EF1 tornado, Rckfrd Cottonwood Ar to Caledonia, 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

2:47 PM CDT (19:47 UTC)

Lifted

3:05 PM CDT (20:05 UTC)

On the ground

18 minutes

Path length

9.2 miles (14.8 km)

Path width

300 yards (274 m)

Deaths

0

Injuries

0

Counties

Winnebago and Boone counties

Touchdown point

42.281, -89.022

Lift-off point

42.369, -88.889

Record number

2008101347-01

22 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 99 mph.

• Tornado Crossed Spring Brook, shingles off nearby apartments to NE. Extensive tree damage, large trees.
• Tree damage at Trainer and Burlwood, no shingle or home damage seen
• some shingles removed, extensive tree damage
• shingles and some siding missing.

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 brief tornado with peak winds of 75 mph touched down near the intersection of Pierpont Avenue and Montague Road and continued northeast into the southwest side of Rockford. The tornado ended near the intersection of Ferguson and Loomis Streets. All of the damage was to trees along the tornado path.

A tornado with peak winds of 100 mph touched down near Guilford Road, east of Alpine Road and traveled approximately 6 miles northeast to Argyle Road where it crossed into Boone County. Numerous trees, power lines, utility poles and fences were blown down from where the tornado touched down through the Mulford Road and Springbrook Road area. Significant tree damage occurred in a localized area near Rock Valley College. Just northeast of Perryville Road, some utility poles were broken along with extensive tree damage and minor roof and siding damage occurred to some homes. Part of the roof was blown off of a Farm and Fleet building along East Riverside Boulevard, just west of Interstate 90. A home suffered siding and roof damage and metal wall panels were blown off a building, both along Paulson Road.

A tornado touched down in southeast Winnebago County and moved northeast crossing into Boone County along Argyle Road. This tornado produced mainly tree damage in Boone County including tree limbs blown down in Caledonia. The tornado ended on the east side of Caledonia, south of Route 173.

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 19:43 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 15:57 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 Milwaukee radar (KMKX), 79 km away, was scanning. The volume nearest the touchdown began at 19:46 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.