Plain-language summary:
The biggest winter storm of the season so far will affect the region with a big snowstorm north of the U.S./Canada border and moderate to heavy snow with mixing with ice pellets and freezing rain to the south. After that, it will turn very cold but also drier, except for a possible Nor'easter that could bring snow to areas south of the U.S./Canada border, though any heavy snow is likely to be to the south of our region. Temperatures moderate starting next weekend, though no major thaws are expected. Weak disturbances could bring light snows, but it otherwise looks mostly dry, with the outside chance of another Nor'easter at some point that would likely favor eastern areas.
Meteorological discussion:
Major winter storm this weekend with a big snowstorm north of the U.S./Canada border, snow with mixing with ice pellets and freezing rain to the south
This
weekend will feature the biggest and most widespread winter storm of the season so far. It
won’t be a classic Nor’easter, but will instead originate from a storm
over the southern Plains tomorrow that will strengthen rather early and
move northeastward to already 980-985 hPa over upstate New York on
Sunday morning before the critical coastal transfer occurs and the
low-pressure jumps to the Maine coast Sunday evening, finally peaking
and occluding in the 960s hPa over the Gulf of St. Lawrence on Monday
and slowing down due to the Greenland blocking developing. There will be
an initial lead wave that brings minor fluffy snow accumulations mostly to areas
south of the U.S./Canada border tonight before the main storm with a lot more moisture arrives on
Sunday. Unlike most other storms this winter, the two-part and slightly
elongated nature of the whole storm means that precipitation will last
for a long time in many areas, perhaps more than 24 hours, aiding in
large snow accumulations.
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| Source: PivotalWeather |
There was a lot of energy forecasted with this system for like a week
already (when it was developing into a rapidly-strengthening bomb
cyclone in the western Pacific!), but how different vorticity maxima
within the overall energy envelope interacted would be a challenge for
models and still kind of is, though it is clear now that the initial
lead wave will be much weaker than the second, stronger storm, which was
not so clear some days ago. A band of heavy snow associated with strong warm frontogenesis will travel northward through northern New England and into southern Quebec on Sunday. The strong storm will be able to
push rather far north and send in warm air in aloft all the way to far
southern Ontario, most of upstate New York, and central and possibly
northern New England, causing a denser snow (lower snow to liquid ratios) and then a changeover to ice
pellets after the heavy snow band passes through, as well as a dry slot. The warm air aloft will be deep enough for freezing rain from the southern Adirondacks to southern Maine, and there could be substantial amounts of freezing rain in those areas where they usually get upslope enhancement from the southeasterly flow.
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| Source: TropicalTidbits |
After the low-pressure transfers to the Maine coast Sunday evening, the warm air aloft will erode, and precipitation will change back to snow for everyone. Areas from southern Vermont to southern Maine that are south of the storm track will just dry out, but north of there, there will be snow, heavy and convective at times, on the back side with cyclonic vorticity advection aloft causing enhanced lift and cooling aloft causing elevated instability for a few hours, even as the main frontogenetic band moves off to the east into Maine.
The
jackpot will be just north of there where no mixing or dry slot occurs,
and the heavy snow band could stay almost stationary for 6+ hours on
Sunday; this is most likely from eastern Ontario to southern/central
Quebec, including Montreal, and then into northern New Brunswick. After Thursday's major snowstorm, it would be the 2nd major snowstorm for these areas in just 4 days! Ice pellets, freezing rain, and dry slotting will substantially cut accumulations down farther north, though there will be a plowable snow accumulation even there beforehand.
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| Source: Weather Prediction Center |
Drier and very cold next week, though small chance of Nor'easter bringing snow south of the U.S./Canada border
After the major weekend storm, a major high-latitude block develops, with northwesterly flow funneling in very cold arctic air (AO index currently at an incredible -5!), but it will be modified slightly by the weekend storm occluding and slowing down over the Gulf of St. Lawrence early next week wrapping in Atlantic warmth and moisture from the east before heading southward into our region, a bit like what happened in early January that gave warm advection snow along and northwest of the Appalachians, but to a lesser extent. This time, the stalled storm will be too far northeast to give us wraparound snow, except a few upslope snow showers in the Laurentians and the Eastern Townships of Quebec. The vertically stacked storm will slowly pull east, but a piece of the broad upper-level trough will retrograde westward into the central Canadian Prairies, which will then steer another system diving into the Rockies and Plains either eastward or northeastward, depending on the orientation and intensity of the disturbances. Most indications are that the storm will reach the mid-Atlantic U.S. East Coast late on Wednesday, and then turn up the coast slightly, but not enough to reach northern New England on north, though the whole broad upper-level trough and any embedded weak disturbances could promote snow showers. However, a few rogue model runs and ensemble members have a stronger storm interacting more favorably with the broad upper-level trough to the northwest and pushing far enough north to give areas from the Adirondacks to southern Maine a decent snowstorm. That appears unlikely but not impossible yet.
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| Source: Climate Prediction Center |
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| Source: TropicalTidbits |
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| Source: TropicalTidbits |
Moderating temperatures starting next weekend but no major thaw is expected, with perhaps weak disturbances bringing light snows
Later next week, the strong high-latitude block cuts off the pipeline of cold arctic air, leaving the cold air that is already in place to slowly modify, with surface high pressure and drier weather dominating, a change from earlier in February. However, the +PNA (upper-level ridging in western North America) will keep upper-level troughing in eastern North America, favoring near to slightly below average temperatures even if we lose the true arctic air. The troughing will also prevent any big thaw, but if positioned east of our region or is not amplified enough, it could just be mostly dry, with the deep westerly to northwesterly flow cutting off any moisture from the Gulf of Mexico or western Atlantic, like in January. There could be a few weak disturbances and/or clippers bringing light snow to the region. There is the outside chance of a Nor'easter in this pattern if any upper-level trough can dig southward enough and amplify just west of our region and pick up any southern jet energy. Maine is the most likely to receive substantial snowfall with this type of late-forming Nor'easter.
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| Source: TropicalTidbits |
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