Wednesday was supposed to be Day 3 of our heat wave this week, but the high at Philly International Airport only reached 89 just after 3:30pm(to be considered a heat wave we need three or more days in a row where the temperature is 90 degrees or higher); we did have showers and thunderstorms break out in the late afternoon, but primarily to the north and west.
Overnight we'll have clouds lingering around with some scattered showers to the east; lows will be in the lower 70s. We'll begin to clear out by the morning commute and have sunshine by the afternoon with highs in the lower 80s and a northerly(to then an easterly) wind. There may be some isolated showers to the south and east as a short wave passes through, but at most there will just be clouds in the afternoon once we reach our convective temperature(the estimated temperature that the surface must warm to for clouds to develop) in the afternoon.
Come Friday high pressure is still in control of our weather and will provide us with a easterly wind that will continue to Saturday as well; highs both days will be in the middle 80s with a mixture of sunshine and clouds. Come Sunday high pressure pushes further offshore and we get a southerly wind; the humidity creeps back up as well as highs approach 90. A series of cold fronts will swing through, starting by Sunday night with showers and thunderstorms. Since the front is weak there will be cooler air behind it, and in fact highs on Monday will be in the lower 90s as the second(and more potent) cold front inches closer to us. We'll have showers and thunderstorms again in the afternoon, through the overnight, and into Tuesday with highs around 90 in the afternoon.
What's interesting is behind the front we'll have very cool and dry Canada air(unseasonably cool!); highs by the middle of the week will barely reach 80! Now remember that you can always follow my 7-day forecast(any time) at