A broken line of supercells, which formed along a front, moved quickly through the Ohio River Valley the evening of October 21st and spun off several tornadoes. The number of tornadoes, time of year, and intensity (one long track EF2 tornado) will mark this event as very rare and significant for this region.
Prior to tornado development, surface temperatures warmed into the low-mid 60s; dew points topped out near 60F.  Forecast soundings indicated modest levels of mean layer CAPE, and a relatively straight hodograph yielding marginal but sufficient storm relative helicity. The overall quick track of the broken line and eastward propagation helped cells sustain rotating updrafts.

Tornado in WASHINGTON, PENNSYLVANIA
From 21-OCT-21 18:30:00 to 21-OCT-21 18:57:00 (EST-5)
Location: INDEPENDENCE
Tornado F-scale: EF2
Property damage: 7.50M
Reported by: NWS Storm Survey

A NWS damage survey confirmed that an EF-2 tornado, with winds
peaking near 130 MPH, tracked through western Washington County
on the evening of October 21, 2021. The length was over 15 miles
long and the width varies in some areas but the maximum was between 600
to 700 yards. This tornado was associated with the same circulation
that initially produced a tornado in Jefferson County, Ohio earlier.
Weak tornado damage was first noted along Brashears Run Road with
a few fallen trees. The storm rapidly intensified along Indian
Camp Rd, where a mobile home had roof damage and a well-structured
deck was ripped and tossed into the neighbors yard. Many trees
were snapped and uprooted as well. Damage in this area was
consistent with winds speeds of 90-95 MPH.
The tornado continued east towards Hopewell Township. Noted roads
that had tree and structure damage, associated with EF-1 damage,
were along Short Cut Road, Scenic Drive, Raccoon Run Road, Possum Hollow
Road, Old Trail Road, Jefferson Avenue, Park View Drive, and
Oakleaf Road.
Peak intensity was reached near Willow Road and Lowry
Lane where a two story home had a roof completely torn off and
tossed about 100 feet and a few portions of the walls collapsed.
With closer inspection, a few of the foundation blocks were
shifted on both sides of the house. Peak wind was near 130 MPH in
this region. A few hundred feet away a farm building was
completely destroyed. As the tornado crossed Lynn Portal Road and
advanced along White Lane, a solid brick home lost the roof and
the attached garage.
The tornado started to weaken, but still continued to hold near
100 MPH winds, as it tracked across McCarrell Road, Western Ave,
and towards the outskirts of the city of Houston, PA. The tornado
appears to have dissipated near North Main Street and Pine Ave
north of Houston, PA.
At least $600,000 of damage was noted by PEMA to four different structures.
The total cost of destruction was estimated by the NWS Storm Surveyor.

Tornado in ALLEGHENY, PENNSYLVANIA
From 21-OCT-21 18:41:00 to 21-OCT-21 18:42:00 (EST-5)
Location: EMSWORTH
Tornado F-scale: EF0
Property damage: 50.00K
Reported by: NWS Storm Survey

A damage survey confirmed that a brief tornado occurred in and
near the Mount Nebo Pointe shopping center.  Damage at the Target
store included broken glass in the entry doors (which were sucked
outward by the wind), as well as damage to a sign on the west-
facing side of the store.  Minor tree damage and tall grass
blowdown was noted on the eastern side of the shopping center and
tree damage was noted at the base of the hill on the western
side.   The circulation lifted very soon after as it reached a
small gully to the east. Damage indicators were consistent with a
maximum wind speed of 70 MPH during this brief event.

