Tornadoes · United States · Minnesota · 2017

EF0 tornado, Bena to Schley, Minnesota, August 3, 2017

From Bena to Schley, this EF0 tornado ran 0.3 miles across Cass County on August 3, 2017, touching down at 6:04 PM CDT and reaching 20 yards wide. It killed nobody.

The rating scale

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

  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.

The record

Rating
EF0
Date
August 3, 2017
Touchdown
6:04 PM CDT (23:04 UTC)
Lifted
6:15 PM CDT (23:15 UTC)
On the ground
11 minutes
Path length
0.3 miles (0.5 km)
Path width
20 yards (18 m)
Deaths
0
Injuries
0
County
Cass County
Touchdown point
47.451, -94.210
Lift-off point
47.450, -94.211
Record number
1708031704-01

What the Weather Service recorded

On the evening of August 3rd, a thunderstorm with surrounding cooler air temperatures passed over the warmer waters of Lake Winnibigoshish producing three waterspouts that lasted for a short duration. Eye witnesses fishing on the lake were able to photograph and videotape two of the waterspouts occurring at the same time with the third one unable to capture digitally.

Multiple reports of photos and video received showing waterspouts on Lake Winnibigoshish. Eye witnesses reported three different waterspouts on the lake with two occurring at the same time.

Multiple reports of photos and video received showing waterspouts on Lake Winnibigoshish. Eye witnesses reported three different waterspouts on the lake with two occurring at the same time.

Multiple reports of photos and video received showing waterspouts on Lake Winnibigoshish. Eye witnesses reported three different waterspouts on the lake with two occurring at the same time.

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

The warnings

No tornado warning for this county appears in the archive as in force at the moment the tornado touched down.

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 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.

International Fa, MN (KINL), 12:00Z

11.1 hours before the tornado, 142 km from the path. August 3, 2017.

Skew-T log-pSkew-T log-p diagram, International Fa, MN at 12:00Z on 2017-08-03Temperature 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 -68, lifted condensation level 1520 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, International Fa, MN at 12:00Z on 2017-08-03The 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 -34 square meters per square second, 0 to 6 km bulk shear 8 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
-68 J/kg
Surface CAPE
0 J/kg
Mixed-layer LCL
1520 m above ground
0-6 km bulk shear
8 kt
0-1 km bulk shear
7 kt
0-1 km storm-relative helicity
-34 m²/s²
0-3 km storm-relative helicity
-43 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
4.5 K/km

Open this sounding in Storm Lab

International Fa, MN (KINL), 00:00Z

0.9 hours after it, 142 km from the path. August 4, 2017.

Skew-T log-pSkew-T log-p diagram, International Fa, MN at 00:00Z on 2017-08-04Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 50 joules per kilogram, CIN -6, lifted condensation level 1482 meters above ground. Wind barbs in knots down the right edge.LCLEL10008507005003002001001 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, International Fa, MN at 00:00Z on 2017-08-04The 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 59 square meters per square second, 0 to 6 km bulk shear 30 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
50 J/kg
Mixed-layer CIN
-6 J/kg
Surface CAPE
325 J/kg
Mixed-layer LCL
1482 m above ground
0-6 km bulk shear
30 kt
0-1 km bulk shear
13 kt
0-1 km storm-relative helicity
59 m²/s²
0-3 km storm-relative helicity
87 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
8.1 K/km

Open this sounding in Storm Lab

The surface observations

Walker (Y49), 46 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
21:15 UTC59.456.3120° 4 kt1019
21:35 UTC59.456120° 4 kt1019
21:55 UTC5956.3150° 5 kt1018.6
22:15 UTC57.256140° 3 kt1019.3RA
22:35 UTC5856.7170° 3 kt1019
22:55 UTC58.556.8230° 3 kt1019
23:15 UTC58.356.7200° 5 kt1018.3
23:35 UTC5652.780° 7 kt191019+TSRA
23:55 UTC5651.6230° 3 kt1018.6
00:15 UTC5653.2240° 3 kt1018.6
00:35 UTC56.3540° 0 kt1018.6
00:55 UTC56.554.30° 0 kt1018.3

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

The radar

The Duluth radar (KDLH), 166 km away, was scanning. The volume nearest the touchdown began at 23:04 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.

What was reported nearby

Local storm reports within 60 km of the path, in the three hours either side.

Time (UTC)ReportWhereCountyRemark
22:15 UTCWATER SPOUT6 Nnw BenaCass, MNMULTIPLE REPORTS AND PHOTOS RECEIVED VIA BROADCAST MEDIA AND SOCIAL MEDIA OF WATERSPOUTS ON LAKE WINNIBIGOSHISH. POTENTIALLY AS MANY AS THREE DIFFERENT WATERSPOUTS WERE OBSERVED WITH TWO OCCURRING AT THE SAME TIME. TIME
22:15 UTCWATER SPOUT6 Nw BenaCass, MNMULTIPLE REPORTS AND PHOTOS RECEIVED VIA BROADCAST MEDIA AND SOCIAL MEDIA. POTENTIALLY AS MANY AS THREE DIFFERENT WATERSPOUTS WERE OBSERVED WITH TWO OCCURRING AT THE SAME TIME. TIME ESITMATED FROM RADAR.
22:15 UTCWATER SPOUT7 Nnw BenaCass, MNMULTIPLE REPORTS AND PHOTOS RECEIVED VIA BROADCAST MEDIA AND SOCIAL MEDIA OF WATERSPOUTS ON LAKE WINNIBIGOSHISH. POTENTIALLY AS MANY AS THREE DIFFERENT WATERSPOUTS WERE OBSERVED WITH TWO OCCURRING AT THE SAME TIME. TIME

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

This ground now

The live radar over the trackEvery 2017 tornado in MinnesotaEvery tornado in Minnesota since 1950Warnings in force in Minnesota nowThe forecast where you are

The other tornadoes of August 3, 2017

4 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
August 36:10 PM EDTEF0Antrim, MI0.155$55,000
August 36:04 PM CDTEF0Cass, MN0.210
August 36:10 PM CDTEF0Cass, MN0.120
August 35:05 PM MSTEF0Maricopa, AZ0.3100

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.