Heavy snow in northern areas through Sunday night, with wintry mix farther south; briefly colder Monday, then milder Tuesday and Wednesday though more snow in Laurentians; two snowstorm chances late week into weekend for southern and eastern areas, though neither appears very likely; wintry weather continues following week, then possibly turning stormier

Plain-language summary: 

 

After a brief thaw with widespread rain yesterday, a winter storm will bring heavy snow, locally >10" (25 cm), from southern and central Quebec to northern Maine tonight through Sunday night, with a mix of snow, ice pellets, and rain farther south with much less accumulation. It will briefly turn colder Monday before a little snow Monday evening along and northwest of the Applachians and then milder temperatures later Tuesday into Wednesday, with intermittent light rain in the St. Lawrence Valley and more substantial snows in the Laurentians. There are then two chances for East Coast Nor'easters (one Thursday into Friday, one next weekend) that could bring moderate to heavy snow to southern and eastern areas, though neither appears particularly likely for now, but it is also too far out to have much confidence in any scenario. Arctic air returns afterward, perhaps with light snow the following Monday, with the wintry weather pattern continuing and possibly turning stormier, even with the possibility of brief thaws.

 

Meteorological discussion: 

 

Heavy snow tonight followed by lighter snow through Sunday night in northern areas, mix of snow, ice pellets, and rain farther south

 

After a brief thaw yesterday with rain well into central Quebec, the storm's cold front brought colder air directly from the north today, just in time for the next storm coming from the southwest and strengthening. The cold air mass is not at all arctic and is actually still considerably warmer than average for January, but it is just cold enough for snow tonight north of the U.S./Canada border and in northern Maine, with temperatures in the entire lowest few kilometers being between 23F (-5C) and 32F (0C). This is quite a departure from models several days ago which almost unanimously showed this storm being the second part of a several-day thaw with almost all rain. Since the storm is strengthening and coming from the southern U.S., it is actually bringing Gulf of Mexico moisture into the marginally cold air, a rarity this season. The storm will not become particularly strong with a lack of true polar jet energy, being well to the north, to give a boost to the storm, but in this case, that will prevent the storm from over-amplifying and flooding the entire region with warm air as models had shown days ago. It will first peak in Lake Huron late tonight before occluding and re-forming and re-strengthening along the Maine coast Sunday night, just in time to cut off the surge of warm air north of the U.S./Canada border. The eastward elongation/occlusion of the storm will promote warm frontogenesis from eastern Ontario to northern Maine, and combined with a moisture-rich and marginally cold air mass with instability aloft, will lead to heavy snow for several hours tonight, perhaps heaviest in the St. Lawrence Valley between Montreal and Quebec City where terrain-enhanced convergence could boost snowfall slightly. The Laurentians to northern Maine will continue to see lighter snow through Sunday night as the occlusion and re-formation occurs. The strengthening upper-level low will also promote instability and upward motion for a time across eastern Ontario and northern New York through southern Quebec and New Hampshire Sunday afternoon and evening, leading to scattered but possibly briefly intense snow showers.

 

Source: TropicalTidbits

 

 

Source: TropicalTidbits

 

 

Source: TropicalTidbits

 

 

Some areas could see >10" (25 cm) of snow total. South of the U.S./Canada border, a messy mixture of snow, ice pellets, and rain is expected, becoming more rain farther south, though it could change to snow during the heaviest precipitation, and slight cold air damming east of the Green Mountains could lead to some more snow and ice pellets in the favored areas there, though without much of a cold air mass to begin with, this is not the ideal setup for cold air damming. In these areas, snow accumulations will be much less though more dense. There will also be less precipitation south of the U.S./Canada border, as that region is farther from the best dynamics given the storm track.

