Plain-language summary:
The first widespread snowstorm of the season arrives tonight into tomorrow. The heaviest snow will fall from the Adirondacks through northern Maine, with generally
3-5" (8-13 cm) expected in lower elevations and 4-8" (10-20 cm) in
higher elevations, except 6-12" (15-30 cm) in northern Maine. In this region, a band of heavy snow will occur for a few hours. To the north, lighter snow will fall, and to the south, a brief initial period of snow will quickly change to a wintry mix and then rain. Behind the storm, it is still cold but not super cold with heavy lake effect snow immediately east and northeast of Lake Ontario and occasional snow showers elsewhere. It gets even colder early next week, with possible snow squalls associated with the cold front. It could turn milder later next week but it is uncertain how long that will last for.
Meteorological discussion:
What a change from earlier in November! The first widespread snowstorm of the season arrives tonight from the southern Adirondacks to central New Hampshire and then the rest of the region tomorrow. There are two disturbances: one over the Great Lakes, bringing light snows there, and another one in the Southeastern U.S. that has a lot more moisture from the Gulf of Mexico and western Atlantic and is already producing heavy snow in Pennsylvania. The two disturbances will interact tonight into tomorrow, a bit too late for a blockbuster snowstorm in our region but in time for a decent snowstorm for many. The southern disturbance will move just offshore the East Coast, strengthen, and become the primary system by tomorrow. This is a classic track for a snowstorm in northern New England and southern/eastern Quebec, to the northwest of the storm. Though the storm will not be strengthening too rapidly, it will be enough for a mesoscale frontogenesis band to form to its northwest, where snowfall rates of up to 1" (2.5 cm) per hour will occur for a short time.
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| Source: Aviation Weather Center |
That said, there are some limiting factors on snowfall amounts. First, it is still mid-November, and so the low-level cold air mass is not especially strong and the western Atlantic water is still quite warm and actually anomalously warm. As such, with the easterly to southeasterly flow, snow will easily change over to a wintry mix and then rain close to the Atlantic coast and likely even into central New Hampshire and central Maine. A slight glaze of ice or thin layer of sleet or ice pellets is possible in this narrow transition zone, but it is unlikely to be significant due to the lack of very cold low-level air. The interior, from northern Vermont through the northern third of Maine on northward, should see all snow. Even then though, surface temperatures near freezing means that the snow will be relatively wet (somewhat low-ratio snow) especially in the Champlain Valley where some downsloping off the Green Mountains with easterly winds will occur. A pronounced precipitation hole or minimum is likely in the northern Connecticut River Valley, in the Littleton, New Hampshire area, due to southeasterly winds downsloping off the White Mountains as often happens in this scenario. Also, with no blocking downstream, the storm will be moving rather quickly, with the heavier frontogenetic band lasting only a few hours at any one location. Eastern Ontario will miss the heavy frontogenetic band entirely but will get some steady light snow from the initial Great Lakes system. All snow directly associated with the storm will end by tomorrow night, with lake-effect snow and upslope snow showers still occurring in the usual spots (for the westerly to northwesterly wind direction).
I think the map below reasonably shows how much snow will fall, with the heaviest from the Adirondacks through northern Vermont, far northern New Hampshire, eastern townships of Quebec, and then into northern Maine. Generally 3-5" (8-13 cm) is expected in lower elevations and 4-8" (10-20 cm) in higher elevations, except 6-12" (15-30 cm) in northern Maine, where the storm and cold air will be stronger, leading to both more precipitation and less marginal temperatures. The biggest potential bust areas are the Champlain Valley and the region from central Vermont to central Maine, where minute details of storm track and a 1F difference will lead to substantial snowfall differences.
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| Source: PivotalWeather |
No
major synoptic-scale storms in the near-future are expected after tomorrow, but we will be stuck on a fairly
cold pattern for quite some time. With cold air across
the still warm Great Lakes and a west-southwesterly flow both persistent later this week, lake
effect snow totals could be epic in some spots, especially off Lakes
Erie and Ontario which have a west-east long axis. As always with
lake-effect snow, there will be big variations over small distances, but
the a few places in the northern Tug Hill Plateau neighboring St. Lawrence Valley in northwestern New York will get up to 36" (90 cm)! Sometime between Friday and early Sunday, a low pressure off to the northwest will turn the wind slightly to southwesterly, allowing lake-effect snow showers from Lake Ontario to travel through the St. Lawrence Valley, perhaps as far as Montreal or Trois-Rivières, with up to 1" (2.5 cm) possible there. However, the Great Lakes will also modify the cold air mass, so it will be colder than average but not super cold like in the Northern Plains.
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| Source: TropicalTidbits |
However, early
next week, a reinforcing shot of cold air will arrive, this time with
more of a northwest flow with little or no modification over the Great Lakes.
Any disturbances/clippers going off to the north will produce at least
scattered and brief snow squalls, perhaps lake-enhanced, associated with their cold fronts. A
couple of days with highs well below freezing are likely and outside
urban areas, nighttime temps down to 5F (-15C) are possible if the high pressure crests overhead on one night, especially if there is
still snow on the ground by then. There might be a warm up after that, but it is too early to determine if it will last -- it could also be quickly squashed by another arctic air mass from the north.
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| Source: TropicalTidbits |
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