Outflow boundaries from convection earlier in the day helped to spark additional thunderstorms in the afternoon and evening on the 9th ahead of an approaching cold front. Where the boundaries collided, thunderstorms with very heavy rain materialized, with rates approaching 2 inches per hour based on radar estimates and spotter reports.
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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.
Outflow boundaries from convection earlier in the day helped to spark additional thunderstorms in the afternoon and evening on the 9th ahead of an approaching cold front. Where the boundaries collided, thunderstorms with very heavy rain materialized, with rates approaching 2 inches per hour based on radar estimates and spotter reports. Convection started over Etna and Shaler, in northern Allegheny county and propogated northward toward Monaca, Ambridge, and Aliquippa in Beaver county. Several road closures were reported with several feet of water on roadways in both locations.
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 Sep 9, 2:37 PM EST, 1 hour 21 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 337 PM EDT WED SEP 9 2015 .SYNOPSIS... SHOWERS AND SOME THUNDERSTORMS ARE LIKELY TONIGHT AND THURSDAY WITH THE PASSAGE OF A COLD FRONT. THIS FRONT WILL END TEMPERATURES BACK TO SEASONAL LEVELS. && .NEAR TERM /THROUGH THURSDAY/... COLD FRONT IS CURRENTLY MOVING ACROSS THE FORECAST AREA...ALTHOUGH SHOWERS REMAIN SOMEWHAT SCATTERED IN COVERAGE AT THIS TIME. CONSIDERING THE AMOUNT OF SUNSHINE THAT WAS PRESENT BEFORE THE ARRIVAL OF SHOWERS...THIS LIKELY HAS ERODED SOME OF THE CAP AND WILL ALLOW FOR GREATER INSTABILITY. THIS COULD ALLOW FOR SOME STRONGER THUNDERSTORMS WITH GUSTY WINDS POSSIBLE. INTENSITY OF RAIN IS EXPECTED TO PICK UP OVERNIGHT AS A WAVE WILL DEVELOP ALONG THE FRONT TO THE SOUTH AND MOVE ALONG THE FRONT. HAVE CONTINUED CATEGORICAL NUMBERS ACROSS THE SOUTHEAST...WITH THE POSSIBILITY OF AN INCH OF RAIN IN THE WEST VIRGINIA/MARYLAND RIDGES. THE FRONT WILL CONTINUE TO INCH EASTWARD ON THURSDAY...AND THE PRIMARY CHANGES DURING THIS TIME PERIOD WERE TO SLIGHTLY ACCELERATE THE DEPARTURE OF RAINFALL AND KEEP CLOUD COVER IN SLIGHTLY LONGER. AFTER 11 DAYS IN A ROW WITH ABOVE NORMAL TEMPERATURES...HIGHS ON THURSDAY SHOULD FINALLY RETURN TOWARDS CLIMATOLOGY WITH VALUES IN THE 70S. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... A PASSING SHOWER COULD REMAIN IN THE WV/MD RIDGES THURSDAY EVENING...BUT DRY WEATHER WILL PREVAIL THURSDAY NIGHT INTO FRIDAY. THERE IS STILL SOME MODEL DISAGREEMENT FOR TIMING WITH THE NEXT FRONT...WITH MODELS NOW INDICATING THE CHANCE FOR A FRIDAY AFTERNOON/EVENING PASSAGE. SPED UP THE TIMING SLIGHTLY FOR THE FRONT...BUT DID NOT HAVE ENOUGH CONFIDENCE TO BUMP UP POPS TO LIKELY AT THIS TIME. IN FACT...THE MORE LIKELY TIME FOR HIGHER POPS WILL PROBABLY COME OVER THE WEEKEND...AS MODELS SHOW STRONG AGREEMENT ON AN UPPER TROUGH BECOMING A CUTOFF LOW AND DRIFTING OVER THE REGION. THIS REQUIRED INCREASING SKY COVER AND PRECIPITATION CHANCES AND DECREASING HIGH TEMPERATURES. SOME LOCATIONS WILL STRUGGLE TO REACH 70 ON SATURDAY. