Monday 10 a.m.
Cooler air advanced from the Great Lakes to the Middle and North Atlantic states during the weekend. The high pressure area marking the center of the cool air mass is moving toward the Carolinas now, and a return southwesterly flow will sponsor a warmup until the next cold front arrives. That flow should be on a line from central New England to southern Illinois on Wednesday, and it will drift southward and stall on a line from North Carolina to southern Missouri on Thursday.
Some showers will accompany the front, and some rain may break out on the north side of it later in the week. At the end of the week and into the weekend, there is quite a variation in model solutions, with some suggesting rain spreads across the Middle Atlantic states then into New England during the weekend.
The dominant cloud type in the summertime is the cumulus. Cumulus clouds can still grow in the fall and winter, but there is less solar heating, and thus less fuel to get these clouds to grow. The clouds in this picture are not associated just with fall, but in summer the same situation would lead clouds with greater vertical development.
This map shows the split flow that is predicted to be in place on New Year's Day. Note how the flow reaching northern Pennsylvania originates far north in Canada, whereas to flow aimed at Virginia comes from Mexico.
The maps I searched for were from December 1960. I was 13 and was thoroughly overjoyed when Philadelphia got 14.6 inches on Dec. 11 and 12. Schools were closed for three days, something that did not happen again until the Blizzard of January '96.
At midnight, the temperature will be in the 50s to low 60s from Virginia to Southern New England... more like late spring than Christmas time. Meanwhile, cold air will be advancing into western parts of Pennsylvania and New York, driven by strong winds. Earlier, this "cold" air mass looked like it would be more potent than it has turned out to be. This map shows the pressure pattern and some temperatures at 9 a.m.
Temperatures are likely to be in the 50s from Boston to Washington, D.C., during the nighttime hours of Christmas Eve. Dry chillier weather will arrive during Christmas Day, with dry weather lasting until at least Saturday.
This picture, which may or may not have been taken very recently, has a red dot near the North Pole. I cannot confirm that a red dot is there on the ground or that it means anything. We will monitor the area for any signs of activity and advise everyone to maintain the spirit of being nice and not naughty.
Rain with areas of fog should spread from Virginia to New Jersey Monday or Monday night then spread into New England for Tuesday. From the mountains of northeastern Pennsylvania into the interior of New England this could at least start as snow or ice. The GFS for 1 AM New Year's Day looks interesting. See the map below. Whether or not this storm develops and where it will snow or rain cannot be precisely predicted two weeks in advance using these models.