WASHINGTON, Pa. - Flooding from Sunday's steady rain is now being observed in parts of Western Pennsylvania, moving the weather threat from a forecast risk to an active local problem in communities south of Pittsburgh.
The National Weather Service said emergency management reported several instances of flash flooding in central Washington County late Sunday morning. Between 1.5 and 2.5 inches of rain had fallen in the warned area, according to the weather service.
A flash flood warning covering central Washington County remained in effect until 1:30 p.m. Sunday. The National Weather Service said flash flooding was already occurring in small creeks and streams, urban areas, highways, streets, underpasses and other low-lying or poorly drained locations.
Communities identified in the warning included Washington, Canonsburg, Avella, Wolfdale, McGovern, Bentleyville, East Washington, New Eagle, Houston, Ellsworth, Claysville, Eighty Four and West Alexander.
The warning expired Sunday afternoon, but a broader flood watch remained in effect for the Pittsburgh area through noon Monday as additional rounds of rain remained possible.
Local flooding documented south of Pittsburgh
WPXI published photographs Sunday showing flooding in Washington and Canton Township following the prolonged rainfall. The images provide visual confirmation that at least some communities are experiencing standing water and local flooding rather than merely facing a forecast threat.
The flooding is consistent with the areas forecasters had identified as having the greatest risk Sunday. CBS Pittsburgh reported earlier in the day that communities south of Pittsburgh, particularly areas around and south of Interstate 70, faced the highest flash-flood potential.
Radar estimates cited by CBS indicated that as much as 2.5 inches of rain had fallen in parts of Washington County by early Sunday morning. The National Weather Service later confirmed similar rainfall totals when it reported observed flash flooding.
The timing of those reports is important. CBS Pittsburgh's forecast published at 11:31 a.m. said no storm reports had yet been received from the affected area. Eleven minutes later, an updated National Weather Service statement at 11:42 a.m. said emergency management had reported several instances of flash flooding.
That progression shows how quickly the situation changed as rainfall accumulated.
No evidence of major regional river flooding
Despite the localized flooding, current federal river observations do not show a major regional river-flooding emergency across the Pittsburgh area.
At 1 p.m. Sunday, the National Weather Service's Pittsburgh hydrology monitor showed the Ohio River at Pittsburgh at 16.65 feet, below its 22-foot flood stage.
Other monitored locations along the Ohio, Monongahela and Allegheny rivers also remained below their listed flood stages at that time. The Monongahela River at Charleroi, for example, was measured at 7.4 feet compared with a 28-foot flood stage.
That distinction means Sunday's primary problem so far is localized flash flooding and drainage flooding caused by heavy rainfall rather than widespread flooding along the region's major rivers.
River conditions can change after additional rainfall moves through a watershed, so those observations represent conditions at 1 p.m. rather than a guarantee that water levels will remain unchanged.
More rain remains possible
The National Weather Service Pittsburgh office said several waves of heavy rainfall were expected across Western Pennsylvania and surrounding areas Sunday and Sunday night. Some storms could produce enough rainfall to cause additional flooding.
The Pittsburgh forecast continued to call for showers and possible thunderstorms Sunday afternoon, followed by another chance of showers and thunderstorms Sunday night.
Additional rainfall is also expected Monday. The weather service has warned that repeated rounds of rain through the middle of the week could eventually produce river rises and broader areas of flooding if enough precipitation accumulates.
That longer-term risk is separate from the flash flooding already documented Sunday in Washington County.
The recent weather history also increases concern about runoff. Western Pennsylvania has experienced repeated heavy-rain events in recent weeks, including significant flooding in parts of the Pittsburgh region earlier in September. Saturated or repeatedly soaked ground can reduce how much additional rainfall can be absorbed before runoff develops.
What residents should know
The most immediate concern remains flooded roads and low-lying areas, particularly in and around Washington County and other communities south of Pittsburgh that receive additional heavy rainfall.
The National Weather Service advises drivers not to attempt to cross flooded roads because the depth and strength of moving water can be difficult to determine. Floodwater can also conceal damaged pavement or other hazards.
As of Sunday afternoon, the available information supports describing the situation as localized flooding rather than a widespread Western Pennsylvania flood emergency. A flash flood warning was issued after emergency management confirmed flooding in central Washington County, and local photographs show flooding in Washington and Canton Township, but major monitored rivers around Pittsburgh remained below flood stage.
The next question is whether additional rounds of rain Sunday night and Monday produce new flash flood warnings or begin causing broader river and creek rises. Residents in flood-prone areas should continue monitoring National Weather Service warnings as the wet pattern continues.