A very unstable airmass was in place over Iowa with CAPE values around 6000 J/kg and lifted indices around -11 C.  The downdraft CAPE was 1500 to 1900 J/kg.  CAPE in the -10 to -30 C layer of the atmosphere was high, in the 800 to 1200 J/kg range, however the freezing level was 15,500 feet, limiting the hail production.  The shear profile was relatively weak with 30 kts of effective shear available.  Predawn temperatures were in the upper 70s to around 80, with dewpoints in the mid 70s.  Precipitable water values were in the 1.5 to 2 inch range, boosted by a 35 kt low level jet.  Thunderstorms formed in two complexes along a weak frontal boundary extending from Minnesota into Kansas.  One of the complexes pushed north and east out of Kansas and Nebraska, the second was over southern Minnesota.  The two filled in during the night as the whole system moved into richer air.  An outflow boundary was located across northern Iowa from the complex in Minnesota, enhancing convection there.  As the storms moved into Iowa, the primary threat came in the form of wind with wind gusts of 40 to 60 MPH associated with the fast moving forward propagating MCS.  Wind damage occurred in the Atlantic area with a tree blocking U.S. Highway 6.  This cluster of storms continued to move across the state at around 55 MPH.  Wind damage occurred in the Des Moines area with tree branches down and power line damage caused by 60 MPH winds.  A 59 MPH wind gust was recorded at the Ames Airport as the storms passed.  As the complex of storms continued east out of central Iowa, widespread damage occurred across Marshall and Tama Counties with winds of 70 to 100 MPH.  Two radio towers were downed, one in central Tama County, the other in northern Polk County.  A local television station's weather radar was destroyed near Alleman, also in Polk County.  Local wind speeds in these areas were estimated as high as 115 MPH.  Widespread power outages were reported with 90% of the power still out in Marshall County, and 75% out in Tama County 12 hours after the event.  Power was out for 3 to 4 days in some places.  Governor Terry Brandstad gave a State Disaster Proclamation to Story, Marshall, and Tama Counties due the extensive damage.  A presidential declaration for major disaster was also given to Story, Marshall, and Tama Counties.  A broad area of severe damage occurred with a path 5 miles wide of EF1 type damage caused by the high winds.  A path, 10 miles wide, of 70 to 80 MPH was surveyed, with a 15 to 20 mile wide path of wind speeds above 60 MPH.  The damage swath was nearly continuous with no evidence of tornadoes.  It extended from southern Story and northern Polk Counties, through Marshall, and Tama Counties, and was about 75 miles in length before exiting the CWA.  Crop losses were substantial with around 40% or greater loss on over 100,000 acres of corn and soy beans.  The corn had much more damage than the bean plants, with damage on these acres estimated at $95,000,000.  Other damage occurred around the area as well.  This derecho event was the most widespread one to affect central and east central Iowa since the June 1998 event.  Some examples of the notable wind speeds estimated from the survey include 96 MPH near Huxley, 94 MPH near Maxwell, 70 to 90 MPH near Marshalltown, 105 MPH east of Garwin, 85 to 97 MPH between Garwin and Union Grove State Park, 100 MPH south of Traer, and south to southwest of Dysart 105 to 115 MPH, with 80 to 100 MPH winds just south of that part of the swath.  One dairy farmer near Dysart reported the total loss of 300 acres of corn and $300,000 damage to the farm.  Several of his dairy cows perished or had to be euthanized.  The farmer said he would have to go out of the farming business after 45 years due to the extent of the loss.  In Tama County, officials reported that 1000 county road signs were destroyed by the high wind.  Meanwhile, the northern part of the system continued to produce strong winds with a 63 MPH wind gust reported at the Fort Dodge Airport.

Heavy Rain in EMMET, IOWA
From 11-JUL-11 00:44:00 to 11-JUL-11 00:44:00 (CST-6)
Location: WELLINGFORD
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Pea size hail and rainfall of 1.8 inches were reported.

Thunderstorm Wind in CASS, IOWA
From 11-JUL-11 01:10:00 to 11-JUL-11 01:10:00 (CST-6)
Location: ATLANTIC
Magnitude: 50.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Tree partially down blocking Highway 6.

Thunderstorm Wind in WEBSTER, IOWA
From 11-JUL-11 02:05:00 to 11-JUL-11 02:05:00 (CST-6)
Location: CLAY WORKS
Magnitude: 55.00 MG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Mesonet

Thunderstorm Wind in POLK, IOWA
From 11-JUL-11 02:22:00 to 11-JUL-11 02:22:00 (CST-6)
Location: LOVINGTON
Magnitude: 60.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Four inch diameter tree limbs were blown down.  Heavy rain reported with winds increasing.

