Tornadoes · United States · Minnesota · 2002

F1 tornado, Downer, Minnesota, September 18, 2002

This F1 tornado ran 1.0 miles across Clay County on September 18, 2002, touching down at 6:57 PM CDT and reaching 25 yards wide. It killed nobody, and did $1,000 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
September 18, 2002
Touchdown
6:57 PM CDT (23:57 UTC)
Path length
1.0 miles (1.6 km)
Path width
25 yards (23 m)
Deaths
0
Injuries
0
Property damage
$1,000
County
Clay County
Touchdown point
46.750, -96.420
Lift-off point
46.750, -96.400
Record number
274

What the Weather Service recorded

A 14x14 foot one thousand pound shed door was torn off a barn and thrown 150 feet on top of a 24 foot high grain bin. Calf pens were also flipped over.

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

The warnings

41 minutes of warning. NWS FGF issued a tornado warning for this county at 23:16 UTC, 41 minutes before the tornado touched down, in force until 00:00 UTC.

Issued (UTC)ExpiredProductOffice
22:28 UTC23:15 UTCSevere Thunderstorm WarningFGF
23:16 UTC00:00 UTCTornado WarningFGF
23:58 UTC00:45 UTCTornado WarningFGF
23:58 UTC00:45 UTCTornado WarningFGF
00:11 UTC06:00 UTCFlash Flood 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 Slight Risk. The outlook in force was issued at 20:21 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.

Aberdeen, SD (KABR), 12:00Z

12.0 hours before the tornado, 257 km from the path. September 18, 2002.

Skew-T log-pSkew-T log-p diagram, Aberdeen, SD at 12:00Z on 2002-09-18Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 613 joules per kilogram, CIN -190, lifted condensation level 786 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, Aberdeen, SD at 12:00Z on 2002-09-18The 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 60 square meters per square second, 0 to 6 km bulk shear 34 knots.193958Sfc1 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
613 J/kg
Mixed-layer CIN
-190 J/kg
Surface CAPE
139 J/kg
Mixed-layer LCL
786 m above ground
0-6 km bulk shear
34 kt
0-1 km bulk shear
12 kt
0-1 km storm-relative helicity
60 m²/s²
0-3 km storm-relative helicity
53 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
4.7 K/km

Open this sounding in Storm Lab

Aberdeen, SD (KABR), 00:00Z

0.0 hours before the tornado, 257 km from the path. September 19, 2002.

Skew-T log-pSkew-T log-p diagram, Aberdeen, SD at 00:00Z on 2002-09-19Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 20 joules per kilogram, CIN -159, lifted condensation level 1588 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, Aberdeen, SD at 00:00Z on 2002-09-19The 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 26 square meters per square second, 0 to 6 km bulk shear 21 knots.193958Sfc1 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
20 J/kg
Mixed-layer CIN
-159 J/kg
Surface CAPE
196 J/kg
Mixed-layer LCL
1588 m above ground
0-6 km bulk shear
21 kt
0-1 km bulk shear
6 kt
0-1 km storm-relative helicity
26 m²/s²
0-3 km storm-relative helicity
13 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
7.1 K/km

Open this sounding in Storm Lab

The surface observations

Moorhead Municipal (JKJ), 22 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
21:57 UTC78.860.8140° 12 kt22995.3
22:17 UTC78.860.8130° 12 kt18995.3VCTS
22:37 UTC78.860.8130° 13 kt995.3TS
22:57 UTC71.666.2300° 9 kt18996.6+VCTSRA
23:17 UTC71.666.2240° 12 kt20997.3+TSRA
23:39 UTC6866.280° 10 kt996.3+TSRA
23:57 UTC6866.2150° 12 kt21996.3-TSRA
00:17 UTC66.262.6120° 17 kt21996.3-VCTSRA
00:37 UTC64.460.890° 16 kt20995.9VCTS
00:57 UTC66.260.8110° 9 kt995.6VCTS
01:17 UTC66.260.8100° 13 kt996.3VCTS
01:37 UTC66.262.6110° 9 kt996.3

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

The radar

The Fargo/Grand Forks radar (KMVX), 111 km away, was scanning. The volume nearest the touchdown began at 23:59 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 2002 tornado in MinnesotaEvery tornado in Minnesota since 1950Warnings in force in Minnesota nowThe forecast where you are

The other tornadoes of September 18, 2002

3 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
September 182:40 PM CDTF0Madison, AL0.120
September 186:16 PM CDTF0Grant, OK1.0200
September 187:29 PM CDTF0Kay, OK0.325

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.