Tornadoes · United States · Illinois · 1991

F3 tornado, Will and Cook counties, Illinois, March 27, 1991

This F3 tornado ran 15.0 miles across Will and Cook counties on March 27, 1991, touching down at 3:55 PM CST and reaching 200 yards wide. It killed nobody and injured 7, and did $5 million to $50 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 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 mphthis tornado

    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
F3
Date
March 27, 1991
Touchdown
3:55 PM CST (21:55 UTC)
Path length
15.0 miles (24.1 km)
Path width
200 yards (183 m)
Deaths
0
Injuries
7
Property damage
$5 million to $50 million
Counties
Will and Cook counties
Touchdown point
41.580, -88.100
Lift-off point
41.700, -87.850
Record number
153

The warnings

22 minutes of warning. NWS LOT issued a tornado warning for this county at 21:33 UTC, 22 minutes before the tornado touched down, in force until 22:15 UTC.

Issued (UTC)ExpiredProductOffice
05:48 UTC06:45 UTCSevere Thunderstorm WarningLOT
08:17 UTC09:00 UTCSevere Thunderstorm WarningLOT
21:33 UTC22:15 UTCTornado WarningLOT
22:09 UTC22:45 UTCTornado WarningLOT

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 High Risk. The outlook in force was issued at 07:20 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.

Green Bay/Straub, WI (KGRB), 12:00Z

9.9 hours before the tornado, 316 km from the path. March 27, 1991.

Skew-T log-pSkew-T log-p diagram, Green Bay/Straub, WI at 12:00Z on 1991-03-27Temperature 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 -9225, lifted condensation level 1516 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, Green Bay/Straub, WI at 12:00Z on 1991-03-27The 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 42 knots.1939587897Sfc1 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
-9225 J/kg
Surface CAPE
0 J/kg
Mixed-layer LCL
1516 m above ground
0-6 km bulk shear
42 kt
0-1 km bulk shear
17 kt
0-1 km storm-relative helicity
59 m²/s²
0-3 km storm-relative helicity
-11 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
5.0 K/km

Open this sounding in Storm Lab

Green Bay/Straub, WI (KGRB), 00:00Z

2.1 hours after it, 316 km from the path. March 28, 1991.

Skew-T log-pSkew-T log-p diagram, Green Bay/Straub, WI at 00:00Z on 1991-03-28Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 95 joules per kilogram, CIN -31, lifted condensation level 1044 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, Green Bay/Straub, WI at 00:00Z on 1991-03-28The 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 -126 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
95 J/kg
Mixed-layer CIN
-31 J/kg
Surface CAPE
135 J/kg
Mixed-layer LCL
1044 m above ground
0-6 km bulk shear
31 kt
0-1 km bulk shear
32 kt
0-1 km storm-relative helicity
-126 m²/s²
0-3 km storm-relative helicity
-85 m²/s²
Significant tornado parameter
-0.0
Supercell composite
-0.6
0-3 km lapse rate
6.9 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 March 27, 1991

28 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
March 2712:30 AM CSTF1Chase, KS11.050$5,000 to $50,000
March 2710:35 PM PSTF1Orange, CA3.053
March 272:00 AM PSTF1San Diego, CA0.210
March 2712:18 PM CSTF2Jackson, IA1.51001$50,000 to $500,000
March 271:20 PM CSTF1Shelby, TN0.550$50 to $500
March 271:50 PM CSTF2Green, WI32.044015$500,000 to $5 million
March 273:50 PM CSTF0Will, IL3.050
March 275:02 PM ESTF1Mecosta, MI1.020$500 to $5,000
March 275:02 PM ESTF0Newaygo, MI0.510
March 274:10 PM CSTF1Kankakee, IL0.550
March 275:15 PM ESTF2Osceola, MI4.070$500 to $5,000
March 275:30 PM ESTF1Osceola, MI2.040$50 to $500
March 274:37 PM CSTF0Will, IL0.550$500 to $5,000
March 276:05 PM ESTF0Osceola, MI1.010$50 to $500
March 276:10 PM ESTF0Tippecanoe, IN0.210
March 276:15 PM ESTF2Ogemaw, MI6.0100$50,000 to $500,000
March 276:15 PM ESTF3Ogemaw, MI35.0100$500,000 to $5 million
March 276:20 PM ESTF3Ogemaw, MI21.0100$500,000 to $5 million
March 276:25 PM ESTF0Cass, IN0.210
March 277:00 PM ESTF2Ingham, MI5.060$50,000 to $500,000
March 277:00 PM ESTF3Calhoun, MI2.040018$50,000 to $500,000
March 277:20 PM ESTF0Madison, IN0.120$500 to $5,000
March 277:28 PM ESTF0Ingham, MI3.030
March 277:37 PM ESTF3Hillsdale, MI5.0400$5 million to $50 million
March 277:20 PM CSTF3Steuben, IN to OH21.0200124$5 million to $50 million
March 278:39 PM ESTF0Monroe, MI0.510
March 278:45 PM ESTF0Monroe, MI0.510
March 278:53 PM ESTF1Saint Clair, MI10.0150$5,000 to $50,000

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.