Thunderstorm Wind in POLK, IOWA
From 11-JUL-11 02:25:00 to 11-JUL-11 02:25:00 (CST-6)
Location: ANKENY
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter estimated a 60 MPH wind gust.

Thunderstorm Wind in STORY, IOWA
From 11-JUL-11 02:43:00 to 11-JUL-11 02:43:00 (CST-6)
Location: AMES
Magnitude: 51.00 MG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: ASOS

Thunderstorm Wind in JASPER, IOWA
From 11-JUL-11 02:57:00 to 11-JUL-11 02:57:00 (CST-6)
Location: BAXTER
Magnitude: 56.00 MG
Property damage: 15.00K
Crop damage: 10.00K
Reported by: Mesonet

Thunderstorm Wind in MARSHALL, IOWA
From 11-JUL-11 03:20:00 to 11-JUL-11 03:20:00 (CST-6)
Location: MARSHALLTOWN
Magnitude: 70.00 MG
Property damage: 50.00K
Crop damage: 50.00K
Reported by: Trained Spotter

Measured winds on personal weather station.  Damage included fences down, trees snapped, and siding ripped from houses.

Thunderstorm Wind in GUTHRIE, IOWA
From 11-JUL-11 01:46:00 to 11-JUL-11 01:46:00 (CST-6)
Location: HERNDON
Magnitude: 50.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Two to four inch diameter limbs blown down in Yale.

Thunderstorm Wind in CASS, IOWA
From 11-JUL-11 01:30:00 to 11-JUL-11 01:30:00 (CST-6)
Location: ATLANTIC
Magnitude: 57.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Several large tree branches were down.  A heavy patio table with umbrella was toppled and blown many feet.  Damage was also done to lawn furniture, garbage containers, and yard decor.  All were blown many feet.

Thunderstorm Wind in POLK, IOWA
From 11-JUL-11 02:20:00 to 11-JUL-11 02:20:00 (CST-6)
Location: POLK CITY
Magnitude: 85.00 EG
Property damage: 150.00K
Crop damage: 250.00K
Reported by: Broadcast Media

A 10 by 34 foot section of a newly constructed house roof was blown off and trusses snapped in half.  Several 18 to 24 foot diameter trees were snapped or topped.  Surrounding corn fields were mostly flattened.

Thunderstorm Wind in POLK, IOWA
From 11-JUL-11 02:20:00 to 11-JUL-11 02:20:00 (CST-6)
Location: POLK CITY
Magnitude: 75.00 EG
Property damage: 100.00K
Crop damage: 100.00K
Reported by: Broadcast Media

Corrugated steel roof from a house was ripped off and thrown approximately 110 meters.  A section of the roof impaled the side of a neighboring house, with part of the metal roof sticking into the living room of the house.

Thunderstorm Wind in POLK, IOWA
From 11-JUL-11 02:25:00 to 11-JUL-11 02:25:00 (CST-6)
Location: POLK CITY
Magnitude: 57.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: NWS Employee

Trees were blown down.

Thunderstorm Wind in STORY, IOWA
From 11-JUL-11 02:25:00 to 11-JUL-11 02:25:00 (CST-6)
Location: SLATER
Magnitude: 61.00 EG
Property damage: 10.00K
Crop damage: 50.00K
Reported by: NWS Employee

Trees down and crop damage reported.

Thunderstorm Wind in STORY, IOWA
From 11-JUL-11 02:25:00 to 11-JUL-11 02:25:00 (CST-6)
Location: SLATER
Magnitude: 57.00 EG
Property damage: 5.00K
Crop damage: 10.00K
Reported by: NWS Employee

Trees blown down.

Thunderstorm Wind in POLK, IOWA
From 11-JUL-11 02:30:00 to 11-JUL-11 02:30:00 (CST-6)
Location: ALLEMAN
Magnitude: 70.00 EG
Property damage: 200.00K
Crop damage: 100.00K
Reported by: Broadcast Media

WHO TV radar was blown into a farm field and destroyed.

Thunderstorm Wind in POLK, IOWA
From 11-JUL-11 02:30:00 to 11-JUL-11 02:30:00 (CST-6)
Location: CROCKER
Magnitude: 96.00 EG
Property damage: 200.00K
Crop damage: 500.00K
Reported by: Trained Spotter

Numerous 10 to 12 inch diameter trees snapped, largest downed were 3 feet in diameter.  Trees laying in different directions.  Power lines down across the area and the Amateur Radio repeater town was down.

