EF0 tornado, Delavan, Wisconsin, August 20, 2018

1. EF065 to 85 mphthis tornado

   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. 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

EF0

Date

August 20, 2018

Touchdown

8:01 PM CDT (01:01 UTC)

Lifted

8:05 PM CDT (01:05 UTC)

On the ground

4 minutes

Path length

0.7 miles (1.1 km)

Path width

150 yards (137 m)

Deaths

0

Injuries

0

Property damage

$15,000

County

Walworth County

Touchdown point

42.627, -88.628

Lift-off point

42.630, -88.642

Record number

1808201901-01

15 damage points were recorded along this path by NWS MKX, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF0. The highest wind the damage implies is 70 mph.

• metal casing around pole blown off and deposited to the southwest in lawn of delavan mercy medical center.
• freestanding dumpster on wheels tipped to the west. partially full.
• several large branches down
• rubber roofing material lifted and set down.

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

An organized and slow moving low pressure area within a very moist airmass resulted in 9 to 15 inches of rain and historic flash flooding from the west side of Madison to Mazomanie, and south to Belleville. State of Emergencies were declared with hundreds of homes flooded and hundreds of citizens evacuated or stranded in the flood waters. The flash flooding of streets and creeks on the west side of Madison resulted in the drowning death of one man. The already high levels of the Yahara Chain of Lakes reached record levels for the end of August into early September. This resulted in sustained flooding in sections of the isthmus in Madison and lakeshore areas of Lake Monona and Lake Waubesa. In addition to the historic flash flooding, one EF0 tornado occurred in Delavan in Walworth Co. A couple firefighters were indirectly struck by lightning and suffered minor injuries in Cross Plains. Lightning also was the cause of a house fire near Cross Plains.

Damage was noted to flags, a large tree limb and metal casing from a US Bank |sign. A small dumpster was also tipped behind the bank. The tornado then tracked to the west northwest through the Wileman Elementary School grounds where numerous large tree limbs were downed. Rubber roofing material on a portion of the school building was lifted and set back in place. The tornado then tracked through residences to the west northwest downing numerous limbs and a rotted/damaged tree. Gutter and roofing damage was noted on one home.

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.

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 General Thunderstorms Risk. The outlook in force was issued at 00:45 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 Milwaukee radar (KMKX), 38 km away, was scanning. The volume nearest the touchdown began at 01:01 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 WisconsinEvery tornado in Wisconsin since 1950Warnings in force in Wisconsin nowThe forecast where you are

5 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.