It's getting to be that time of the year. Cooler airmasses, clear nights, and longer nights are allowing parts of the region the opportunity to cool more effortlessly than they had in past weeks and months. The season's first frost advisories are out for tonight across the Poconos plus Northampton County in Pennsylvania, plus Northwest Jersey, as clear skies overnight and light winds should allow for temperatures to drop into the 30's up to our north.
The closest location to the city for 30's tonight may be Quakertown. Most suburban locations should drop into the 40's overnight...similar to last night and plenty crisp for September.
Frost is not likely this far south but we could see a sub 50 degree night in the city tonight if everything breaks right. Even that might be a bit tough to pull off at the Airport (Northeast Philly should have a good shot at the 40's tonight) but a sub 50 low at the Airport is doable if everything breaks right.
The frost chances are a one shot deal this week -- nights should be progressively less cool over the balance of the week as we warm up in advance of a frontal boundary that crosses the region on Saturday or Sunday with a chance of showers and storms.