Showers and thunderstorms formed along a nearly stationary boundary that crept southeastward from the Great Lakes. 6 inches and weak steering flow along the boundary led to a few areas of training thunderstorms.
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.
Showers and thunderstorms formed along a nearly stationary boundary that crept southeastward from the Great Lakes. Precipitable water values of around 1.6 inches and weak steering flow along the boundary led to a few areas of training thunderstorms. Rainfall amounts of 1.5 to 3.0 inches on already saturated ground led to several areas of flash flooding in Washington, Allegheny, and Westmoreland Counties. The worst flooding was near Herminie, where up to 14 homes were impacted and a mobile home was shifted off of its foundation.
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 10, 1:23 PM EST, 52 minutes earlier.
Area Forecast Discussion National Weather Service Pittsburgh PA 223 PM EDT Fri Aug 10 2018 .SYNOPSIS... An active weather pattern through the weekend, but no day will be a wash out. A pesky upper level low pressure parked over the Ohio Valley brings scattered showers and thunderstorms mostly during the afternoon and evening hours through the middle of next week. && .NEAR TERM /THROUGH SATURDAY/... Numerous showers with embedded thunder have fired up right on cue along a surface convergence boundary. This activity will increase in coverage until about 5pm when it becomes more scattered as atmosphere becomes less stable due to rain cooled air. No diurnal trend in pops tonight given plenty of moisture in low levels and residual outflow boundaries coupled with a surface convergence zone. Still pinpointing areas south of I-76 as locations with highest percentage to see a shower overnight. High water risk is elevated through early evening for training of storms and weak steering winds. As of 2pm rain rates have not been overly high from thunderstorms, but if a location gets hit two or three times, we could see problems in low lying and more flood prone areas. Areas of fog could develop overnight if we loose nocturnal stratocu especially if a location gets a shower or storm today. Saturday will be a repeat of today given a lingering surface boundary, copious amounts of low level relative humidity, and a passing shortwave trough. The area of concern shifts a little farther south to the I-70 - US 50 corridor in West Virginia. Right now, given run of dry weather there doesn't appear to be a flash flooding concern. Likely pops are predicted in the aforementioned region. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... Overall little if any change in the forecast with respect to pops. Upper level low pressure remains camped over the Ohio Valley. Pops take on a more diurnal trend Saturday night onward. && .LONG TERM /MONDAY THROUGH FRIDAY/... Highlights: - Redundant Forecast afternoon/evening pop up storms - Temperatures just below normal - Strong front Thursday Extended range ensembles remain in lock step for this time frame as a upper level low creates daily precipitation chances across the region. As daytime heating destabilizes the atmosphere, showers and isolated storms will pop up during the afternoon and evening hours. Monday and Tuesday in the mountains appear to be the day with the greatest coverage as it coincides with the passing of a stronger shortwaves. Confidence not as high farther west as southeast flow sets up and that may protect the windward side of the Appalachians for a couple of days. A synoptic cold front is still forecast to cross Thursday afternoon evening. Depending how much sunshine is observed during the day and if the timing holds, it could present a severe weather risk. The associated mid level cyclone will pass north of Lake Erie which is where most of the upper level dynamics reside, therefore confidence remains below 30% for inclusion into hazardous weather outlook. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... Scattered showers and thunderstorms will continue to increase in coverage through the evening as a shortwave helps push a boundary, that is currently bisecting the region, to the south. Expect brief restrictions to MVFR and IFR as thunderstorms pass over a terminal, with greatest confidence that this will occur at PIT, AGC, LBE, and HLG. Loss of diurnal heating should decrease shra/tsra coverage overnight, though the lingering boundary supports the continuation of VCSH with some possible restrictions in fog as a result of this afternoon/evenings rainfall. Fog coverage will be dependent on how much clearing there is, but opted to at least make mention of this at most sites overnight. OUTLOOK... Brief restrictions are possible through Tue, especially in the aftn/eve, in convection with a persistent upper trough across the region. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. &&
