EF0 tornado, Blooming Grove, Wisconsin, August 8, 2011

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.

Rating

EF0

Date

August 8, 2011

Touchdown

7:13 PM CDT (00:13 UTC)

Lifted

7:22 PM CDT (00:22 UTC)

On the ground

9 minutes

Path length

1.2 miles (1.9 km)

Path width

20 yards (18 m)

Deaths

0

Injuries

0

County

Dane County

Touchdown point

43.067, -89.366

Lift-off point

43.053, -89.353

Record number

1108081813-01

An unusual tornado event occurred during the early evening hours of August 8th. A vigorous short wave moved across the region in the early evening hours. While deep layer wind shear was weak, there was enough instability, with CAPE values around 700 J/Kg, to produce strong enough updrafts to ingest low-level vorticity and stretch it to produce non-supercell tornadoes (land-spout variety). A weak EF0 tornado formed as a shower moved over a weak, west to east orientated low-level atmospheric boundary over Lake Monona in Madison, southeast of the State Capitol.

Law enforcement officials, as well as many members of the general public, reported a tornado that formed and stayed over Lake Monona, about 1 mile east of Law Park in the City of Madison. The tornado tracked south, then southeast, over the lake before dissipating west of Squaw Bay, about 1/4 mile north of Waunona Park. No damage was reported. The tornado kicked up water spray, estimated about 20 feet wide at the surface of the water expanding to 40 feet wide about 40 feet above the water. Many public reports of the tornado/waterspout came into local law enforcement, along with photos and video clips of the vortex from a variety of locations around the lake. The associated condensation funnel never developed more than half-way down to the water surface. Though actually a waterspout, it is being termed a tornado in the official Storm Data report due to National Weather Service rules that limit waterspout reports to bodies of water with a designated marine zone. Lake Monona does not have an assigned marine zone number. The exact starting point was Lat 43.06722 and Lon -89.36588, the mid-point was Lat 43.05864 and Lon -89.36147, and the end point was Lat 43.05263 and Lon -89.35266. The average path width was 15 yards. This tornado-waterspout had estimated wind speeds of 30 to 40 mph based on eyewitness reports. This value is below the minimum wind speed of an EF-0 tornado which is 65 mph in the current EF-Scale.

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

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

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 General Thunderstorms Risk. 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.

Madison (MSN), 9 km from the path, in the two hours either side.

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

The Milwaukee radar (KMKX), 67 km away, was scanning. The volume nearest the touchdown began at 00:11 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

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.