EF1 tornado, Hanover to St Michael, Minnesota, May 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 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 10, 2011

Touchdown

7:55 PM CDT (00:55 UTC)

Lifted

8:01 PM CDT (01:01 UTC)

On the ground

6 minutes

Path length

3.1 miles (5.1 km)

Path width

25 yards (23 m)

Deaths

0

Injuries

0

Property damage

$500,000

County

Wright County

Touchdown point

45.170, -93.704

Lift-off point

45.215, -93.694

Record number

1105101855-01

During the late afternoon of Tuesday, May 10th, a line of severe thunderstorms developed along the leading edge of a strong dry line moving across southern and central Minnesota. Once the thunderstorms developed, several became super cells and produced large hail across portions of the Twin Cities metro area, then northwest along the Mississippi River valley, and north to Mille Lacs Lake. Numerous reports of golf ball size hail occurred with these storms, along with an isolated tornado near St. Michael, Minnesota.

One home lost part of its roof, and others lost shingles. Several homes had windows blown in. Several dozen trees and a number of power poles were broken or knocked down. Siding and soffits were ripped off a few houses. Numerous backyard fences were blown over. A pole barn was lifted up about three feet before being set back down. The tornado was photographed and videotaped by several people. The condensation funnel was not fully extended, and the debris cloud never extended as high as the condensation funnel. The tornado was a marginal EF-1, with winds near 90 mph.

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

0 minutes of warning. NWS MPX issued a tornado warning for this county at 00:55 UTC, 0 minutes before the tornado touched down, in force until 01:30 UTC.

The county was under a tornado watch, issued at 00:46 UTC and running to 03:31 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 Slight Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 19:55 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.

Buffalo (CFE), 12 km from the path, in the two hours either side.

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

The Minneapolis radar (KMPX), 40 km away, was scanning. The volume nearest the touchdown began at 00:56 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 MinnesotaEvery tornado in Minnesota since 1950Warnings in force in Minnesota 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.