The good news regarding the upcoming cool front and its chance of storms is that the stall and cutoff scenario that the GFS was trying to paint a few days ago is going out the window. This next front will clear through by Sunday morning and not hang out for days on end, cutting off from the main jet. This results in a Saturday that will transition from an ok start to a stormy finish with a round or two of thunder and the potential for heavy rainfall.
Thankfully, we're not looking at the prospect of five inches of rain from this next batch of stuff that will come through -- the threat axis for heavier rains will fall to our north over the Poconos, Upstate New York, Ontario, and Quebec. However, the front has some solid dynamics with it and the surface low associated with it will be intensifying as it lifts northeast through the St. Lawrence Valley of Canada. The result will be the threat for thunderstorms Saturday afternoon and evening from west to east across the region.
As of now, we're not in a severe risk for Saturday but there's a chance we could get a gusty thunderstorm or some quasi-line of gusty wind and thunder to develop that could bring some relatively nasty weather to the East Coast. The front's movement is fast enough that any heavy rainfall threat should be short duration and not last a terribly long time -- but could be enough to produce localized flooding in brief instances to our north. If this occurs, the Poconos into the Lehigh Valley might be the "best bets" for any flood potential.
The front's quick movement also means improving weather on Sunday locally and lower humidity levels for next week as dew point values drop into the 50's, temperatures stay shy of 80 for a couple of days even in Philadelphia, and a "hint" of Fall is felt in the Poconos.