Tornadoes · United States · Iowa · 2017
EF0 tornado, Larrabee, Iowa, August 18, 2017
This EF0 tornado ran 0.8 miles across Cherokee County on August 18, 2017, touching down at 9:21 PM CDT and reaching 50 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 18, 2017
- Touchdown
- 9:21 PM CDT (02:21 UTC)
- Lifted
- 9:25 PM CDT (02:25 UTC)
- On the ground
- 4 minutes
- Path length
- 0.8 miles (1.3 km)
- Path width
- 50 yards (46 m)
- Deaths
- 0
- Injuries
- 0
- County
- Cherokee County
- Touchdown point
- 42.850, -95.490
- Lift-off point
- 42.840, -95.482
- Record number
- 1708182021-01
The damage survey
3 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 80 mph.
- 3 to 5 inch branches broken
Survey points are preliminary and are the raw material the published rating was built from. Source: NWS Damage Assessment Toolkit.
What the Weather Service recorded
A severe thunderstorm with a history of producing tornadoes moved out of southwest Minnesota into northwest Iowa and produced the strongest tornado of the year in the Sioux Falls area of responsibility.
Tornado resulted in minor crop and tree damage.
From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.
The warnings
27 minutes of warning. NWS FSD issued a tornado warning for this county at 01:54 UTC, 27 minutes before the tornado touched down, in force until 02:30 UTC.
The county was under a severe thunderstorm watch, issued at 21:51 UTC and running to 03:50 UTC.
| Issued (UTC) | Expired | Product | Office |
|---|---|---|---|
| 21:51 UTC | 03:50 UTC | Severe Thunderstorm Watch | FSD |
| 01:54 UTC | 02:30 UTC | Tornado Warning | FSD |
| 02:26 UTC | 03:00 UTC | Tornado Warning | FSD |
| 02:53 UTC | 03:30 UTC | Severe Thunderstorm Warning | FSD |
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. The outlook in force was issued at 01:19 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.
Omaha, NE (KOAX), 00:00Z
2.4 hours before the tornado, 185 km from the path. August 19, 2017.
- Mixed-layer CAPE
- 1353 J/kg
- Mixed-layer CIN
- -118 J/kg
- Surface CAPE
- 2831 J/kg
- Mixed-layer LCL
- 1673 m above ground
- 0-6 km bulk shear
- 45 kt
- 0-1 km bulk shear
- 18 kt
- 0-1 km storm-relative helicity
- 30 m²/s²
- 0-3 km storm-relative helicity
- 61 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 1.1
- 0-3 km lapse rate
- 7.7 K/km
Omaha, NE (KOAX), 12:00Z
9.6 hours after it, 185 km from the path. August 19, 2017.
- Mixed-layer CAPE
- 0 J/kg
- Mixed-layer CIN
- -85180 J/kg
- Surface CAPE
- 0 J/kg
- Mixed-layer LCL
- 1912 m above ground
- 0-6 km bulk shear
- 22 kt
- 0-1 km bulk shear
- 21 kt
- 0-1 km storm-relative helicity
- 83 m²/s²
- 0-3 km storm-relative helicity
- 146 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
- 0-3 km lapse rate
- 3.2 K/km
The radar
The Sioux Falls radar (KFSD), 130 km away, was scanning. The volume nearest the touchdown began at 02:20 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 |
|---|---|---|---|---|
| 01:07 UTC | TORNADO | 5 Nw Melvin | Osceola, IA | EF2 TORNADO TRAVELED 6 MILES WITH A 250 YARD WIDE PATH. THE TORNADO LIFTED AT 8:27 ABOUT A 1/2 MILE SOUTHWEST OF MELVIN. |
| 01:30 UTC | HAIL 1.75 | 4 E Primghar | O'Brien, IA | BROADCAST MEDIA RELAY OF A PUBLIC REPORT. |
| 01:41 UTC | HAIL 1 | 2 W Hartley | O'Brien, IA | |
| 01:44 UTC | HAIL 1.5 | 3 E Primghar | O'Brien, IA | TIME ESTIMATED FROM RADAR. |
| 01:44 UTC | HAIL 1.75 | 4 E Primghar | O'Brien, IA | HAIL FROM 830PM TO 845PM. TIME OF LARGEST HAIL ESTIMATED FROM RADAR. |
| 01:50 UTC | TSTM WND DMG | 2 Nw Melvin | Osceola, IA | FARMSTEAD DAMAGED. NO INJURIES. |
| 01:56 UTC | HAIL 1 | 4 N Sutherland | O'Brien, IA | TIME ESTIMATED FROM RADAR. |
| 01:56 UTC | HAIL 1.25 | 3 Nnw Sutherland | O'Brien, IA | TIME ESTIMATED FROM RADAR. |
| 02:20 UTC | TSTM WND DMG | 3 Ese Larrabee | Cherokee, IA | TWISTED TREES, CORN FLATTENED AROUND 3 MILES EAST, 1 MILE SOUTH OF LARRABEE. TIME ESTIMATED FROM RADAR. |
| 02:20 UTC | HAIL 1 | 5 Ene Larrabee | Cherokee, IA | TIME ESTIMATED FROM RADAR. |
| 02:21 UTC | TORNADO | 3 Ese Larrabee | Cherokee, IA | DELAYED REPORT. EF0 TORNADO SURVEYED 3 ESE LARRABEE. TRAVELED 0.3 MILES WITH A PATH WIDTH OF 25 YARDS. MINOR CROP AND TREE DAMAGE. TORNADO LIFTED AT 9:27 PM. |
From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.
This ground now
The live radar over the trackEvery 2017 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are
The other tornadoes of August 18, 2017
7 more were confirmed in the United States that day.
| Date | Time | Rating | Where | Path (mi) | Width (yd) | Deaths | Injuries | Damage |
|---|---|---|---|---|---|---|---|---|
| August 18 | 5:40 PM EDT | EF0 | Indian River, FL | 0.2 | 20 | |||
| August 18 | 6:29 PM EDT | EF0 | Brevard, FL | 0.4 | 15 | $8,000 | ||
| August 18 | 7:26 PM CDT | EF1 | Nobles, MN | 3.0 | 100 | $500,000 | ||
| August 18 | 7:37 PM CDT | EF1 | Nobles, MN | 1.3 | 100 | |||
| August 18 | 7:47 PM CDT | EF1 | Osceola, IA | 1.6 | 100 | |||
| August 18 | 7:47 PM CDT | EF1 | Nobles, MN | 1.6 | 100 | |||
| August 18 | 8:07 PM CDT | EF2 | Osceola, IA | 5.1 | 250 | $300,000 |
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.