EF1 tornado, Cromwell, Iowa, October 9, 2018

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 mphthis tornado

   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. 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.

Rating

EF1

Date

October 9, 2018

Touchdown

5:09 PM CDT (22:09 UTC)

Lifted

5:15 PM CDT (22:15 UTC)

On the ground

6 minutes

Path length

2.3 miles (3.7 km)

Path width

250 yards (229 m)

Deaths

0

Injuries

0

Property damage

$40,000

Crop damage

$1,000

County

Union County

Touchdown point

41.028, -94.420

Lift-off point

41.060, -94.435

Record number

1810091609-01

14 damage points were recorded along this path by NWS DMX, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF1. The highest wind the damage implies is 110 mph.

• garage destroyed debris in field
• garage attached by nails, not bolted down
• Entire garage gone, but nailed down versus bolted
• Plastic fencing destroyed, pieces of roof, garage, etc scattered into field.

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

A relatively stationary frontal boundary remained over Iowa on the 9th, a day after the same boundary produced a couple of tornadoes, strong storms, and heavy rainfall. In similar fashion, the environment was conducive for rotating storms. Running down the list of conducive features, LCLs were under 1000m, SBCAPE values were in the 1000-2000 J/kg range, effective bulk shear was in excess of 40kts, and effective storm relative helicity was in excess of 200 m2/s2. All in all, it was not going to take much for storms to rotate and have the potential to product funnel clouds and at least brief tornadoes. Scattered showers and storms were persistent through the afternoon and early evening, with a number producing brief tornadoes.

This tornado developed between Creston and Cromwell in western Union county and traveled on a somewhat unusual northwest path. Tornado was mostly in open rural cropland for nearly two miles producing only crop damage. However, the tornado encountered farmsteads along Clover Avenue about one half mile south of 170th Street. A garage was destroyed on the west side of the road and was rated EF1 damage given generally poor construction. Additional EF1 damage was observed with the nearby house with a portion of the roof and truss structure removed. Tree damage was observed across the road at an adjacent house. Additional minor damage was found about one quarter mile farther up the road with the last damage noted north of 170th Street on the west side of the road where a few roof panels were blown off an old metal shed.

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

No tornado warning for this county appears in the archive as in force at the moment the tornado touched down. One was issued for the county at another hour that day.

The county was under a tornado watch, issued at 18:48 UTC and running to 01:12 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 Slight Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 19:58 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 Des Moines radar (KDMX), 96 km away, was scanning. The volume nearest the touchdown began at 22:09 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 2018 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

22 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.