Tornado in ALLEGHENY, PENNSYLVANIA
From 21-OCT-21 18:47:00 to 21-OCT-21 18:55:00 (EST-5)
Location: ALLISON PARK
Tornado F-scale: EF1
Property damage: 500.00K
Crop damage: 100.00K
Reported by: NWS Storm Survey

A damage survey confirmed that a tornado tracked across the
southern portion of Hampton Township, PA.  This tornado was
associated with the same circulation that initially produced a
brief tornado earlier in Mount Nebo. Damage was first noted in the
area of Auld and Forest Avenues, in the form of light structural
damage to homes.  The tornado strengthened on Linden Drive, with
several snapped hardwood and softwood trees, as well as the
uplift of a roof.  Damage in this area was consistent with wind
speeds of 90 to 95 MPH.  Snapped and uprooted trees were seen as
the tornado continued across Parkview Lane and then to Duncan
Avenue. Farther east, in the Church Hill area, snapped and
uprooted trees were observed, with one large tree on a house on
Cole Avenue, and some other minor structural damage where Cole
intersects with Miller Avenue as well as Cella Lane, representing
a rough tornado track width of 200 yards.  The tornado weakened
considerably after it crossed Route 8 and into Bryant, before
causing more damage in the vicinity of Middle Road. Widespread
snapped hardwood trees were seen between John Giel Drive and
Green Valley Drive, and a cinder-block outbuilding was destroyed,
with debris being blown downwind 1/4 mile.  Damage here was
consistent with 100 to 105 MPH wind.  Tree damage continued ENE
into Hartwood Acres Park and then to Dorseyville Road, where the
damage path finally ended as the tornado dissipated. NWS
Pittsburgh is grateful to  Hampton Township and Allegheny County
EMA for their assistance with this damage survey.
Damage cost was estimated using information from the local emergency manager.

Tornado in BEAVER, PENNSYLVANIA
From 21-OCT-21 17:56:00 to 21-OCT-21 17:59:00 (EST-5)
Location: NEW GALILEE
Tornado F-scale: EF1
Reported by: NWS Storm Survey

The National Weather Service in Pittsburgh conducted a storm
survey in far northern Beaver County just northeast of New Galilee.
The damage was confined along either side of Fairlane Boulevard /
State Route 351. Majority of the damage was hardwood and softwood
trees missing large branches. One softwood tree was uprooted, which
was the damage indicator that warranted the EF1 rating. One of the
large branches fell onto a detached garage causing damage to the
roof. The tornado lifted prior to reaching the intersection of State
Route 351 and Big Beaver Boulevard.

Tornado in WASHINGTON, PENNSYLVANIA
From 21-OCT-21 18:58:00 to 21-OCT-21 19:00:00 (EST-5)
Location: GALE
Tornado F-scale: EF1
Reported by: NWS Storm Survey

The National Weather Service conducted a survey off E Finley Dr in
Washington County. The damage path was oriented west-to-east near
a road that consisted of farms and residences. Damage consisted
of several snapped and uprooted hardwood trees, roof damage to a
shed, and a completely destroyed barn. Estimated Maximum Wind Speed...100 mph.

Tornado in WASHINGTON, PENNSYLVANIA
From 21-OCT-21 19:07:00 to 21-OCT-21 19:10:00 (EST-5)
Location: THOMAS
Tornado F-scale: EF1
Property damage: 325.00K
Reported by: NWS Storm Survey

A NWS damage survey confirmed that an EF-1 tornado, with winds
speeds ranging between 90 to 95 MPH, tracked through portions of
Peters Township in Washington County on the evening of October
21, 2021. The length was 1.5 miles and the width in some areas
was about 100 to 200 yards. This tornado was associated with the same
circulation that initially produced an EF-1 tornado in Jefferson
County, OH and an EF-2 in Hopewell Township a few miles to the
west.
A few broken branches were noted along Thomas Road near
Peters Lake Park. However, the tornado quickly intensified as it
cross Hill Place Road. Trees were uprooted and snapped in the
vicinity of Springdale Road and Sunrise Lane. A number of new and
well-structured brick homes had window damage, a garage blown
out, shingle damage, and trees snapped. The tornado weakened and
dissipated just west of Bower Hill Road.
A detailed review by PEMA noted damage to 4 homes on Hill Place Road,
5 homes on Sunrise Road, 5 homes on Springdale Road, 1 home on
Buckingham Drive, and 2 homes on Sienna Trail.

