A cold front entered northwest Iowa during the early morning hours of the 2nd.  The airmass was relatively unstable with CAPE in the 2000 to 3000 J/kg range and lifted indices of -5 to -8 C.  A considerable amount of downdraft CAPE was available with values ranging from 1100 to 1500 J/kg.  The atmosphere was moderately sheared with 30 to 45 kts of shear available.  CAPE in the -10 to -30 C layer of the atmosphere was between 400 and 800 J/kg, however the freezing level of 16,500 feet limited hail growth in many of the storms.  Precipitable water values were around 1.8 inches as a low level jet of 40 to 50 kts drew moisture northeast into the state.  A large supercell developed over northwest Iowa.  The storm tracked east across the northwest into the north central counties.  It produced hail of 1.5 inches in diameter in Palo Alto County, and 61 MPH winds in Hancock County.  As the storms moved into Worth County, strong winds downed tree branches and power lines with winds of around 60 MPH reported.  There were numerous reports of 40 to 50 mph winds and pea to dime size hail along its track.  The storm produced very strong winds east of Northwood in Worth County.  High winds flattened corn crops and also bent the propeller tip of a wind generator.

Hail in PALO ALTO, IOWA
From 02-SEP-11 03:31:00 to 02-SEP-11 03:31:00 (CST-6)
Location: MALLARD
Magnitude: 1.50 
Property damage: 2.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Trained spotter reports quarter to ping pong ball size hail.

Thunderstorm Wind in HANCOCK, IOWA
From 02-SEP-11 04:25:00 to 02-SEP-11 04:25:00 (CST-6)
Location: MILLER
Magnitude: 53.00 MG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: AWOS

Thunderstorm Wind in WORTH, IOWA
From 02-SEP-11 04:44:00 to 02-SEP-11 04:44:00 (CST-6)
Location: DEER CREEK
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 25.00K
Reported by: Trained Spotter

Trees and power lines were down.  Winds estimated around 60 MPH along with penny size hail.

Thunderstorm Wind in WORTH, IOWA
From 02-SEP-11 04:45:00 to 02-SEP-11 04:45:00 (CST-6)
Location: GRAFTON
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Spotter estimated winds over 50 MPH.  Several 2 to 3 inch diameter branches were blown down throughout Grafton.  An 8 inch and 12 inch diameter tree were both reported down just north of town with power reported out.

Hail in PALO ALTO, IOWA
From 02-SEP-11 03:25:00 to 02-SEP-11 03:25:00 (CST-6)
Location: CURLEW
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 5.00K
Reported by: Public

Thunderstorm Wind in WORTH, IOWA
From 02-SEP-11 04:47:00 to 02-SEP-11 04:47:00 (CST-6)
Location: MELTONVILLE
Magnitude: 70.00 EG
Property damage: 250.00K
Crop damage: 100.00K
Reported by: Public

Two separate wind mills were damaged, one had a propeller bent in half and the second had a tip snapped off.  Numerous trees and power lines were damaged and corn was flattened.

Thunderstorm Wind in WINNEBAGO, IOWA
From 02-SEP-11 04:24:00 to 02-SEP-11 04:24:00 (CST-6)
Location: FOREST CITY
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A street sign was blown over and a large trampoline flipped.  Several large limbs down.