Tornadoes · United States · Iowa · 2021
EF0 tornado, Goldfield to Florence, Iowa, August 20, 2021
From Goldfield to Florence, this EF0 tornado ran 4.0 miles across Wright County on August 20, 2021, touching down at 9:05 PM CDT and reaching 190 yards wide. It killed nobody.
The rating scale
Tracks are drawn in the color of the rating. The Enhanced Fujita scale rates the damage rather than measuring the wind: the speeds are what that damage is taken to imply.
EF065 to 85 mphthis tornado
Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.
EF186 to 110 mph
Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.
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.
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.
EF4166 to 200 mph
Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.
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.
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
- EF0
- Date
- August 20, 2021
- Touchdown
- 9:05 PM CDT (02:05 UTC)
- Lifted
- 9:10 PM CDT (02:10 UTC)
- On the ground
- 5 minutes
- Path length
- 4.0 miles (6.5 km)
- Path width
- 190 yards (174 m)
- Deaths
- 0
- Injuries
- 0
- Crop damage
- $1,000
- County
- Wright County
- Touchdown point
- 42.761, -93.914
- Lift-off point
- 42.776, -93.837
- Record number
- 2108202005-01
What the Weather Service recorded
Pre-frontal (warm sector) and cold frontal forced thunderstorms (linear and multicellular) moved across portions of northern Iowa during the evening hours of August 20th producing three tornadoes and heavy rainfall. ||Environmental conditions were favorable for strong to severe storms, including MUCAPE in excess of 3000-4000 J/kg, bulk effective shear around 30 kts ahead of and around 40 kts along the front, 0-3 km bulk shear around 30 to 35 kts roughly perpendicular to storms (especially those ahead of the front), and LCLs around and under 1000m.
Tornado north of Goldfield remained in mostly rural agricultural fields, although some minor tree damage occurred at one farmstead Path was determined using high resolution satellite imagery.
From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.
The warnings
No tornado warning for this county appears in the archive as in force at the moment the tornado touched down.
| Issued (UTC) | Expired | Product | Office |
|---|---|---|---|
| 02:05 UTC | 03:00 UTC | Severe Thunderstorm Warning | DMX |
| 02:46 UTC | 03:30 UTC | Severe Thunderstorm Warning | DMX |
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 forecast that day
The Storm Prediction Center had this point in a Slight Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 00:52 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 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.
Minneapolis, MN (KMPX), 00:00Z
2.1 hours before the tornado, 233 km from the path. August 21, 2021.
- Mixed-layer CAPE
- 395 J/kg
- Mixed-layer CIN
- -100 J/kg
- Surface CAPE
- 717 J/kg
- Mixed-layer LCL
- 1368 m above ground
- 0-6 km bulk shear
- 24 kt
- 0-1 km bulk shear
- 29 kt
- 0-1 km storm-relative helicity
- 233 m²/s²
- 0-3 km storm-relative helicity
- 303 m²/s²
- Significant tornado parameter
- 0.2
- Supercell composite
- 2.4
- 0-3 km lapse rate
- 6.8 K/km
Minneapolis, MN (KMPX), 12:00Z
9.9 hours after it, 233 km from the path. August 21, 2021.
- Mixed-layer CAPE
- 0 J/kg
- Mixed-layer CIN
- -84123 J/kg
- Surface CAPE
- 1 J/kg
- Mixed-layer LCL
- 995 m above ground
- 0-6 km bulk shear
- 51 kt
- 0-1 km bulk shear
- 27 kt
- 0-1 km storm-relative helicity
- 14 m²/s²
- 0-3 km storm-relative helicity
- 50 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
- 0-3 km lapse rate
- 4.1 K/km
The surface observations
Clarion (CAV), 10 km from the path, in the two hours either side.
| Time (UTC) | Temp (°F) | Dew point (°F) | Wind | Gust (kt) | Pressure (mb) | Weather |
|---|---|---|---|---|---|---|
| 00:15 UTC | 82.4 | 78.8 | 150° 13 kt | 20 | 1006.1 | |
| 00:35 UTC | 82.4 | 80.6 | 150° 11 kt | 19 | 1006.8 | |
| 00:55 UTC | 82.4 | 80.6 | 140° 15 kt | 1005.8 | ||
| 01:15 UTC | 82.4 | 80.6 | 150° 12 kt | 19 | 1006.4 | |
| 01:35 UTC | 82.4 | 80.6 | 150° 14 kt | 1005.8 | ||
| 01:55 UTC | 82.4 | 80.6 | 130° 11 kt | 18 | 1006.4 | |
| 02:15 UTC | 78.8 | 78.8 | 330° 17 kt | 23 | 1009.5 | |
| 02:35 UTC | 69.8 | 69.8 | 350° 7 kt | 21 | 1009.5 | FG |
| 02:55 UTC | 69.8 | 69.8 | 310° 12 kt | 20 | 1009.5 | FG |
| 03:15 UTC | 69.8 | 68 | 180° 11 kt | 1009.8 | BR | |
| 03:35 UTC | 69.8 | 68 | 150° 11 kt | 1009.5 | ||
| 03:55 UTC | 68 | 68 | 130° 6 kt | 13 | 1008.5 | BR |
From the Iowa Environmental Mesonet's archive of airport observations.
The radar
The Des Moines radar (KDMX), 116 km away, was scanning. The volume nearest the touchdown began at 02:04 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.
What was reported nearby
Local storm reports within 60 km of the path, in the three hours either side.
| Time (UTC) | Report | Where | County | Remark |
|---|---|---|---|---|
| 00:55 UTC | TSTM WND DMG | 1 W Dakota City | Humboldt, IA | 4 IN TREE BRANCH SNAPPED - 2 BRANCHES. ALSO REPORTED PONDING OF WATER IN CITY STREETS. |
| 02:04 UTC | TSTM WND GST 48 | 4 Ene Renwick | Wright, IA | PEAK WIND THUS FAR FROM CWOP. |
| 02:12 UTC | TSTM WND GST 52 | 3 N Goldfield | Wright, IA | PEAK WIND THUS FAR FROM CWOP MESONET STATION. |
From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.
This ground now
The live radar over the trackEvery 2021 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are
The other tornadoes of August 20, 2021
6 more were confirmed in the United States that day.
| Date | Time | Rating | Where | Path (mi) | Width (yd) | Deaths | Injuries | Damage |
|---|---|---|---|---|---|---|---|---|
| August 20 | 3:34 PM CDT | EF0 | Osceola, IA | 3.6 | 30 | $30,000 | ||
| August 20 | 4:18 PM CDT | EF0 | Cass, ND | 0.4 | 40 | |||
| August 20 | 6:30 PM CDT | Unrated | Kandiyohi, MN | 0.1 | 10 | |||
| August 20 | 6:42 PM CDT | EF0 | Stearns, MN | 2.1 | 50 | |||
| August 20 | 8:03 PM CDT | Unrated | Pocahontas, IA | 1.2 | 20 | |||
| August 20 | 8:19 PM CDT | Unrated | Humboldt, IA | 2.2 | 60 |
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.