EF1 tornado, Potosi to Potosi Wshngtn Co Ar, Missouri, April 8, 2015

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

April 8, 2015

Touchdown

3:30 PM CDT (20:30 UTC)

Lifted

3:38 PM CDT (20:38 UTC)

On the ground

8 minutes

Path length

4.1 miles (6.6 km)

Path width

300 yards (274 m)

Deaths

0

Injuries

0

County

Washington County

Touchdown point

37.945, -90.799

Lift-off point

37.920, -90.731

Record number

1504081430-01

18 damage points were recorded along this path by NWS LSX, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF1. The highest wind the damage implies is 104 mph.

• church complex west side of Potosi. roof shingles blown off
• mobile home used for storage. roof off. debris blown to west. Power poles leaning to west polespoles also leaning to
• roof blown off building and canopy
• canopy and front part of roof damaged

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

A cold front was moving through the region, triggering showers and thunderstorms. There were numerous reports of large hail, a tornado in Washington County Missouri and several reports of flash flooding.

The tornado formed and caused damage on the west side of Potosi. Roof shingles were blown off several church buildings, trees were downed, and a mobile home used for storage was destroyed. The tornado moved east-southeast down High Street in Potosi causing roof damage to several businesses, downed trees, power lines and business signs. The tornado crossed Highway 21 and continued along Highway 8 causing tree damage in the Spring Town Road area. About a half mile east of the Potosi city limits the tornado destroyed a building at a saw mill along Highway 8. The tornado continued for about another half mile causing tree damage and then dissipated.

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

23 minutes of warning. NWS LSX issued a tornado warning for this county at 20:07 UTC, 23 minutes before the tornado touched down, in force until 20:30 UTC.

The county was under a severe thunderstorm watch, issued at 19:23 UTC and running to 21:09 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 Enhanced Risk, with a 0.10 chance of a tornado within 25 miles, in the hatched area where significant tornadoes were expected. The outlook in force was issued at 19:32 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 St Louis radar (KLSX), 86 km away, was scanning. The volume nearest the touchdown began at 20:29 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 2015 tornado in MissouriEvery tornado in Missouri since 1950Warnings in force in Missouri nowThe forecast where you are

6 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.