An Alberta Clipper system has now formed in the Canadian province of Alberta and will quickly push across southern Canada, clipping the northern tier of the United States with a quick shot of snow (hence the name). This system will become rather potent by Alberta Clipper standards. The strengthening system will pass to the north of New England with a secondary low possibly forming off the coast, along the system's triple point (where a warm, cold and occluded front meet).
Scattered snow showers will likely break out across Vermont in the afternoon on Wednesday before sliding eastward into New Hampshire and Maine as the afternoon and evening wear on. By late in the evening to the first part of the night, widespread snow showers will have overspread much of New England. The coastal plain will likely see rain showers or a mix over snow. Snow showers will likely be more widespread and steadiest through Thursday morning.
Below: NAM showing potential weather very early Thursday morning:
Scattered showers (snow for most, rain at the coast) will continue through much of Thursday, gradually becoming less and less widespread. Showers will break up from west to east. There will be a chance for briefly heavier snowfall rates both during the bulk of the storm Thursday morning as well as toward the end of the storm Thursday afternoon as the front sweeps through. It is possible for scattered snow squalls to develop Thursday afternoon.
Below: NAM showing potential weather around Thursday mid-morning:
For much of New England, this will be the standard Alberta Clipper snowfall with a few inches likely across a wide swath of the region. As per usual, the higher snowfall amounts will favor higher terrain with the Greens, Whites and Berkshires seeing more than the lower elevations in the area. There will be a period of steady snow with briefly heavier rates. For this reason, snowfall may end up rather varied. This will be a light and fluffy snow across much of the region, with wet and heavy snow closer to the coast.
The strengthening nature of the storm will allow for higher snowfall rates and higher amounts across interior eastern Maine, which will likely be the jackpot zone for New England, who has the best chance at seeing six or more inches. A winter storm watch has been issued for Aroostook, Piscataquis and northern Penobscot counties in Maine and Bennington county in Vermont.
Below: Probability of at least 6 inches of snow by Thursday evening:
Alberta Clipper systems are a bit more straightforward than other types of winter storms in New England, so guidance hasn't changed much over the last 24 hours. With that said, there is one aspect that will need to be monitored with the storm that could affect totals. The storm will be strengthening as it moves north of New England. How strong the system gets and how quickly it can strengthen will play into the rain/snow line and snowfall rates.
The stronger the storm gets, the more moisture will get pulled into the system. This would allow for heavier snowfall rates across the interior. This increased moisture would also draw more mild air farther north. So, while a stronger storm would result in heavier snowfall, it would also push the rain/snow line farther north, limiting total snowfall farther inland. With that said, the heaviest band of snow will likely set up just north and west of the rain/snow line across Maine.
Another aspect of this storm will be increasing wind gusts. Winds will likely begin to pick up later in the day Thursday as the front passes through New England. A wind advisory may be issued for Cape Cod and the South Shore as gusts could reach toward 50mph. Elsewhere could see gusts of 25-40mph. Friday will remain windy with gusts of 30-40mph likely region-wide. This wind will help usher in a very cold air mass for the weekend, with widespread 20s to low 30s for highs and teens overnight.
Blustery conditions will create a wind chill factor as well, making it feel very cold outside. Areas that see several inches of light and fluffy snow could see impacts from blowing and drifting snow on Friday.
Below: Temperatures at the 850mb level (about 4,700 feet above sea level) late this week. These temperatures of 5-10° at this level will support sub-freezing high temperatures across much of New England over the weekend:
A milder air mass looks to move back in after this weekend bringing temperatures back to near seasonable levels. Another quick clipper system may move through Saturday to Saturday night, but this one appears to be weakening upon arrival and snow accumulation chances currently look pretty low, with more scattered, light snow showers across the north looking like the most likely outcome.
Below: Current weather map for Saturday morning, showing the weakening system near the Great Lakes, sending some snow shower chances into northern New England:
New England's weather may stay more on the active side as the next system appears poised to move through early to mid next week. This system is currently showing signs of being more of an inside runner, but strength, timing and impacts remain to be seen with this one as the all important overall setup remains rather vague a week out.
Below: Current weather map for Tuesday morning (December 10):
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