Plain-language summary:
After a widespread snowfall last night, with the heaviest in eastern Ontario and southwestern Quebec, it will cool down and dry out tonight but only briefly. A period of light snow tomorrow evening will transition to scattered light freezing rain or rain tomorrow night. After a thaw on Tuesday and Wednesday, a major storm will bring heavy rain and/or snow, with who getting what not certain yet. It will turn much colder for Thursday and Friday before a warmup begins later next weekend. The following week looks relatively mild though perhaps not extremely warm and snow is still possible with the right setup.
Meteorological discussion:
An Alberta clipper that brought a widespread light to moderate snow (heaviest in eastern Ontario and southwestern Quebec) since yesterday evening is weakening and moving off to the east, with little precipitation in our region now. A cold high pressure system over central Quebec will push cold low-level air into the region tonight into tomorrow morning, but the cold air will not push very far south, with a front stalling in southern or central New England as another storm pushes into the Great Lakes. A weak disturbance ahead of the main storm will produce precipitation across the region, heaviest in the southern Adirondacks to southern New Hampshire closer to the disturbance and where upslope southeasterly flow will enhance precipitation. With the low-level cold air in place ahead of the storm, precipitation will start as snow except in the southern St. Lawrence Valley and southwestern Adirondacks, where the cold air will never really get in. Low-level cold air damming east of the Green Mountains as well as low-level cold air channeling southwestward through the St. Lawrence and Ottawa River valleys could lead to a period of light freezing rain and ice pellets Monday night in those areas as warm air moves in from the southwest aloft, though the precipitation will take a bit of a lull during that time. Farther south and west, precipitation will transition to scattered rain showers or stop entirely as dry air moves in at the mid-levels.
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| Source: PivotalWeather |
As the Great Lakes storm passes to the north, warm air will flood in at all levels, though the cold air damming will try its best to hang on especially east of the Green Mountains. As this happens, a trough will deepen considerably over the central U.S., with a ridge in the western Atlantic amplifying. Combined with a disturbance rounding the base of the trough in the southern U.S., this amplified pattern will lead to a rapidly intensifying storm tracking quickly from the southeast U.S. into our region Wednesday into Thursday. Exactly where the storm tracks will determine who experiences heavy snow (if anybody) and who experiences heavy rain and a warmup, which appears likely to be most of the region. Since the previous storm will scour out the low-level cold air, any snow is reliant on cold air pouring in on the back side. Such a situation is always trickier to get snow than if the cold air was already in place. With the cold air coming in kind of late, it appears that most areas will see only or primarily rain until the storm reaches at least northern New England. Then, a narrow area of heavy snow for up to 8 hours could occur to the northwest of the storm track, and then the heavy snow area expands quickly in Quebec as the storm strengthens and taps into colder air. With cold air coming in, rain will change to snow for some areas before precipitation ends completely, especially along and northwest of the Appalachians, though the storm track trending northwest suggests that this might be mainly confined to the Adirondacks and Laurentians.
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