Today's forecast is right out of a meteorology 101 textbook. This morning's weather balloon measurements show that the lowest mile-and-a-half or so of the atmosphere is saturated. To agitate all that moisture there is a cold front along the Delaware River that is slowly moving eastward. To literally top it all off the leading edge of a trough in the jet stream is a bit further west of the cold front and also rotating eastward. Just like you accelerate when you drive out of a corner, so does the jet stream. That acceleration stretches the jet stream, air gets sucked up from below to fill the void, lifting air expands and cools, cooling saturated air forces water vapor to condense and clouds and rain ensue. Whew, that's about five chapters of a textbook in one sentence.
Anyway, rain is pretty much inevitable from this afternoon until after midnight. Some of those showers will be heavy and there is a slight chance of thunderstorms. A flash flood watch is in effect starting at noon. The high this afternoon will creep up to the low 70s.
The cold front, currently about 80 miles west of the city, is expected to pass through the city around 3 a.m. A little math shows that to be an eastward speed of less than 5 mph. Once the front passes the rain will end. It will take a while to clear out the humidity so Saturday will start out cloudy but we should see sun by the afternoon. Tomorrow's high is expected to reach the mid 70s. Sunday won't be quite that warm but it will be mostly sunny.