On August 22nd, showers and thunderstorms developed near and south of a dewpoint gradient extending from Indiana, PA to New Philadelphia, OH. Outflow from these storms allowed a few additional cells to develop over Allegheny County.
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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.
On August 22nd, showers and thunderstorms developed near and south of a dewpoint gradient extending from Indiana, PA to New Philadelphia, OH. Outflow from these storms allowed a few additional cells to develop over Allegheny County. The slow-moving storms produced instances of wind damage and flash flooding.
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 22, 5:57 PM EST, 1 hour 13 minutes earlier.
Area Forecast Discussion...UPDATED National Weather Service Pittsburgh PA 657 PM EDT Sat Aug 22 2020 .SYNOPSIS... Scattered showers and thunderstorms can be expected through the weekend, mainly during the afternoon and evening. Temperature will remain above average. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... A subtle warm front is pushing slowly northward across the region as as an upper level ridge amplifies over the region in response to a shortwave trough digging into the western Great Lakes. The ridge is helping to push the surface boundary northward which is promoting the expansion of muggy air to the north. This airmass is more unstable which is allowing for the development of scattered convection, mainly south and east of PIT. The convection is pulsing, as the rising heights aloft and warmer air aloft has created a a cap which is limiting the vertical extent of the storms. Once the storm gusts out, these gust fronts create new convection and this process will continue through sunset. Hires models are showing additional activity firing overnight along the northward drifting warm front, so have included slight chance to low chance PoPs overnight. Temperatures overnight remain warm and muggy air will overspread the entire region. Areas of fog may develop late tonight, but it looks to be confined to the river valleys. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... Areas of fog and low-level clouds may take a few hours after sunrise to "mix-out" due to deep low-level moisture Sunday morning. Otherwise, the low-level disturbance south of our region today will continue north into the Ohio Valley and prompt scattered, mainly diurnally- supported, showers and thunderstorms. Severe storms are not likely to develop with warm, moist air aloft dropping DCAPE values. Heavy rain showers may occur Sunday evening, as widespread PWAT values climb to 1.50 inches, but there should be enough steerage aloft to keep storms moving and avoid areas of isolated flooding. Another round of diurnal precipitation is forecast for Monday. && .LONG TERM /TUESDAY THROUGH SATURDAY/... An upper-level trough is expected to amplify on Tuesday as it crosses into eastern Canada. A strong deep-layer wind field accompanying this system may prompt severe storms Tuesday for portions of region. At the moment, the Storm Prediction Center has a 15% Outlook for strong storms. A number of shortwaves embedded in an upper-level trough will keep showers and thunderstorms in the forecast throughout the later part of the week. Also, monitoring of any developed tropical activity in the Gulf Mexico may be heightened as remnants have the potential to enter the Upper Mississippi Valley over the weekend. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... General VFR forecast through the period. The probabilities of a storm encountering a port is small, so have left out the mention in the forecast. Development will need to be monitored, with amendments as required. A shield of broken middeck clouds will overspread the region tonight. This will prevent widespread fog development. With higher dewpoints also overspreading the region, will limit the mention of fog to the ones that saw predawn fog on Saturday. .Outlook... VFR conditions will largely prevail through much of the next week with only temporary restrictions with daily afternoon thunderstorms and morning fog. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. &&
Hazardous Weather Outlook National Weather Service Pittsburgh PA 332 AM EDT Sat Aug 22 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>514-230745- 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- 332 AM EDT Sat Aug 22 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. No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Sunday through Friday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to Standard Operating Procedures.
Special Weather Statement National Weather Service Pittsburgh PA 749 PM EDT Sat Aug 22 2020 PAZ021-029-230015- Washington-Allegheny- 749 PM EDT Sat Aug 22 2020 ...A STRONG THUNDERSTORM CAPABLE OF PRODUCING HAIL WILL AFFECT EAST CENTRAL WASHINGTON AND SOUTHEASTERN ALLEGHENY COUNTIES... At 748 PM EDT, a strong thunderstorm was located over Baldwin, or over Bethel Park. the storm is nearly stationary. Hail up to the size of nickels is possible with this storm. Locations impacted include... Pittsburgh... Mount Lebanon... Bethel Park... McMurray... McKeesport... Gastonville... West Mifflin... Baldwin... Upper St. Clair... Scott Township... Whitehall... South Park Township... This includes the following highways... Interstate 79 in Pennsylvania between mile markers 52 and 63. Interstate 376 in Pennsylvania between mile markers 63 and 75. Frequent cloud to ground lightning is occurring with this storm. Seek safe shelter inside a building or vehicle. LAT...LON 4041 7984 4026 7984 4023 8014 4048 8013 TIME...MOT...LOC 2348Z 093DEG 2KT 4034 7999
The Pittsburgh radar (KPBZ), 25 km away, was scanning. The volume nearest the first event began at 00:10 UTC.
4 thunderstorm wind, 2 flash flood, 1 flood. Local standard time, as filed.
A large tree was reported to be blown down and blocking the road near the intersection of Poplar Avenue and Race Street.
Power poles were blown down, with live wires causing a road closure at the 3900 block of Brentwood Road.
A tree was blown down onto a house on Forestview Drive.
Large trees were reported to be blown down in Mount Lebanon.
Flooding was reported at the intersection of Brownsville Road and Hacienda Drive.
Streets Run was overflowing onto the road.
Connor Road was flooded in Mount Lebanon.
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: 915526, 915529, 915537, 915539, 915543, 915545, 915546.