December's first week will feature generally mild weather. 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 pattern 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 trend colder, likely next week, but for those who thought the November chill was insufferable, 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 is 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 top down 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 will be forthcoming for a little while.