EF1 tornado, Elroy to Blooming Glen, Pennsylvania, August 18, 2021

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

August 18, 2021

Touchdown

12:25 AM EDT (04:25 UTC)

Lifted

12:40 AM EDT (04:40 UTC)

On the ground

15 minutes

Path length

8.8 miles (14.1 km)

Path width

140 yards (128 m)

Deaths

0

Injuries

0

Counties

Montgomery and Bucks counties

Touchdown point

40.284, -75.322

Lift-off point

40.392, -75.235

Record number

2108182225-01

37 damage points were recorded along this path by NWS PHI, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF1. The highest wind the damage implies is 105 mph.

• Convergent pattern in corn field

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

The remnants of Tropical Storm Fred affected the mid-Atlantic region on the night of August 18 into the predawn hours of August 19. In addition to heavy rain and areas of flooding, Fred's remnants brought a threat for severe weather. As the center of the system moved from central Pennsylvania into the Finger Lakes region of New York, it became increasingly frontal in nature. A warm sector air mass overspread the eastern mid-Atlantic. Instability was limited due to the overnight timing. However, strong shear and forcing combined with tropical moisture allowed for widespread convection to occur as Fred's remnants moved through. Several instances of damaging wind and a couple of tornadoes occurred in the region during the overnight hours, before the system departed on the morning of the 19th.

A line of thunderstorms moved across Montgomery and Bucks Counties |early on the morning of August 19th as the remnants of Tropical Storm|Fred moved across central Pennsylvania. As a velocity couplet formed across Montgomery County, a tornado |formed roughly a mile and a half south of Souderton, PA around |12:25 AM EDT, where it brought down a tree branch and tore siding |off of a residence on Garrison Lane. From there, the tornado |appears to have lifted briefly before bringing down a few small |trees and branches along Township Line Road, near County Line Rd at Bethlehem Pike. The tornado then moved into Bucks County, where its path continued.

After crossing into Bucks County, the tornado then |brought down several trees and branches in the Hidden Springs |mobile home community. Here, several trees were brought down on |homes and across roadways while also leading to minor damage to |the roofs and siding of several residences in the community. The |tornado then proceeded northeastward into Hilltown Township in |Bucks County as it brought down numerous trees in a trajectory |towards Silverdale. Several trees along this line were also |brought down. A metal roof was even torn off of a garage along |Green Street in Silverdale. Several large branches were then |brought down, damaging a roof to a farmhouse along Souderton Road.|The tornado continued its path northeast, bringing down small |trees and snapping the tops of several pine trees at residences |along Woodlawn Drive and Blue School Road. Lastly, the tornado |began to lift as it neared the opposite end of Hilltown Township, |but not before it ripped a section of roofing off an auto repair |shop along North Dublin Pike at the intersection of Blue School |Road.

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. One was issued for the county at another hour that day.

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 00:51 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 Philadelphia radar (KDIX), 86 km away, was scanning. The volume nearest the touchdown began at 04:25 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 2021 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.