EF1 tornado, Colby to Poniatowski, Wisconsin, May 21, 2024

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

May 21, 2024

Touchdown

7:47 PM CDT (00:47 UTC)

Lifted

7:50 PM CDT (00:50 UTC)

On the ground

3 minutes

Path length

2.1 miles (3.4 km)

Path width

60 yards (55 m)

Deaths

0

Injuries

0

County

Marathon County

Touchdown point

44.862, -90.046

Lift-off point

44.885, -90.018

Record number

2405211847-01

53 damage points were recorded along this path by NWS ARX and NWS GRB, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF1. The highest wind the damage implies is 107 mph.

• Barn not anchored or fastened
• Major loss of roofing on barn

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

A line of thunderstorms developed ahead of a cold front during the early evening on Tuesday (5/21) and tracked through much of northeast Wisconsin through the rest of the evening. Straight line winds produced wind damage along with 5 tornadoes.

A tornado developed just southwest of the Village of Unity in Clark County (NWS La Crosse warning area) at 7:34 pm CDT. The tornado produced damage in the western portion of Unity before crossing Highway 13 into western Marathon County at 7:35 pm CDT while producing additional damage in the northeast side of Unity including damage to an outbuilding along County Highway P. The tornado continued to produce scattered tree damage as it tracked northeast across Chokecherry Road and Juneberry Road. The tornado lifted near Mulberry Road at 7:41 pm CDT with straight line winds continuing northeast to County Road N just southeast of Colby. Total path length is estimated to be 4.07 miles long, with a width of 110 yards. Peak wind estimated to be around 105 mph.

A tornado formed at 7:47 pm CDT west of Fenwood in western Marathon County and continued northeast before dissipating at 7:50 pm CDT. Total path length is estimated to be 2.11 miles long, with a width of 60 yards. Peak wind estimated to be around 87 mph.

A tornado formed at 7:51 pm CDT northwest of Edgar in western Marathon County and continued northeast before dissipating at 7:54 pm CDT between the village of Athens and the town of Rib Falls. Total path length is estimated to be 2.13 miles long, with a width of 80 yards. Peak wind estimated to be around 92 mph.

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

5 minutes of warning. NWS GRB issued a tornado warning for this county at 00:42 UTC, 5 minutes before the tornado touched down, in force until 01:15 UTC.

The county was under a tornado watch, issued at 23:43 UTC and running to 02:05 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 Enhanced Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 19:57 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.

Marshfield (MFI), 29 km from the path, in the two hours either side.

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

The La Crosse radar (KARX), 149 km away, was scanning. The volume nearest the touchdown began at 00:48 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 2024 tornado in WisconsinEvery tornado in Wisconsin since 1950Warnings in force in Wisconsin nowThe forecast where you are

42 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.