A reinforcing shot of comfortable air will work towards the region on Saturday with a frontal boundary and a disturbance along said front. The combination of the two will result in thunderstorms firing in scattered or broken lines and passing through the region.
These storms are already firing across the Great Lakes and moving east-southeast at a leisurely pace...but they could (if they hold together) move into the Lehigh Valley or Central Pennsylvania early tomorrow morning. We might have a few early morning storms popping across the sky in a few spots -- a number of models suggest this as a possibility.
More storms may fire up on Saturday afternoon as the frontal boundary slides south into the immediate Delaware Valley. The afternoon threat is dependent a bit on whether any morning activity zaps the atmosphere of energy and how much sunshine breaks out. Modeling is inconsistent on coverage and placement of storms with some of the higher resolution modeling less aggressive than the GFS and Euro on the threat.
In any case, the chance of storms does exist and some of them could be strong to perhaps severe. We're not in a slight risk for severe but the Storm Prediction Center has the city and points south and east in a five percent chance area for severe, noting the possibility that a storm or two could reach severe criteria. Gusty winds, perhaps hail, would loom as the threats from the strongest of storms.
It also does not appear that we will see the same level of risk for heavy rainfall as what fell in some portions of the area yesterday -- two inches plus in parts of Delaware and in Chester County, with five plus inches in coastal counties of Maryland. These storms don't appear to have the same level of moisture support as yesterday's did on the whole.