EF0 tornado, Nimrod to Osnawa, Minnesota, June 17, 2010

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

June 17, 2010

Touchdown

5:30 PM CDT (22:30 UTC)

Lifted

5:48 PM CDT (22:48 UTC)

On the ground

18 minutes

Path length

14.8 miles (23.7 km)

Path width

200 yards (183 m)

Deaths

0

Injuries

0

Property damage

$2,000

Counties

Wadena and Cass counties

Touchdown point

46.610, -94.880

Lift-off point

46.749, -94.648

Record number

1006171630-01

Conditions were ripe by the afternoon of the 17th for a major severe weather outbreak. A surface low had moved into east central North Dakota with an occluded front extending to the southeast. Warm and humid air was in place ahead of the front, with a much drier airmass pushing in behind it. The 500mb low was located over northwest North Dakota with a nice southwest to northeast upper jet pushing into eastern North Dakota. Two lines of convection formed by late afternoon, one from Roseau County down toward Eastern Otter Tail County and the other over east central North Dakota. Nearly all the cells that formed took on a classic hook shape with rotation very evident on radar imagery. Multiple tornado warnings were issued before the event wound down by mid evening. The strongest tornadoes were determined to be EF4 tornadoes, two in west central Minnesota and one in northeast North Dakota.

A significant, widespread severe weather outbreak occurred across a large portion of central and east central Minnesota. A powerful mid summer storm system over the western Dakotas, combined with warm moist air surging northward from the Gulf of Mexico, provided the ingredients for tornadoes, destructive winds, and large hail across parts of the Northland. ||In addition, several storms in the Cass Lake and Lake Winnibigoshish area of north central Minnesota produced a large amount of one to two inch diameter hail, which is about quarter to slightly larger than golf ball size.

The tornado tracked east-northeastward intermittently for about 5 miles, where it reached the Cass County line east of Nimrod. The tornado continued northeast into Cass County for several more miles. Numerous large tree branches were broken down along this path. Peak winds were estimated at 80 mph.

The tornado continued from Wadena County. Trees were snapped along its path, including County Road 2 and 64 up to the west side of Deer Lake.

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

34 minutes of warning. NWS FGF issued a tornado warning for this county at 21:56 UTC, 34 minutes before the tornado touched down, in force until 23:00 UTC.

The county was under a tornado watch, issued at 17:45 UTC and running to 01:23 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 0.10 chance of a tornado within 25 miles, in the hatched area where significant tornadoes were expected. The outlook in force was issued at 20:06 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 Duluth radar (KDLH), 195 km away, was scanning. The volume nearest the touchdown began at 22:32 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 2010 tornado in MinnesotaEvery tornado in Minnesota since 1950Warnings in force in Minnesota nowThe forecast where you are

73 more were confirmed in the United States that day.

All 74 of them

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.