F1 tornado, Dunvilla, Minnesota, July 12, 2004

1. F040 to 72 mph

   Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.

2. F173 to 112 mphthis tornado

   Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

3. F2113 to 157 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. F3158 to 206 mph

   Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.

5. F4207 to 260 mph

   Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

6. F5261 to 318 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

F1

Date

July 12, 2004

Touchdown

11:15 PM CDT (04:15 UTC)

Path length

5.0 miles (8.0 km)

Path width

50 yards (46 m)

Deaths

0

Injuries

0

Property damage

$400,000

County

Otter Tail County

Touchdown point

46.700, -96.150

Lift-off point

46.670, -96.070

Record number

1438

Many large trees were blown down and some blocked state highway 34. Four trees fell on a house on Tamarac Lake, where many other trees were blown down. On Pelican Lake, numerous oak trees were damaged. One oak tree fell on a roof. Trees also fell on a recreational vehicle and on several boats.

Intermittent tree damage occurred from the east side of Lake Lizzie to Dent. Power outages occurred from trees falling on power lines. On West McDonald Lake, a 30 foot mobile home was overturned against an oak tree that was split in half. A tree also fell on a boat, destroying it. At Spirit Lake, 20 trees were damaged at a resort, some falling on resort cabins. A dock was also damaged. At Hoffman Lake, property owners reportedly saw the tornado coming across the lake. Many trees fell on homes or other property.

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

20 minutes of warning. NWS FGF issued a tornado warning for this county at 03:55 UTC, 20 minutes before the tornado touched down, in force until 05:00 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. The outlook in force was issued at 02:10 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.

Detroit Lakes (DTL), 23 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), 131 km away, was scanning. The volume nearest the touchdown began at 04:15 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 2004 tornado in MinnesotaEvery tornado in Minnesota since 1950Warnings in force in Minnesota nowThe forecast where you are

13 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.