The remnant low pressure center of Hurricane Ida passed across West Virginia and the Central Appalachian Mountains from late August 31st through September 1st.  The abundant moisture associated with the low intersected a frontal zone which was nearly stalled in the area of the Ohio Valley.  Strong isentropic and frontogenetically-induced lift led to periods of heavy rain over much of southwestern Pennsylvania over the two-day period, both from thunderstorms ahead of the low and from a period of tropical rainfall during the morning of the 1st.  Rain tapered off by the afternoon as the remnants of Ida pulled towards the Mid-Atlantic coast.
The heaviest rainfall over the two-day period was observed in Westmoreland, Allegheny, and Washington Counties, with totals of 3 to 5 inches common. Lesser totals were noted to the north and south of this area, with areas near Interstate 80 mainly receiving a half-inch or less. The heavy rainfall resulted in widespread flooding of roads and streams, with several instances of evacuations noted.  Particularly hard hit were the municipalities of Millvale, Bridgeville, and Scott, all of which issued disaster declarations.  In Stowe Township, a school bus was trapped in flood waters, requiring the rescue of two adults and seven children.  Other rescues of trapped motorists were noted. Twenty-four residents had to be evacuated from an assisted living facility in Oakdale, where water up to 18 inches deep was observed across the town.
Despite the heavy rain and numerous instances of flash and areal flooding, widespread river flooding was not observed after the rainfall ceased.  A dry slot near the Mason-Dixon Line on the morning of the 1st kept rainfall totals lower on the headwaters of the Monongahela River, allowing area reservoirs to mitigate the impact of the tropical rain downstream.  Thus, while short-term flooding was significant over a portion of the region, the overall event did not have the same impact as Gordon in 2018 or Frances/Ivan in 2014.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 08:50:00 to 01-SEP-21 12:24:00 (EST-5)
Location: STONEVILLA
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

New Alexandria Road was flooded.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 09:15:00 to 01-SEP-21 12:24:00 (EST-5)
Location: NEW FLORENCE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Flooding was reported on Furnace Lane.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 09:13:00 to 01-SEP-21 12:24:00 (EST-5)
Location: DELMONT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: State Official

Flooding was reported in a barn with livestock on Business Route 66.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 09:27:00 to 01-SEP-21 12:24:00 (EST-5)
Location: PAULTON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Flooding was reported on Park Road.  The road was closed.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 09:40:00 to 01-SEP-21 12:24:00 (EST-5)
Location: LOYALHANNA
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

On Latrobe Crabtree Road, flooding was reported.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 09:40:00 to 01-SEP-21 12:24:00 (EST-5)
Location: SUXOR
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: State Official

Flooding was reported on South Carbon Street.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 09:53:00 to 01-SEP-21 12:24:00 (EST-5)
Location: CARBON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

State Route 119 was flooded near Shady Lane.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 10:00:00 to 01-SEP-21 10:23:00 (EST-5)
Location: OAKMONT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Flooding was observed on Plum Street between 6th Street and Dark Hollow Road.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 10:12:00 to 01-SEP-21 12:24:00 (EST-5)
Location: CRABTREE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Crabtree Creek was overflowing its banks, causing flooding on Rizzo Road.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 10:19:00 to 01-SEP-21 12:24:00 (EST-5)
Location: CARBON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: State Official

Route 119 was closed in both directions in the area of South Grande Boulevard due to flooding.

Heavy Rain in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 01:00:00 to 01-SEP-21 10:23:00 (EST-5)
Location: MONESSEN
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Rainfall total since 2 AM of 3.04 inches.

Heavy Rain in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 01:00:00 to 01-SEP-21 09:45:00 (EST-5)
Location: ALLISON PARK
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Since midnight, 2.82 inches were observed. Total rainfall for the event is 4.20 inches.

Heavy Rain in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 01:00:00 to 01-SEP-21 10:38:00 (EST-5)
Location: CLIFF MINE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

A storm total rainfall of 5.18 inches was seen.

Heavy Rain in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 00:00:00 to 01-SEP-21 09:00:00 (EST-5)
Location: GREENSBURG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A total of 2.46 inches of rain was measured through 10 AM.

Heavy Rain in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 00:00:00 to 01-SEP-21 11:00:00 (EST-5)
Location: ROSEDALE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A  24-hour rainfall measurement of 3.25 inches was observed.

