The awaited transition to colder weather continues - and the United States will plunge deeper into winter air in the time period between Christmas and the New Year (as always, click on images to enlarge). I continue to see this as a plunge to colder weather that - for the Northeastern United States - will last into the New Year. As the jet stream winds aloft sag southward in this period, the door will open for cold Canadian air to dive across the Plains and through the nation's mid-section, making a deep intrusion to the Southeastern United States in the first half of the period, then relaxing in the second half. In the Northeast, there will be some temperature fluctuations associated with an active storm track, but many of the days in this period should actually feature near-normal temperatures, and that is the forecast for the Northeast averaged over the period.
I have fairly high confidence that this pattern will result in at least one sizeable storm for the Northeast, responsible for heavy snow in at least Northern and...this time...Central New England. Southern New England is likely to at least see a wintry mix but certainly may be in the game for snow - at least for some in Southern New England - as the storm track nudges south of where it's been through mid-December. Of course, this slight southward suppression of the storm track is logical not only because of the evolving jet stream pattern and establishing cold air, but also because of the developing snowpack in the North Country of New England. A snowpack helps to hold cold air in place, or more accurately, resists incoming surges of warmth. That said, the lack of below normal cold in the Northeast is the reason I can't promise snow for all of Southern New England, at least not with the storm slated for December 26/27. I do expect above normal precipitation, regardless, owing to the continued active flow of disturbances from the Pacific Ocean, interacting with baroclinicity resulting from the southward surges of cold air.