The National Weather Service office in Baltimore/Washington has expanded a Flood Watch and Slight Risk of severe thunderstorms westward to cover additional portions of the Shenandoah Valley and the I-81 corridor.
A surface front and a strong shortwave moving from the Ohio and Tennessee Valleys will bring widespread thunderstorm activity to the region through Friday. Ample moisture from a tropical air mass, with precipitable water values of 2 to 2.25 inches, will support heavy rainfall.