Thunderstorm Wind in POLK, IOWA
From 11-JUL-11 02:25:00 to 11-JUL-11 02:25:00 (CST-6)
Location: ANKENY
Magnitude: 61.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: NWS Employee

Shingles ripped off the roof of a house and tree damage was reported.

Thunderstorm Wind in STORY, IOWA
From 11-JUL-11 02:35:00 to 11-JUL-11 02:35:00 (CST-6)
Location: HUXLEY
Magnitude: 57.00 EG
Property damage: 5.00K
Crop damage: 10.00K
Reported by: Emergency Manager

Power lines down along Highway 69 near the Polk County line.

Thunderstorm Wind in STORY, IOWA
From 11-JUL-11 02:45:00 to 11-JUL-11 02:45:00 (CST-6)
Location: MAXWELL
Magnitude: 70.00 EG
Property damage: 10.00K
Crop damage: 15.00K
Reported by: Emergency Manager

Roof ripped off of a mobile home.

Thunderstorm Wind in STORY, IOWA
From 11-JUL-11 02:50:00 to 11-JUL-11 02:50:00 (CST-6)
Location: COLLINS
Magnitude: 57.00 EG
Property damage: 10.00K
Crop damage: 10.00K
Reported by: Emergency Manager

Shed destroyed.

Thunderstorm Wind in MARION, IOWA
From 11-JUL-11 03:00:00 to 11-JUL-11 03:00:00 (CST-6)
Location: PELLA
Magnitude: 75.00 EG
Property damage: 50.00K
Crop damage: 50.00K
Reported by: Emergency Manager

Roof blown off of a building.

Thunderstorm Wind in MARSHALL, IOWA
From 11-JUL-11 03:09:00 to 11-JUL-11 03:09:00 (CST-6)
Location: MARSHALLTOWN
Magnitude: 85.00 EG
Property damage: 500.00K
Crop damage: 50.00K
Reported by: Emergency Manager

Extensive damage reported in Marshalltown.  Trees over roads, trees on homes, gas leaks, and structural damage.

Thunderstorm Wind in TAMA, IOWA
From 11-JUL-11 03:25:00 to 11-JUL-11 03:25:00 (CST-6)
Location: TOLEDO
Magnitude: 75.00 EG
Property damage: 200.00K
Crop damage: 250.00K
Reported by: Broadcast Media

Trees and power lines down all over the place.

Thunderstorm Wind in MARSHALL, IOWA
From 11-JUL-11 03:23:00 to 11-JUL-11 03:23:00 (CST-6)
Location: ALBION
Magnitude: 75.00 EG
Property damage: 50.00K
Crop damage: 100.00K
Reported by: Trained Spotter

Numerous large trees down with a couple on the house.  Outbuilding damage at the residence as well.  A funnel cloud also was reported.

Thunderstorm Wind in TAMA, IOWA
From 11-JUL-11 03:35:00 to 11-JUL-11 03:35:00 (CST-6)
Location: CLUTIER
Magnitude: 96.00 EG
Property damage: 500.00K
Crop damage: 200.00K
Reported by: Law Enforcement

Significant damage to the Clutier Fire Department building.  Significant damage throughout the county.

Thunderstorm Wind in TAMA, IOWA
From 11-JUL-11 03:35:00 to 11-JUL-11 03:35:00 (CST-6)
Location: GLADBROOK
Magnitude: 75.00 EG
Property damage: 50.00K
Crop damage: 25.00K
Reported by: Broadcast Media

Numerous trees down.  Electricity out.

Thunderstorm Wind in TAMA, IOWA
From 11-JUL-11 03:40:00 to 11-JUL-11 03:40:00 (CST-6)
Location: DYSART
Magnitude: 75.00 EG
Property damage: 350.00K
Crop damage: 250.00K
Reported by: Broadcast Media

Numerous trees down, windows broken out and rescue crews called out.

Thunderstorm Wind in TAMA, IOWA
From 11-JUL-11 03:25:00 to 11-JUL-11 03:25:00 (CST-6)
Location: TOLEDO
Magnitude: 78.00 EG
Property damage: 150.00K
Crop damage: 250.00K
Reported by: Trained Spotter

Barn and brick silo flattened.  Many trees down, some 3 feet in diameter.

Thunderstorm Wind in TAMA, IOWA
From 11-JUL-11 03:41:00 to 11-JUL-11 03:41:00 (CST-6)
Location: DYSART
Magnitude: 70.00 EG
Property damage: 30.00K
Crop damage: 50.00K
Reported by: Broadcast Media

Tree limbs down and power out.  A swing set was wrapped around a tree.