Heavy Rain in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 00:00:00 to 01-SEP-21 13:16:00 (EST-5)
Location: LOGANS FERRY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

An event total rainfall measurement of 3.70 inches was reported.

Heavy Rain in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 00:00:00 to 01-SEP-21 13:17:00 (EST-5)
Location: ROOK
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

The event total rainfall was measured to be 4.58 inches.

Heavy Rain in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 00:00:00 to 01-SEP-21 13:19:00 (EST-5)
Location: MONESSEN
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

A 24 hour rainfall total of 2.04 inches was reported.

Heavy Rain in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 00:00:00 to 01-SEP-21 13:00:00 (EST-5)
Location: STRAW PUMP
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

An event total rainfall of 4.36 inches was reported.

Heavy Rain in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 00:00:00 to 01-SEP-21 16:18:00 (EST-5)
Location: OKLAHOMA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: State Official

And event total rainfall of 3.10 inches was reported.

Heavy Rain in FAYETTE, PENNSYLVANIA
From 01-SEP-21 00:00:00 to 01-SEP-21 16:41:00 (EST-5)
Location: CHALKHILL
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

An event storm total of 2.49 inches was reported.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 08:00:00 to 01-SEP-21 10:23:00 (EST-5)
Location: OAKDALE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Flooding was reported throughout Oakdale Borough.  The fire and police stations were evacuated.  Approximately 18 inches of water was reported throughout the town.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 05:24:00 to 01-SEP-21 10:23:00 (EST-5)
Location: ROOK
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: County Official

Water was reported to be flowing into a residence on Salem Drive, and flooding was also occurring on Bower Hill Road.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 05:30:00 to 01-SEP-21 10:23:00 (EST-5)
Location: BOWER HILL
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: County Official

Flooding was occurring on Spring Valley Road.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 05:36:00 to 01-SEP-21 10:23:00 (EST-5)
Location: BOWER HILL
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Flooding was occurring on McLaughlin Run Road.  The road was being closed.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 05:49:00 to 01-SEP-21 10:23:00 (EST-5)
Location: PINE FORKS
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

A video on social media showed that Piney Fork was out of its banks and flowing onto Piney Fork Road.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 05:50:00 to 01-SEP-21 10:23:00 (EST-5)
Location: BLAWNOX
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Flooding was reported on the 800 block of Freeport Road, which was closed.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 05:53:00 to 01-SEP-21 10:23:00 (EST-5)
Location: ETNA
Flood cause: Heavy Rain
Property damage: 1.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Flooding was reported on Seavey Road.  A school bus was disabled on the road.

Flash Flood in WASHINGTON, PENNSYLVANIA
From 01-SEP-21 05:56:00 to 01-SEP-21 10:23:00 (EST-5)
Location: VENICE
Flood cause: Heavy Rain
Property damage: 1.00K
Crop damage: 0.00K
Reported by: 911 Call Center

On State Route 980, a car was stuck in the water up to its headlights.

Flash Flood in WASHINGTON, PENNSYLVANIA
From 01-SEP-21 05:56:00 to 01-SEP-21 10:23:00 (EST-5)
Location: BERTHA
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Flooding was reported on Langeloth Road.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 06:03:00 to 01-SEP-21 10:23:00 (EST-5)
Location: BOWER HILL
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Evacuations were occurring due to flooding at the intersection of Baldwin Street and Railroad Street.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 06:20:00 to 01-SEP-21 10:23:00 (EST-5)
Location: ETNA
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Flooding was occurring at the 1000 block of Evergreen Avenue.  The road was closed.

Flash Flood in WASHINGTON, PENNSYLVANIA
From 01-SEP-21 06:26:00 to 01-SEP-21 10:23:00 (EST-5)
Location: LAWRENCE HILLS
Flood cause: Heavy Rain
Property damage: 1.00K
Crop damage: 0.00K
Reported by: 911 Call Center

A male was trapped in a vehicle at the intersection of Hahn Drive and Maple Lane.

