Tornadoes · United States · Illinois · 1977

F1 tornado, Sangamon County, Illinois, August 6, 1977

This F1 tornado ran 5.9 miles across Sangamon County on August 6, 1977, touching down at 4:45 PM CDT and reaching 30 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 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
August 6, 1977
Touchdown
4:45 PM CDT (21:45 UTC)
Path length
5.9 miles (9.5 km)
Path width
30 yards (27 m)
Deaths
0
Injuries
0
County
Sangamon County
Touchdown point
39.550, -89.600
Lift-off point
39.600, -89.500
Record number
657

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.

Salem-Leckrone, IL (KSLO), 12:00Z

9.8 hours before the tornado, 117 km from the path. August 6, 1977.

Skew-T log-pSkew-T log-p diagram, Salem-Leckrone, IL at 12:00Z on 1977-08-06Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 1052 joules per kilogram, CIN -56, lifted condensation level 932 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, Salem-Leckrone, IL at 12:00Z on 1977-08-06The 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 94 square meters per square second, 0 to 6 km bulk shear 22 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
1052 J/kg
Mixed-layer CIN
-56 J/kg
Surface CAPE
513 J/kg
Mixed-layer LCL
932 m above ground
0-6 km bulk shear
22 kt
0-1 km bulk shear
21 kt
0-1 km storm-relative helicity
94 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
4.9 K/km

Open this sounding in Storm Lab

Salem-Leckrone, IL (KSLO), 00:00Z

2.2 hours after it, 117 km from the path. August 7, 1977.

Skew-T log-pSkew-T log-p diagram, Salem-Leckrone, IL at 00:00Z on 1977-08-07Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 2099 joules per kilogram, CIN -14, lifted condensation level 1410 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, Salem-Leckrone, IL at 00:00Z on 1977-08-07The 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 71 square meters per square second, 0 to 6 km bulk shear 27 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
2099 J/kg
Mixed-layer CIN
-14 J/kg
Surface CAPE
2294 J/kg
Mixed-layer LCL
1410 m above ground
0-6 km bulk shear
27 kt
0-1 km bulk shear
14 kt
0-1 km storm-relative helicity
71 m²/s²
0-3 km storm-relative helicity
121 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
7.1 K/km

Open this sounding in Storm Lab

This ground now

The live radar over the trackEvery 1977 tornado in IllinoisEvery tornado in Illinois since 1950Warnings in force in Illinois nowThe forecast where you are

The other tornadoes of August 6, 1977

19 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
August 64:25 PM CDTF1Sangamon, IL7.860
August 64:30 PM CDTF0Sangamon, IL0.8350
August 64:30 PM CDTF1Sangamon, IL6.160
August 64:35 PM CDTF0Sangamon, IL0.810
August 64:35 PM CDTF0Sangamon, IL1.923
August 64:36 PM CDTF1Sangamon, IL1.3350
August 64:36 PM CDTF2Sangamon, IL2.3350
August 64:37 PM CDTF1Sangamon, IL1.050
August 64:38 PM CDTF1Sangamon, IL6.233$5,000 to $50,000
August 64:45 PM CDTF3Sangamon, IL4.1100$500,000 to $5 million
August 64:47 PM CDTF1Sangamon, IL3.6150
August 64:50 PM CDTF0Sangamon, IL0.650
August 64:51 PM CDTF0Sangamon, IL0.217
August 64:53 PM CDTF0Sangamon, IL0.210
August 64:55 PM CDTF0Christian, IL1.117
August 64:57 PM CDTF1Sangamon, IL2.250$50,000 to $500,000
August 65:00 PM CDTF1Christian, IL2.840
August 65:10 PM CDTF1Sangamon, IL3.390
August 610:00 PM CDTF1Chippewa, WI0.1101$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.