Hazardous Weather Outlook National Weather Service Pittsburgh PA 1223 PM EDT Fri Aug 10 2018 PAZ014-020>023-029-031-073>076-WVZ001>004-509>512-111630- Butler-Beaver-Allegheny-Armstrong-Indiana-Washington-Greene- Westmoreland-Westmoreland Ridges-Fayette-Fayette Ridges-Hancock- Brooke-Ohio-Marshall-Monongalia- Ridges of Eastern Monongalia and Northwestern Preston-Preston- Eastern Preston- 1223 PM EDT Fri Aug 10 2018 This Hazardous Weather Outlook is for southwest Pennsylvania, west central Pennsylvania, western Pennsylvania, northern West Virginia and northern panhandle of West Virginia. .DAY ONE...This Afternoon and Tonight. Showers and a few thunderstorms are expected today, with the greatest concentration expected during the afternoon and evening. Some of the thunderstorms could produce locally heavy rainfall, and localized flash flooding is possible if a location is hit by multiple bouts of heavy rain. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. MDZ001-OHZ039>041-048>050-057>059-068-069-PAZ007>009-013-015-016- WVZ012-021-513-514-111630- Garrett-Tuscarawas-Carroll-Columbiana-Coshocton-Harrison-Jefferson- Muskingum-Guernsey-Belmont-Noble-Monroe-Mercer-Venango-Forest- Lawrence-Clarion-Wetzel-Marion-Western Tucker-Eastern Tucker- 1223 PM EDT Fri Aug 10 2018 This Hazardous Weather Outlook is for western Maryland, east central Ohio, northwest Pennsylvania, west central Pennsylvania, western Pennsylvania and northern West Virginia. .DAY ONE...This Afternoon and Tonight. No hazardous weather is expected at this time. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. No hazardous weather is expected at this time. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
The Pittsburgh radar (KPBZ), 33 km away, was scanning. The volume nearest the first event began at 19:16 UTC.
18 flash flood, 1 heavy rain. Local standard time, as filed.
County 911 officials reported that the intersection of Route 51 and Lewis Run Road was closed due to flooding.
County 911 officials reported that the intersection of Route 885 and Lebanon Church Road was closed due to high water.
The county emergency manager reported that the 4800 block of Streets Run Road was flooded.
County 911 officials reported that West Newton Road and Fire Hall Avenue in Herminie were closed due to flooding.
The county emergency manager reported that the intersection of Scenery Drive and Boston Hollow Road were closed due to flooding.
The county emergency manager reported that the intersection of Becks Run Road and Brownsville Road were closed due to flooding, with 2 to 3 feet of water on the road.
The county emergency manager reported that the police found a vehicle stranded with people inside at 1000 Cochran Mill Road.
The county emergency manager reported that the intersection of Cochran Mill Road and Wilson Road was closed due to flooding.
The county emergency manager reported that Happy Hollow Road was closed from Long Acre Drive to Scenery Drive due to flooding.
The county emergency manager reported that a vehicle was stuck in flood waters at the intersection of Derr Road and Pierce Road in Sewickley Township.
The county emergency manager reported that the intersection of Apples Mill Road and Hildenbrand Road in Sewickley Township was closed due to flooding.
The county emergency manager reported that 14 homes were flooded with 2 feet of water, with one mobile home knocked off of its foundation. Route 136 and Hutchinson Road were washed out, with numerous other roads flooded in the area.
The county emergency manager reported that State Route 40 and Franklin Farms Road in North Franklin were closed due to flooding.
The county emergency manager reported that Jefferson Avenue and West Maiden Streets were closed due to flooding.
According to the county emergency manager, flooding occurred at 63 Cole School Road in Jefferson Township.
The county emergency manager reported flooding at 123 Cecil Henderson Road in Cecil.
The post office at 1620 Smith Township State Road was flooded according to the county emergency manager.
County 911 officials reported that Cedar Grove Road was flooded with a car submerged.
An NWS employee reported that 1.70 inches of rain fell in 1 hour and 40 minutes.
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: 779344, 779347, 779350, 779352, 779353, 779361, 779367, 779368, 779370, 779371, 779373, 779377, 779381, 779382, 779385, 779386, 779387, 779388, 779398.