The National Weather Service has issued a Flash Flood Warning for Montgomery County until 8:45 pm.

From the National Weather Service:

Between 2.5 and 4 inches of rain have fallen. Additional rainfall amounts of 1 to 3 inches are possible in the warned area. Flash flooding is already
occurring with numerous streams and creeks in flood stage including Valley Forge, French Creek, and the East Bank of the Brandywine Creek.

A Flash Flood Warning is issued when a flash flood is imminent or occurring. If you are in a flood prone area move immediately to high ground. A flash flood is a sudden violent flood that can take from minutes to hours to develop. It is even possible to experience a flash flood in areas not immediately receiving rain.