Tornadoes · United States · Illinois · 2021

Unrated tornado, DeKalb County, Illinois, August 10, 2021

Name: Unrated tornado, DeKalb County, Illinois, August 10, 2021
Start: 2021-08-10T23:33:00.000Z
End: 2021-08-10T23:34:00.000Z
Location: DeKalb County, Illinois

This Unrated tornado ran 0.6 miles across DeKalb County on August 10, 2021, touching down at 6:33 PM CDT and reaching 20 yards wide. It killed nobody.

The rating scale

Tracks are drawn in the color of the rating. The Enhanced Fujita scale rates the damage rather than measuring the wind: the speeds are what that damage is taken to imply.

EF065 to 85 mph
Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.
EF186 to 110 mph
Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.
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.
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.
EF4166 to 200 mph
Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.
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.
Unratedthis tornado
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.

The record

Rating: Unrated
Date: August 10, 2021
Touchdown: 6:33 PM CDT (23:33 UTC)
Lifted: 6:34 PM CDT (23:34 UTC)
On the ground: 1 minutes
Path length: 0.6 miles (1.0 km)
Path width: 20 yards (18 m)
Deaths: 0
Injuries: 0
County: DeKalb County
Touchdown point: 42.039, -88.933
Lift-off point: 42.041, -88.922
Record number: 2108101733-01

The damage survey

1 damage points were recorded along this path by NWS LOT, in the Damage Assessment Toolkit the survey teams carry.

Chaser video shows the tornado crossing Route 64

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

The warnings

No tornado warning for this county appears in the archive as in force at the moment the tornado touched down.

The county was under a severe thunderstorm watch, issued at 20:47 UTC and running to 00:57 UTC.

Issued (UTC)	Expired	Product	Office
17:00 UTC	00:00 UTC	Heat Advisory	LOT
20:47 UTC	00:57 UTC	Severe Thunderstorm Watch	LOT
23:10 UTC	00:15 UTC	Severe Thunderstorm Warning	LOT
23:16 UTC	00:30 UTC	Severe Thunderstorm Warning	LOT
00:13 UTC	01:00 UTC	Severe Thunderstorm Warning	LOT

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 forecast that day

The Storm Prediction Center had this point in a Enhanced Risk, with a 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 19:54 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 air that afternoon

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.

Davenport, (KDVN), 12:00Z

11.6 hours before the tornado, 138 km from the path. August 10, 2021.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed. The warm shading is its CAPE, the cool shading the inhibition it has to break through.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km. RM and LM are the right and left moving storms Bunkers' method gives; the shaded area is the 0 to 1 km storm-relative helicity.

Mixed-layer CAPE: 3755 J/kg
Mixed-layer CIN: -67 J/kg
Surface CAPE: 1646 J/kg
Mixed-layer LCL: 819 m above ground
0-6 km bulk shear: 12 kt
0-1 km bulk shear: 16 kt
0-1 km storm-relative helicity: -37 m²/s²
0-3 km storm-relative helicity: 4 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0
0-3 km lapse rate: 4.3 K/km

Open this sounding in Storm Lab

Davenport, (KDVN), 00:00Z

0.4 hours after it, 138 km from the path. August 11, 2021.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed. The warm shading is its CAPE, the cool shading the inhibition it has to break through.

Hodograph

Mixed-layer CAPE: 856 J/kg
Mixed-layer CIN: -155 J/kg
Surface CAPE: 324 J/kg
Mixed-layer LCL: 940 m above ground
0-6 km bulk shear: 42 kt
0-1 km bulk shear: 28 kt
0-1 km storm-relative helicity: 77 m²/s²
0-3 km storm-relative helicity: 160 m²/s²
Significant tornado parameter: -0.0
Supercell composite: -1.4
0-3 km lapse rate: 5.1 K/km

Open this sounding in Storm Lab

The radar

The Chicago radar (KLOT), 85 km away, was scanning. The volume nearest the touchdown began at 23:33 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.

