Tornadoes · United States · Illinois · 1978

F1 tornado, Cook County, Illinois, April 18, 1978

This F1 tornado ran 6.1 miles across Cook County on April 18, 1978, touching down at 4:55 PM CST and reaching 177 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 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
April 18, 1978
Touchdown
4:55 PM CST (22:55 UTC)
Path length
6.1 miles (9.8 km)
Path width
177 yards (162 m)
Deaths
0
Injuries
0
Property damage
$50,000 to $500,000
County
Cook County
Touchdown point
41.670, -87.830
Lift-off point
41.750, -87.770
Record number
109

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.

Peoria Regional, IL (KPIA), 12:00Z

10.9 hours before the tornado, 190 km from the path. April 18, 1978.

Skew-T log-pSkew-T log-p diagram, Peoria Regional, IL at 12:00Z on 1978-04-18Temperature 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 -122, lifted condensation level 571 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, Peoria Regional, IL at 12:00Z on 1978-04-18The 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 54 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
-122 J/kg
Surface CAPE
0 J/kg
Mixed-layer LCL
571 m above ground
0-6 km bulk shear
54 kt
0-1 km bulk shear
26 kt
0-1 km storm-relative helicity
142 m²/s²
0-3 km storm-relative helicity
144 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
4.1 K/km

Open this sounding in Storm Lab

Peoria Regional, IL (KPIA), 00:00Z

1.1 hours after it, 190 km from the path. April 19, 1978.

Skew-T log-pSkew-T log-p diagram, Peoria Regional, IL at 00:00Z on 1978-04-19Temperature 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 -14702, lifted condensation level 1380 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, Peoria Regional, IL at 00:00Z on 1978-04-19The 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 49 square meters per square second, 0 to 6 km bulk shear 12 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
0 J/kg
Mixed-layer CIN
-14702 J/kg
Surface CAPE
0 J/kg
Mixed-layer LCL
1380 m above ground
0-6 km bulk shear
12 kt
0-1 km bulk shear
18 kt
0-1 km storm-relative helicity
49 m²/s²
0-3 km storm-relative helicity
62 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
7.3 K/km

Open this sounding in Storm Lab

The surface observations

Chicago (MDW), 9 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
21:00 UTC6154130° 13 kt999.7
22:00 UTC6254100° 14 kt998.6
23:00 UTC5751150° 6 kt998
23:06 UTC210° 29 kt491000
23:24 UTC210° 14 kt221000
00:00 UTC5243190° 6 kt1000
00:25 UTC130° 8 kt1000

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

This ground now

The live radar over the trackEvery 1978 tornado in IllinoisEvery tornado in Illinois since 1950Warnings in force in Illinois nowThe forecast where you are

The other tornadoes of April 18, 1978

17 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
April 1812:30 AM CSTF4Lawrence, MS19.1100431$50,000 to $500,000
April 181:00 AM CSTF1Smith, MS45.8100$5,000 to $50,000
April 182:00 AM CSTF2Lawrence, AL6.833$50,000 to $500,000
April 182:00 AM CSTF1Marshall, TN0.110$5,000 to $50,000
April 183:45 AM CSTF1White, TN0.5440$50,000 to $500,000
April 186:00 AM CSTF1Clay, AL0.3100$5,000 to $50,000
April 1812:30 PM ESTF1Colquitt, GA13.377$5,000 to $50,000
April 183:00 PM CSTF0Lowndes, AL0.120
April 184:45 PM ESTF1Nassau, FL0.320$5,000 to $50,000
April 185:05 PM ESTF2Polk, GA4.1200$50,000 to $500,000
April 185:00 PM CSTF3Monroe, AL10.522030$500,000 to $5 million
April 185:15 PM CSTF2Coosa, AL0.180$5,000 to $50,000
April 186:45 PM ESTF1Volusia, FL0.520$50,000 to $500,000
April 186:45 PM ESTF1Lake, FL1.050$50,000 to $500,000
April 187:20 PM ESTF1Caroline, MD0.110$5,000 to $50,000
April 188:32 PM CSTF0Coffee, AL0.2100$5,000 to $50,000
April 1811:38 PM CSTF1Montgomery, AL0.74203$50,000 to $500,000

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.