This week will feature a very festive clipper system and a warming trend as the week goes on. This warming trend will not be nearly as pronounced as it could have been, however. Quiet and seasonable weather is expected for Christmas (and the rest of the week thereafter as well).
MONDAY
High pressure will crest over New England today. Temperatures aloft will begin to moderate today, but remain very cold. This will allow for Monday to get a notch warmer than Sunday, but remain well below freezing in most spots. A big difference from Sunday is that winds will be much lighter with the high pressure overhead. This will also bring another day of sunshine. Ocean-effect snow showers over Cape Cod will come to an end this morning as the wind slackens.
TUESDAY
A clipper system will push its way through New England late tonight into Tuesday. With plenty of cold air in place, this will be an all snow event for a vast majority of New England. Only the South Shore and Cape Cod will have much of a chance at seeing non-frozen precipitation. The system will lift its warm front into New England, which will provide the forcing for widespread. snow showers.
Snow showers will begin to break out this evening across western New England before steadily pushing eastward as the night goes on. Most of New England will be under the gun for snow showers by midnight Tuesday. The system will be moving along, with snow ending from west to east through the morning hours. Some snow may be lingering across eastern Massachusetts and Maine's coastal plain into the early afternoon.
Below: HRRR showing potential weather around midnight Tuesday (1st image) and mid-Tuesday morning (2nd image):
Clippers typically see better forcing for precipitation on the northeast side of the low pressure center. This system is currently expected to cut straight through New England, leaving northern New England on the juicier side while southern New England may get into a dry slot, leading to a shorter window of snowfall. Snow showers are currently expected region-wide, but they are currently looking to persist for a longer period of time across the north.
A period of widespread light snowfall will persist for several hours across northern New England, allowing for a wide swath of 2-5 inches of snow. With the shorter window of snowfall across central and southern New England, amounts will be more limited. The jackpot zones currently look to be the northern Green Mountains and Downeast Maine. Both of these areas have the best shot at 4-6 inches. These two areas will see the highest QPF. Downeast Maine will also see increased moisture stream into the system off the ocean.
Overall, snowfall amounts have been on the upward trend over the past 24 hours. This is due to the increase in moisture for the storm to work with as well as a trend toward stronger forcing for snow showers along the system's warm front. A low-level jet stream has also trended weaker. Stronger winds aloft can "shatter" snowflakes, leading to drier snow and less snowfall overall. With a trend toward weaker winds aloft, this may not happen as much. With that said, the low-level jet may still be strong enough where this comes into play and our above snowfall forecast does take that into consideration.
The steadiest and most prolonged snow band with this system will be focused just to the north of the warm front. With the system passing through New England, this will keep the warm frontal forcing in northern New England. Southern and central New England will see snow more toward the back end of the event as the trailing cold front pushes through. This will be a very light, fluffy snow with ratios on the order of 13-18:1. This type of snow can accumulate and pile up very quickly.
A winter weather advisory has been posted for northern Vermont and northern New Hampshire, as well as Downeast Maine. Snow will wrap up for many in the morning with a majority just about done by midday. As stated above, eastern areas may see snow linger into the early to mid afternoon. Some clearing is expected behind the system, especially for the western half of the region.
WEDNESDAY-FRIDAY
After Tuesday's clipper, an expansive ridge will build over the eastern United States. This will lead to a notable warm-up for much of the country as well as Canada. New England, however, will likely miss a bulk of this warmth as surface high pressure just to the north of the region will continue to filter colder air into the region at the surface. It will warm-up compared to the beginning of the week, but this warm-up will likely be around seasonable to slightly above average levels rather than well above average like areas farther west.
Below: CMC showing temperature departure from average on Thursday afternoon. You can see wide swaths of well above average warmth across North America, but locally, it is much more subdued:
Temperatures may be a bit tricky this week as the cold surface high pressure likely sets up an inversion, where there is a layer of warm air aloft, trapping colder air at the surface in the mountain valleys. Other than the temperatures, the weather during this time will be straightforward, with calm and mainly dry conditions under the ridge with variable clouds.
For Christmas day/start of Hanukkah itself, the day will be a quiet one with seasonable temperatures. Some ocean-effect snow/rain showers are possible across southeast Massachusetts, but other than that it will be calm and seasonable with not much else to say about the day. After Christmas, a warm-up is still expected to an extent, with each day potentially a couple degrees warmer than the last.
WEEKEND
There is uncertainty this weekend on how the expansive ridge plays out. The question is how quickly will the ridge break down? New England's next chance at widespread precipitation will likely come early next week. The timing of the breakdown of the ridge will determine the exact timing on this precipitation chance.
The other question will be how much of the warmer air can get into New England this weekend. The general warming trend is expected to continue into the weekend, but just how mild it can get remains to be seen. Saturday has already begun to trend cooler. These temperature profiles will dictate precipitation type for the upcoming disturbance.
Below: Current weather map for Sunday morning (December 29), showing the next system approaching from the west:
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