The combination of strong daytime heating and a gradual cooling aloft from an approaching upper level system is setting the stage for the potential for strong to severe thunderstorms late Tuesday afternoon into the first part of the evening.
We see thunderstorms forming over southern Pa. and over the higher terrain of eastern West Virginia and western Virginia. This Virginia activity seems more related to the upper level system supporting this development and a weakening cool front. This front will move through the immediate Baltimore area just before daybreak Wednesday. So, ahead of this front we see a few rounds of showers and thunderstorms. This first round expected later Tuesday afternoon should be the strongest as far as the potential for severe weather. Activity later Tuesday will still bring downpours and some gusty winds.
Once the front moves through slightly drier air aloft will move in from the west. However, this looks pretty incomplete looking at the latest model output. We still see enough moist air lingering and enough instability aloft to support a few random showers and thunderstorms across the region Wednesday mostly during the afternoon and evening. A weak area of high pressure will move into the region Wednesday night and Thursday and this should help bring a dry and stable weather pattern across the viewing area.