Tornadoes · United States · Iowa · 1985

F1 tornado, Marion and Mahaska counties, Iowa, May 11, 1985

This F1 tornado ran 2.0 miles across Marion and Mahaska counties on May 11, 1985, touching down at 4:40 PM CDT and reaching 50 yards wide. It killed nobody and injured 4, 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 11, 1985
Touchdown
4:40 PM CDT (21:40 UTC)
Path length
2.0 miles (3.2 km)
Path width
50 yards (46 m)
Deaths
0
Injuries
4
Property damage
$5,000 to $50,000
Counties
Marion and Mahaska counties
Touchdown point
41.270, -92.880
Lift-off point
41.270, -92.850
Record number
220

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

9.7 hours before the tornado, 282 km from the path. May 11, 1985.

Skew-T log-pSkew-T log-p diagram, Peoria Regional, IL at 12:00Z on 1985-05-11Temperature 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 -7807, lifted condensation level 677 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 1985-05-11The 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 51 square meters per square second, 0 to 6 km bulk shear 14 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
-7807 J/kg
Surface CAPE
0 J/kg
Mixed-layer LCL
677 m above ground
0-6 km bulk shear
14 kt
0-1 km bulk shear
32 kt
0-1 km storm-relative helicity
51 m²/s²
0-3 km storm-relative helicity
116 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
4.0 K/km

Open this sounding in Storm Lab

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

2.3 hours after it, 282 km from the path. May 12, 1985.

Skew-T log-pSkew-T log-p diagram, Peoria Regional, IL at 00:00Z on 1985-05-12Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 782 joules per kilogram, CIN -60, lifted condensation level 976 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 1985-05-12The 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 118 square meters per square second, 0 to 6 km bulk shear 37 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
782 J/kg
Mixed-layer CIN
-60 J/kg
Surface CAPE
1446 J/kg
Mixed-layer LCL
976 m above ground
0-6 km bulk shear
37 kt
0-1 km bulk shear
16 kt
0-1 km storm-relative helicity
118 m²/s²
0-3 km storm-relative helicity
207 m²/s²
Significant tornado parameter
0.4
Supercell composite
3.2
0-3 km lapse rate
6.5 K/km

Open this sounding in Storm Lab

The surface observations

Ottumwa (OTM), 40 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
20:00 UTC7263150° 25 kt331000
21:00 UTC7563150° 20 kt30998
22:00 UTC7462140° 22 kt29998
22:36 UTC140° 21 kt997
23:00 UTC7055360° 11 kt998.3TS
23:20 UTC160° 7 kt998

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

This ground now

The live radar over the trackEvery 1985 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

The other tornadoes of May 11, 1985

23 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
May 113:45 PM CDTF0Holt, NE0.550
May 113:58 PM CDTF0Polk, IA1.050$5,000 to $50,000
May 114:10 PM CDTF0Parker, TX0.530
May 114:22 PM CDTF0Charles Mix, SD0.110
May 114:30 PM CDTF0Charles Mix, SD0.110
May 115:15 PM CDTF0Poweshiek, IA1.020$5,000 to $50,000
May 115:15 PM CDTF0Douglas, SD20.010
May 115:55 PM CDTF0Hanson, SD15.010
May 116:03 PM CDTF0Davison, SD0.110
May 116:04 PM CDTF0McCook, SD0.110
May 116:04 PM CDTF0Miner, SD4.0100
May 116:08 PM CDTF0McCook, SD0.110
May 116:15 PM CDTF0Miner, SD0.110
May 116:15 PM CDTF0Sanborn, SD0.110
May 116:24 PM CDTF0Douglas, SD0.110
May 116:24 PM CDTF0Sanborn, SD0.110
May 116:46 PM CDTF0Miner, SD5.010
May 116:51 PM CDTF0Miner, SD4.010
May 117:08 PM CDTF0Kingsbury, SD0.110
May 117:40 PM CDTF0Douglas, MN0.517
May 117:40 PM CDTF0Kingsbury, SD0.110
May 1112:10 AM CDTF1Green Lake, WI2.02001$500,000 to $5 million
May 1112:36 AM CDTF1Fond du Lac, WI0.150$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.