Plain-language summary:
Some light lower-elevation rain turning to snow and higher-elevation snow is expected this afternoon and evening south of a line from Ottawa to Montreal to Sherbrooke, with light accumulations in higher elevations and first snowflakes of the season for many lower-elevation locations. It will then turn quite cold later tonight except in far southwestern areas. It will be sunny and cool on Monday, but then there will be a period of rain Tuesday afternoon and evening before turning much warmer and windier for Wednesday and Thursday. Some showers will accompany the sharp cold front on Friday, with it being much cooler next weekend but likely most as cool as the current cold air mass. The cold shot will likely be short-lived, with another warmup occurring after that. The weather pattern generally looks quite changeable for the foreseeable future though.
Meteorological discussion:
A weak disturbance swinging on the southwestern side of an upper-level trough over eastern Canada tracking along a cold front slowly pushing south is bringing a narrow area of rain and snow from northern Ontario to western Quebec. This zone will push southeastward into northern New York, northern Vermont, and northern New Hampshire this evening, with areas to the north remaining dry. Higher elevations will receive snow with a light accumulation, with snow mixing in rain possibly even at the St. Lawrence and Champlain Valley floors if precipitation becomes heavy enough. A cold surface high pressure builds into southern Quebec behind it later tonight, with a reinforcing cold air mass, clearing skies, and calm winds, ensuring the coldest night of the season for most (below freezing even in urban areas and areas near large bodies of water, with 25F/-4C or below in most places), except in far southwestern areas farther away from the surface high pressure, away from the coldest air and clearest sky.
The surface high pressure will move to the southeast for Monday and Tuesday and expand, with the cold air quickly modifying as a strong upper-level ridge builds in the central and eastern U.S., the downstream response to the upper-level trough digging into the western U.S. (-PNA). It will be sunny and still cool on Monday, but then strong warm advection coupled with a weak upper-level disturbance will bring a period of clouds and rain late Tuesday afternoon into Tuesday night, and then it will warm up to well-above average temperatures on Wednesday and Thursday with strong southerly to southwesterly winds caused by a broad surface high pressure to the south and elongated low-pressure systems tracking to the north. It could reach 75F (24C) in some lower-elevation locations.
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| Source: TropicalTidbits |
A sharp cold front will pass through on Friday, likely accompanied by some showers, though the weakening nature of the associated upper-level trough goes against there being heavy rainfall. Another surface high pressure in Quebec will lead to much cooler temperatures next weekend. However, it doesn't look at cool as the current cold air mass, and continued upper-level troughing in the western U.S. will promote more ridging in eastern North America right afterward, with a quick warmup expected again for the following week. With a positive NAO and AO indicating a lack of blocking, it seems like a rather changeable weather pattern for the foreseeable future, with fast-moving weather systems bringing alternating warm and cold air masses as well as regular rainfall. The PNA turning neutral to slightly positive could allow more cold air to enter our region after the warmup.
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| Source: TropicalTidbits |
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| Source: TropicalTidbits |
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| Source: Climate Prediction Center |
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