EF1 tornado, Winterset Arpt to Patterson, Iowa, August 20, 2019

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

August 20, 2019

Touchdown

5:21 AM CDT (10:21 UTC)

Lifted

5:23 AM CDT (10:23 UTC)

On the ground

2 minutes

Path length

1.2 miles (2.0 km)

Path width

150 yards (137 m)

Deaths

0

Injuries

0

Property damage

$5,000

Crop damage

$500

County

Madison County

Touchdown point

41.486, -93.932

Lift-off point

41.470, -93.920

Record number

1908200421-01

Generally speaking, a bit of everything occurred during an overnight/early morning severe mesoscale convective system that rolled across Iowa. The predominant weather revolved around damaging winds and heavy rainfall, though a few instances of severe hail and low end tornadoes were experienced as well. Among the reports, numerous trees were downed, buildings damaged or destroyed from straight line winds or one of the weak tornadoes, and numerous instances of 2 to 4 plus inches of heavy rainfall. ||On the setup side of the coin, a lot of factors were in line for the event to potentially be a sustained nocturnal severe weather event. The previous day, the 19th, saw surface high pressure begin to exit the region eastward and allowing southerly return flow to work into eastern Nebraska and western Iowa. Tied in with mid to upper 70 dew points and steep mid-level lapse rates, a large area of 4000 plus J/kg CAPE values developed across eastern Nebraska and western Iowa and slowly built eastward. Additionally, effect bulk shear was consistently in the 40 to 50 kt range and low level shear roughly oriented to expected storm motion. As the evening progressed and the low level jet finally began to ramp up, boosting warm air advection and positive moisture flux, storms began to develop and eventually congeal. Organization, at least with regards to strong to severe criteria, was not immediate, waiting until around 5am local time to produce its first severe report. Severe reports then continued as the system moved southeast over the next 4 plus hours.

The first of three tornadoes associated with a rapidly advancing QLCS. The tornado produced EF1 damage to a rural residence along with damage to trees in the area.

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 severe thunderstorm watch, issued at 04:58 UTC and running to 11:53 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. The outlook in force was issued at 06:02 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.

Des Moines (DSM), 24 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), 33 km away, was scanning. The volume nearest the touchdown began at 10:18 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 2019 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

2 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.