The end of our comfortable weather is at hand -- tomorrow marks the official transition out of the low humidity, cool morning pattern that we've been in and the beginning of our march towards the season's first run of 90 degree weather as a warm front approaches and pushes through the region over the course of the day.
This warm front is accompanied by a disturbance in the atmosphere, which will add instability and pop that will help produce showers and some thunderstorms around the region tomorrow. Modeling suggests it could be into the Philly metro as early as the morning hours (if you believe the NAM), while other modeling suggests midday or early afternoon as the timing. Given how these warm air advances sometimes out-run modeling, it would not shock me if we get some showers in here by the rush hour tomorrow.
Tomorrow probably isn't going to be the nicest of days from Philly on north as this warm front's precipitation tends to be more widespread across the northern half of the region, which means clouds and showers. Thunderstorms may fire in the afternoon to our south, where the air will be a bit warmer as the warm front will have advanced into Delaware and Maryland. Given the difference between a warmer, less showery south of town and a cloudier, cooler north of the city, temperatures will probably have a decent spread between Allentown and Dover -- probably 60's to near 80 tomorrow afternoon from north to south.
Wednesday is when the warmup really takes hold as the warm front clears through, with sunshine gradually taking over during the course of the day.