EF1 tornado, Blue Grass, Minnesota, July 4, 2012

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

July 4, 2012

Touchdown

9:05 PM CDT (02:05 UTC)

Lifted

9:18 PM CDT (02:18 UTC)

On the ground

13 minutes

Path length

4.0 miles (6.4 km)

Path width

75 yards (69 m)

Deaths

0

Injuries

0

County

Wadena County

Touchdown point

46.570, -95.030

Lift-off point

46.550, -94.967

Record number

1207042005-01

On the morning of July 4th, a cold front pushed into central North Dakota, eventually reaching eastern North Dakota around the noon hour. Ahead of the front, a stationary boundary also set up, basically running along the U. S. Highway 2 corridor. South of this stationary boundary temperatures surged into the 90s with dew points in the low 70s, resulting in a heat advisory for portions of the area. Precipitable water values were also quite high, ranging around two inches, which increased the probability for heavy rain with any of the thunderstorms. As the boundaries continued to move east during the day, showers and thunderstorms marched from near Sarles, North Dakota, along and north of the U. S. Highway 2 corridor to near Bemidji, Minnesota.

The tornado snapped several oak, pine, and poplar trees along its intermittent path. It also cracked or snapped at least two power poles, shifted a barn off its foundation, and peeled siding and roofing off a couple of homes and farm buildings along its path. Peak winds were estimated at 95 mph.

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

10 minutes of warning. NWS FGF issued a tornado warning for this county at 01:55 UTC, 10 minutes before the tornado touched down, in force until 02:45 UTC.

The county was under a tornado watch, issued at 02:00 UTC and running to 05:11 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 01:01 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.

Wadena Municipal (ADC), 20 km from the path, in the two hours either side.

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

The Fargo/Grand Forks radar (KMVX), 207 km away, was scanning. The volume nearest the touchdown began at 02:04 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

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.