The incoming colder pattern next week will produce the coldest mornings of the winter so far on Tuesday, Wednesday, and Thursday. I won't classify this as "arctic invasion" although some hype on the cold will probably be pretty high. Our lows probably will not bottom out below what we had last winter in Philly (14) in this stretch -- we don't have snow cover and the "trend" in cold has been to back it off a notch or two.
That said, the upcoming stretch will still be pretty cold by late January standards.
The below graphic shows projected lows on Wednesday morning around the region. 15-20 from I-295 on northwest, with 10-15 from Allentown-Harrisburg north into the Poconos. We could see some near zero lows in Bradford and perhaps in the northeast tip of Pennsylvania.
None of this is record breaking or even approaching records. It doesn't help there will not be much snow on the ground. We *might* have a clipper move through the region Monday night into Tuesday that could fire off a pittance of snow -- modeling has wavered on showing this but we're not going to dispute the possibility that as the surge of colder air pushes in it comes with a little flurry or light snow action. This could help notch temperatures down further if it happens...but we're not saying it's likely at this point and merely a possibility.
What does look likely is the coldest mornings of the winter...not that getting below 25 is an incredibly hard task but this winter it has been.