Tornadoes · United States · Iowa · 1977

F1 tornado, Davis County, Iowa, May 4, 1977

This F1 tornado ran 4.3 miles across Davis County on May 4, 1977, touching down at 2:58 PM CDT and reaching 20 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 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
May 4, 1977
Touchdown
2:58 PM CDT (19:58 UTC)
Path length
4.3 miles (6.9 km)
Path width
20 yards (18 m)
Deaths
0
Injuries
0
Property damage
$5,000 to $50,000
County
Davis County
Touchdown point
40.720, -92.370
Lift-off point
40.750, -92.280
Record number
199

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

8.0 hours before the tornado, 230 km from the path. May 4, 1977.

Skew-T log-pSkew-T log-p diagram, Peoria Regional, IL at 12:00Z on 1977-05-04Temperature 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 -8348, lifted condensation level 630 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 12:00Z on 1977-05-04The 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 56 square meters per square second, 0 to 6 km bulk shear 20 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
0 J/kg
Mixed-layer CIN
-8348 J/kg
Surface CAPE
0 J/kg
Mixed-layer LCL
630 m above ground
0-6 km bulk shear
20 kt
0-1 km bulk shear
12 kt
0-1 km storm-relative helicity
56 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
4.4 K/km

Open this sounding in Storm Lab

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

4.0 hours after it, 230 km from the path. May 5, 1977.

Skew-T log-pSkew-T log-p diagram, Peoria Regional, IL at 00:00Z on 1977-05-05Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 634 joules per kilogram, CIN -28, lifted condensation level 1006 meters above ground. Wind barbs in knots down the right edge.LCLLFCEL10008507005003002001001 km2 km3 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 1977-05-05The 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 82 square meters per square second, 0 to 6 km bulk shear 21 knots.193958Sfc1 km3 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
634 J/kg
Mixed-layer CIN
-28 J/kg
Surface CAPE
285 J/kg
Mixed-layer LCL
1006 m above ground
0-6 km bulk shear
21 kt
0-1 km bulk shear
25 kt
0-1 km storm-relative helicity
82 m²/s²
0-3 km storm-relative helicity
194 m²/s²
Significant tornado parameter
0.2
Supercell composite
1.2
0-3 km lapse rate
6.8 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 May 4, 1977

29 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
May 49:30 AM CDTF1Allen, KS0.350$500 to $5,000
May 412:30 PM CDTF2Miami, KS11.950$50,000 to $500,000
May 412:40 PM CDTF3Bates, MO29.8500215
May 42:00 PM CDTF1Saline, MO0.150$5,000 to $50,000
May 42:15 PM CDTF3Lafayette, MO26.210015$500,000 to $5 million
May 42:45 PM CDTF3Pettis, MO11.270024$5 million to $50 million
May 43:30 PM CDTF2Lee, IA2.060$50,000 to $500,000
May 43:56 PM CDTF2Des Moines, IA2.010$5,000 to $50,000
May 44:00 PM CDTF2Henry, IA0.1301$50,000 to $500,000
May 44:10 PM CDTF1Henry, IA0.120$5,000 to $50,000
May 44:20 PM CDTF3Colfax, NE7.6200$50,000 to $500,000
May 44:25 PM CDTF0Stanton, NE0.220
May 45:15 PM CDTF1Saunders, NE0.520$500 to $5,000
May 45:40 PM CDTF4Clay, MO12.04005$500,000 to $5 million
May 46:15 PM CDTF4Ray, MO48.68801$500,000 to $5 million
May 46:18 PM CDTF1Swift, MN2.017$5,000 to $50,000
May 47:05 PM CDTF3Douglas, KS31.63001$500,000 to $5 million
May 47:20 PM CDTF2Webster, IA1.0704$500,000 to $5 million
May 47:30 PM CDTF1Pocahontas, IA1.010$500 to $5,000
May 47:32 PM CDTF4Webster, IA2.07014$50,000 to $500,000
May 48:00 PM CDTF2Johnson, KS7.870$50,000 to $500,000
May 48:15 PM CDTF0Guthrie, IA1.010
May 48:26 PM CDTF1Guthrie, IA1.030$5,000 to $50,000
May 49:00 PM CDTF2Martin, MN0.110$5,000 to $50,000
May 49:30 PM CDTF1Boone, IA0.110$5,000 to $50,000
May 410:00 PM CDTF3Tama, IA17.830$50,000 to $500,000
May 411:15 PM CDTF1Tama, IA1.020$5,000 to $50,000
May 411:30 PM ESTF1Carroll, IN1.0501$5,000 to $50,000
May 411:45 PM CDTF1Jasper, IN0.520$5,000 to $50,000

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.