As New England's weak storm system continues to move away, it will create a northwest flow in its wake. This flow will begin to pump colder air into the region, though the drop will not be sharp. Thursday will be a mainly seasonable day across New England without too much of a rise in temperatures from morning lows. From this afternoon, colder temperatures will continue to push into New England before peaking (or bottoming out) on Sunday as Arctic air arrives.
While this cold continues to filter into New England, two weather features around on Friday and Saturday continue to be watched. These features are an Alberta Clipper that will be weakening and diving south of New England while a coastal storm develops offshore. The big question all week has been how much these two features interact (or phase).
More interaction occurring earlier would result in more precipitation for New England while lesser interaction occurring later would result in a glancing blow or a complete miss from the coastal storm. All week, guidance has been keen on the latter situation, which precludes New England from getting a decent thump of snow. This still appears to be the case, however, a glancing blow is becoming more likely rather than a miss altogether.
The coastal storm will be deepening as it moves up the coast, but with the current timing, it looks to pass outside the benchmark, with a bulk of moisture expected to remain offshore. There is still some spread among guidance in just how far west (or close to New England's coastal plain) the higher moisture can push.
As of now, a period of snow showers is likely Friday afternoon into Saturday morning. These snow showers will likely be most numerous near the coast with lesser activity farther inland. Eastern Massachusetts, eastern Maine (especially Downeast Maine) and maybe the Green Mountains (from the clipper system itself) are positioned the best to see light accumulations. As of now, these accumulations look to be on the order of coatings to a couple inches.
Below: Current probability of seeing at least 2 inches of snow by Saturday afternoon:
The immediate coast of southern New England, including all of the South Shore and Cape Cod, may see some mixing and rain showers Friday afternoon before a cooling boundary layer collapses to the coast, switching the rain to snow showers. With an outside-the-benchmark track, Cape Cod will have the best chance to see the heavier precipitation, though much of this would likely be rain and mixing over snow. Downeast Maine is another area to watch for the potential of a period of steadier precipitation.
Below: HRRR showing potential weather Friday afternoon (1st image) and early Saturday morning (2nd image):
Once this system passes, it will swing the door wide open for very cold air to sweep into New England. Broad cyclonic flow will allow for continued scattered snow showers on Saturday, mainly across interior New England. Strong high pressure builds for later Saturday into Sunday, helping to usher in the arctic temperatures.
The coldest day of this stretch will be Sunday. Highs on Sunday will range from the low teens across the north to low 20s in southern New England. Both Saturday night and Sunday will be very cold, with single digits, on either side of zero, likely across the entire region. Sunday night into Monday morning may be the colder of the nights due to optimal radiational cooling conditions. Lows in the -10s will be possible across the north. Before the high crests over New England, a breeze will bring feels-like temps down Sunday morning.
Temperatures will remain very cold on Monday before starting to moderate back toward more seasonable levels by Christmas Eve. Speaking of Christmas Eve, The overall unsettled pattern looks to continue into next week with a fast moving disturbance possibly moving through around next Tuesday to Wednesday.
A weak disturbance is currently poised to move into the Great Lakes area around Monday to Tuesday morning. After that, confidence drops as guidance is having trouble figuring out where it goes from there, but should it scoot through New England with ample moisture, it could bring a round of festive flakes (or rain showers) for Christmas Eve into Christmas morning. How it actually pans out remains to be seen.
Below: Current weather map for Tuesday morning (December 24) showing the aforementioned disturbance over the Great Lakes:
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