The prospect of the first significant frost event of the year looms larger this morning than it did a couple of days ago. Freeze watches are already up for the Poconos for Friday night into Saturday morning due to the potential for temperatures dropping into the 20's and 30's to our north. I would not be surprised to see frost advisories blanket much of the region as well when we get to Friday night into Saturday.
A reinforced shot of chill will cross the region on Friday night and Saturday thanks to a front crossing the region early in the day Friday. A breezy and somewhat chilly Friday (highs will be similar to today but winds will gust over 25 mph in spots, making it feel cooler than today) will be followed by diminishing winds and clear skies for Friday night. This will allow the bottom to fall out of the thermometer across the region.
It's possible that the city drops below 40 as well...but at minimum, if the city avoids 40 for a low, almost the rest of the region will drop into the 30's. The NAM (below) shows the potential for subfreezing lows as close to us as the outer north and west burbs, with frost possible just about anywhere outside of I-95, the Shore, and Delaware Bay to the south. The best chances for a killing frost will reside across the northern burbs, the Lehigh Valley, and Berks County.
This chill will not last long -- the roller coaster of October will swing quickly back in a warmer direction by Sunday as highs flirt with or exceed 70 across much of the region as a warm front surges through the region.