F2 tornado, Derry to Millwood, Pennsylvania, August 15, 1997

1. F040 to 72 mph

   Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.

2. F173 to 112 mph

   Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

3. F2113 to 157 mphthis tornado

   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. F3158 to 206 mph

   Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.

5. F4207 to 260 mph

   Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

6. F5261 to 318 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

F2

Date

August 15, 1997

Touchdown

6:10 PM EDT (22:10 UTC)

Path length

3.5 miles (5.6 km)

Path width

200 yards (183 m)

Deaths

0

Injuries

2

Property damage

$800,000

County

Westmoreland County

Touchdown point

40.330, -79.320

Lift-off point

40.350, -79.270

Record number

580

A severe thunderstorm produced a tornado that produced substantial damage in a residential area east-northeast of Latrobe along the foothills of the Chestnut Ridge. The tornado first touched down 1 mile west of Derry. The tornado completely destroyed a large tier of metal stadium bleachers at a high school football field and wrapped them against a utility pole. A nearby roof of a business was damaged and a mobile home was completely destroyed and a few mobile homes sustained damage. The tornado then tracked through a rural area, damaging some farm buildings and downing field corn. The tornado continued its rapid (estimated forward speed 50-60 miles per hour) northeast track and caused significant damage in a mobile home park in Derry. The tornado crossed Route 217 and downed trees across railroad tracks and then entered a residential area in Millwood. One frame house in Millwood was severely damaged and part of a room addition collapsed and trapped a resident, who was treated at the scene. A resident of a mobile home sustained minor injuries as well. Numerous trees were uprooted and large branches and power lines were downed along the track of the storm. One home along Route 217 had a branch embedded into the house siding. The tornado was estimated to have wind speeds of between 90 and 120 miles per hour, briefly attaining an F-2 rating on the Fujita Tornado Scale. All tolled, 7-8 mobile homes were destroyed (3 totally decimated), 10-12 sustained major damage, 15-18 sustained minor damage. One frame house was heavily damaged and about 10 sustained minor damage. One car was destroyed when a tree fell on it. Parked next to the auto was another car with two occupants that were not injured. About 10 other cars were damaged. An open-air church in Millwood was also heavily damaged. The tornado appeared to have dissipated as it entered the heavily wooded slopes of the Chestnut Ridge.

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 05:56 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 Pittsburgh radar (KPBZ), 81 km away, was scanning. The volume nearest the touchdown began at 22:07 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.

The live radar over the trackEvery 1997 tornado in PennsylvaniaEvery tornado in Pennsylvania since 1950Warnings in force in Pennsylvania nowThe forecast where you are

1 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.