Unrated tornado, Ocheyedan, Iowa, August 8, 2021

1. EF065 to 85 mph

   Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.

2. EF186 to 110 mph

   Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

3. EF2111 to 135 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. EF3136 to 165 mph

   Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.

5. EF4166 to 200 mph

   Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

6. EF5over 200 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. Unratedthis tornado

   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.

Rating

Unrated

Date

August 8, 2021

Touchdown

4:36 PM CDT (21:36 UTC)

Lifted

4:38 PM CDT (21:38 UTC)

On the ground

2 minutes

Path length

0.8 miles (1.3 km)

Path width

40 yards (37 m)

Deaths

0

Injuries

0

County

Osceola County

Touchdown point

43.454, -95.583

Lift-off point

43.445, -95.575

Record number

2108081536-01

6 damage points were recorded along this path by NWS FSD, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF0. The highest wind the damage implies is 74 mph.

• Emergency manager observed a small roof portion of a chicken barn had been ripped off the northwest end.
• Drone video shows large branches broken in tree line. Photo courtesy of Dan Gottschalk.
• Drone photo shows large swath of corn felled. Photo courtesy of Dan Gottschalk.
• Drone photo shows wide swath of corn felled in open field. Photo courtesy of Dan Gottschalk.

Survey points are preliminary and are the raw material the published rating was built from. Source: NWS Damage Assessment Toolkit.

An isolated thunderstorm traveled southeast from southwest Minnesota into northwest Iowa along with a compact mesoscale convective vortex. Unstable lapse rates led to brief tornadic development along the track.

The tornado began just east of Starling Avenue north of 140th Street, traveling south southeast across open fields before lifting just west of the Devil's Ridge Wildlife Management Area south of 140th Street. The path was defined on Sentinel satellite imagery through crops. The average path width was 40 yards.

The tornado spun up around one-half mile west of Ocheyedan south of 160th Street. The tornado traveled south southeast along Tanager Avenue where it damaged a few trees along the road. After a little over a mile, the path shifted to the southeast. Just before the tornado dissipated near the intersection of 180th Street and Tyler Avenue, a small portion of a chicken barn roof was damaged. The average path width was 50 yards, defined by drone video. Property damage costs are a rough estimate.

From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.

7 minutes of warning. NWS FSD issued a tornado warning for this county at 21:29 UTC, 7 minutes before the tornado touched down, in force until 22:00 UTC.

Every warning and watch covering the touchdown point that day, from the Iowa Environmental Mesonet's archive of National Weather Service products. Lead time is measured from the issue of the warning in force to the touchdown time in the database, both of which were recorded to the minute by different people.

The Storm Prediction Center had this point in a Marginal Risk, with a 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 20:00 UTC.

SPC's Day 1 convective outlook as it stood when the tornado began, read at the touchdown point. The same archive is on the radar archive.

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.

The Sioux Falls radar (KFSD), 94 km away, was scanning. The volume nearest the touchdown began at 21:38 UTC.

Open the radar archive at this moment, over the track

Reflectivity and velocity, decoded from the Level II archive in the browser. Volumes take a few seconds to open the first time.

Local storm reports within 60 km of the path, in the three hours either side.

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

The live radar over the trackEvery 2021 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

9 more were confirmed in the United States that day.

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.

NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.