Plain-language summary:
An unseasonably cool and cloudy pattern will dominate for the next few days with slow moderation beyond that. Widespread showers will occur on Wednesday in southern and eastern Quebec as well as northern New England. The higher elevations of eastern Vermont, northern New Hampshire, eastern townships of Quebec, and especially northern and western Maine, will even see accumulating snow Wednesday night into early Friday before drying out for the weekend. Lower elevations of the St. Lawrence and Champlain Valleys may see flurries with a dusting possible Wednesday night, especially near northwestern facing slopes. Sunshine slowly returns this weekend, but with northerly flow and cool (but not as cool) conditions continuing, and with frost and freezes likely everywhere. Temperatures approach but not exceed average by early next week.
Meteorological Discussion:
The cool pattern will begin tomorrow with a barely closed off upper-level low approaching from the Great Lakes, accompanied by deep northerly flow from still ice and snow covered Hudson Bay and central Canada. The disturbance will produce valley rain showers (Ottawa, St. Lawrence, and Champlain Valleys) and mountain snow showers tomorrow before it strengthens as it reaches the Maine coast. As it strengthens, it will wrap the cold air into the northwest side and generate its own cold air through upward motion, clouds, and precipitation causing, rain will change to snow in eastern Vermont, northern New Hampshire,
eastern townships of Quebec, and especially northern and western Maine (where up to 4" (10 cm) is possible). This is not going to be anywhere near a repeat of last Tuesday's Nor'easter, even though it will be moving slower, as it will get going too late for any appreciable snow west of there. Flurries could be seen in the St. Lawrence and Champlain Valleys with a dusting possible, especially late Wednesday night, when it is the coldest and there is no influence of the sun, and near the northwestern facing slopes. I said this in my last post too, but I really think this is the last chance of any snow accumulation in the lower elevations. The northwestern Adirondacks could also get a little upslope snow Wednesday night.
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| Source: TropicalTidBits |
Afterwards, the storm will stall or move very slowly eastward as it occludes, with snow continuing in western and northern Maine through Friday, though gradually becoming lighter and more intermittent. Although it will be dry farther west, it will still be rather cloudy, under the influence of the moist cyclonic circulation. It will dry out by Saturday, with at least breaks of sun for most as the storm pulls farther east but still close enough for a cool (though not as cold) northerly flow to dominate. However, with clearer nighttime skies and lighter winds, nights might actually be slightly colder, with widespread frost and freezes.
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| Source: TropicalTidBits |
This slow motion is associated with the North Atlantic Oscillation (NAO) being most negative since November 2021 or earlier. This corresponds to Greenland blocking, which means systems move much more slowly than usual, causing the trough over eastern North America to be stuck for several days.
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| Source: NCEP |
The NAO is expected go back to neutral by early May. As this occurs, the trough will slowly move out by early next week, with the storm continuing to pull away and sunshine becoming more abundant. The high sun angle will also quickly modify the cold air mass. As such, temperatures will gradually approach climatological averages by early next week.