 

Source: Weather Prediction Center

 

 

Briefly colder Monday, then a bit of snow northern areas Monday evening before milder again late Tuesday into Wednesday, though significant snow still possible in Laurentians 

 

Colder, though still not arctic air briefly returns behind the storm, but another Alberta clipper already approaches our region later Monday. A much weaker initial wave will produce light snows along and northwest of the Appalachians Monday evening, followed by the much stronger Alberta clipper Tuesday night into Wednesday night that although will not truly tap into Gulf of Mexico moisture, is strong enough to pull in considerably milder air from the southwest. Most of the region south of the U.S./Canada will simply stay dry and relatively mild during this period. The St. Lawrence Valley could see a little snow initially followed by intermittent light rain, while only the Laurentians is likely to see significant snowfall with both upslope enhancement and cooler temperatures, given the storm track well to the north.

 

Source: TropicalTidbits

 

 

Two chances of Nor'easter snowstorms mostly for southern and eastern areas late week into weekend, though neither appears very likely

 

Such a clipper track normally just brings a cold front with brief snow showers after it passes, but in this case, additional pieces of energy will dive into a deepening upper-level trough in the eastern U.S., aided by an upper-level ridge building in western North America (+PNA) after a brief pause earlier this week. Some, though not overly strong high-latitude blocking (-AO, though the NAO is surprisingly slightly positive) will also help. This could lead to a coastal Nor'easter low-pressure system forming Thursday into Friday that slows down as the polar jet retreats and leaves the storm behind, and this position would be better to tap into Atlantic moisture and produce significant snows, though for now, most indications are that this will only be from southern Vermont to southern Maine, and perhaps not even that, given that the Alberta clipper leaves behind a slightly positively tilted upper-level trough (trough axis oriented southwest to northeast) that would steer a storm more to the east than to the north. It is also being kicked out by more pieces of energy entering the Midwest U.S. 

 

Source: TropicalTidbits

 

 

Source: Climate Prediction Center

 

 

Those additional pieces of energy themselves constitute another Nor'easter storm threat for next Saturday into Sunday. However, most indications are again that they will likely fail to interact favorably to phase into a big storm, staying separate or not timed right, the southern disturbance being too weak or too slow lagging behind the northern disturbance, and/or perhaps with another Alberta clipper approaching for the following Monday helping to kick everything to the south and out to sea. To get a big storm, the southern disturbance has to be strong enough and run just ahead of the northern disturbance that would guide the moisture-rich southern disturbance northward up the East Coast and also cause it to strengthen, which also requires the upper-level trough to be strong and sharp enough. The most likely area to get hit would be eastern New England, though there would still be lighter snow elsewhere from the northern disturbance. Another miss for a Nor'easter would fit a common theme in recent years with many pieces of energy but never phasing to create a big storm even with a favorable upper-level trough position in the eastern U.S. However, it is too far out to rule out any scenario, including a big storm scenario, as relatively small differences in the disturbances will determine the outcome, and there is large corresponding model disagreement.

 

Source: TropicalTidbits

 

 

Arctic air returns afterward, possibly with light snow for following Monday and then potential stormier weather pattern starting later in the week with continued wintry pattern 

 

After another possible Alberta clipper bringing light snow for following Monday, a true arctic air mass will likely push into the region, leading to the coldest temperatures since the beginning of January if not mid-December. The overall weather pattern likely will retrograde later in the week, with the coldest air retreating to western Canada (classic -PNA La Niña weather pattern), with a southeast U.S. ridge appearing but not being particularly strong. This could promote a classic Colorado low track from southwest to northeast that picks up Gulf of Mexico moisture and runs it into the arctic air mass dominating Canada, leading to frequent snow and ice events, though we have seen this pattern in long-range model forecasts earlier this winter, and they mostly have not happened. There could also be more low-pressure systems coming out of the Pacific Northwest or Canadian Rockies instead of from the southern and central Rockies, which would promote more Alberta clipper tracks with less moisture. In either case, with the arctic air mass remaining strong in Canada and some high-latitude blocking persisting (at least AO being negative) will keep things wintry in our region (though brief thaws are possible if the southeast U.S. ridge is stronger than modeled) and possibly stormy also.

 

Source: TropicalTidbits