EF0 tornado, Fombell to Middle Lancaster, Pennsylvania, July 10, 2017

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

July 10, 2017

Touchdown

3:57 PM EDT (19:57 UTC)

Lifted

4:01 PM EDT (20:01 UTC)

On the ground

4 minutes

Path length

3.2 miles (5.1 km)

Path width

75 yards (69 m)

Deaths

0

Injuries

0

Property damage

$30,000

Counties

Beaver and Butler counties

Touchdown point

40.828, -80.189

Lift-off point

40.842, -80.131

Record number

1707101357-01

Shortwave digging through an upper trough helped to develop two convective systems that crossed the upper Ohio Valley on the 10th. Moderate instability and shear provided for intensification of the second system over central and eastern Ohio but both produced scattered reports of wind damage. An EF-0 tornado was also confirmed in Beaver county, Pennsylvania that then continued into Butler county.

National Weather Service survey team confirmed a tornado near Fombell in Beaver County that continued into Lancaster Township in Butler County in Western Pennsylvania on Jul 10, 2017. A coherent, continuous swath of damage was discovered from near Bowers Lane/North Camp Run Road in Fombell east-northeastward to near the Strawberry Ridge Golf Course in Lancaster Township. Damage was universally to trees, consisting of snapped large limbs and trunk snappage or uproots of both healthy and unhealthy trees. At its most significant, the damage exhibited a rotationally-convergent debris pattern consistent with a weak tornado as it traversed a hillside through the golf course. Observers on the golf course at the time of this storm event reported tree debris being lofted and swirled cyclonically, which was consistent with the debris pattern noted by the survey team. Although not an accepted damage indicator, corn stalks just upstream from this location also were laid over and exhibited a swirl pattern. It should be noted that no structural damage was discovered at any point through the survey path. This lack of damage to structures enables the team to cap the storm's estimated wind speed. Farther to the northeast (at least as far as Eagle Mill Road and Whitestown Road), a coherent, discontinuous damage swath was noted, but lacked sufficient conclusive evidence to identify its origin. It is entirely possible that this damage was an extension of the tornado, but the debris was too sparse for any conclusions. The survey team has concluded that a brief, weak tornado occurred from near Bowers Lane through at least the Scott Ridge Road/McNulty Lane area. The damage was consistent with a tornado of peak wind speed of 60-70 mph, which yields a rating of EF0 on the Enhanced Fujita Scale.

National Weather Service survey team confirmed a tornado near Fombell in Beaver County that continued into Lancaster Township in Butler County in Western Pennsylvania on Jul 10, 2017. A coherent, continuous swath of damage was discovered from near Bowers Lane/North Camp Run Road in Fombell east-northeastward to near the Strawberry Ridge Golf Course in Lancaster Township. Damage was universally to trees, consisting of snapped large limbs and trunk snappage or uproots of both healthy and unhealthy trees. At its most significant, the damage exhibited a rotationally-convergent debris pattern consistent with a weak tornado as it traversed a hillside through the golf course. Observers on the golf course at the time of this storm event reported tree debris being lofted and swirled cyclonically, which was consistent with the debris pattern noted by the survey team. Although not an accepted damage indicator, corn stalks just upstream from this location also were laid over and exhibited a swirl pattern. It should be noted that no structural damage was discovered at any point through the survey path. This lack of damage to structures enables the team to cap the storm's estimated wind speed. Farther to the northeast (at least as far as Eagle Mill Road and Whitestown Road), a coherent, discontinuous damage swath was noted, but lacked sufficient conclusive evidence to identify its origin. It is entirely possible that this damage was an extension of the tornado, but the debris was too sparse for any conclusions. The survey team has concluded that a brief, weak tornado occurred from near Bowers Lane through at least the Scott Ridge Road/McNulty Lane area. The damage was consistent with a tornado of peak wind speed of 60-70 mph, which yields a rating of EF0 on the Enhanced Fujita Scale.

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 Slight Risk, with a 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 16:18 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.

Butler Co. (Awos) (BTP), 19 km from the path, in the two hours either side.

From the Iowa Environmental Mesonet's archive of airport observations.

The Pittsburgh radar (KPBZ), 34 km away, was scanning. The volume nearest the touchdown began at 19:55 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 2017 tornado in PennsylvaniaEvery tornado in Pennsylvania since 1950Warnings in force in Pennsylvania 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.