A weather pattern shift appears to be unfolding, bringing much colder temperatures and the threat of measurable snow to portions of the heavily populated I-95 corridor in the eastern United States. After a stretch of relatively tame weather this week, the stage may be set next week for a weather pattern more supportive of colder air and winter storm formation in the days after.
For Monday through Wednesday, a more pronounced ridge aloft will move across the Eastern US. While a surface high pressure system will be in place for part of Monday, this will ease offshore by Monday night. While the high eases in the east, the upper-level pattern should begin to change quite a bit. Rather than have a ridge in the eastern United States, a ridge will set-up over the western US and Canada. With a ridge setting there, a downstream trough will amplify in the eastern United States. In a pattern where there’s a western ridge and eastern trough, temperatures tend to fall and conditions turn stormy in and around the trough while conditions turn mild and typically dry in the area of the ridge. As this initial trough sets up Tuesday, a cold front will push through the eastern US. The cooling behind this front may be fairly limited though, however, a much more substantial cold front should move through later in the week.
While the much colder cold front arrives East, the trough should amplify too. An atmospheric traffic jam of sorts should also pop-up over the Atlantic, slowing down storm systems flowing through the eastern trough. With these ingredients coming together –the cold front, a low pressure system, a building trough in the East, and a blocking pattern over the Atlantic– the eastern United States could see it’s first significant winter storm of the season.
The major global forecast models, namely the American GFS and the European ECMWF, have been offering up different solutions of how and when these ingredients will come together and how a resulting snow event could unfold. The latest American GFS model suggests this could happen as early as December 7 with a better chance around December 12; the European ECMWF suggests things could become wintry as early as December 6 with the better chance for a storm system around December 10.
It is far too early to say with certainty how this evolution to a wintry weather pattern will happen and what storms will form as the evolution continues. But it is becoming more likely than not that wintry weather will make an appearance around the I-95 corridor between Washington, DC and Boston, MA before Christmas …and perhaps 2 weeks prior.