Thunderstorm Wind in TAMA, IOWA
From 11-JUL-11 03:25:00 to 11-JUL-11 03:25:00 (CST-6)
Location: TOLEDO
Magnitude: 100.00 EG
Property damage: 300.00K
Crop damage: 500.00K
Reported by: Trained Spotter

A 180 foot radio tower was snapped with many trees down.

Thunderstorm Wind in POLK, IOWA
From 11-JUL-11 02:25:00 to 11-JUL-11 02:25:00 (CST-6)
Location: DODGE FLD ARPT
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: NWS Employee

Several large tree branches down along Merle Hay road.  Largest was 4 to 5 inches in diameter.

Thunderstorm Wind in MARSHALL, IOWA
From 11-JUL-11 03:04:00 to 11-JUL-11 03:04:00 (CST-6)
Location: LA MOILLE
Magnitude: 70.00 EG
Property damage: 50.00K
Crop damage: 50.00K
Reported by: Emergency Manager

Power poles snapped in half near Highway 30 and the 330 Junction.

Thunderstorm Wind in POWESHIEK, IOWA
From 11-JUL-11 03:12:00 to 11-JUL-11 03:12:00 (CST-6)
Location: GRINNELL
Magnitude: 61.00 EG
Property damage: 50.00K
Crop damage: 10.00K
Reported by: Law Enforcement

Trees down, transformers down, and power outages.

Thunderstorm Wind in MARSHALL, IOWA
From 11-JUL-11 03:13:00 to 11-JUL-11 03:13:00 (CST-6)
Location: QUARRY
Magnitude: 65.00 EG
Property damage: 40.00K
Crop damage: 50.00K
Reported by: Emergency Manager

Semi-truck blown over on Highway 30 near Le Grand.

Thunderstorm Wind in TAMA, IOWA
From 11-JUL-11 03:22:00 to 11-JUL-11 03:22:00 (CST-6)
Location: MONTOUR
Magnitude: 61.00 EG
Property damage: 50.00K
Crop damage: 100.00K
Reported by: Law Enforcement

Estimated winds of 70 to 100 MPH between Montour and Toledo.  Road signs blown down with power outages.

Thunderstorm Wind in TAMA, IOWA
From 11-JUL-11 03:30:00 to 11-JUL-11 03:30:00 (CST-6)
Location: GARWIN
Magnitude: 96.00 EG
Property damage: 750.00K
Crop damage: 250.00K
Reported by: Trained Spotter

Many power lines and trees down in the area, including one 3.5 foot diameter tree.  A grain bin was flattened and at least part of a roof was in the yard.  Windows were blown out and siding was ripped from the house.

Thunderstorm Wind in POLK, IOWA
From 11-JUL-11 02:23:00 to 11-JUL-11 02:23:00 (CST-6)
Location: HERROLD
Magnitude: 51.00 MG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Official NWS Observations

Measured at the NWS office in Johnston.

Tornado in WEBSTER, IOWA
From 11-JUL-11 01:52:00 to 11-JUL-11 01:56:00 (CST-6)
Location: MOORLAND NESLER ARPT
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 10.00K
Reported by: Airplane Pilot

An intermittent path captured by photographs from an airplane.  The narrow path was entirely in fields of corn and soybeans as it moved nearly due east.

Thunderstorm Wind in POWESHIEK, IOWA
From 11-JUL-11 03:25:00 to 11-JUL-11 03:25:00 (CST-6)
Location: GRINNELL
Magnitude: 57.00 EG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Newspaper

Numerous trees uprooted and blown down by high winds.

Thunderstorm Wind in GUTHRIE, IOWA
From 11-JUL-11 01:50:00 to 11-JUL-11 01:50:00 (CST-6)
Location: STUART
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Newspaper

Several trees were blown down by high winds.

Thunderstorm Wind in BOONE, IOWA
From 11-JUL-11 02:30:00 to 11-JUL-11 02:30:00 (CST-6)
Location: MADRID
Magnitude: 75.00 EG
Property damage: 50.00K
Crop damage: 25.00K
Reported by: Newspaper

High winds tore part of the roof off of a stick built house.

Thunderstorm Wind in JASPER, IOWA
From 11-JUL-11 03:00:00 to 11-JUL-11 03:00:00 (CST-6)
Location: MONROE
Magnitude: 61.00 EG
Property damage: 15.00K
Crop damage: 10.00K
Reported by: Newspaper

High winds downed several trees.

Thunderstorm Wind in MARSHALL, IOWA
From 11-JUL-11 03:05:00 to 11-JUL-11 03:05:00 (CST-6)
Location: LURAY
Magnitude: 75.00 EG
Property damage: 150.00K
Crop damage: 250.00K
Reported by: Law Enforcement

One to two miles of topped trees along the Haverhill blacktop just south of Marshalltown.