EF1 tornado, Yorkville to Crystal Lawns, Illinois, August 10, 2020

1. EF065 to 85 mph

   Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.

2. EF186 to 110 mphthis tornado

   Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

3. EF2111 to 135 mph

   Considerable damage. Roofs torn off well-built houses, frame homes shifted on their foundations, mobile homes destroyed, large trees snapped or uprooted, cars lifted off the ground.

4. EF3136 to 165 mph

   Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.

5. EF4166 to 200 mph

   Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

6. EF5over 200 mph

   Incredible damage. Strong frame houses swept off their foundations, car-sized missiles thrown more than 100 meters, steel-reinforced concrete badly damaged, high-rise buildings deformed.

7. Unrated

   The survey recorded a tornado but could not put a number on it, most often because it crossed open country and damaged nothing a rating can be read from.

Rating

EF1

Date

August 10, 2020

Touchdown

3:15 PM CDT (20:15 UTC)

Lifted

3:30 PM CDT (20:30 UTC)

On the ground

15 minutes

Path length

14.4 miles (23.3 km)

Path width

250 yards (229 m)

Deaths

0

Injuries

0

Counties

Kendall and Will counties

Touchdown point

41.621, -88.455

Lift-off point

41.566, -88.186

Record number

2008101415-01

23 damage points were recorded along this path by NWS LOT, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF1. The highest wind the damage implies is 110 mph.

• Outbuilding destroyed and deposited 800 feet away from original location.
• Six power poles snapped near their base
• "7 large utility poles snapped 10’ up that were new, with at least one made of redwood, 3 miles north of Somonauk on Somonauk Road just south of Chicago Road. Here, straight line winds estimated at around 90 MPH were found in a swath that was about 500’ wide on Somonauk Road. No damage path was noted leading up to, or past, the poles." From Gilert Sebenste Survey.
• Large portion of the brick wall at Hill-Top Drive In was toppled. No known damage indicator. Debris fell in place or was pushed from south to north onto a parked truck. https://www.theherald-news.com/lists/2020/08/11/e6317db80d3f4686a433c273187c5ab1/index.xml?page=1

Survey points are preliminary and are the raw material the published rating was built from. Source: NWS Damage Assessment Toolkit.

During the late morning through the afternoon of Monday August 10th, a line of intense thunderstorms known as a derecho brought widespread severe wind damage across Iowa, northern Illinois and northern Indiana.||In north central and northeast Illinois alone, the severe winds of 60 to 100 mph downed or damaged tens of thousands of trees, as well as caused severe damage to homes, businesses, and infrastructure. There were 10 injuries reported in north central and northeast Illinois within the NWS Chicago/Romeoville County Warning Area (CWA). Local officials estimated that nearly one million customers lost power across northern Illinois at the height of the derecho and some people were without power for several days. Damage was estimated to be in the hundreds of millions of dollars in north central and northeast Illinois, with several billions of dollars in damages across the entire Corn Belt region including significant damage to crops and agriculture infrastructure. While much of the damage was due to straight line winds, there were also 14 tornadoes documented in north central and northeast Illinois.||The combination of high moisture, explosive instability and very strong atmospheric wind flow for mid-summer had developed quickly over the Corn Belt region on the morning of August 10th. This resulted in a progressive, well-organized complex of storms for hundreds of miles and at times traveling nearly 70 mph. After bringing extensive damage from extreme wind speeds in Iowa that morning, the damage transitioned across northern Illinois from widespread wind damage to narrow, brief and intense swaths associated with compact circulations within the thunderstorm line, some of which were associated with tornadoes.

A tornado with peak winds of 105 mph touched down near Walsh Drive, just north of Route 71. A pergola was destroyed, siding was ripped off a house and parts of a fence and a tree were thrown over a road. Eyewitness accounts indicated the debris was lifted and twirled. The tornado continued moving east southeast producing damage to trees along Route 126. The most significant damage was found east of Schlapp Road along Wheeler Road where trees were mangled, a farm building was destroyed with debris deposited in a nearby field and a large grain bin was bent inward. Wood panels were thrown into the ground leaving scour marks in the grass. Six utility poles were snapped along Ridge Road and a 1000-1500 pound auger was moved about 50 feet. This is where the tornado likely reached peak intensity. The tornado continued southeast crossing into Will County just south of Renwick Road.

A tornado touched down in central Kendall County and moved southeast crossing into Will County just south of Renwick Road. Tree damage occurred along the path in Will County including a tree blown down near Caton Farm and Drauden Road. Minor roof damage occurred with some shingles blown off and some fences were blown down. One house lost half of the shingles on its roof with vents torn off, just east of Route 59. The tornado lifted near Caton Farm Road, just west of Interstate 55.

From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.

4 minutes of warning. NWS LOT issued a tornado warning for this county at 20:11 UTC, 4 minutes before the tornado touched down, in force until 20:45 UTC.

The county was under a severe thunderstorm watch, issued at 16:28 UTC and running to 21:25 UTC.

Every warning and watch covering the touchdown point that day, from the Iowa Environmental Mesonet's archive of National Weather Service products. Lead time is measured from the issue of the warning in force to the touchdown time in the database, both of which were recorded to the minute by different people.

The Storm Prediction Center had this point in a Moderate Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 19:38 UTC.

SPC's Day 1 convective outlook as it stood when the tornado began, read at the touchdown point. The same archive is on the radar archive.

The radiosonde launches on either side of the tornado, from the nearest station that was launching then, drawn and analyzed the way Storm Lab does: the same diagram, the same parcel and shear definitions SPC's mesoanalysis uses.

The Chicago radar (KLOT), 20 km away, was scanning. The volume nearest the touchdown began at 20:15 UTC.

Open the radar archive at this moment, over the track

Reflectivity and velocity, decoded from the Level II archive in the browser. Volumes take a few seconds to open the first time.

Local storm reports within 60 km of the path, in the three hours either side.

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

The live radar over the trackEvery 2020 tornado in IllinoisEvery tornado in Illinois since 1950Warnings in force in Illinois nowThe forecast where you are

26 more were confirmed in the United States that day.

Ratings are the survey's, read off the damage rather than measured; the rating scale is above. Tornado counts rise through the record as reporting improved, so a year in the 1950s is not comparable with one today except for the strongest tornadoes, which were always noticed.

NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.