The coldest part of this week's cold snap is now moving into the Midwest and will be over the Northeast tomorrow night and Friday. This video has more, including a look at what could be a major precipitation producer at the beginning of next week.
This map shows the pervasiveness of the northwesterly flow of bitterly cold air behind a cold front that is contributing to snowfall from Washington, D.C., to New York City this morning. Clearing will follow the frontal passage.
In previous winters, I have talked about the upper stratospheric cold signal, where the normal vortex over the North Pole weakens or actually reverses to form a high pressure. That reversal has often been a sign of impending blocking aloft. In blocking patterns, storms are forced south of their usual paths and it often turns colder. This winter, we have seen that such a setup is not required to make it get cold or snowy. The vortex has remained over the pole all winter, and is rooted in place now, as shown on this map from the University of Wyoming.
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.