EF2 Tornado — Montgomery, Pennsylvania

2021-09-01 · near Flourtown, Montgomery, Pennsylvania

Event narrative

A semi-discrete supercell thunderstorm began to exhibit rotation

over Delaware County, PA around 5:15 PM on September 1. The

rotation continued north-northeast into Montgomery County, and

eventually strengthened enough to produce a tornado. Minor tree

damage was first observed along Stenton Ave in Fort Washington in

the area of the Philadelphia Cricket Club. A path of tree damage

was observed heading northeast along Joshua Rd and through Fort

Washington State Park. Some minor shingle and siding damage to

houses was also seen.

Damage became more severe after the tornado crossed the

Pennsylvania Turnpike. At this time the tornado also moved into a

more residential area. Damage was observed along Montgomery Ave,

Spring Ave, and Prospect Ave and numerous crossing streets of

those. This mainly consisted of numerous snapped and uprooted

trees with minor to moderate roofing and siding damage to a number

of homes. The worst damage was observed slightly farther

northeast in the area of Stuart Creek in Upper Dublin. A number of

homes suffered partial to near total loss of roofing with many

damaged to the point of being uninhabitable. At least one home

experienced partial collapse of exterior walls consistent with EF2

tornado damage. Nearly all trees were snapped or heavily damaged

in this area as well.

Damage continued along Route 309 to the area of Upper Dublin High

School. The high school itself suffered roofing damage, and

significant roofing loss occurred to an Upper Dublin Township

building adjacent to the high school. A number of residences along

Loch Alsh Ave and several surrounding streets were also damaged.

A woman was killed when a tree fell on her home on Kenyon Dr, the

only known tornado-related fatality from this tornado or any

tornado during this regional outbreak.

Further northeast, damage occurred on and around the Temple

University Ambler Campus, again consisting of considerable tree

damage and partial roofing loss on a number of homes and

university buildings. The tornado then moved into Maple Glen,

crossing a heavily developed area near Norristown Rd at Limekiln

Pike. Snapped trees and mostly minor roofing and siding damage to

several commercial buildings was observed in this area. The

tornado remained continuous but did begin to lose some intensity

as it moved into Horsham Twp, traveling east of Limekiln Pike. A

number of trees were snapped along Babylon Rd. Near Horsham Rd,

roofing damage occurred to a veterinary hospital, along with

additional large trees snapped. Damage appeared to end not long

after that point. The tornado crossed Horsham Rd, but little to no

damage was observed in a couple of parks across the road,

approaching the Bucks County line. The tornado is believed to have

lifted in that area.

Wider weather episode

The remnants of Hurricane Ida impacted the mid-Atlantic on September 1, 2021. As it moved northward, Ida began transitioning to a strong mid-latitude cyclone with pronounced frontal features, but with continued tropical moisture. On a regional level, the remnants of Ida became one of the most severe natural disasters in US history, due to a combination of several tornadoes, some of them strong, as well as catastrophic flooding over a large and densely populated area. The severe weather threat unfolded as the system's developing warm front lifted northward from the Delmarva region into Pennsylvania and New Jersey. South of the warm front, partial clearing and moderate to strong instability developed. Meanwhile, very strong shear and forcing, along with tropical moisture, were present within the warm sector. The result was widespread convection in the form of both supercell and quasi-linear thunderstorms. A number of storms became severe across the region, producing several tornadoes and other instances of wind damage. This continued an exceptionally active stretch of high end severe weather in the region, coming barely a month after the tornado outbreak of July 29.

View location on OpenStreetMap → (40.1070, -75.2380)

Source: NOAA Storm Events Database, event_id 972354. Narrative written by the NWS forecast office that issued the report.