What was reported nearby

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

Time (UTC)	Report	Where	County	Remark
22:46 UTC	TSTM WND DMG	1 N Rockford	Winnebago, IL	TREE DOWNED ON POWERLINES ALONG AUBURN STREET NEAR RIDGE AVENUE. TIME ESTIMATED BY RADAR.
22:50 UTC	TSTM WND DMG	2 E Rockford	Winnebago, IL	POWER LINES DOWNED ON STATE STREET NEAR PALM AVENUE. TIME ESTIMATED BY RADAR.
22:55 UTC	TSTM WND DMG	3 Ese Loves Park	Winnebago, IL	8-IN DIAMETER TREE DOWN ALONG SPRING BROOK ROAD WEST OF MULFORD ROAD. TIME ESTIMATED BY RADAR.
23:00 UTC	TSTM WND DMG	Roscoe	Winnebago, IL	LARGE TREE UPROOTED IN ROSCOE AREA. TIME ESTIMATED BY RADAR.
23:05 UTC	TSTM WND DMG	Leaf River	Ogle, IL	MULTIPLE TREES DOWNED IN LEAF RIVER, INCLUDING SOME LARGE BRANCHES. TIME ESTIMATED BY RADAR.
23:12 UTC	TSTM WND DMG	Pecatonica	Winnebago, IL	POWER LINES DOWNED IN THE VICINITY OF PECATONICA. TIME ESTIMATED BY RADAR.
23:15 UTC	TSTM WND DMG	Rockton	Winnebago, IL	PHOTO SHARED VIA SOCIAL MEDIA SHOWS LARGE BRANCH DOWNED IN ROCKTON AREA.
23:25 UTC	TSTM WND GST 58	1 Nnw Rochelle	Ogle, IL	PRIVATE WEATHER STATION REPORTED 58 MPH GUST IN NORTHWEST ROCHELLE.
23:29 UTC	TSTM WND DMG	1 N New Milford	Winnebago, IL	TREES DOWN IN CHEROKEE HILLS NEIGHBORHOOD OF NEW MILFORD. TIME ESTIMATED BY RADAR.
23:33 UTC	TSTM WND DMG	2 Ne Fairdale	De Kalb, IL	DAMAGE TO AGRICULTURE AND SOME TREES IN THE VICINITY OF KIRKLAND. GENERAL AREA WAS IN FAR NORTHWEST DEKALB COUNTY NORTH OF QUARRY ROAD AND SOUTHWEST OF CHERRY VALLEY ROAD. TIME ESTIMATED BY RADAR.
23:34 UTC	TSTM WND GST 55	Rockford Airport	Winnebago, IL	RECORDED AT THE ROCKFORD ASOS.
23:35 UTC	TSTM WND GST 56	2 Ssw Rochelle	Ogle, IL	RECORDED AT THE ROCHELLE AWOS.
23:38 UTC	TSTM WND DMG	2 Ne Lake In The Hills	Mchenry, IL	BILLBOARD DESTROYED ALONG VIRGINIA AVE IN CRYSTAL LAKE.
23:38 UTC	TSTM WND DMG	2 Ne Lake In The Hills	Mchenry, IL	MULTIPLE TREES AND POWER LINES DOWNED IN THE CRYSTAL LAKE, ALGONQUIN, CARY, AND MCHENRY AREAS. TIME ESTIMATED BY RADAR.
23:39 UTC	TSTM WND DMG	1 E Crystal Lake	Mchenry, IL	NUMEROUS TREES AND TREE LIMBS DOWNED NEAR PINGREE ROAD AND US31 IN CRYSTAL LAKE. TIME ESTIMATED BY RADAR.
23:44 UTC	TSTM WND DMG	Sandwich	De Kalb, IL	TREE DOWNED ON POWER LINES NEAR LISBON STREET AND GREEN STREET IN SANDWICH. TIME ESTIMATED BY RADAR.
23:45 UTC	TSTM WND GST 45	1 Wsw Oakwood Hills	Mchenry, IL
23:48 UTC	TSTM WND DMG	2 Ese Timberlane	Boone, IL	APPROXIMATELY 2 FOOT DIAMETER TREE SNAPPED AT BASE.
