EF2 tornado, Argonne to Armstrong Creek, Wisconsin, April 10, 2011

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 mph

   Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

3. EF2111 to 135 mphthis tornado

   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

EF2

Date

April 10, 2011

Touchdown

7:30 PM CDT (00:30 UTC)

Lifted

7:51 PM CDT (00:51 UTC)

On the ground

21 minutes

Path length

12.0 miles (19.3 km)

Path width

600 yards (549 m)

Deaths

0

Injuries

0

Property damage

$215,000

Counties

Forest and Florence counties

Touchdown point

45.639, -88.823

Lift-off point

45.750, -88.634

Record number

1104101830-01

16 damage points were recorded along this path by NWS MQT, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF2. The highest wind the damage implies is 115 mph.

• Start of Tornado Track. Trees snapped and uprooted.
• Two garages destroyed. RV rolled and destroyed. House only minor damage to roof and soffits. Large trees snapped and thrown 75 yards. Convergent pattern tin tree damage. Path width -- approx 350 yds.
• Part of roof was removed. All exterior walls standing. Chimney intact.
• Single wide mobile home overturned into trees. Several out buildings also destroyed.

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

Thunderstorms developed along and ahead of a cold front as it encountered moist and unstable air across Wisconsin.||A record number of tornadoes for April struck Wisconsin on April 10. Fifteen twisters affected the state as a strong spring storm moved across the western Great Lakes. In the National Weather Service Green Bay service area of northeast Wisconsin, ten tornadoes were reported, a record single-day outbreak for any month of the year.||In addition to the tornadoes, the lines of thunderstorms that developed produced plenty of straight line wind damage and large hail. Wind gusts, some estimated in the 80 mph to 100 mph range, downed numerous trees, damaged a small building, caused an injury and damage to two homes, toppled an 80-foot tall radio tower, threw a carport two houses away, and caused major damage to two industrial buildings. The largest hail reported was baseball size near Winneconne in Winnebago County.

A tornado developed about 3.5 miles southeast of Argonne and moved northeast into Florence County. The storm uprooted and snapped hundreds of trees, some of which fell on vacation cabins along the storm's path. The hardest hit area was several miles east of Argonne shortly after the tornado developed. A large part of the roof of a house was removed (DI 2, DOD 6). The tornado continued northeast into Florence County at 7:46 pm CDT (1846 CST). The average width of the tornado was 250 yards.

A second tornado formed in Forest County about four miles west of Armstrong Creek at 8:03 pm CDT (1903 CST). The tornado snapped and uprooted trees and damaged two houses. One of the houses sustained significant roof damage (DI 2, DOD 4) as the tornado moved across the area. The average width was 125 yards.

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

15 minutes of warning. NWS GRB issued a tornado warning for this county at 00:15 UTC, 15 minutes before the tornado touched down, in force until 00:45 UTC.

The county was under a tornado watch, issued at 20:21 UTC and running to 02:08 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 0.15 chance of a tornado within 25 miles, in the hatched area where significant tornadoes were expected. 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 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 Marquette radar (KMQT), 130 km away, was scanning. The volume nearest the touchdown began at 00:29 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 2011 tornado in WisconsinEvery tornado in Wisconsin since 1950Warnings in force in Wisconsin nowThe forecast where you are

15 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.