Tornadoes · United States · Iowa · 1979

F0 tornado, Davis County, Iowa, June 20, 1979

This F0 tornado ran 3.6 miles across Davis County on June 20, 1979, touching down at 1:20 AM CDT and reaching 30 yards wide. It killed nobody, and did $5,000 to $50,000 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 mphthis tornado

    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 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
F0
Date
June 20, 1979
Touchdown
1:20 AM CDT (06:20 UTC)
Path length
3.6 miles (5.8 km)
Path width
30 yards (27 m)
Deaths
0
Injuries
0
Property damage
$5,000 to $50,000
County
Davis County
Touchdown point
40.780, -92.420
Lift-off point
40.830, -92.370
Record number
378

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

6.3 hours before the tornado, 236 km from the path. June 20, 1979.

Skew-T log-pSkew-T log-p diagram, Peoria Regional, IL at 00:00Z on 1979-06-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 724 joules per kilogram, CIN -97, lifted condensation level 2217 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 1979-06-20The 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 5 square meters per square second, 0 to 6 km bulk shear 9 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
724 J/kg
Mixed-layer CIN
-97 J/kg
Surface CAPE
1544 J/kg
Mixed-layer LCL
2217 m above ground
0-6 km bulk shear
9 kt
0-1 km bulk shear
14 kt
0-1 km storm-relative helicity
5 m²/s²
0-3 km storm-relative helicity
64 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

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

5.7 hours after it, 236 km from the path. June 20, 1979.

Skew-T log-pSkew-T log-p diagram, Peoria Regional, IL at 12:00Z on 1979-06-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 1516 joules per kilogram, CIN -78, lifted condensation level 979 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 1979-06-20The 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 48 square meters per square second, 0 to 6 km bulk shear 38 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
1516 J/kg
Mixed-layer CIN
-78 J/kg
Surface CAPE
1803 J/kg
Mixed-layer LCL
979 m above ground
0-6 km bulk shear
38 kt
0-1 km bulk shear
19 kt
0-1 km storm-relative helicity
48 m²/s²
0-3 km storm-relative helicity
15 m²/s²
Significant tornado parameter
0.3
Supercell composite
0.9
0-3 km lapse rate
5.8 K/km

Open this sounding in Storm Lab

This ground now

The live radar over the trackEvery 1979 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

The other tornadoes of June 20, 1979

9 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
June 201:50 PM EDTF0Bay, MI0.827$5,000 to $50,000
June 202:35 PM EDTF0Suwannee, FL0.110under $50
June 202:14 PM ESTF0Putnam, IN0.110
June 202:45 PM CDTF1Winnebago, WI0.1102$50,000 to $500,000
June 203:30 PM CDTF1Marinette, WI0.1101$50,000 to $500,000
June 204:15 PM CDTF1Racine, WI0.1101$5,000 to $50,000
June 204:20 PM CDTF0Iron, MI0.110$500 to $5,000
June 205:53 PM EDTF0Marquette, MI0.110
June 206:41 PM EDTF2Lenawee, MI0.627$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.