As a weak cold front dropped south from the Great Lakes on the afternoon of August 27th, a line of thunderstorm was able to develop ahead of the boundary, with a lake breeze off of Lake Erie also aiding initiation. Sufficient shear plus a strong mid-level jet combined with an unstable environment to create a good severe threat as the storms move to the ESE.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS PBZ wrote it up.
As a weak cold front dropped south from the Great Lakes on the afternoon of August 27th, a line of thunderstorm was able to develop ahead of the boundary, with a lake breeze off of Lake Erie also aiding initiation. Sufficient shear plus a strong mid-level jet combined with an unstable environment to create a good severe threat as the storms move to the ESE. The Storm Prediction Center anticipated the threat, placing the region under a slight risk of severe storms. Damaging wind ended up being the primary concern, as many reports of tree and power line damage were received. In a couple of instances, automobiles became involved. At least 55,000 electrical customers across southwest Pennsylvania were without power at one point during the storms. Minor structural damage was reported in a few cases.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Pittsburgh, PA wrote its last area forecast discussion before the first event at Aug 27, 2:03 PM EST, 1 hour 52 minutes earlier.
Area Forecast Discussion National Weather Service Pittsburgh PA 303 PM EDT Thu Aug 27 2020 .SYNOPSIS... Strong to severe thunderstorms are possible again this evening and again on Friday. Widespread rain is expected Friday night through Saturday with drier weather expected Sunday and Monday. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... No change was made for the afternoon update as convection has been limited thus far by very warm, and dry mid levels. Nevertheless, a shortwave moving across the Lakes region indicates a mid level thermal trough which is expected to support dvlpmnt and more balanced updraft potential by early eve. SPC has maintained a slight risk over the forecast area given downdraft potential and increased deep layer shear, especially over the I80 corridor. The severe threat will diminish as instability wanes this eve; however, enough WNW flow aloft will remain with weak shortwaves to keep isolated/scattered showers going in the warm, moist environment. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY/... Showers and thunderstorms will continue on Friday with a crossing weak sfc low and advancing upper trough amid increasing deep tropical moisture with the remnants of Laura. Isolated severe storms are possible during the afternoon hours with strong, damaging winds being the primary threat. Training storms may also cause localized flash flooding. The remnants of Hurricane Laura will cross the region late Friday night into Saturday, eventually merging with the low/trough crossing southern Ontario. Meanwhile, a cold front will cross the upper Midwest into the Ohio Valley. Deep tropical moisture associated with Laura's remnants in advance of this front will serve as the focus for widespread rainfall late Friday night into Saturday. Efficient rainfall with training thunderstorms will pose a flash flooding threat across the area. WPC has highlight most of the region in a slight risk for excessive rainfall. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... The pattern becomes more amplified on Saturday as a ridge builds over the upper Midwest. This feature will cross the Ohio Valley late in the weekend, bringing a dry period to the area for Sunday and Monday. Precipitation chances return on Tuesday with a crossing trough. Near-average temperatures are expected through the long term. && .AVIATION /19Z THURSDAY THROUGH TUESDAY/... Isolated to scattered thunderstorms will be possible through the evening within disturbed flow aloft with best chance from PIT nwd. Convection should generally diminish overnight with the loss of diurnal heating, though additional shortwaves may keep isolated showers going into Friday. Moisture pooling along the eastern slopes will likely lead to MVFR cig development Friday morning, with a stationary sfc boundary sitting north of the forecast area. Additional shortwave support plus increasing tropical moisture will lead to more widespread convection Friday. .Outlook... Restrictions due to showers and thunderstorms are likely through Saturday as remnants of Laura move past the region. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. &&