Flash Flood in WASHINGTON, PENNSYLVANIA
From 01-SEP-21 06:28:00 to 01-SEP-21 10:23:00 (EST-5)
Location: MC CONNELLS MILL
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: State Official

Western Avenue was closed between Meddings Road and McConnells Mill Road due to flooding.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 06:35:00 to 01-SEP-21 10:23:00 (EST-5)
Location: MC KEES ROCKS
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: 911 Call Center

A school bus was stuck in water at the intersection of Ohio Street and Center Street.  2 adults and 7 children were trapped.  They were eventually rescued with no injuries.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 06:51:00 to 01-SEP-21 10:23:00 (EST-5)
Location: LIBRARY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Library Road was closed between Kings School Road and Clifton Road due to flooding.  A rail line in the area was also closed.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 06:53:00 to 01-SEP-21 10:23:00 (EST-5)
Location: LIBRARY
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Multiple homes were flooded on Church Street.

Flash Flood in WASHINGTON, PENNSYLVANIA
From 01-SEP-21 07:00:00 to 01-SEP-21 10:23:00 (EST-5)
Location: MC MURRAY
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Valley Brook Road from East McMurry Road to Friar Lane was impassable due to flooding.

Heavy Rain in FAYETTE, PENNSYLVANIA
From 01-SEP-21 05:49:00 to 01-SEP-21 10:23:00 (EST-5)
Location: WHITSETT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

A total of 2.06 inches of  rain was measured through 7 AM.

Flash Flood in INDIANA, PENNSYLVANIA
From 01-SEP-21 07:15:00 to 01-SEP-21 12:15:00 (EST-5)
Location: PALMERTON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Indiana County officials reported flooded roadways across Indiana County, including the township of West Wheatfield.

Flash Flood in INDIANA, PENNSYLVANIA
From 01-SEP-21 07:18:00 to 01-SEP-21 12:15:00 (EST-5)
Location: CHEVY CHASE HGTS
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Several roads were flooded in the town of Indiana.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 07:10:00 to 01-SEP-21 10:23:00 (EST-5)
Location: ETNA
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

According to a submitted video, Girtys Run in Millvale by Frederick Street was overflowing on to roads, just shy of reaching houses.

Heavy Rain in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 07:00:00 to 01-SEP-21 07:00:00 (EST-5)
Location: CARNOT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

A total of 2.08 inches of rain was measured through 8 AM.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 07:36:00 to 01-SEP-21 10:23:00 (EST-5)
Location: SHEARERSBURG
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Hulton Road was reported to be flooded.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 07:41:00 to 01-SEP-21 10:23:00 (EST-5)
Location: OAKDALE
Flood cause: Heavy Rain
Property damage: 30.00K
Crop damage: 0.00K
Reported by: State Official

An assisted living facility was flooding and being evacuated.  Twenty-four people were in the building at the time.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 07:45:00 to 01-SEP-21 10:23:00 (EST-5)
Location: SYGAN
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Flooding was reported on Blythe Road, with some residents being evacuated.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 07:36:00 to 01-SEP-21 10:23:00 (EST-5)
Location: NORTH WASHINGTON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Flooded roads occurred in Washington township, including North Washington Road, Pine Run Road, and Pine Run Church Road.

Heavy Rain in WASHINGTON, PENNSYLVANIA
From 01-SEP-21 00:00:00 to 01-SEP-21 07:00:00 (EST-5)
Location: STRABANE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

This was a 24-hour rain accumulation  of 4.20 inches through 8 AM.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 08:10:00 to 01-SEP-21 10:23:00 (EST-5)
Location: MOWEEN
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Flooding was reported on Tunnelton Road.

Flash Flood in ALLEGHENY, PENNSYLVANIA
From 01-SEP-21 08:11:00 to 01-SEP-21 10:23:00 (EST-5)
Location: BALDWIN
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: 911 Call Center

A swift water team responded to Streets Run Road for a vehicle stuck in water with one occupant.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 08:32:00 to 01-SEP-21 10:23:00 (EST-5)
Location: RADEBAUGH
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: 911 Call Center

An underpass on North Greengate Road was flooded with four feet of water.  A vehicle was stuck in the water, with one person escaping through the vehicle window.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 08:29:00 to 01-SEP-21 10:23:00 (EST-5)
Location: NORTH WASHINGTON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Water on Goldfinch Lane is approximately waist deep.  About 12 mobile homes have water to their front porch, with four families evacuated.

Flash Flood in WESTMORELAND, PENNSYLVANIA
From 01-SEP-21 08:50:00 to 01-SEP-21 12:24:00 (EST-5)
Location: NEW FLORENCE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: 911 Call Center

Flooding was reported at the intersection of Shannon Creek Road and Michigan Lane.