Persistent series of Arctic air masses through at least next weekend before uncertain potential short-lived thaw following week, but could also turn stormier; swath of light snow through tonight, then snow especially northern areas Tuesday night into Wednesday night, then mostly dry through weekend with possible occasional light snow

Plain-language summary:

 

The region is experiencing an incredibly persistent weather pattern featuring one Arctic air mass after another for the foreseeable future. A swath of minor fluffy snow will occur this afternoon into tonight from southeastern Ontario to central Maine before it turns very cold Monday night. Temperatures quickly moderate through Wednesday night with snow for many, with the heaviest occurring north of the U.S./Canada border and especially in the St. Lawrence Valley and Laurentians. It then turns very cold again through at least next weekend, but it appears relatively dry, though occasional light snows are possible. There is the potential for a thaw for the following week, but it is unlikely to last long and could be pushed south of our region and lead to a stormier weather pattern instead.

 

Meteorological discussion:

More arctic air through Monday, swath of light snow from eastern Ontario to central Maine this afternoon into tonight

The incredibly persistent weather pattern featuring one Arctic air mass after another continues. A very weak low-pressure system, enhanced by the still warm waters of Lakes Huron and Ontario, will bring a swath of 1-4" (2-10 cm) of snow from southeastern Ontario through central Maine this afternoon into tonight, with very cold Arctic air behind it. Despite the lack of moisture, the cold temperatures and strongest ascent through the dendritic growth layer (the portion of the atmospheric column between -10C and -20C) favors the formation of large dendrites that have a lot of air pockets and can stack up quickly even with little water content, with snow-to-liquid ratios up to 25:1 being possible, in areas in which any banding sets up where stronger ascent and heavier precipitation rates occur. Outside of those zones, the weaker ascent could still favor small snowflakes. Monday night could be as cold as Thursday night for many, with temperatures below 0F (-18C) outside urban areas and away from major bodies of water.

 

Source: Aviation Weather Center and TropicalTidbits

 

 

Clippers to bring milder temperatures and moderate snowstorm for northern areas and higher elevations Tuesday night into Wednesday night 

 

The extreme cold will not last long, as a series of two Alberta clippers will dive southeastward into the Great Lakes by Tuesday, bringing southerly flow of somewhat warmer air. The first clipper is weaker but will still bring light snow Tuesday night given the warm advection into the Arctic air mass, especially in the Adirondacks on northward where the dynamics are stronger. The second stronger clipper will dive a bit farther south and then recurve slightly to the east-northeast straight into the St. Lawrence Valley on Wednesday. This slight curvature, as opposed to a pure east-southeast motion, allows the storm to pick up a little Gulf of Mexico moisture while it tracks farther south in the Midwest U.S., and the overall setup leading to the east-northeast motion afterwards leads to stronger ascent and precipitation. As such, a swath of 4-8" (10-20 cm) of snow is likely along and just to the north of the low-pressure track, mostly north of the U.S./Canada border, with the Laurentians and St. Lawrence Valley likely receiving the heaviest due to both ideal storm track and terrain-induced low-level convergence. Upslope areas of the southern Adirondacks could also receive large accumulations from heavy snow at the start of the storm. To the south of the low-pressure system, a period of snow will be followed by slight drying and a brief thaw with southwesterly flow, though higher elevations will continue to receive snow. The Champlain Valley will likely get downsloped for a time Wednesday evening due to the southwesterly flow, leading to less precipitation. A little snow is likely on the back side for areas along and northwest of the Appalachians later Wednesday night.

 

Source: TropicalTidbits

 

 

More Arctic air and mostly dry later Thursday into next weekend, though weak clippers could bring occasional light snows 

 

Yet another arctic air mass blasts in behind the clipper, lasting likely at least several days starting later Thursday into next weekend. The main contributor is continued upper-level ridging in Alaska (-EPO) promoting arctic air to continuously spill into the mid-latitudes. The upper-level ridge near the U.S. West Coast (though not penetrating northward enough into Canada to register as a +PNA) and slight Greenland blocking (-NAO) are helping but may be of secondary importance in this case. This time, the upper-level trough in eastern North America is so deep that it will cut off any Gulf of Mexico moisture, overwhelming the region with dry northwesterly flow. However, weak clippers could still produce occasional light snows, with the cold temperatures leading to higher snow-to-liquid ratios and a fluffier snow that can accumulate efficiently even with relatively little moisture.

 

Source: TropicalTidbits

 

 

Source: Climate Prediction Center

 

 

Uncertain potential for short-lived thaw following week, but could also be stormier 

 

For the following week, there are signs that the weather pattern will loosen or shift westward at least temporarily, with the Alaskan upper-level ridge shifting west into the Bering Sea some upper-level troughing entering the western U.S. (PNA turning slightly negative), which will promote an upper-level ridge downstream to build over at least the central and southern U.S., but it remains unclear if the thaw can actually push northeastward into our region. It will certainly turn milder for Monday and Tuesday of following week as another clipper approaches or tracks to the north of our region, but it is unclear how intense or sustained any warmer weather is. It is possible that the little Greenland blocking and some upper-level troughing over Atlantic Canada is just enough to shove the warmth southeastward into the southeast U.S., like in November, with our region being in the battleground between the mild air to the south and still Arctic air to the north, in which case we could actually receive stormier weather with precipitation type dependent on details that are way too early to determine. If it is configured right, it could actually be a snowier weather pattern with multiple opportunities for decent snowfalls, and if the thaw instead does reach our region, most indications are that will not last long, with Arctic air never far away to the north and ready to rush in behind any cold front. But even then, there looks to be more of a presence of at least some upper-level ridging in the southern U.S., meaning that deep upper-level troughs overwhelming all of eastern North America with dry air are less likely, raising the possibility of battleground storminess, snowy weather (given all the Arctic air around), as well potential additional thaws.

Source: TropicalTidbits