Hazardous Weather Outlook...UPDATED National Weather Service Pittsburgh PA 508 AM EDT Thu Aug 27 2020 MDZ001-OHZ039>041-048>050-057>059-068-069-PAZ007>009-013>016-020>023- 029-031-073>076-WVZ001>004-012-021-509>514-280915- Garrett-Tuscarawas-Carroll-Columbiana-Coshocton-Harrison- Jefferson OH-Muskingum-Guernsey-Belmont-Noble-Monroe-Mercer-Venango- Forest-Lawrence-Butler-Clarion-Jefferson PA-Beaver-Allegheny- Armstrong-Indiana-Washington-Greene-Westmoreland-Westmoreland Ridges- Fayette-Fayette Ridges-Hancock-Brooke-Ohio-Marshall-Wetzel-Marion- Monongalia-Ridges of Eastern Monongalia and Northwestern Preston- Preston-Eastern Preston-Western Tucker-Eastern Tucker- 508 AM EDT Thu Aug 27 2020 This Hazardous Weather Outlook is for western Maryland, east central Ohio, northwest Pennsylvania, southwest Pennsylvania, western Pennsylvania, northern West Virginia and the northern panhandle of West Virginia. .DAY ONE...Today and tonight. Isolated to scattered severe storms are possible this afternoon and evening. Damaging wind gusts and large hail will be the primary threats, but an isolated tornado will also be possible. Heavy downpours with stronger thunderstorms may pose a localized flash flooding hazard. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. A slight risk for severe thunderstorms will be possible on Friday. Stay tuned for changes to these threats. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to Standard Operating Procedures.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PITTSBURGH PA
105 PM EDT THU AUG 27 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0247 PM TSTM WND DMG 3 ESE LEWISVILLE 40.49N 79.28W
08/25/2020 INDIANA PA SOCIAL MEDIA
SEVERAL SNAPPED TREES AND DAMAGE TO A BARN ALONG ROUTE
217 BETWEEN BLAIRSVILLE AND AULTMAN. TIME ESTIMATED
BASED ON RADAR.
&&
EVENT NUMBER PBZ2001264
JFSpecial Weather Statement
National Weather Service Pittsburgh PA
418 PM EDT Thu Aug 27 2020
PAZ007-008-272045-
Venango-Mercer-
418 PM EDT Thu Aug 27 2020
...A STRONG THUNDERSTORM CAPABLE OF PRODUCING GUSTY WIND WILL AFFECT
NORTHEASTERN MERCER AND SOUTHWESTERN VENANGO COUNTIES...
At 417 PM EDT, a strong thunderstorm was located 10 miles east of
Greenville, or 14 miles northwest of Grove City, moving southeast at
30 mph.
Wind gusts up to 45 mph are possible with this storm.
Locations impacted include...
Stoneboro... Polk...
Sandy Lake... Clintonville...
Fredonia... Jackson Center...
Barkeyville... Maurice K Goddard State Park...
This includes the following highways...
Interstate 79 in Pennsylvania between mile markers 122 and 132.
Interstate 80 in Pennsylvania between mile markers 26 and 33.
This storm may intensify, so monitor local radio or television
stations for additional information and possible warnings from the
National Weather Service.
LAT...LON 4136 8028 4138 8028 4141 8018 4135 7983
4120 7987 4118 7999 4130 8026
TIME...MOT...LOC 2017Z 301DEG 27KT 4135 8020
BrownSpecial Weather Statement
National Weather Service Pittsburgh PA
448 PM EDT Thu Aug 27 2020
PAZ007-008-013>015-022-272115-
Armstrong-Butler-Clarion-Venango-Lawrence-Mercer-
448 PM EDT Thu Aug 27 2020
...A LINE OF STRONG THUNDERSTORMS CAPABLE OF PRODUCING GUSTY WIND
WILL AFFECT SOUTHEASTERN MERCER...SOUTHWESTERN VENANGO...NORTHEASTERN
LAWRENCE...NORTHERN BUTLER...NORTHWESTERN ARMSTRONG AND SOUTHWESTERN
CLARION COUNTIES...
At 448 PM EDT, radar indicated strong thunderstorms were located
along a line extending from 11 miles south of Franklin to 8 miles
northeast of Slippery Rock to near Grove City. Movement was south at
25 mph.
Wind gusts up to 55 mph are possible with these storms.
Locations impacted include...
Butler... Grove City...
Homeacre-Lyndora... Shanor-Northvue...
Meridian... Slippery Rock...
Meadowood... Oak Hills...
Mercer... Prospect...
Chicora... East Brady...
This includes the following highways...
Interstate 79 in Pennsylvania between mile markers 103 and 119.
Interstate 80 in Pennsylvania between mile markers 16 and 45.
