December's first week will feature a generally mild regime overall. The cold trough that dominated much of November, bringing us our first month of below average temperatures since last August, has been replaced with a more zonal regime in the atmosphere. This is allowing temperatures to moderate quite a bit through Wednesday and still remain close to normal through the end of the week as the cold air core entrenches over the Yukon and Alaska this week.
Don't get too giddy with hopes for warmth all winter. We will tend colder, likely next week, but for those who thought November was insufferable in terms of cold the following week provides a bit of a breather in the pattern.
The warmest of the days this week will be Tuesday, with highs that flirt with or exceed 65 across Philly and the burbs. It's not record-setting warmth as the record on Tuesday will be 73 in Philadelphia; however, it's going to be over 15 degrees above what is normal for this time of the year and a good day to drive around with the roof open on your car.
A cold front crosses the region on Tuesday night into Wednesday, bringing some showers and an end to the warmup. A larger storm system begins to organize for the weekend or early next week -- modeling varies in how that storm comes together and impacts us but there are signs for showers and a brief warmup in advance of that weekend storm. Signs point to a colder middle third of December than what we're going to experience this week but no true "arctic" invasions of cold are forthcoming for a little while.