EF0 tornado, Mahtomedi to Grant, Minnesota, November 10, 2012

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

November 10, 2012

Touchdown

11:21 PM CST (05:21 UTC)

Lifted

11:27 PM CST (05:27 UTC)

On the ground

6 minutes

Path length

4.3 miles (7.0 km)

Path width

100 yards (91 m)

Deaths

0

Injuries

0

Property damage

$200,000

County

Washington County

Touchdown point

45.080, -92.960

Lift-off point

45.110, -92.882

Record number

1211102321-01

7 damage points were recorded along this path by NWS MPX, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF0. The highest wind the damage implies is 80 mph.

• Begining of tornado track 3
• Beginning of tornado track 4
• Several trees snapped or uprooted. High end EF0 or near EF1 damage.

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

A record breaking day occurred across the Upper Midwest as temperatures soared into the 60s and 70s across southern Minnesota during the afternoon of Saturday, November 10th. Thunderstorms developed across eastern Nebraska late in the day, and moved northeast across southern Minnesota during the evening. A powerful low level jet of 65 knots developed ahead of a strong cold front late Saturday evening. This low level jet combined with ample instability to create several lines of thunderstorms across southern Minnesota. One line of thunderstorms moved through the southern and eastern metro area of the Twin Cities, and produced four EF-0 tornadoes, along with damaging straight line winds. One tornado moved through the Burnsville area, the second moved through Eagan, the third occurred near Lilydale, and the fourth hit Mahtomedi and Grant. In addition to the tornadoes, there was a long path of damaging straight line winds that caused numerous large trees to blow down onto houses, cars and other public and private structures. These were the latest Minnesota tornadoes in a calendar year in the Storm Prediction Center database (which began in 1950), although there may have been one later tornado on Nov 16, 1931 (but records of tornadoes were not maintained before 1950).

Hundreds of trees were toppled or snapped. Some trees fell on cars, houses and sheds. The tornado touched down in Mahtomedi, just east of the White Bear Lake shore, and it moved northeast into the northeastern part of Grant. The most significant damage was shortly after touchdown, near the intersection of Hazel and Moccasin in far northern Mahtomedi, where strong EF-0 damage was noted.

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, with a 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 00:52 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.

St Paul / Lake Elmo (21D), 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), 58 km away, was scanning. The volume nearest the touchdown began at 05:19 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 2012 tornado in MinnesotaEvery tornado in Minnesota since 1950Warnings in force in Minnesota nowThe forecast where you are

3 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.