The upcoming week of weather will be a bit of a yo-yo, with a couple of fronts coming in from the northwest propping up some short-fused heat events while we cool down to average in the front's wake. Along with the frontal boundaries coming towards the region, the potential for some thunderstorms does exist starting late tonight and continuing through Tuesday (when front #1 moves through the region).
Tonight's thunder threat is dependent on whether or not thunderstorms develop this afternoon in the Great Lakes and track east and southeast towards the region. Computer modeling from the GFS and NAM both suggest that parts of Pennsylvania could see a MCS thunderstorm complex track through late tonight or early tomorrow morning (one complex of storms is shown below on last night's high resolution NAM). This complex of storms probably tracks north of the city but it does merit a passing mention in case it slips closer to us...again, if it even develops.
Monday promises to be a bit more summery and humid -- after a couple of cool days a return to 90 degrees looks possible. Along with that, the first front will approach the region and bring a chance for thunderstorms in the afternoon to parts of the region. Computer modeling hints that the best chances will reside over the Lehigh Valley, Central Pennsylvania, and Poconos, and points west of there. Thunderstorm development will be scattered around -- not everyone gets in on it -- but there could be some locally strong storms in spots. The NAM hints that the Philly metro could get a thunderstorm on Monday night as afternoon and evening development to our west slips on through.
The front will cross the region on Tuesday -- with probably the hottest day of the week forthcoming from a temperature standpoint (could get into the mid 90's). Scattered storms will accompany the front as it crosses through. It won't storm all of the time on Monday or Tuesday and most of these storms will be scattered around -- it will though provide some additional rain to places that need it around here.