Unrated tornado, Lindgren to Harcourt, 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

11:47 PM CDT (04:47 UTC)

Lifted

11:54 PM CDT (04:54 UTC)

On the ground

7 minutes

Path length

1.9 miles (3.0 km)

Path width

160 yards (146 m)

Deaths

0

Injuries

0

Crop damage

$1,000

County

Webster County

Touchdown point

42.315, -94.204

Lift-off point

42.300, -94.174

Record number

2108082247-01

Five tornadoes occurred in Webster county during the late evening hours as a lone supercell moved southeast. They tornadoes remained in rural areas with damage confined to crops.||The aforementioned supercell began hours earlier in eastern South Dakota/SW Minnesota and trekked to the SE along the SB/MUCAPE gradients within a supportive environment for continued maintenance and rotation. Vicinity MUCAPE values were 2000-3000 J/kg, effective bulk shear 35-40+ kts, LCL values under 1000m, effective helicity around 100-200 m2/s2. Additionally, SBCIN values increased to the S/W/SW of the storm, aiding in allowing it to exist largely by its lonesome.

Weak tornado occurred southwest of Otho and remained in rural areas. Path was determined using high resolution satellite data. No damage indicators were impacted, hence the EFU rating.

Weak tornado occurred north of Harcourt and remained in rural areas. Path was determined using high resolution satellite data. No damage indicators were impacted, hence the EFU rating.

Weak tornado occurred northeast of Harcourt and remained in rural areas. Path was determined using high resolution satellite data. No damage indicators were impacted, hence the EFU rating.

Weak tornado occurred east of Harcourt and remained in rural areas. Path was determined using high resolution satellite data. No damage indicators were impacted, hence the EFU rating.

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

17 minutes of warning. NWS DMX issued a tornado warning for this county at 04:30 UTC, 17 minutes before the tornado touched down, in force until 05:00 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 00:50 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.

Fort Dodge (FOD), 27 km from the path, in the two hours either side.

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

The Des Moines radar (KDMX), 75 km away, was scanning. The volume nearest the touchdown began at 04:47 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.