These storms may intensify, so monitor local radio or television
stations for additional information and possible warnings from the
National Weather Service.
LAT...LON 4097 7954 4086 7973 4080 8001 4123 8025
4122 7998 4133 7979
TIME...MOT...LOC 2048Z 346DEG 24KT 4123 7985 4117 7997 4117 8014
BrownThe Pittsburgh radar (KPBZ), 63 km away, was scanning. The volume nearest the first event began at 20:55 UTC.
59 thunderstorm wind. Local standard time, as filed.
Phillips School Road was closed due to a tree and wires down across the roadway.
Many trees and power poles were reported to be blown over around Knox.
Numerous trees were reported to be down in Brookville, and power lines were felled on to a van.
Numerous trees were reported down at the intersection of Saniga Road and Pleasure Valley Lane.
Across Interestate 80, multiple trees were reported to be blown down.
A tree was blown on to a residence on Florence Avenue.
A tree was felled on to a house.
Downed branches and light roof damage were reported near Sligo. Also, power outages were seen near Rimersburgh.
Downed trees were observed in Falls Creek.
Large trees were blown over on Coventry Drive.
A tree was reported to be blown down on Hinchberger Road.
A tree was downed by wind off Woodland Avenue south of Butler.
A tree was blown on to a home off of Sportsman Road.
Rikers Road was closed due to trees being blown down across the road.
Along Elderberry Hill Road, there were numerous reports of trees down.
Phillips School Road was closed due to a tree and wires down across the roadway.
A tree was reported to be blown down on Dime Road in Bethel Township.
Power lines were reported to be down on Smyerstown Road.
Trees were reported to be blown down on Setree Drive.
A tree was downed on Smiley Road in Banks Township.
Trees were downed on Juneau Road.
On Old Indiana Road, trees were blown down.
On Glen Campbell Road, power lines were downed by the wind.
Power poles and wires were reported down.
Several trees and power poles were blown down in the vicinity of River Road.
Trees were reported to be blown down in Arnold.
A tree was reported to be blown down on Anthony Run Road.
Telephone poles were downed on Parkwood Road.
Trees were reported to be blown down on Johnsonburg road.
Numerous trees were blown down in New Kensington, and several power outages were reported.
A tree was blown down on Sharon Road, with another report of power lines down on a car.
Trees were blown down, and caught on fire after falling on power lines along Ferguson Road.
Power lines were blown down on College Lodge Road.
Along Solley Road, trees were blown down.
A tree was reported to be blown down on Highway 119 in Homer City.
Numerous trees and wires were reported to be down across New Kensington.
Power lines were blown down on Lucerne Road.
Power lines were blown down on Clymer Road.
In Edgeworth Borough, a tree was downed on to a house.
Numerous trees and wires were blown down at the intersection of Quaker Road and Meadow Lane.
Large trees were blown down on Stoops Ferry Road.
Trees were blown down on Route 553.
Multiple trees were down at the corner of State Route 711 and Wilson Street.
A tree was blown down and blocking the intersection of McCoy Road and Island Avenue.
Multiple trees were downed by wind in Carnegie.
A large tree was blown down on to a house on Justus Street, causing roof damage.
A tree was blown down, blocking the roadway.
Evergreen Road was closed due to wires being blown down.
Trees were blown down on Arch Avenue and Sleepy Hollow Road in Castle Shannon.
A tree was reported to be blown on to a house.
A tree was blown down on a home.
A tree was blown down on to a house.
Trees were blown down on to a road.
A motor vehicle accident occurred when a car crashed into a downed tree.
Trees were reported to be blown down.
Trees were blown down near Lowber.
Trees were reported to be blown down near Scottdale.
A large tree was blown down near the corner of Layton and Falbo Roads.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2020Every state in 2020This day in weather historyWarnings in Pennsylvania, August 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 916361, 916363, 916364, 916365, 916366, 916367, 916368, 916369, 916370, 916371, 917006, 917007, 917008, 917009, 917010, 917011, 917012, 917013, 917014, 917018, 917019, 917020, 917024, 917025, 917027, 917030, 917032, 917034, 917035, 917036, 917038, 917040, 917041, 917042, 917044, 917045, 917046, 917047, 917048, 917049, and more.