Plain-language summary:
It is turning cooler and drier today, but it will snow in from the southern Adirondacks to southern Maine tonight into tomorrow morning, with light snow accumulations even at lower elevations. It will be unseasonably cold with widespread snow on Tuesday, perhaps the last one of the season at lower elevations, with substantial accumulations from the Laurentians to northern Maine and lighter snow accumulations to the south. It will be cold but mostly sunny on Wednesday before turning milder and more unsettled for Friday and next weekend, with potentially several days of showery, cool, and cloudy weather, with perhaps even some snow at very high elevations. It will likely warm up at least somewhat the following week, though sustained spring warmth still seems rather unlikely, with some cool and showery days still likely at times.
Meteorological discussion:
Cooler and drier today, then snow from southern Adirondacks to southern Maine tonight into tomorrow morning
A discombobulated storm is pushing east of our region, with cooler and drier air pushing in behind the storm. However, this push will be slowed by another storm approaching our region from the southwest tonight. It will not be very strong, but its location just south of our region, along with colder air coming in just in time, means that it will snow from the southern Adirondacks to southern Maine tonight into early tomorrow morning, even at lower elevations, with minor snow accumulations. The perfect timing, occurring late at night into early in the morning when it is the coldest and before the April sun angle has an effect, will help snow to stick to the ground.
Unseasonably cold with snow on Tuesday, heaviest from Laurentians to northern Maine
While this is happening, the North American weather pattern is changing and substantially amplifying, with an upper-level ridge in western North America extending all the way to the Yukon Territory (+PNA), and forcing a downstream upper-level trough to dig into the Great Lakes on Monday, pulling air straight from the arctic. This is also helped by high-latitude ridging (-NAO and -AO).
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| Source: TropicalTidbits |
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| Source: Climate Prediction Center |
Along the leading edge of the arctic air mass, an initially weak shortwave will strengthen and move northeastward, before sort of occluding, and the upper-level trough barely cuts off as it moves into far southern Quebec on Tuesday, and then sliding east-southeastward and re-strengthening slightly in Maine. To the north of the storm track, there will be several hours of moderate to heavy snow across the Laurentians, the northern St. Lawrence Valley close to Quebec City, and into northern Maine, occurring Monday night into Tuesday evening. In this area, there could be a narrow zone of 15-25 cm of snow! To the south, there could be an initial band of heavy snow (snow squall) associated with the cold front moving west to east Monday night into Tuesday morning, and then some snow showers and squalls on the back side of the storm as it gets colder, with only minor snow accumulations at lower elevations. Incredibly for April, for many areas, the back side of the storm will feature be a dry, fluffy snow, at least when surface temperatures are not above freezing, as any bit of warmth will be confined to near the surface, with very cold air aloft and most of the synoptic-scale ascent being in the dendritic growth zone with not-too-strong winds that would fracture the dendritic snowflakes. This is a tricky setup though, as the very cold air aloft and the April sun angle produces very low static stability, and the rather unstable setup means that any forcing can produce a large response in lowering surface pressures or promoting ascent, with much of the snow being at least somewhat convective, and models will have a hard time simulating these processes with instability and therefore the storm strength and location correctly. There are still considerable model disagreements on storm location and speed despite it only being 2 days from now. The convective nature is also leading to the low-pressure system being of smaller scale then a typical synoptic-scale low-pressure system, with a rather narrow area of heavy snow. I suspect that this will be the last widespread accumulating snow at lower elevations, though surprises sometimes happen in April.
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