A powerful line of severe thunderstorms produced a derecho which tracked across eastern Iowa and northwest Illinois on the afternoon of Monday, August 10th, resulting in widespread straight line wind damage. The cost of damage from this storm was extreme, reaching an estimated 7.5 billion dollars along the path of these storms from Iowa through Illinois.  Two brief tornadoes have been confirmed within the widespread swath of wind damage, one just north of the Eastern Iowa Airport in Linn County Iowa, and one just south of Freeport, Illinois. These tornadoes have been designated as EF-U, as there was no observable damage directly attributable to the tornadoes from which an EF-scale rating could be assigned. While an average of two derechos a year occur across the area, a derecho of this intensity is a roughly once-in-a-decade occurrence. Another unusual aspect of this derecho was the duration of the strong winds, with gusts over 60 mph for over an hour at some locations.
The most extreme winds, estimated at 110-140 mph, destroyed or damaged numerous outbuildings, barns, grain bins, homes, mobile homes, apartment buildings, trees, and power poles in parts of Benton, Linn, Jones, Cedar, and Clinton Counties. The Cedar Rapids area was particularly hard hit. One fatality occurred in Linn County, as a tree fell on a cyclist. Several homes, apartment complexes, and businesses sustained damage consistent with 130-140 mph winds. Radio transmission towers in Marion and Clinton, Iowa collapsed due to winds estimated around 130 mph. Wind gusts of 80-100 mph were common as the line of storms moved through the Quad Cities area and then through northwest Illinois. A small pocket of winds estimated at 100-110 mph impacted Princeton, IL in Bureau County, where a 150 foot communications tower collapsed and numerous power poles were snapped. In addition to the damage, numerous long-duration power outages occurred across the region. Damage to crops was considerable along the derecho path. Numerous semi trucks were also blown off roadways along the path of the derecho.

Tornado in STEPHENSON, ILLINOIS
From 10-AUG-20 13:12:00 to 10-AUG-20 13:17:00 (CST-6)
Location: FLORENCE
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

A tornado moved through cropland just south of Freeport. The tornado began just west of Florence, and moved N/NE for about 4.5 miles before dissipating at the southern edge of Freeport.  The path was found in high resolution satellite imagery and confirmed by UAS survey. The tornado was on the leading edge of a larger swath of damaging straight line winds. There was no damage directly attributable to the tornado from which an EF-scale rating could be assigned. Thus, the tornado is designated EF-U.

Thunderstorm Wind in ROCK ISLAND, ILLINOIS
From 10-AUG-20 12:08:00 to 10-AUG-20 13:50:00 (CST-6)
Location: ILLINOIS CITY
Magnitude: 70.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Widespread straight-line winds that produced extensive damage were reported throughout Rock Island County, associated with a derecho. These winds lasted around an hour in total, even though the initial line of storms moved out fast. Damaging straight-line winds continued and were associated with the rear inflow jet. Maximum wind speeds were reported up to 80 mph  These estimates were determined based off damage surveys and photos submitted through social media. These strong winds extensively damaged most trees, crops, and a few structures in their path. Prolonged power outages resulted from this storm damage.

Thunderstorm Wind in MERCER, ILLINOIS
From 10-AUG-20 12:10:00 to 10-AUG-20 13:30:00 (CST-6)
Location: ELIZA
Magnitude: 70.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Widespread straight-line winds that produced extensive damage were reported throughout Mercer County, associated with a derecho. These winds lasted around an hour in total, even though the initial line of storms moved out fast. Damaging straight-line winds continued and were associated with the rear inflow jet. Maximum wind speeds were reported up to 80 mph  These estimates were determined based off damage surveys and photos submitted through social media. These strong winds damaged many trees, crops, and a few structures in their path.

Thunderstorm Wind in HENRY, ILLINOIS
From 10-AUG-20 12:30:00 to 10-AUG-20 14:00:00 (CST-6)
Location: WARNER
Magnitude: 70.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Widespread straight-line winds that produced extensive damage were reported throughout Henry County, associated with a derecho. These winds lasted around an hour in total, even though the initial line of storms moved out fast. Damaging straight-line winds continued and were associated with the rear inflow jet. Maximum wind speeds were reported up to 80 mph  These estimates were determined based off damage surveys and photos submitted through social media. These strong winds damaged many trees, crops, and a few structures in their path.