23:50 UTC	TSTM WND GST 57	5 Ene Herbert	Mchenry, IL	PRIVATE WEATHER STATION REPORTED 57 MPH WIND GUST SOUTHWEST OF MARENGO NEAR HARMONY ROAD AND GENOA ROAD.
23:50 UTC	TSTM WND GST 60	4 Nw Harvard	Mchenry, IL	PRIVATE WEATHER STATION REPORTED 60 MPH GUST NORTHWEST OF HARVARD NEAR LAWRENCE ROAD AND MAXON ROAD.
23:50 UTC	HAIL 0.88	2 N Belvidere	Boone, IL	RELAYED VIA WINNEBAGO EMA.
23:52 UTC	TSTM WND DMG	Marengo	Mchenry, IL	BRANCH DOWNED IN MARENGO AREA. REPORT RELAYED VIA MPING. TIME ESTIMATED BY RADAR.
23:53 UTC	TSTM WND GST 58	2 Wnw Sugar Grove	Kane, IL	RECORDED AT THE AURORA-SUGAR GROVE ASOS.
23:55 UTC	TSTM WND GST 57	2 Ne Union	Mchenry, IL	GUST OF 57 MPH NEAR FRANKLINVILLE ROAD AND IL-176. TIME ESTIMATED BY RADAR.
00:00 UTC	TSTM WND GST 67	3 Sse Harvard	Mchenry, IL	MEASURED WITH ANEMOMETER. LARGE TREES UPROOTED.
00:03 UTC	TSTM WND DMG	2 N Bull Valley	Mchenry, IL	PUBLIC REPORT OF TREE BRANCHES DOWNED NEAR BULL VALLEY. RELAYED VIA MPING. TIME ESTIMATED BY RADAR.
00:05 UTC	TSTM WND DMG	Greenwood	Mchenry, IL	NUMEROUS TREES DOWNED NEAR WONDER LAKE. ONE TREE HAS MOST BRANCHED REMOVED. TIME ESTIMATED BY RADAR.
00:11 UTC	TSTM WND DMG	Elgin	Kane, IL	NUMEROUS REPORTS OF TREE BRANCHES DOWNED IN ELGIN AND VICINITY. RELAYED VIA MPING. TIME ESTIMATED BY RADAR.
00:11 UTC	TSTM WND DMG	Sleepy Hollow	Kane, IL	DELAYED REPORT. RELAYED VIA SOCIAL MEDIA. LARGE TREE LIMBS BLOWN DOWN AND LARGE TREE BLOWN DOWN OR UPROOTED NEAR BEAU BRUMMEL DR AND SLEEPY HOLLOW RD.
00:12 UTC	TSTM WND DMG	West Dundee	Kane, IL	DELAYED REPORT RELAYED VIA SOCIAL MEDIA. MULTIPLE LARGE TREES AND TREE LIMBS BLOWN DOWN THROUGHOUT TOWN. TIME ESTIMATED BY RADAR.
00:15 UTC	TSTM WND DMG	Algonquin	Mchenry, IL	PUBLIC REPORT OF AN UPROOTED AND ANOTHER SNAPPED TREE IN ALGONQUIN. TIME ESTIMATED BY RADAR.
00:30 UTC	TSTM WND GST 55	3 Wsw Montgomery	Kendall, IL	PRIVATE WEATHER STATION REPORTED 55 MPH WIND GUST NEAR MONTGOMERY. TIME ESTIMATED BY RADAR.

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

This ground now

The live radar over the track Every 2021 tornado in Illinois Every tornado in Illinois since 1950 Warnings in force in Illinois now The forecast where you are

The other tornadoes of August 10, 2021

3 more were confirmed in the United States that day.

Date	Time	Rating	Where	Path (mi)	Width (yd)	Damage
August 10	4:43 PM CDT	EF0	Hodgeman, KS	0.2	50
August 10	5:50 PM EDT	EF0	Pasco, FL	0.1	25	$10,000
August 10	5:58 PM CDT	EF1	Outagamie, WI	2.0	40

What this means

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.

Sources

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