Saturday's warmth and late day storms (for some of us) departed and brought a sunny, cooler Sunday to the region. The start to this week's weather will firmly establish that fall officially began this weekend, as mornings will be cool and crisp; however, there are two chances for showers lurking later in the week.
Monday and Tuesday morning will see tempatures in the 40s in many locations outside of the city. With plenty of sunshine, temperatures will rebound each afternoon—near 70 on Monday, and into the 70s on Tuesday—as high pressure nudges offshore and warmer air begins to move in. Nice weather will also be in the cards for late Thursday and Friday, with temperatures in the 70s both afternoons.
There are two chances for rain this week—Wednesday with showers, mostly late in the day, and this weekend with a slow-moving storm system. Wednesday's system looks to cross the region towards dinner and through the night and doesn't look like a huge deal. Some showers, perhaps a rumble of thunder, are possible. A more robust chance of rain is possible Saturday into Sunday although timing and details are still up in the air a bit for that storm system. The second system will draw some Gulf moisture northeast and could bring us a steadier rainfall.
September's weather pattern has been relatively active, in some respects similar to last year. Eight inches of rain fell last week in the Poconos with last Tuesday's storm system and some locations close to home are running double the "normal" in rainfall. There's little correlation between active September weather patterns and winter weather as some winters with active patterns in September have produced relatively snowy winters (2004-05 had 30" of snow in Philly) and others, like last year's, were more active in October than February. It does show a transition in season though and the gradual steps towards winter will continue.