIC
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A large tree limb fell onto a power line which subsequently fell onto a truck.

Thunderstorm Wind in ADAIR, IOWA
From 06-AUG-11 21:22:00 to 06-AUG-11 21:22:00 (CST-6)
Location: ORIENT
Magnitude: 65.00 EG
Property damage: 40.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Metal sheds were dented from high winds.  Part of the roof was peeled off with many tree limbs down.

Thunderstorm Wind in ADAIR, IOWA
From 06-AUG-11 21:23:00 to 06-AUG-11 21:23:00 (CST-6)
Location: ORIENT
Magnitude: 61.00 EG
Property damage: 30.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Roof torn off of a hog house and a large tree was down on a trailer at the intersection of 310th St and Henry A Wallace Road.

Thunderstorm Wind in CLARKE, IOWA
From 06-AUG-11 21:56:00 to 06-AUG-11 21:56:00 (CST-6)
Location: OSCEOLA
Magnitude: 65.00 EG
Property damage: 10.00K
Crop damage: 5.00K
Reported by: CoCoRaHS

High winds damaged trees and tore shingles off of a house.

Thunderstorm Wind in FRANKLIN, IOWA
From 07-AUG-11 02:14:00 to 07-AUG-11 02:14:00 (CST-6)
Location: HAMPTON
Magnitude: 54.00 EG
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Winds of 60 to 65 MPH produced widespread tree damage in the town of Hampton.  Numerous trees and limbs were downed through town.  Many location were without power due to branches falling on power lines.

Thunderstorm Wind in DAVIS, IOWA
From 06-AUG-11 23:35:00 to 06-AUG-11 23:35:00 (CST-6)
Location: FLORIS
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Newspaper

Thunderstorm winds toppled tree branches and power lines.

Thunderstorm Wind in LUCAS, IOWA
From 06-AUG-11 22:30:00 to 06-AUG-11 22:30:00 (CST-6)
Location: CHARITON
Magnitude: 61.00 EG
Property damage: 25.00K
Crop damage: 10.00K
Reported by: Newspaper

High winds downed a 12 foot diameter oak tree that was about 200 years old and damaged buildings.  Winds were estimated around 70 MPH.