The system that will become New England's Thanksgiving storm is now working across the country. The system will dive into the Tennessee Valley before moving northeast, emerging off the Mid-Atlantic coast during the day Thursday. The storm will strengthen as it moves across southern New England and into the Gulf of Maine. How much the storm can strengthen before exiting the Gulf of Maine Thursday night will determine much about impacts.
ALERTS
TIMING
Light precipitation will likely begin to enter into western New England early Thursday morning, possibly before sunrise. Rain and snow showers at the beginning will be on the lighter side. Precipitation will steadily push eastward and fill in as the morning goes on. By the late morning and midday, precipitation will likely have overspread much of New England outside of Maine.
Throughout the morning and into midday, precipitation will follow the rule of elevation with higher elevations seeing snow and lower elevations switching from an initial mix to plain rain. The immediate coastal plain will start as rain and stay rain during this time.
Below: HRRR showing potential weather around sunrise Thursday (1st image) and around midday Thursday (2nd image):
Thursday afternoon and evening, the storm will likely cross southeastern New England as it travels to the Gulf of Maine. The storm will likely be strengthening during this time. At this time, colder air will wrap around the backside of the system. Combine this with potential dynamic cooling due to the strengthening of the system, and the rain/snow line will try to inch back toward the northern New England coastline as the afternoon and evening wear on.
The afternoon into the evening is also when snowfall rates will likely be heaviest for interior northern New England. Much of southern New England (outside the Berkshires) will remain rain. Precipitation will spread across Maine through the afternoon. Snowfall rates and how close the snowfall can get to the coast in the evening will come down to how quickly the storm can strengthen. This will be discussed more in the "snow" section below. Mid-afternoon through the evening is likely when the bulk of accumulations will occur.
Below: HRRR showing potential weather mid-afternoon Thursday (1st image) and Thursday evening (2nd image):
As we've been saying for a while, this will be a progressive storm that will not linger around for too long. Precipitation will shut down from west to east starting Thursday evening and continue through Thursday night, with eastern Maine seeing steadier precipitation likely end late Thursday night into early Friday morning.
Below: HRRR showing potential weather late Thursday night:
SNOW/MIX
The general timing of mixing and snowfall will likely be much of northern New England starting as a mix or snowfall before a changeover to plain rain from lower elevation to higher elevation as the morning wears on into the early afternoon. Snowfall will likely begin to ramp up and potentially try to make its way back toward the coast through the afternoon and into the evening.
As one would expect in an earlier season storm, snowfall will likely be terrain based. The jackpot zone will likely be over the White and Maine mountains. Here, the storm will start and end as snowfall. Amounts will drop heading south with the foothills and Lakes Region likely seeing a few inches. The Green Mountains may not see as high of snowfall rates as higher elevations farther east as it will take time for the storm to strengthen.
Amounts will really drop off heading to the coast and southern New England. The Berkshires and Worcester Hills may be able to pick up a couple inches. The northern New England coastal plain will see little if any accumulation. Lower elevations across southern New England will see all rain. The best chance for notable accumulations will be at or above 1,000 feet region-wide. Areas across far northern New England will be on the fringe of the system, with lighter snowfall rates. The Champlain Valley will see mainly rain or a mix.
The big question on snowfall will be how quickly can the storm strengthen? The Euro model is standing its ground that the storm will be able to deepen in time to bring higher amounts than what is being advertised above. There's limited blocking with this system, leading to a less amplified and more progressive storm. There is a distinct lack of colder air ahead of the storm.
While Tuesday's storm has ushered in a cooler air mass, it certainly won't be mid-winter like. On top of this, there is no strong area of high pressure to the north of New England to filter colder air into the system as it occurs. None of this is conducive for a particularly strong storm system to develop. The nor'easter is extremely unlikely to rapidly intensify as it passes New England. The easterly flow off the ocean, which is sitting around the upper 40s to 50° in the Gulf of Maine, will send mild marine air over land in eastern areas.
With that in mind, we're steering more toward guidance that favors a slower strengthening of the storm and therefore lower snow totals. With that said, dynamic cooling is still favored to occur Thursday afternoon. This occurs when precipitation rates become heavy enough to cool the atmosphere, which allows for rain or a mix to change to snow. Areas that are already snowing will see heavier snowfall rates develop. The level of dynamic cooling that can occur will play a large role in snowfall amounts across northern New England.
Current Weather Prediction Center probability of seeing at least 6 inches of snow:
The biggest limiting factor for snowfall will be a distinct lack of winter-like air ahead of the system. With a bulk of the precipitation coming during the daylight hours, it may be difficult to get snow to stick, especially as it mixes with rain. Areas south of the mountains will likely be contending with some mixing at some point during the day. The rain/snow line will likely collapse closer to the coast in the evening. How close it can get to the coast before the bulk of the precipitation wraps up will be something to watch closely.
Another note on precipitation type is that the overall setup is not favorable for a widespread "messy mix" type of storm. It will either be raining or snowing, with a rather narrow band of a rain/snow mix, which will be moving around as the day goes on. There will be very little by way of sleet or freezing rain.
Thermal profiles will be marginal with the system, so there will likely be a sharp cutoff in snowfall amounts (again, the rain/snow line needs to be hammered down). The type of snow will likely be of the wetter and heavier variety; snow ratios will likely be lower than 10:1. Areas that see five or more inches of this snow could see scattered broken tree limbs and power outages.
BUST POTENTIAL
As we've said all along, bust potential is high with this one. The main way the storm could bust will be if the storm doesn't strengthen much. Dynamic cooling will be needed to produce heavy snowfall rates. This process won't occur if the storm can't deepen. The fast-moving nature of the system will make it difficult for the storm to gain too much strength. Marginal temperature profiles will make the rain/snow line finicky. Areas most likely to underachieve will be the Lakes Regions of New Hampshire and Maine. Areas most likely to overachieve will be the Green Mountains.
RAIN
This will likely be another decent soaking for southern New England and the coastal plain of northern New England. A widespread half an inch to an inch of rain is likely across these areas. Thanksgiving will be a washout for areas that see rain for the entirety of the event. Lesser rainfall amounts will naturally be seen where more snow falls farther north.
Much of New England does remain in a drought, with most of southern New England in either a severe or extreme drought (the drought monitor is updated every Thursday and has not yet taken into account the rainfall from late last week). While the timing of the storm coming on Thanksgiving day isn't ideal, the precipitation it brings is needed. Rainfall rates will not exceed flash flood guidance.
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