Tornadoes · United States · Minnesota · 1977

F2 tornado, Scott and Le Sueur counties, Minnesota, May 21, 1977

This F2 tornado ran 19.3 miles across Scott and Le Sueur counties on May 21, 1977, touching down at 3:36 PM CDT and reaching 100 yards wide. It killed nobody, and did $50,000 to $500,000 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 mph

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

  3. F2113 to 157 mphthis tornado

    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
F2
Date
May 21, 1977
Touchdown
3:36 PM CDT (20:36 UTC)
Path length
19.3 miles (31.1 km)
Path width
100 yards (91 m)
Deaths
0
Injuries
0
Property damage
$50,000 to $500,000
Counties
Scott and Le Sueur counties
Touchdown point
44.520, -93.630
Lift-off point
44.800, -93.520
Record number
352

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 (KSTC), 12:00Z

8.6 hours before the tornado, 21 km from the path. May 21, 1977.

Skew-T log-pSkew-T log-p diagram, Minneapolis, MN at 12:00Z on 1977-05-21Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 0 joules per kilogram, CIN -10070, lifted condensation level 1186 meters above ground. Wind barbs in knots down the right edge.LCL10008507005003002001001 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 1977-05-21The 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 -7 square meters per square second, 0 to 6 km bulk shear 32 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
0 J/kg
Mixed-layer CIN
-10070 J/kg
Surface CAPE
0 J/kg
Mixed-layer LCL
1186 m above ground
0-6 km bulk shear
32 kt
0-1 km bulk shear
17 kt
0-1 km storm-relative helicity
-7 m²/s²
0-3 km storm-relative helicity
35 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
2.7 K/km

Open this sounding in Storm Lab

Minneapolis, MN (KSTC), 00:00Z

3.4 hours after it, 21 km from the path. May 22, 1977.

Skew-T log-pSkew-T log-p diagram, Minneapolis, MN at 00:00Z on 1977-05-22Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 58 joules per kilogram, CIN -15, lifted condensation level 608 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 1977-05-22The 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 141 square meters per square second, 0 to 6 km bulk shear 52 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
58 J/kg
Mixed-layer CIN
-15 J/kg
Surface CAPE
118 J/kg
Mixed-layer LCL
608 m above ground
0-6 km bulk shear
52 kt
0-1 km bulk shear
15 kt
0-1 km storm-relative helicity
141 m²/s²
0-3 km storm-relative helicity
227 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.1
0-3 km lapse rate
5.6 K/km

Open this sounding in Storm Lab

The surface observations

Minneapolis (MSP), 37 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
19:00 UTC656290° 9 kt1011.9SHRA
19:05 UTC80° 8 kt1011.5SHRA
20:00 UTC696570° 11 kt1010.5
21:00 UTC706370° 10 kt1009.1
22:00 UTC6964100° 16 kt1008.1SHRA FG

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

This ground now

The live radar over the trackEvery 1977 tornado in MinnesotaEvery tornado in Minnesota since 1950Warnings in force in Minnesota nowThe forecast where you are

The other tornadoes of May 21, 1977

15 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
May 211:30 AM CDTF2Pottawatomie, OK9.2100$50,000 to $500,000
May 213:00 AM CDTF0Cleveland, OK0.150$500 to $5,000
May 212:25 PM CDTF0Buffalo, NE0.120
May 214:00 PM CDTF0Boyd, NE0.230
May 215:45 PM CDTF1Harrison, MO1.0100$5,000 to $50,000
May 217:00 PM CDTF0Posey, IN0.310
May 217:30 PM CDTF0Deuel, SD0.110
May 217:30 PM CDTF0Deuel, SD0.110
May 217:30 PM CDTF0Deuel, SD0.110
May 217:30 PM CDTF0Deuel, SD0.110
May 217:30 PM CDTF1Deuel, SD0.110$5,000 to $50,000
May 218:00 PM CDTF1Grundy, MO3.8150$5,000 to $50,000
May 219:30 PM CDTF1Grant, SD0.110$500 to $5,000
May 219:30 PM CDTF0Codington, SD0.110
May 219:30 PM CDTF0Codington, SD0.110

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.