More agreement on Thursday's storm is starting to come together, which is expected now that the main piece of the storm has begun to move over land across the western United States. The system will exit the Mid-Atlantic coast and track across New England Thursday to Friday morning. It's starting to become more likely that the storm will track inside the benchmark, likely close to, or over, Cape Cod and into the Gulf of Maine.
As far as the all important timing goes for Thanksgiving, precipitation will spread from southwest to northeast through the day on Thursday. It will likely begin around or just after sunrise for much of southern New England before steadily spreading north and east as the morning and afternoon wears on. By early afternoon, precipitation will likely be falling just about everywhere in New England outside of northern and eastern Maine.
Below: CMC showing potential weather around sunrise on Thursday (remember this is just one model's interpretation):
Precipitation (rain and heavy, wet snow) will likely continue through the daylight hours for all of New England, leading to a wet and raw Thanksgiving day for many. Many areas in southern New England away from the coast and in northern New England may start as snow, or a rain/snow mix before changing over to plain rain from lower elevations to higher elevations. A rain/snow line will likely set up across the interior, though its position and movement during the day will need to be worked out over the next 24 hours.
Just as the storm started, it will end from southwest to northeast across New England. It will likely end during the overnight hours Thursday to Friday for southern New England and Friday morning for much of northern New England. This is a rather fast and progressive system, so it won't be a long duration one. The system will be running along the jet stream with minimal blocking. This fast and progressive pattern is the main reason the storm was kicked back up to Thanksgiving instead of coming through on Friday, as initially thought.
Below: CMC showing potential weather around mid-afternoon Thursday (remember this is just one model's interpretation):
As stated 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 will usher 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 is the final nail in the coffin for snow across much of southern New England and the coastal plain of northern New England. This will be a primarily rain event in these areas.
As one would expect in this earlier season storm, snowfall will likely be terrain based as a rain/snow line works its way north and up in elevation. Currently, a couple inches of snow is favored for the Berkshires and maybe Worcester Hills (at or above 1,000 feet) with a few inches across the Monadnocks and interior of New Hampshire and Maine, including the Lakes Regions of New Hampshire and Maine.
The Greens, Whites and Maine mountains will stand the best chance at several inches of snow, possibly in the 3-6 inch range with some locally higher amounts possible. Mountain valleys will likely come away with this less than the slopes. Again, the setup isn't favorable for a blockbuster storm. No matter what snowfall maps may look like, bust potential will be high with this one. Currently, the Weather Prediction Center has the Green, White and Maine mountains at a 40% chance to see at least four inches of snow.
Below: Current Weather Prediction Center probability of at least 2 inches of snow. The percentages will likely increase as confidence increases on exactly where the rain/snow line will set up:
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.
As far as rainfall goes, 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. The most rain will likely fall across southeast Massachusetts and Rhode Island, where probabilities of over an inch of rain spike. Thanksgiving will certainly have a washout feel where it rains all day.
Below: QPF for Thursday morning to Friday morning. QPF includes rainfall as well as melted snow. This will fall as all rain across much of southern New England the northern New England coastal plain. Farther north it includes the amount of liquid that would come out of the snow if it were melted down:
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 storm coming on Thanksgiving isn't ideal, the precipitation it brings will be beneficial. Rainfall rates will not exceed flash flood guidance.
As stated before, this is a relatively quick-mover that will be in and out around 24 hours. The system will likely wrap into Nova Scotia by Friday morning before continuing to move away from New England. The storm will open the door for much colder air to enter New England. Add in the post-storm breeze, and it will be feeling like winter to open meteorological winter. The Climate Prediction Center now gives a good portion of southern New England an 80-90% chance for below average temperatures the first week of December.
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