Tornadoes · United States · Illinois · 1991

F0 tornado, Saint Clair County, Illinois, May 11, 1991

This F0 tornado ran 0.1 miles across Saint Clair County on May 11, 1991, touching down at 3:50 PM CDT and reaching 350 yards wide. It killed nobody.

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 mphthis tornado

    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 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
F0
Date
May 11, 1991
Touchdown
3:50 PM CDT (20:50 UTC)
Path length
0.1 miles (0.2 km)
Path width
350 yards (320 m)
Deaths
0
Injuries
0
County
Saint Clair County
Touchdown point
38.600, -89.820
Record number
489

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 forecast that day

The Storm Prediction Center had this point in a General Thunderstorms Risk. The outlook in force was issued at 06:24 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.

Paducah/Barkley, KY (KPAH), 12:00Z

8.8 hours before the tornado, 197 km from the path. May 11, 1991.

Skew-T log-pSkew-T log-p diagram, Paducah/Barkley, KY at 12:00Z on 1991-05-11Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 601 joules per kilogram, CIN -11, lifted condensation level 573 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, Paducah/Barkley, KY at 12:00Z on 1991-05-11The 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 25 square meters per square second, 0 to 6 km bulk shear 14 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
601 J/kg
Mixed-layer CIN
-11 J/kg
Surface CAPE
763 J/kg
Mixed-layer LCL
573 m above ground
0-6 km bulk shear
14 kt
0-1 km bulk shear
9 kt
0-1 km storm-relative helicity
25 m²/s²
0-3 km storm-relative helicity
42 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
5.5 K/km

Open this sounding in Storm Lab

Paducah/Barkley, KY (KPAH), 00:00Z

3.2 hours after it, 197 km from the path. May 12, 1991.

Skew-T log-pSkew-T log-p diagram, Paducah/Barkley, KY at 00:00Z on 1991-05-12Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 1283 joules per kilogram, CIN -1, lifted condensation level 679 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, Paducah/Barkley, KY at 00:00Z on 1991-05-12The 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 69 square meters per square second, 0 to 6 km bulk shear 22 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
1283 J/kg
Mixed-layer CIN
-1 J/kg
Surface CAPE
2292 J/kg
Mixed-layer LCL
679 m above ground
0-6 km bulk shear
22 kt
0-1 km bulk shear
13 kt
0-1 km storm-relative helicity
69 m²/s²
0-3 km storm-relative helicity
89 m²/s²
Significant tornado parameter
0.0
Supercell composite
1.8
0-3 km lapse rate
6.8 K/km

Open this sounding in Storm Lab

This ground now

The live radar over the trackEvery 1991 tornado in IllinoisEvery tornado in Illinois since 1950Warnings in force in Illinois nowThe forecast where you are

The other tornadoes of May 11, 1991

20 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
May 1111:20 AM MDTF0Garfield, MT0.210
May 116:13 PM MDTF0Fall River, SD0.550
May 116:20 PM MDTF1Fall River, SD1.073$50,000 to $500,000
May 116:38 PM MDTF0Fall River, SD0.750
May 117:47 PM CDTF0Castro, TX0.230
May 116:54 PM MDTF0Converse, WY0.120
May 118:02 PM CDTF0Cimarron, OK0.570
May 118:17 PM CDTF0Swisher, TX0.230
May 118:30 PM CDTF0Randall, TX0.130
May 118:45 PM CDTF0Randall, TX0.230
May 118:05 PM MDTF0Meade, SD0.550
May 119:05 PM CDTF0Lamb, TX0.330
May 119:05 PM CDTF0Swisher, TX0.130
May 118:10 PM MDTF1Pennington, SD0.550$50,000 to $500,000
May 118:10 PM MDTF2Meade, SD1.03005$50,000 to $500,000
May 118:10 PM MDTF3Meade, SD2.050020$500,000 to $5 million
May 118:39 PM MDTF0Weston, WY0.120
May 119:52 PM CDTF1Hale, TX3.5802$50,000 to $500,000
May 119:10 PM MDTF0Baca, CO2.027
May 1110:50 PM CDTF1Hale, TX1.270$500 to $5,000

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.