Tornadoes · United States · Wisconsin · 2021

EF0 tornado, Tiffany to Clinton, Wisconsin, August 9, 2021

From Tiffany to Clinton, this EF0 tornado ran 3.2 miles across Rock County on August 9, 2021, touching down at 2:52 PM CDT and reaching 25 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 mphthis tornado

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

  2. EF186 to 110 mph

    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
EF0
Date
August 9, 2021
Touchdown
2:52 PM CDT (19:52 UTC)
Lifted
3:06 PM CDT (20:06 UTC)
On the ground
14 minutes
Path length
3.2 miles (5.2 km)
Path width
25 yards (23 m)
Deaths
0
Injuries
0
County
Rock County
Touchdown point
42.558, -88.909
Lift-off point
42.587, -88.859
Record number
2108091352-01

What the Weather Service recorded

A round of thunderstorms develop along a weak front that was moving through the region and produced a tornado in Rock County.

Brief tornado spotted by Clinton Fire Department and a storm chaser. Tornado started west of Clinton, crossed I-43 and ended by Hwy 140 north of Clinton. Minor tree damage was noted along with some crop markings.

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

The warnings

No tornado warning for this county appears in the archive as in force at the moment the tornado touched down. One was issued for the county at another hour that day.

Issued (UTC)ExpiredProductOffice
20:08 UTC20:32 UTCTornado WarningMKX

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 Marginal Risk. The outlook in force was issued at 16:27 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

7.9 hours before the tornado, 170 km from the path. August 9, 2021.

Skew-T log-pSkew-T log-p diagram, Davenport, at 12:00Z on 2021-08-09Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 1676 joules per kilogram, CIN -63, lifted condensation level 705 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, Davenport, at 12:00Z on 2021-08-09The 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 171 square meters per square second, 0 to 6 km bulk shear 43 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
1676 J/kg
Mixed-layer CIN
-63 J/kg
Surface CAPE
296 J/kg
Mixed-layer LCL
705 m above ground
0-6 km bulk shear
43 kt
0-1 km bulk shear
24 kt
0-1 km storm-relative helicity
171 m²/s²
0-3 km storm-relative helicity
208 m²/s²
Significant tornado parameter
0.3
Supercell composite
2.7
0-3 km lapse rate
4.7 K/km

Open this sounding in Storm Lab

Davenport, (KDVN), 00:00Z

4.1 hours after it, 170 km from the path. August 10, 2021.

Skew-T log-pSkew-T log-p diagram, Davenport, at 00:00Z on 2021-08-10Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 2409 joules per kilogram, CIN -17, lifted condensation level 1156 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, Davenport, at 00:00Z on 2021-08-10The 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 49 square meters per square second, 0 to 6 km bulk shear 16 knots.1939Sfc1 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
2409 J/kg
Mixed-layer CIN
-17 J/kg
Surface CAPE
3368 J/kg
Mixed-layer LCL
1156 m above ground
0-6 km bulk shear
16 kt
0-1 km bulk shear
18 kt
0-1 km storm-relative helicity
49 m²/s²
0-3 km storm-relative helicity
165 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
6.5 K/km

Open this sounding in Storm Lab

The surface observations

Janesville/Rock (JVL), 14 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
18:45 UTC73.473.4170° 9 kt151008.8+RA
19:45 UTC73.473.4240° 10 kt211008.5-RA
20:45 UTC75.275.2190° 5 kt1008.1
21:45 UTC80.680.60° 0 kt1008.5

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

The radar

The Milwaukee radar (KMKX), 52 km away, was scanning. The volume nearest the touchdown began at 19:54 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)ReportWhereCountyRemark
19:55 UTCFUNNEL CLOUDClintonRock, WIPUBLIC REPORTS OF A FUNNEL CLOUD WEST OF CLINTON RELAYED THROUGH THE ROCK COUNTY SHERIFFS OFFICE. STORM CHASER ALSO REPORTED A ROTATING WALL CLOUD 4 MILES WEST OF CLINTON AROUND 2:50 PM.
19:58 UTCTORNADO1 N ClintonRock, WIMULTIPLE PUBLIC REPORTS OF A TORNADO WITH INTERMITTENT TOUCH DOWNS JUST NORTH OF I-43 ALONG WI WHY 140.
20:02 UTCTORNADO3 Se AvalonRock, WIFIRE DEPT REPORTS A TOUCH DOWN NEAR THE INTERSECTION OF SOUTH CARVER ROCK ROAD AND EAST CREEK ROAD.

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

This ground now

The live radar over the trackEvery 2021 tornado in WisconsinEvery tornado in Wisconsin since 1950Warnings in force in Wisconsin nowThe forecast where you are

The other tornadoes of August 9, 2021

19 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
August 94:35 PM CDTEF0DeKalb, IL0.120
August 94:44 PM CDTEF1DeKalb, IL1.880
August 94:45 PM CDTEF1McHenry, IL0.470
August 95:24 PM CDTEF1Kane, IL3.8100
August 95:28 PM CDTEF0DeKalb, IL6.850
August 96:03 PM CDTUnratedLee, IL1.375
August 96:13 PM CDTEF1DeKalb, IL1.5150
August 96:13 PM CDTUnratedBureau, IL0.05
August 96:26 PM CDTEF0DeKalb, IL0.220
August 96:28 PM CDTEF0Kane, IL3.9400
August 96:38 PM CDTUnratedKane, IL0.110
August 96:57 PM CDTEF1Bureau, IL3.0525
August 97:16 PM CDTEF1Towner, ND5.0200$2,000
August 97:24 PM CDTUnratedBureau, IL1.1100
August 98:34 PM CDTEF0Griggs, ND0.350
August 99:20 PM CDTEF2Steele, ND2.9300$150,000
August 99:42 PM CDTEF1Grand Forks, ND1.1150$1,000
August 910:55 PM CDTEF1Polk, MN3.6200$120,000
August 911:05 PM CDTEF0Polk, MN2.2150$5,000

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.