Damage cost was estimated by NWS Storm Surveyor.

Tornado in BEAVER, PENNSYLVANIA
From 21-OCT-21 18:11:00 to 21-OCT-21 18:15:00 (EST-5)
Location: HAZEN
Tornado F-scale: EF1
Reported by: NWS Storm Survey

The National Weather Service in Pittsburgh conducted a storm survey
in far northeastern Beaver County in Franklin Township eastward to
Harmony Township, Butler County. The damage, much like previous ones
for this event, was regulated to hardwood and softwood trees. There
was no structure damage observed along the track.
Damage initially started on American School Road then east along
North Camp Run Road. The most intense damage was recorded farther
down American School Road where at least 30 hardwood trees were
uprooted or had large branches blown down. As the tornado continued down
American School Road, downed softwood trees and hardwood trees snapped
at the trunk were observed. The tornado lifted as it crossed into
Butler County just beyond the intersection of American School Road
and Scott Ridge Road.

Tornado in BUTLER, PENNSYLVANIA
From 21-OCT-21 18:33:00 to 21-OCT-21 18:51:00 (EST-5)
Location: MT CHESTNUT
Tornado F-scale: EF0
Reported by: NWS Storm Survey

A damage survey confirmed a discontinuous tornado path causing
sporadic tree damage of varying intensity as it tracked across
central Butler County. The most significant damage was noted
along Woodcrest Road, where numerous trees were snapped or
uprooted and flagpoles were bent over by the wind.  Damage was
consistent with wind up to 80 mph. This tornado was part of a
radar-indicated circulation that began in Beaver County.

Tornado in WASHINGTON, PENNSYLVANIA
From 21-OCT-21 18:59:00 to 21-OCT-21 19:00:00 (EST-5)
Location: PLEASANT GROVE
Tornado F-scale: EF1
Reported by: NWS Storm Survey

A NWS damage survey, conducted both by ground and aerial drone,
confirmed that an EF-1 tornado, with speeds ranging between 80 and
90 mph, tracked through eastern portions of East Finley township
on the evening of October 21, 2021. The tornado initially touched
down on open farmland approximately 0.4 miles west of Quaker Ridge
road, where drone footage discovered damage to several trees
along opposing tree lines, with a distinct scouring pattern
observed in the open pasture between them. The tornado continued
eastward through wooded area, producing the most significant
damage to a cluster of trees along Quaker Ridge Road adjacent to
the parking area for Pennsylvania State Games lands. At least 10
mature trees of up to 8 inches in diameter were snapped anywhere
from 1/4 to 3/4 of the way up the trunk line. The tornado
continued east across Quaker Ridge road into the woodlands for
another 100 ft, producing lesser tree damage until dissipating.
This damage is coincident with a strong radar signature from both
the NWS Pittsburgh and Pittsburgh International Airport Doppler
radars. A thorough survey of the area several miles west and east
of this tornado yielded no additional damage.

Tornado in BUTLER, PENNSYLVANIA
From 21-OCT-21 18:15:00 to 21-OCT-21 18:16:00 (EST-5)
Location: MIDDLE LANCASTER
Tornado F-scale: EF1
Reported by: NWS Storm Survey

This is a continuation of the tornado track that began in Franklin Township, Beaver County.  The summary of the full tornado path is included below.
The National Weather Service in Pittsburgh conducted a storm survey
in far northeastern Beaver County in Franklin Township eastward to
Harmony Township, Butler County. The damage, much like previous ones
for this event, was regulated to hardwood and softwood trees. There
was no structure damage observed along the track.
Damage initially started on American School Road then east along
North Camp Run Road. The most intense damage was recorded farther
down American School Road where at least 30 hardwood trees were
uprooted or had large branches blown down. As the tornado continued down
American School Road, downed softwood trees and hardwood trees snapped
at the trunk were observed. The tornado lifted as it crossed into
Butler County just beyond the intersection of American School Road
and Scott Ridge Road.