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... BROAD UPPER LEVEL TROUGHING IS FORECAST TO DEVELOP OVER THE EASTERN CONUS FOR THE LONG TERM PERIOD...LEADING TO COOLER TEMPERATURES AND LOW PRECIP CHANCES. EXTENDED GRIDS WERE CONSTRUCTED CLOSE TO WPC GUIDANCE. && .AVIATION /20Z WEDNESDAY THROUGH MONDAY/... COLD FRONT MOVING SLOWLY THROUGH THE FORECAST AREA THIS EVENING. GUSTY SHOWERS AND THUNDERSTORMS WILL INCREASE THROUGH THE LATE EVENING AND COULD RESULT IN TEMPORARY RESTRICTIONS WITH INDIVIDUAL CELLS. EVENTUAL MVFR CONDITIONS ARE EXPECTED BY LATE EVENING MAINLY SOUTH OF KPIT WHERE BETTER MOISTURE POOLING ALONG THE FRONT IS EXPECTED. EXPECTING VERY GRADUAL IMPROVEMENT THROUGH THE DAY THURSDAY. TAX OUTLOOK...THURSDAY THROUGH MONDAY... RESTRICTIONS ARE POSSIBLE AGAIN BY THE WEEKEND WITH AN UPPER TROUGH. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. &&
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE PITTSBURGH PA 330 AM EDT WED SEP 9 2015 MDZ001-OHZ039>041-048>050-057>059-068-069-PAZ007>009-013>016-020>023- 029-031-073>076-WVZ001>004-012-021>023-041-100730- 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-PRESTON-TUCKER- 330 AM EDT WED SEP 9 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN MARYLAND...EAST CENTRAL OHIO...NORTHWEST PENNSYLVANIA...SOUTHWEST PENNSYLVANIA...WEST CENTRAL PENNSYLVANIA...NORTHERN WEST VIRGINIA AND NORTHERN PANHANDLE OF WEST VIRGINIA. .DAY ONE...TONIGHT. NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY. 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.
The Pittsburgh radar (KPBZ), 24 km away, was scanning. The volume nearest the first event began at 20:58 UTC.
8 flash flood, 3 heavy rain, 1 thunderstorm wind. Local standard time, as filed.
Local 911 call center reported trees down in Shaler and O'Hara Township.
Local 911 reported Butler Street, near the Advance Auto Parts, was closed due to flooding. In addition, the intersection with Crescent Road was shut down.
Local 911 center reported several roadways closed in and around Shaler due to flash flooding. The roadways included Saxonburg Boulevard, with debris reported on the roadway; Route 8 between McDonalds and Kmart; and the intersection of Glen Scott and Glenn Douglas Drive, where one foot of water was reported on the roadway. Also, a landslide was reported on Middle Road and sewage was backing up into flooded homes on Morgan Avenue.
Local 911 reported that the northbound lane of William Flynn Highway, at the intersection of Spencer Lane was flooded and being shut down. Six cars were reported to be stuck in water, which was half way up the doors. Also, there was water flowing into the Goss Gas building. In addition, the intersection of Maple and Glenn Avenues was reported to be flooded with a partial roadway collapse.
Local 911 center reported that the intersection of Delta and Alpha Drive was flooded, with water up to the windows of cars.
National Weather Service employee reported 5.22 inches of rain occurred in a little over two hours.
National Weather Service employee reported 2 inches in one hour.
Trained spotter reported 1.9 inches in one hour.
Local 911 center reported that Route 989 was closed due to flash flooding near Economy.
Local 911 reported that Franklin Avenue is closed due to flash flooding in Aliquippa.
Local 911 reported that both Forest Street in Baden and Route 65 in Ambridge are closed due to flooding. One person was pulled from a vehicle trapped in high water on Route 65.
Local 911 reported numerous roads closed around Bell Acres.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2015Every state in 2015This day in weather historyWarnings in Pennsylvania, September 2015
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: 599354, 602174, 602175, 602391, 602392, 599355, 599353, 599352, 602170, 602171, 602172, 602393.