Tornadoes · United States · Minnesota · 2004

F1 tornado, Ottertail, Minnesota, August 2, 2004

This F1 tornado ran 12.0 miles across Otter Tail County on August 2, 2004, touching down at 4:05 AM CDT and reaching 100 yards wide. It killed nobody, and did $200,000 of property damage.

The rating scale

Tracks are drawn in the color of the rating. The Fujita scale rates the damage rather than measuring the wind: the speeds are what that damage is taken to imply.

  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.

The record

Rating
F1
Date
August 2, 2004
Touchdown
4:05 AM CDT (09:05 UTC)
Path length
12.0 miles (19.3 km)
Path width
100 yards (91 m)
Deaths
0
Injuries
0
Property damage
$200,000
County
Otter Tail County
Touchdown point
46.430, -95.850
Lift-off point
46.420, -95.580
Record number
1563

What the Weather Service recorded

The tornado tracked from the Pickerel Lake area, across Ottertail Lake, to around 2 miles southwest of Ottertail. Numerous trees were uprooted or snapped off. Boat lifts and docks were strewn around the lake shores. Downed trees fell on the roofs of several homes. Power poles were snapped off causing widespread power outages. Several people reported a loud "freight train" sound.

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

The warnings

19 minutes of warning. NWS FGF issued a tornado warning for this county at 08:46 UTC, 19 minutes before the tornado touched down, in force until 09:30 UTC.

Issued (UTC)ExpiredProductOffice
08:04 UTC08:45 UTCTornado WarningFGF
08:46 UTC09:30 UTCTornado WarningFGF
09:30 UTC10:00 UTCSevere Thunderstorm WarningFGF
11:14 UTC12:00 UTCSevere Thunderstorm WarningFGF

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 forecast that day

The Storm Prediction Center had this point in a General Thunderstorms Risk. The outlook in force was issued at 06:19 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 air that afternoon

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.

Minneapolis, MN (KMPX), 00:00Z

9.1 hours before the tornado, 240 km from the path. August 2, 2004.

Skew-T log-pSkew-T log-p diagram, Minneapolis, MN at 00:00Z on 2004-08-02Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 2637 joules per kilogram, CIN -22, lifted condensation level 947 meters above ground. Wind barbs in knots down the right edge.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed. The warm shading is its CAPE, the cool shading the inhibition it has to break through.
HodographHodograph, Minneapolis, MN at 00:00Z on 2004-08-02The wind through the lowest 10 kilometers as a curve, rings every 10 meters per second labeled in knots. Zero to 1 km storm-relative helicity 31 square meters per square second, 0 to 6 km bulk shear 32 knots.1939Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km. RM and LM are the right and left moving storms Bunkers' method gives; the shaded area is the 0 to 1 km storm-relative helicity.
Mixed-layer CAPE
2637 J/kg
Mixed-layer CIN
-22 J/kg
Surface CAPE
3101 J/kg
Mixed-layer LCL
947 m above ground
0-6 km bulk shear
32 kt
0-1 km bulk shear
6 kt
0-1 km storm-relative helicity
31 m²/s²
0-3 km storm-relative helicity
105 m²/s²
Significant tornado parameter
0.3
Supercell composite
1.8
0-3 km lapse rate
6.6 K/km

Open this sounding in Storm Lab

Minneapolis, MN (KMPX), 12:00Z

2.9 hours after it, 240 km from the path. August 2, 2004.

Skew-T log-pSkew-T log-p diagram, Minneapolis, MN at 12:00Z on 2004-08-02Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 2242 joules per kilogram, CIN -138, lifted condensation level 763 meters above ground. Wind barbs in knots down the right edge.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed. The warm shading is its CAPE, the cool shading the inhibition it has to break through.
HodographHodograph, Minneapolis, MN at 12:00Z on 2004-08-02The wind through the lowest 10 kilometers as a curve, rings every 10 meters per second labeled in knots. Zero to 1 km storm-relative helicity 53 square meters per square second, 0 to 6 km bulk shear 38 knots.19395878Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km. RM and LM are the right and left moving storms Bunkers' method gives; the shaded area is the 0 to 1 km storm-relative helicity.
Mixed-layer CAPE
2242 J/kg
Mixed-layer CIN
-138 J/kg
Surface CAPE
1103 J/kg
Mixed-layer LCL
763 m above ground
0-6 km bulk shear
38 kt
0-1 km bulk shear
14 kt
0-1 km storm-relative helicity
53 m²/s²
0-3 km storm-relative helicity
82 m²/s²
Significant tornado parameter
0.0
Supercell composite
5.9
0-3 km lapse rate
4.3 K/km

Open this sounding in Storm Lab

The surface observations

Fergus Falls (FFM), 37 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
07:15 UTC71.668130° 7 kt1009.5
07:35 UTC71.666.2130° 9 kt1008.5
08:00 UTC73.466.2130° 8 kt1008.8
08:15 UTC73.466.2130° 5 kt1008.8
09:00 UTC64.462.630° 11 kt251010.2
09:15 UTC64.462.660° 8 kt1010.8
09:35 UTC66.262.6110° 8 kt1011.2
10:00 UTC64.460.8110° 5 kt1010.8
10:15 UTC64.460.890° 9 kt1010.2
10:35 UTC66.262.680° 8 kt1010.2
11:00 UTC6862.680° 7 kt1010.5

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

The radar

The Fargo/Grand Forks radar (KMVX), 173 km away, was scanning. The volume nearest the touchdown began at 09:05 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.

This ground now

The live radar over the trackEvery 2004 tornado in MinnesotaEvery tornado in Minnesota since 1950Warnings in force in Minnesota nowThe forecast where you are

The other tornadoes of August 2, 2004

4 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
August 23:06 AM CDTF0Wilkin, MN0.525
August 23:15 AM CDTF1Otter Tail, MN7.0100$10,000
August 26:00 PM EDTF0Bradley, TN0.330$20,000
August 29:03 PM MDTF0Cherry, NE0.120

What this means

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.

Sources

NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.