Tornadoes · United States · Illinois · 2020

EF1 tornado, LaSalle County, Illinois, August 10, 2020

This EF1 tornado ran 0.9 miles across LaSalle County on August 10, 2020, touching down at 2:59 PM CDT and reaching 150 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.

  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.

The record

Rating
EF1
Date
August 10, 2020
Touchdown
2:59 PM CDT (19:59 UTC)
Lifted
3:00 PM CDT (20:00 UTC)
On the ground
1 minutes
Path length
0.9 miles (1.4 km)
Path width
150 yards (137 m)
Deaths
0
Injuries
0
County
LaSalle County
Touchdown point
41.353, -88.845
Lift-off point
41.352, -88.828
Record number
2008101359-01

The damage survey

10 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.

  • Loss of siding and a large portion of the roof at a retail business. Siding damage most severe on north facing side. From Gilbert Sebenste survey.
  • Large tree branches broken/snapped near the top. From Gilbert Sebenste survey.
  • Damage to roof and some siding of a retail business. From Gilbert Sebenste survey.
  • Damaged utility pole. From Gilbert Sebenste survey.

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

The forecast that day

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 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.

Lincoln, IL (KILX), 12:00Z

8.0 hours before the tornado, 135 km from the path. August 10, 2020.

Skew-T log-pSkew-T log-p diagram, Lincoln, IL at 12:00Z on 2020-08-10Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 1597 joules per kilogram, CIN -128, lifted condensation level 1046 meters above ground. Wind barbs in knots down the right edge.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
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.
HodographHodograph, Lincoln, IL at 12:00Z on 2020-08-10The wind through the lowest 10 kilometers as a curve, rings every 10 meters per second labeled in knots. Zero to 1 km storm-relative helicity 167 square meters per square second, 0 to 6 km bulk shear 21 knots.193958Sfc1 km3 km6 km9 kmRMLM
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
1597 J/kg
Mixed-layer CIN
-128 J/kg
Surface CAPE
962 J/kg
Mixed-layer LCL
1046 m above ground
0-6 km bulk shear
21 kt
0-1 km bulk shear
22 kt
0-1 km storm-relative helicity
167 m²/s²
0-3 km storm-relative helicity
241 m²/s²
Significant tornado parameter
0.0
Supercell composite
1.6
0-3 km lapse rate
3.8 K/km

Open this sounding in Storm Lab

The surface observations

Peru (VYS), 26 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
00:00 UTC

From the Iowa Environmental Mesonet's archive of airport observations.

The radar

The Chicago radar (KLOT), 69 km away, was scanning. The volume nearest the touchdown began at 19:59 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.

This ground now

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

The other tornadoes of August 10, 2020

26 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
August 1011:30 AM CDTUnratedMarshall, IA1.050
August 1011:36 AM CDTUnratedMarshall, IA0.450
August 1011:39 AM CDTEF1Marshall, IA2.9100$20,000
August 1012:01 PM CDTUnratedTama, IA1.540
August 1012:31 PM CDTUnratedLinn, IA0.940
August 1012:32 PM CDTEF0Grant, WI0.650$15,000
August 102:12 PM CDTEF0Stephenson, IL4.650
August 102:37 PM CDTEF0Winnebago, IL1.650
August 102:47 PM CDTEF1Winnebago, IL9.2300
August 102:50 PM CDTEF0DeKalb, IL6.340
August 103:05 PM CDTEF1McHenry, IL5.7200
August 103:12 PM CDTEF1Kane, IL1.240
August 103:15 PM CDTEF1Kendall, IL14.4250
August 103:35 PM CDTEF1DuPage, IL0.4100
August 103:38 PM CDTEF0Walworth, WI3.350$12,000
August 103:39 PM CDTEF1DuPage, IL2.1200
August 103:41 PM CDTEF1Lake, IL to WI6.3150$250,000
August 103:54 PM CDTEF1Cook, IL4.8300
August 103:57 PM CDTEF0Cook, IL2.0350
August 103:59 PM CDTEF1Cook, IL3.2300
August 104:04 PM CDTEF0Kankakee, IL1.5150
August 105:05 PM EDTEF1Washington, NY1.5100$75,000
August 104:15 PM CDTEF0Newton, IN0.940
August 106:32 PM EDTEF1Saint Joseph, IN2.4100
August 106:55 PM EDTEF1Kosciusko, IN3.1100
August 107:43 PM EDTEF0Kosciusko, IN0.250

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.