Reality is checking back in after two days of September-like warmth in the Delaware Valley. After highs of 68 and 71, respectively over the past two days, today's high of 63 (likely high) occurred at 1 AM. We're now in the 40's and we won't get anywhere back near 63 by day's end...and just as likely, by week's end.
The past 24 hours has seen a rather marked cooldown across the Eastern US as the fleeting warmth of last weekend's and yesterday's warm surge is replaced by the return of chill. Temperatures between 7 AM yesterday and 7 AM today are anywhere from 30 to 35 degrees cooler as colder air marches east in the wake of the cold front.