An unstable airmass remained in place across Iowa with dewpoint temperatures remaining in the upper 60s to low 70s.  A nearly stationary frontal boundary was in place across the state extending from the east central counties to the southwest corner of the state.  Thunderstorms erupted on the north side of the front during the evening.  CAPE values were between 2000 and 4000 J/kg, with downdraft CAPE of 1100 to 1600 J/kg.  The lifted index was in the -4 to -6 C range.  The freezing level was quite high, though it had fallen some during the day.  It was just over 14,000 feet by evening.  CAPE in the -10 to -30 C layer of the atmosphere was between 300 and 700 J/kg.  Moisture was drawn north over the frontal boundary by a low level jet of 25 kts.  Precipitable water values increased to 1.6 to 1.9 inches.  The storms produced high winds as they progressed across the state.  One storm broke several 10 inch branches south of Hubbard in Hardin County.  This storm continued eastward and produced strong winds as it moved through Black Hawk County.  Winds were measured around 60 MPH in the Waterloo area.  Another cluster of storms moved into western Iowa and spread into the central counties.  Winds around 75 MPH occurred in Audubon County.  The strong winds, at least 60 MPH, continued east into Guthrie County before the storms weakened.  There were numerous reports of trees downed, along with power line damage.  Extensive damage occurred in Hardin County as winds of 75 MPH caused crop damage, ripped part of the roof off of a machine shed, and flattened several grain bins.  A classic wet microburst took place south of Hubbard as well.  Winds started around 1030 PM and lasted for about 8 minutes.  The damage was concentrated in an area about 2 miles south of Hubbard where 3 farms sustained major damage,  and a 4th farm had more minor damage.  Specifically, one farm lost 12 trees (snapped).  Two trees landed on and destroyed a grain bin.  Also, the west-facing machine shed door was collapsed and portions of the roof (including the roof structure itself) were blown off.   The next 2 farms to the south also sustained significant damage to trees with many snapped about halfway up the trunk.  The farm just to the north also lost several large trees.  Based on the duration of the winds, damage to the farms, type and condition of the trees, etc., estimated winds were in the 80-85 MPH range.  In terms of crops, most of these farms are growing soybeans which were flattened, and part of the corn crop was blown down. Heavy rain also was reported in Bremer County with reports of around 3 inches of rain in under 2 hours.  Around 2 inches of rain fell in an hour in Black Hawk County.  Lightning struck a building in Cedar Falls, setting it  on fire.  There were also reports of two tree fires in the city of Cedar Falls.

Thunderstorm Wind in BLACK HAWK, IOWA
From 02-SEP-11 22:45:00 to 02-SEP-11 22:45:00 (CST-6)
Location: EVANSDALE
Magnitude: 51.00 MG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Mesonet

Thunderstorm Wind in BLACK HAWK, IOWA
From 02-SEP-11 22:49:00 to 02-SEP-11 22:49:00 (CST-6)
Location: (ALO)WATERLOO MUNI A
Magnitude: 52.00 MG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: AWOS

Thunderstorm Wind in BLACK HAWK, IOWA
From 02-SEP-11 22:47:00 to 02-SEP-11 22:47:00 (CST-6)
Location: WATERLOO
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Small tree limbs down.

Thunderstorm Wind in BLACK HAWK, IOWA
From 02-SEP-11 22:40:00 to 02-SEP-11 22:40:00 (CST-6)
Location: CEDAR FALLS
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter estimated a wind gust of 60 MPH.

Thunderstorm Wind in HARDIN, IOWA
From 02-SEP-11 21:40:00 to 02-SEP-11 21:40:00 (CST-6)
Location: HUBBARD
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: NWS Employee

Several branches down, some 10 inches in diameter.

Thunderstorm Wind in GUTHRIE, IOWA
From 02-SEP-11 21:55:00 to 02-SEP-11 21:55:00 (CST-6)
Location: GUTHRIE CENTER
Magnitude: 52.00 EG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter estimated 60 MPH winds.

