Tornadoes · United States · Iowa · 1977

F1 tornado, Johnson County, Iowa, August 15, 1977

This F1 tornado ran 0.5 miles across Johnson County on August 15, 1977, touching down at 12:15 AM CDT and reaching 60 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, estimated from the damage record rather than surveyed
Date
August 15, 1977
Touchdown
12:15 AM CDT (05:15 UTC)
Path length
0.5 miles (0.8 km)
Path width
60 yards (55 m)
Deaths
0
Injuries
0
Property damage
$50,000 to $500,000
County
Johnson County
Touchdown point
41.670, -91.600
Record number
690

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), 00:00Z

5.3 hours before the tornado, 201 km from the path. August 16, 1977.

Skew-T log-pSkew-T log-p diagram, Peoria Regional, IL at 00:00Z on 1977-08-16Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 670 joules per kilogram, CIN -50, lifted condensation level 942 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 1977-08-16The 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 43 square meters per square second, 0 to 6 km bulk shear 36 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
670 J/kg
Mixed-layer CIN
-50 J/kg
Surface CAPE
1440 J/kg
Mixed-layer LCL
942 m above ground
0-6 km bulk shear
36 kt
0-1 km bulk shear
10 kt
0-1 km storm-relative helicity
43 m²/s²
0-3 km storm-relative helicity
85 m²/s²
Significant tornado parameter
0.1
Supercell composite
1.0
0-3 km lapse rate
5.4 K/km

Open this sounding in Storm Lab

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

6.7 hours after it, 201 km from the path. August 16, 1977.

Skew-T log-pSkew-T log-p diagram, Peoria Regional, IL at 12:00Z on 1977-08-16Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 416 joules per kilogram, CIN -49, lifted condensation level 689 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 1977-08-16The 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 72 square meters per square second, 0 to 6 km bulk shear 28 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
416 J/kg
Mixed-layer CIN
-49 J/kg
Surface CAPE
663 J/kg
Mixed-layer LCL
689 m above ground
0-6 km bulk shear
28 kt
0-1 km bulk shear
27 kt
0-1 km storm-relative helicity
72 m²/s²
0-3 km storm-relative helicity
64 m²/s²
Significant tornado parameter
0.1
Supercell composite
0.6
0-3 km lapse rate
4.9 K/km

Open this sounding in Storm Lab

This ground now

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

The other tornadoes of August 15, 1977

6 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
August 152:30 PM CDTF0Tate, MS0.110
August 155:00 PM CDTF0Monona, IA0.220
August 157:45 PM CDTF0Polk, IA0.260
August 159:30 PM CDTF1Lancaster, NE0.110$5,000 to $50,000
August 159:30 PM CDTF1Iowa, IA0.220$5,000 to $50,000
August 1512:10 AM CDTF1Johnson, IA2.060$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.