Plain-language summary:
A prolonged winter storm will first bring snow, ice pellets, and freezing rain from eastern Ontario to central New England tonight into Saturday, while it stays mostly dry to the north. After a brief break for most Saturday evening, there will be freezing rain everywhere on Sunday before changing to rain Sunday evening or night, depending on location. The greatest ice accretion will occur in the St. Lawrence Valley, the Laurentian foothills, and east of the Green Mountains. It will then briefly warmup substantially on Monday with rain showers and possibly a thunderstorm before turning much colder again but drier on Tuesday and Wednesday. It will then warm up and rain on Thursday. However, most of the first half of April will likely be chilly with no lasting spring warmth, and even with snow opportunities, especially in higher elevations.
Meteorological discussion:
Part 1 of winter storm, tonight into Saturday: heavy snow from northern Ontario to southern Maine, ice pellets and freezing rain to the south
A strong and broad upper-level trough dominating the western U.S. (-PNA) is pumping a downstream ridge over the central and eastern U.S., with almost summerlike temperatures in many areas. However, at the same time, a strong and broad surface Arctic high pressure system centered over Hudson Bay will provide unusually cold low-level air into our region. This incredibly strong temperature contrast means that the warm, moist air from the south will be forced over the arctic low-level air in a process called "overrunning", generating a zone of heavier precipitation. In this case, a very elongated area of low pressure, something we have not seen often in recent years, will promote an almost stationary surface front positioned just south of our region tonight into Saturday night, leaving our region on the cold side. This is the first part of the extended winter storm. The elongated low-pressure's heavy precipitation zone will be relatively narrow, extending from northern Ontario to central New England, though it will be slightly less intense farther east. There could be almost continuous precipitation for 24 hours in this area before there is a brief break ahead of a stronger storm ejecting out of the U.S. Plains.
Although the surface front is stationary, there will be some warm advection aloft, which is also helping to promote rising air and precipitation. This means that although everywhere except the southern Adirondacks to southern New Hampshire will initially start as snow this evening, it will slowly change to ice pellets and then freezing rain from southwest to northeast, though the changeover will likely never make it north of the U.S./Canada border even by tomorrow afternoon, when precipitation will likely stop or lighten temporarily. Northern Maine through the northern Laurentians will not see any precipitation during this first part of the extended winter storm. A narrow zone of heavy snow, with a few places seeing >6", will occur from northern Ontario to southern Maine, with a lot of ice pellets and freezing rain just to the south of there. Given the dendritic growth zone being quite high up (500-600 hPa) and rather shallow, snow-to-liquid ratios will be rather low, likely ~10:1, indicating a slightly wetter snow. Total precipitation amounts could be >1" in some spots. Normally, in the spring, it is the low-levels that struggle to be cold enough during winter storms, but in this case, the temperature contrast is so fierce that there will still be a pronounced low-level temperature inversion (colder near the surface than aloft), especially given that the thick clouds and precipitation will negate any effects of the late March sun angle.
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| Source: TropicalTidbits |
Part 2 of winter storm: freezing rain, most in St. Lawrence Valley, Laurentian foothills, and east of Green Mountains, then changing to rain and warming up
The second part of the storm will feature a much stronger and more consolidated low-pressure system that will track from the central U.S. Plains into the Great Lakes and then deep into central Quebec Sunday into Monday. This will feature much stronger warm advection, pushing the warm front northward more quickly. However, the low-level cold air will hang on for a while even as warm air overwhelms aloft, and usually in these setups, takes longer to scour out than modeled. As such, everywhere will see freezing rain for a time Sunday before the southerly winds strengthen and push the warm air in. The areas that see the most freezing rain will be the typical favored areas in this setup: in the St. Lawrence Valley and Laurentian foothills where low-level cold air is channeled from the northeast through the valley, and east of the Green Mountains of Vermont into Maine, where cold air damming will occur. However, it is unlikely that anybody will see a prolonged (>18 hr) period of icing given the strength of the storm and the warm push. Also, in a storm like this, the heaviest precipitation will likely occur to the northwest of the storm track, well to the northwest of our region. Still, some areas could see up to 1/2" (12 mm) of ice accretion, with untreated roads and sidewalks becoming slippery and maybe even isolated power outages. By Monday, temperatures will spike into the 50s and 60s F (10-20C) throughout the region with scattered rain showers, and any snow and ice on the ground will quickly melt. The temperature spike will be brief, with a strong cold front bringing showers and possibly even a thunderstorm or two Monday afternoon and evening.
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