Tornadoes · United States · Illinois · 1968

F3 tornado, Mason and Logan counties, Illinois, May 15, 1968

This F3 tornado ran 12.6 miles across Mason and Logan counties on May 15, 1968, touching down at 3:30 PM GMT-5 and reaching 600 yards wide. It killed nobody and injured 25, and did $500,000 to $5 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
May 15, 1968
Touchdown
3:30 PM GMT-5 (20:30 UTC)
Path length
12.6 miles (20.3 km)
Path width
600 yards (549 m)
Deaths
0
Injuries
25
Property damage
$500,000 to $5 million
Counties
Mason and Logan counties
Touchdown point
40.230, -89.830
Lift-off point
40.280, -89.550
Record number
198

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

8.5 hours before the tornado, 47 km from the path. May 15, 1968.

Skew-T log-pSkew-T log-p diagram, Peoria Regional, IL at 12:00Z on 1968-05-15Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 2320 joules per kilogram, CIN -33, lifted condensation level 952 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 1968-05-15The 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 46 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
2320 J/kg
Mixed-layer CIN
-33 J/kg
Surface CAPE
220 J/kg
Mixed-layer LCL
952 m above ground
0-6 km bulk shear
46 kt
0-1 km bulk shear
24 kt
0-1 km storm-relative helicity
25 m²/s²
0-3 km storm-relative helicity
34 m²/s²
Significant tornado parameter
0.0
Supercell composite
1.4
0-3 km lapse rate
4.7 K/km

Open this sounding in Storm Lab

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

3.5 hours after it, 47 km from the path. May 16, 1968.

Skew-T log-pSkew-T log-p diagram, Peoria Regional, IL at 00:00Z on 1968-05-16Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 850 joules per kilogram, CIN -142, lifted condensation level 1174 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 00:00Z on 1968-05-16The 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 338 square meters per square second, 0 to 6 km bulk shear 66 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
850 J/kg
Mixed-layer CIN
-142 J/kg
Surface CAPE
494 J/kg
Mixed-layer LCL
1174 m above ground
0-6 km bulk shear
66 kt
0-1 km bulk shear
39 kt
0-1 km storm-relative helicity
338 m²/s²
0-3 km storm-relative helicity
403 m²/s²
Significant tornado parameter
0.0
Supercell composite
6.5
0-3 km lapse rate
5.3 K/km

Open this sounding in Storm Lab

The surface observations

Springfield (SPI), 46 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
19:00 UTC786680° 16 kt
20:00 UTC8571150° 17 kt
21:00 UTC8469170° 20 kt999.7
22:00 UTC8664190° 19 kt

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

This ground now

The live radar over the trackEvery 1968 tornado in IllinoisEvery tornado in Illinois since 1950Warnings in force in Illinois nowThe forecast where you are

The other tornadoes of May 15, 1968

32 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
May 153:28 PM GMT-5F2Rice, MN15.43333$50,000 to $500,000
May 153:45 PM GMT-5F3Miami, KS to MO2.750$5,000 to $50,000
May 154:10 PM GMT-5F5Franklin, IA62.160013462$5 million to $50 million
May 154:30 PM GMT-5F2Johnson, MO5.22002$50,000 to $500,000
May 154:45 PM GMT-5F2Hendricks, IN8.8105$50,000 to $500,000
May 154:45 PM GMT-5F1Ray, MO3.650$5,000 to $50,000
May 154:57 PM GMT-5F5Fayette, IA13.15005156$5 million to $50 million
May 154:58 PM GMT-5F1Fayette, IA0.3300$500 to $5,000
May 155:00 PM GMT-5F1DeWitt, IL25.41,000450$500,000 to $5 million
May 155:00 PM GMT-5F0Freeborn, MN0.110
May 155:00 PM GMT-5F2Johnson, MO12.350$5,000 to $50,000
May 155:00 PM GMT-5F1Lafayette, MO4.950$5,000 to $50,000
May 155:07 PM GMT-5F1Dodge, MN7.820$50,000 to $500,000
May 155:40 PM GMT-5F1Steele, MN16.627$5,000 to $50,000
May 155:45 PM GMT-5F1Audubon, IA2.02501$5,000 to $50,000
May 156:00 PM GMT-5F1Jasper, MO2.5503$5,000 to $50,000
May 157:15 PM GMT-4F1Wayne, OH1.0367$5,000 to $50,000
May 156:15 PM GMT-5F2Howard, IA4.7250$5,000 to $50,000
May 156:45 PM GMT-5F1Fillmore, MN8.477$5,000 to $50,000
May 156:50 PM GMT-5F3Iroquois, IL7.1400$500,000 to $5 million
May 158:00 PM GMT-4F2Wayne, OH1.0440$5,000 to $50,000
May 157:30 PM GMT-5F3Baxter, AR7.3200325$5,000 to $50,000
May 158:15 PM GMT-5F1Fulton, AR0.110$500 to $5,000
May 158:40 PM GMT-5F1Jefferson, MO5.9100$5,000 to $50,000
May 159:36 PM GMT-5F4Independence, AR0.3300724$500,000 to $5 million
May 159:45 PM GMT-5F3Saint Clair, IL2.0200460$50,000 to $500,000
May 159:45 PM GMT-5F4Jackson, AR20.925035364$5,000 to $50,000
May 159:50 PM GMT-5F2Butler, MO0.2201$5,000 to $50,000
May 1510:20 PM GMT-5F1Dunklin, MO1.517$50 to $500
May 1510:51 PM GMT-5F2Tippecanoe, IN0.110$500 to $5,000
May 1511:30 PM GMT-5F2Clinton, IN0.110$5,000 to $50,000
May 1512:20 AM GMT-5F1Shelby, TN0.110

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.