1:20 PM | *Major pattern change to cold likely to bring multiple snow threats as well during December*
A major pattern change is going to begin in the Mid-Atlantic region during the middle of next week that will likely result in an extended period of colder-than-normal temperatures. In addition, snow will likely become a threat on multiple occasions during the month of December - potentially as early as at the end of next week.
Extremely cold air has been building up on the other side of the North Pole during the past several days and some of this Arctic air will be able to push into the central and eastern US by the latter part of next week thanks to changes in the upper atmosphere. Specifically, this change to sustained cold in the Mid-Atlantic region will be the result of a combination of strong high-latitude blocking (i.e., nearly stationary strong high pressure over Greenland and northern Canada), an intensifying upper-level trough in the central and eastern US, and strong high pressure ridging along the west coasts of Canada and the US.
The weather associated with this transition period to a cold pattern can be summarized as follows: 1) mild with rain, perhaps on the heavy side, in the Tuesday night/Wednesday time period ahead of a pattern-changing strong cold front, 2) cold air intrusion late Wednesday and Thursday with strong NW winds, and 3) the potential for some snow at the end of next week depending on the interaction of two strong upper-level waves of energy as they heads towards the east coast.
The 12Z operational GFS 500 mb forecast map for next Thursday night shows a complex pattern with two separate waves of energy following the mid-week passage of a strong cold frontal system. Depending on the ultimate interaction between these two upper-level systems, there is the chance that a storm forms along the east coast at the end of next week as suggested by the latest (12Z) operational GFS model run. There would likely be enough cold air in place for snow in the immediate I-95 corridor if this storm does indeed form along the coast. While the cold air intrusion is quite definite at this stage for later next week, the prospects for snow are far less certain at this particular time. In fact, the 12Z Euro model doesn't develop a storm nearly as rapidly as today's GFS and it likely would form too late for any snow in the immediate I-95 corridor - but still a close call and something to closely monitor.
One of the factors arguing against snow this time of year in the immediate I-95 corridor is the fact that the western Atlantic Ocean is still relatively warm compared to sea surface temperatures expected in January, February or even in March. The relative warmth of the western Atlantic in early December is always an obstacle to overcome for accumulating snow in the big cities of the I-95 corridor since it can impact boundary-layer temperatures and make it difficult to stay at or below freezing when there is any kind of an ocean-component to the low-level winds (i.e., E or NE). If this initial snow threat does not materialize at the end of next week, others are quite likely to follow by the middle and latter parts of December in this unfolding sustained cold weather pattern.
Meteorologist Paul Dorian
Video discussion on upcoming pattern change: