EF0 tornado, Percy, Iowa, May 3, 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

May 3, 2018

Touchdown

7:48 PM CDT (00:48 UTC)

Lifted

7:50 PM CDT (00:50 UTC)

On the ground

2 minutes

Path length

1.1 miles (1.7 km)

Path width

25 yards (23 m)

Deaths

0

Injuries

0

County

Marion County

Touchdown point

41.487, -93.246

Lift-off point

41.500, -93.233

Record number

1805031848-01

2 damage points were recorded along this path by NWS DMX, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF0. The highest wind the damage implies is 80 mph.

• Path through trees including 2 trees that were snapped off near the base

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

For a third consecutive day, a boundary found itself draped from NE to SW roughly cutting the state of Iowa in half. Similar afternoon conditions resulted as well with 1000 - 2000 J/kg MUCAPE, little CIN, and borderline to good effective bulk shear around 30 to 40 kts and pushing 50 kts at times. With storms more closely rooted to the boundary, low level helicity in excess of 150 m2/s2 raised at least some concern for tornadoes. After a few initial discrete cells, storms eventually congealed into a progressive QLCS that moved across central Iowa and produced 3 weak tornadoes just east of the Des Moines metro area along with a few reports of wind damage and sub-severe hail.

Tree damage associated with a short lived tornado just adjacent to Des Moines River. Tornado was reported by public.

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

23 minutes of warning. NWS DMX issued a tornado warning for this county at 00:25 UTC, 23 minutes before the tornado touched down, in force until 01:00 UTC.

The county was under a severe thunderstorm watch, issued at 22:24 UTC and running to 02:00 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 20:00 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), 48 km away, was scanning. The volume nearest the touchdown began at 00:45 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

9 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.