Residents along the Wissahickon Creek corridor and low-lying areas of Whitemarsh, Plymouth, and Whitpain townships face a serious flash flood risk through Wednesday afternoon, with the most dangerous conditions expected Tuesday afternoon and evening.
The National Weather Service's Mount Holly, N.J., office issued the flood watch Monday, covering southeastern Pennsylvania including all of Montgomery County. The watch runs from 8 a.m. Tuesday, July 28, through 2 p.m. Wednesday.
The NWS forecaster discussion published Monday identified Tuesday as the most likely day for severe weather and flash flooding, driven by a surface low-pressure system developing to the west and pulling warm, moist air into the region nearly all day.
Where the risk is highest
Whitemarsh Township's largest floodplain runs along the Wissahickon Creek, much of it within Fort Washington State Park, according to the township's open space plan. A second major floodplain stretches along the township's western border near the Schuylkill River.
The Plymouth Creek Sub-Basin, which drains from Butler Pike to Ridge Pike to Stenton Avenue, carries water through Plymouth Meeting and Cold Point. Spring Mill Creek drains the southern portion of the township, including Marble Hall, Lafayette Hill and parts of Plymouth Meeting, before joining the Schuylkill River near Spring Mill.
In Whitpain Township, the Wissahickon Creek corridor near Blue Bell Pike and Mount Pleasant Avenue is a documented flood-prone area.
Montgomery County's 11-acre floodplain restoration site along the Wissahickon Creek near Skippack Pike was itself damaged by Hurricane Ida flooding in September 2021. That flood overwhelmed the creek's banks in hours.
Wind and power outage risk
AccuWeather forecasts wind gusts between 60 and 70 mph from the strongest thunderstorms, strong enough to down trees and damage power lines across eastern Pennsylvania. The NWS Tuesday forecast calls for a high near 81°F, south winds of 5 to 10 mph with gusts up to 25 mph, and a 100% chance of precipitation.
What to watch for
The NWS warns that excessive runoff may flood rivers, creeks, streams and other low-lying locations. Residents near the Wissahickon and its tributaries, including Prophecy Creek, Sandy Run, and Sunnybrook Creek, should monitor conditions through the watch's expiration at 2 p.m. Wednesday.
Thursday's forecast shows only a 30% chance of afternoon showers, and Friday is expected to be sunny with a high near 86°F.
Residents should check with Whitemarsh, Plymouth, and Whitpain township offices for any event cancellations or schedule changes due to the storm.
