Tornadoes · United States · Michigan · 2003

F1 tornado, Calhoun County, Michigan, July 20, 2003

This F1 tornado ran 8.0 miles across Calhoun County on July 20, 2003, touching down at 2:15 PM EDT and reaching 880 yards wide. It killed nobody, and did $1.0 million 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
July 20, 2003
Touchdown
2:15 PM EDT (18:15 UTC)
Path length
8.0 miles (12.9 km)
Path width
880 yards (805 m)
Deaths
0
Injuries
0
Property damage
$1.0 million
County
Calhoun County
Touchdown point
42.320, -85.180
Lift-off point
42.320, -85.180
Record number
552

The warnings

21 minutes of warning. NWS GRR issued a tornado warning for this county at 17:54 UTC, 21 minutes before the tornado touched down, in force until 18:45 UTC.

Issued (UTC)ExpiredProductOffice
17:54 UTC18:45 UTCTornado WarningGRR
18:43 UTC19:15 UTCTornado WarningGRR

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, with a 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 16:19 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.

Detroit, MI (KDTX), 12:00Z

6.3 hours before the tornado, 150 km from the path. July 20, 2003.

Skew-T log-pSkew-T log-p diagram, Detroit, MI at 12:00Z on 2003-07-20Temperature 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 -81349, lifted condensation level 1593 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, Detroit, MI at 12:00Z on 2003-07-20The 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 92 square meters per square second, 0 to 6 km bulk shear 31 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
-81349 J/kg
Surface CAPE
0 J/kg
Mixed-layer LCL
1593 m above ground
0-6 km bulk shear
31 kt
0-1 km bulk shear
15 kt
0-1 km storm-relative helicity
92 m²/s²
0-3 km storm-relative helicity
118 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
4.9 K/km

Open this sounding in Storm Lab

Detroit, MI (KDTX), 00:00Z

5.7 hours after it, 150 km from the path. July 21, 2003.

Skew-T log-pSkew-T log-p diagram, Detroit, MI at 00:00Z on 2003-07-21Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 1227 joules per kilogram, CIN -2, lifted condensation level 788 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, Detroit, MI at 00:00Z on 2003-07-21The 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 142 square meters per square second, 0 to 6 km bulk shear 44 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
1227 J/kg
Mixed-layer CIN
-2 J/kg
Surface CAPE
1810 J/kg
Mixed-layer LCL
788 m above ground
0-6 km bulk shear
44 kt
0-1 km bulk shear
22 kt
0-1 km storm-relative helicity
142 m²/s²
0-3 km storm-relative helicity
156 m²/s²
Significant tornado parameter
0.8
Supercell composite
4.7
0-3 km lapse rate
7.1 K/km

Open this sounding in Storm Lab

The radar

The Grand Rapids radar (KGRR), 70 km away, was scanning. The volume nearest the touchdown began at 18:15 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.

This ground now

The live radar over the trackEvery 2003 tornado in MichiganEvery tornado in Michigan since 1950Warnings in force in Michigan nowThe forecast where you are

The other tornadoes of July 20, 2003

16 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
July 202:50 AM CDTF0LaMoure, ND0.050
July 202:50 AM CDTF1Dickey, ND2.040
July 204:00 AM CDTF0Marshall, SD0.125
July 205:40 PM CDTF0Stanton, NE0.020
July 205:50 PM CDTF1Stanton, NE2.0400
July 206:30 PM CDTF1Platte, NE1.5400
July 206:37 PM CDTF0Platte, NE0.020
July 206:56 PM CDTF0Nance, NE0.120
July 207:05 PM CDTF0Woodbury, IA0.150
July 208:15 PM CDTF0Humboldt, IA0.125
July 2010:17 PM CDTF1Benton, IA6.8150$200,000
July 2010:47 PM CDTF0Jones, IA3.535$10,000
July 2010:58 PM CDTF2Linn, IA1.0300$500,000
July 2011:06 PM CDTF2Linn, IA0.3200$2.0 million
July 2011:24 PM CDTF1Cedar, IA2.4440$1.0 million
July 2011:52 PM CDTF1Linn, IA0.570$10,000

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.