Shortwave passage and modest instability supported isolated strong to severe storms on the 21st.
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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.
Shortwave passage and modest instability supported isolated strong to severe storms on the 21st.
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 21, 2:38 PM EST, 12 minutes earlier.
Area Forecast Discussion National Weather Service Pittsburgh PA 338 PM EDT Mon Aug 21 2017 .SYNOPSIS... A sequence of weak upper-level disturbances will provide isolated showers and thunderstorms today. Widespread showers and thunderstorms are expected on Tuesday as a cold front crosses the region. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Convection from this morning that took advantage of the modest instability noted in the 12Z sounding has subsided as the low- amplitude trough that supported it continues to move ewd. Shortwave ridging will spell a brief erosion of convective cloud cover, though cirrus may still provide at least a partial obscuration of the sky during peak eclipse viewing. A second, weak shortwave trough over central OH will advance ewd this afternoon and may provide a second round of modest convection as low-level warm advection weakens the H7 inversion. Lacking any focused sfc boundary, broad PoPs were employed in the forecast this afternoon along the diffuse warm front, with modest increases focused around current storms. Any showers and storms will weaken this evening with loss of heating, and some clearing is expected in the wake of the associated shortwave trough. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/... A strong upper low will dig into the Great Lakes on Tue and acquire a neutral to negative tilt through the day in concert with the movement of a mid-level jet maximum. The system's associated cold front will approach the Ohio Valley during the early evening, but a prefrontal trough is expected to be the focus for daytime convection in the area. Abundant low-level moisture, steepening lapse rates and strong effective bulk shear will support the development of strong to severe thunderstorms by early afternoon along the sharpening sfc trough. CAPE on the order of 2000 J/kg and effective shear of 40-50kt will promote organized, severe convection. Given the deep-layer shear orientation roughly parallel to the sfc feature, storms should congeal quickly into an intense convective line that will move sewd into the instability axis. Damaging wind gusts will be the primary threat, but hail also is possible in more intense, cellular updrafts ahead of the line. Storms will exit sewd by early evening with rain lingering into the evening behind the storms as the cold front traverses the region. High pressure will build in on Wed/Wed eve, with little chance of rain as dry air invades. && .LONG TERM /THURSDAY THROUGH MONDAY/... Although ensembles still show spread in their upper pattern solutions, it appears that broad surface high pressure under an ern-CONUS trough/midwestern ridge pattern is progged to support a generally-dry air mass through the period. Daily temperatures below climatological average can be expected through early next week. && .AVIATION /20Z MONDAY THROUGH SATURDAY/... General VFR is expected for the period although a crossing shortwave may spawn isold to sct convection. Expect rapid deterioration of conditions on Tuesday as widespread precip will herald the advance of cold front. .Outlook... With passage of an early Wed cold front, general VFR can be expected for the remainder of the week. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && Kramar
Hazardous Weather Outlook...UPDATED National Weather Service Pittsburgh PA 334 PM EDT Mon Aug 21 2017 MDZ001-OHZ039>041-048>050-057>059-068-069-PAZ007>009-013>016-020>023- 029-031-073>076-WVZ001>004-012-021-509>514-221945- Garrett-Tuscarawas-Carroll-Columbiana-Coshocton-Harrison-Jefferson- Muskingum-Guernsey-Belmont-Noble-Monroe-Mercer-Venango-Forest- Lawrence-Butler-Clarion-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- 334 PM EDT Mon Aug 21 2017 This Hazardous Weather Outlook is for western Maryland, east central Ohio, northwest Pennsylvania, southwest Pennsylvania, west central Pennsylvania, western Pennsylvania, northern West Virginia and northern panhandle of West Virginia. .DAY ONE...This Afternoon and Tonight. Isolated severe thunderstorms are possible this afternoon, capable of strong to damaging wind gusts. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Scattered severe thunderstorms capable of damaging wind gusts and isolated large hail are possible Tuesday afternoon and evening. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed on Tuesday afternoon. Kramar
Special Weather Statement National Weather Service Pittsburgh PA 314 PM EDT MON AUG 21 2017 PAZ022-023-211945- Armstrong-Indiana- 314 PM EDT MON AUG 21 2017 ...A STRONG THUNDERSTORM CAPABLE OF PRODUCING SMALL HAIL AND GUSTY WIND WILL AFFECT SOUTHWESTERN INDIANA AND SOUTHEASTERN ARMSTRONG COUNTIES... At 314 PM EDT, a strong thunderstorm was located 10 miles east of Vandergrift, moving southeast at 10 mph. Wind gusts up to 45 mph and small hail are possible with this storm. Locations impacted include... Indiana... Homer City... Black Lick... West Lebanon... Chevy Chase Heights... Ernest... Elderton... Creekside... Shelocta... Lucerne Mines... Jacksonville... LAT...LON 4057 7950 4074 7941 4070 7907 4045 7919 TIME...MOT...LOC 1914Z 292DEG 10KT 4063 7937 CL
The Pittsburgh radar (KPBZ), 79 km away, was scanning. The volume nearest the first event began at 19:49 UTC.
1 thunderstorm wind. Local standard time, as filed.
The public reported several trees down in Shelocta.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2017Every state in 2017This day in weather historyWarnings in Pennsylvania, August 2017
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: 719733.