A lingering upper level low pressure system drifting across Pennsylvania promoted low convective temperatures, allowing numerous showers and thunderstorms to develop, which concentrated near disturbances around the upper low. Decent instability and strong low-level lapse rates promoted damaging wind gusts and hail.
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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.
A lingering upper level low pressure system drifting across Pennsylvania promoted low convective temperatures, allowing numerous showers and thunderstorms to develop, which concentrated near disturbances around the upper low. Decent instability and strong low-level lapse rates promoted damaging wind gusts and hail. Moisture overall was not excessive for August, but thanks to weak flow near the upper low, storm motion was generally 10 knots or less. This promoted a few instances of flash flooding as well.
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 13, 10:28 AM EST, 55 minutes earlier.
Area Forecast Discussion National Weather Service Pittsburgh PA 1128 AM EDT Mon Aug 13 2018 .SYNOPSIS... Scattered showers and perhaps a rumble of thunder persist through Tuesday. Dry weather should briefly return Wednesday under high pressure before another weather system returns the chance of rainfall late Thursday through Saturday. && .NEAR TERM /THROUGH TUESDAY/... Updated to add Garrett County to a Flash Flood Watch rest of the forecast on track. Previous discussion follow: Tweaked pops for the mid morning update. We are watching nearly stationary showers in Garrett county for potential flooding issues. Latest CAMs still show as atmosphere reaches its trigger values between 18-21Z is when numerous showers and storms are forecast to develop. Heavy rainfall, not because the atmosphere is super tropical (PWATS less than 1.50"), but due to storm motion around five knots is the main reason. The highest PWATs are progged across Ern PA and the Mid Atlantic region, though light winds at the sfc and aloft should result in a slow storm movement across our area. Heavy downpours combined with this slow storm speed should result in a localized flood threat across far Ern OH through Wrn PA, WV and MD. Will include this potential in the Hazardous Weather Outlook. Near seasonal average highs are expected. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... Convection should diminish this evening with waning instability. The upper low is progged to begin tracking E-NE Tuesday, exiting the Upper OH Valley region Tuesday night. Scattered showers/thunderstorms, with a diurnal trend, are still expected until the low's exit. Less precip coverage and increasing flow should result in little flood potential for Tuesday. Dry weather should return Wednesday under building ridging. Temperatures should average near or just above seasonal levels. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Highlights: - Wet Weather Returns Thursday night - Saturday - Dry Sunday and Monday - Temperatures above normal GEFS/EPS have a good handle on the late week weather system, but diverge on arrival of the next system just beyond day 7. Surface cold front has been pushed back 12 hours from the forecast late last week. It will be crossing Thursday night into Friday. With this timing, potential for severe weather is very low. There will be plenty of clouds not to mention best upper level dynamics cross through the Great Lakes. GEFS has over a 60% probability of greater than 0.01" of rain which is in lock step with forecast, so may tweak pops a smudge higher given increased confidence. After the front crosses Friday morning, mid level trough remains over the region allowing impulses to cross in northwest flow. Will keep chance pops given cooling aloft interacting with daytime heating. A transitory ridge arrives Sunday and Monday allowing dry weather. H8 temps don't move much over the next seven days, so daytime will be in the lower to mid 80s && .AVIATION /15Z MONDAY THROUGH FRIDAY/... Timed showers and storms based on the hi res guidance, which starts to suggest development by 18-21z but opted to maintain VCTS at this time until confidence is better that any specific terminal will experience a storm. Expect brief MVFR/IFR restrictions in any t-storm, with heavy rain. Activity should greatly diminish to isolated showers/storms by 02Z. Lingering clouds could once again hinder fog development at some locales, although any location that receives rain today and can manage to clear out overnight may of course see visibility restriction. OUTLOOK... Occasional afternoon/evening restrictions are once again possible Tuesday in showers/storms around the lingering upper low. Patchy overnight fog is again possible where rain falls and skies can clear. A mostly VFR Thursday may be followed by restriction potential on Thursday with low pressure. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. &&
Hazardous Weather Outlook National Weather Service Pittsburgh PA 308 AM EDT Mon Aug 13 2018 MDZ001-OHZ050-059-069-PAZ007>009-013>016-020>023-029-031-073>076- WVZ001>004-012-021-509>514-140715- Garrett-Jefferson-Belmont-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- 308 AM EDT Mon Aug 13 2018 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...Today and Tonight. Scattered to numerous slow moving showers and thunderstorms are expected today. Locally heavy rain could result in isolated flooding, especially in the afternoon and early evening. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. 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. OHZ039>041-048-049-057-058-068-140715- Tuscarawas-Carroll-Columbiana-Coshocton-Harrison-Muskingum-Guernsey- Noble- 308 AM EDT Mon Aug 13 2018 This Hazardous Weather Outlook is for east central Ohio. .DAY ONE...Today and Tonight. The probability for widespread hazardous weather is low. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. 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 1204 PM EDT MON AUG 13 2018 PAZ022-131630- Armstrong- 1204 PM EDT MON AUG 13 2018 ...A STRONG THUNDERSTORM CAPABLE OF PRODUCING HAIL...GUSTY WIND AND HEAVY RAIN WILL AFFECT SOUTHWESTERN ARMSTRONG COUNTY... At 1203 PM EDT, a strong thunderstorm was located over Ford City, or over Kittanning, moving south at 10 mph. Wind gusts up to 45 mph and hail up to the size of nickels are possible with this storm. Locations impacted include... Kittanning... Ford City... Freeport... West Kittanning... Worthington... West Hills... Manorville... Ford Cliff... Applewold... Lenape Heights... Crooked Creek Lake Park... Torrential rainfall also is occurring with this storm and may cause localized flooding. Do not drive your vehicle through flooded roadways. LAT...LON 4085 7967 4085 7946 4066 7939 4068 7968 TIME...MOT...LOC 1603Z 357DEG 7KT 4079 7955 34
The Pittsburgh radar (KPBZ), 64 km away, was scanning. The volume nearest the first event began at 16:23 UTC.
4 hail, 3 thunderstorm wind, 1 flood, 1 heavy rain, 1 flash flood, 1 lightning. Local standard time, as filed.
County 911 officials reported that trees and wires were blown down around Manor Township.
Reports of hail in Allegheny County were shared on social media.
County 911 officials reported that trees were blown down on Keyser Road.
Citizens of Allegheny County reported hail.
A trained spotter of Armstrong County reported hail.
County 911 officials reported that water was covering the road near Route 30, and that lane restrictions have been made.
A trained spotter reported that 1.72 inches of rain fell in one hour, with 0.97 inches of that amount measured in 28 minutes.
Broadcast media reported that several trees were uprooted near Rices Landing.
Flash flooding was observed by a trained spotter near Bigler Drive.
A 45 year old male was struck by lightning in Schenley Park, and was transported to the hospital in critical condition.
The local media reported hail.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2018Every state in 2018This day in weather historyWarnings in Pennsylvania, August 2018
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: 779975, 779965, 779976, 779966, 779967, 779964, 779970, 779977, 779963, 781731, 779968.