Thunderstorm Wind in WHITESIDE, ILLINOIS
From 10-AUG-20 12:40:00 to 10-AUG-20 13:55:00 (CST-6)
Location: SHADY BEACH
Magnitude: 70.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Widespread straight-line winds that produced extensive damage were reported throughout Whiteside County, associated with a derecho. These winds lasted around an hour in total, even though the initial line of storms moved out fast. Damaging straight-line winds continued and were associated with the rear inflow jet. Maximum wind speeds were reported up to 80 mph  These estimates were determined based off damage surveys and photos submitted through social media. These strong winds damaged many trees, crops, and a few structures in their path.

Thunderstorm Wind in CARROLL, ILLINOIS
From 10-AUG-20 12:45:00 to 10-AUG-20 13:50:00 (CST-6)
Location: SAVANNA
Magnitude: 70.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Widespread straight-line winds that produced extensive damage were reported throughout Carroll County, associated with a derecho. These winds lasted around an hour in total in any one location, even though the initial line of storms moved out fast. Damaging straight-line winds continued and were associated with the rear inflow jet. Maximum wind speeds were reported up to 80 mph  These estimates were determined based off damage surveys and photos submitted through social media. These strong winds damaged many trees, crops, and a few structures in their path.

Thunderstorm Wind in JO DAVIESS, ILLINOIS
From 10-AUG-20 12:50:00 to 10-AUG-20 13:30:00 (CST-6)
Location: WHITTON
Magnitude: 70.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Widespread straight-line winds that produced extensive damage were reported throughout Jo Daviess County, associated with a derecho. These winds lasted around an hour in total in any one location, even though the initial line of storms moved out quickly. Damaging straight-line winds continued and were associated with the rear inflow jet. Maximum wind speeds were reported up to 80 mph  These estimates were determined based off damage surveys and photos submitted through social media. These strong winds damaged many trees, crops, and a few structures in their path.

Thunderstorm Wind in STEPHENSON, ILLINOIS
From 10-AUG-20 13:05:00 to 10-AUG-20 13:55:00 (CST-6)
Location: LORAN
Magnitude: 70.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Widespread straight-line winds that produced extensive damage were reported throughout Stephenson County, associated with a derecho. These winds lasted around an hour in total in any one location, even though the initial line of storms moved out quickly. Damaging straight-line winds continued and were associated with the rear inflow jet. Maximum wind speeds were reported up to 80 mph  These estimates were determined based off damage surveys and photos submitted through social media. These strong winds damaged many trees, crops, and a few structures in their path.

Thunderstorm Wind in BUREAU, ILLINOIS
From 10-AUG-20 13:00:00 to 10-AUG-20 14:20:00 (CST-6)
Location: MINERAL
Magnitude: 87.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Widespread straight-line winds that produced extensive damage were reported throughout Bureau County, associated with a derecho. These winds lasted around an hour in total, even though the initial line of storms moved out fast. Damaging straight-line winds continued and were associated with the rear inflow jet. Maximum wind speeds were reported up to 100 mph  These estimates were determined based off damage surveys and photos submitted through social media. These strong winds damaged many trees, crops, and a few structures in their path. A large radio tower was destroyed near Princeton, Illinois.

Thunderstorm Wind in PUTNAM, ILLINOIS
From 10-AUG-20 13:25:00 to 10-AUG-20 14:20:00 (CST-6)
Location: GOOSE LAKE
Magnitude: 70.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Widespread straight-line winds that produced extensive damage were reported throughout Putnam County, associated with a derecho. These winds lasted around an hour in total, even though the initial line of storms moved out fast. Damaging straight-line winds continued and were associated with the rear inflow jet. Maximum wind speeds were reported up to 80 mph  These estimates were determined based off damage surveys and photos submitted through social media. These strong winds damaged many trees, crops, and a few structures in their path.

Hail in STEPHENSON, ILLINOIS
From 10-AUG-20 12:35:00 to 10-AUG-20 12:35:00 (CST-6)
Location: FREEPORT
Magnitude: 2.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Reported in Freeport from a separate supercell before the derecho straight-line wind damage occurred.

Thunderstorm Wind in WARREN, ILLINOIS
From 10-AUG-20 12:40:00 to 10-AUG-20 12:50:00 (CST-6)
Location: LITTLE YORK
Magnitude: 65.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

A few trees were blown down in Little York, as well as a few power lines.

Thunderstorm Wind in WARREN, ILLINOIS
From 10-AUG-20 12:50:00 to 10-AUG-20 13:00:00 (CST-6)
Location: MONMOUTH
Magnitude: 65.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Several trees and a few power lines were blown down in Monmouth.