One cool front passed through the Mid-Atlantic region yesterday morning and a secondary front will move through later tomorrow. It is this second front that will usher in the coolest air so far this season for the Mid-Atlantic region with 40’s likely as low temperatures early Friday morning in some of the northern and western suburbs of the big cities along I-95 between DC and NYC.
The atmospheric setup tomorrow night will be quite favorable for temperatures to drop rapidly as high pressure settles in right on top of the region (see 12Z NAM forecast map for Friday morning). The move overhead of this Canadian-born high pressure system will allow for clear skies and the tapering off of afternoon northwest breezes in the Mid-Atlantic region. Some interior sections of the Mid-Atlantic could drop into the 30’s by early Friday morning (e.g. Poconos) and frost is not out of the question in portions of upstate Pennsylvania, New York and interior New England. Meanwhile, the city of Philadelphia is likely to bottom out in the low-to-mid 50’s which would be the coolest morning there since late May (current normal morning low around 65 degrees at PHL). High temperatures on Friday afternoon will hold in the refreshingly cool low-to-mid 70’s in most Mid-Atlantic locations, but will rebound to near 80 degrees on Saturday as the high shifts to an offshore position.