Thunderstorm Wind in BLACK HAWK, IOWA
From 02-SEP-11 22:43:00 to 02-SEP-11 22:43:00 (CST-6)
Location: (ALO)WATERLOO MUNI A
Magnitude: 51.00 MG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: AWOS

Thunderstorm Wind in AUDUBON, IOWA
From 02-SEP-11 21:30:00 to 02-SEP-11 21:30:00 (CST-6)
Location: AUDUBON
Magnitude: 65.00 EG
Property damage: 30.00K
Crop damage: 10.00K
Reported by: COOP Observer

Numerous tree branches were down all over town.

Heavy Rain in BREMER, IOWA
From 03-SEP-11 07:40:00 to 03-SEP-11 07:40:00 (CST-6)
Location: READLYN
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Rainfall total of 2.7 inches, Received from KWWL TV.

Heavy Rain in BREMER, IOWA
From 03-SEP-11 08:20:00 to 03-SEP-11 08:20:00 (CST-6)
Location: DENVER
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Rainfall total of 3.3 inches.  Received from KWWL TV.

Heavy Rain in BLACK HAWK, IOWA
From 03-SEP-11 10:01:00 to 03-SEP-11 10:01:00 (CST-6)
Location: DEWAR
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Rainfall total from the storm was 2.00 inches.

Thunderstorm Wind in HAMILTON, IOWA
From 02-SEP-11 20:45:00 to 02-SEP-11 20:45:00 (CST-6)
Location: JEWELL
Magnitude: 50.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Large tree limb down in town.

Thunderstorm Wind in HAMILTON, IOWA
From 02-SEP-11 20:45:00 to 02-SEP-11 20:45:00 (CST-6)
Location: JEWELL
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Large tree blocking a road off of Highway 69.

Thunderstorm Wind in HARDIN, IOWA
From 02-SEP-11 21:20:00 to 02-SEP-11 21:20:00 (CST-6)
Location: HUBBARD
Magnitude: 65.00 EG
Property damage: 100.00K
Crop damage: 50.00K
Reported by: NWS Employee

Ten large trees snapped in half with a couple of the trees hitting and destroying two grain bins.  Many large branches down, some 10 inches in diameter.  A machine shed lost parts of its roof and the doors to the building were blown in.

Thunderstorm Wind in HARDIN, IOWA
From 02-SEP-11 21:45:00 to 02-SEP-11 21:45:00 (CST-6)
Location: NEW PROVIDENCE
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Tree damage throughout town.

Thunderstorm Wind in HARDIN, IOWA
From 02-SEP-11 21:45:00 to 02-SEP-11 21:45:00 (CST-6)
Location: NEW PROVIDENCE
Magnitude: 65.00 EG
Property damage: 50.00K
Crop damage: 100.00K
Reported by: Fire Department/Rescue

Grain bin destroyed.  Large tree down with crop damage.

Thunderstorm Wind in BLACK HAWK, IOWA
From 02-SEP-11 22:45:00 to 02-SEP-11 22:45:00 (CST-6)
Location: WATERLOO
Magnitude: 60.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

One to three inch diameter branches blown down.

Thunderstorm Wind in HARDIN, IOWA
From 02-SEP-11 21:30:00 to 02-SEP-11 21:38:00 (CST-6)
Location: HUBBARD
Magnitude: 72.00 EG
Property damage: 500.00K
Crop damage: 500.00K
Reported by: NWS Employee

A microburst took place on 2 farmsteads in the area with 80 to 85 MPH winds causing damage to buildings and crops.

Lightning in BLACK HAWK, IOWA
From 03-SEP-11 00:45:00 to 03-SEP-11 00:45:00 (CST-6)
Location: CEDAR FALLS
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Newspaper

A building and two trees were set ablaze by lightning.

Thunderstorm Wind in GRUNDY, IOWA
From 02-SEP-11 22:30:00 to 02-SEP-11 22:30:00 (CST-6)
Location: DIKE
Magnitude: 61.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Newspaper

Thunderstorms moved through the Dike area causing extensive tree damage on the south side of Dike.