Changeable weather pattern with two clippers bringing areas of light to moderate snow to northern areas through Monday night, then clipper brings widespread snow Wednesday; coldest air of the season afterward followed by potential weekend storm possibly finally starting stormier period

Plain-language summary:

 

A very changeable weather pattern will evolve over the next 5 days, with two clippers bringing light to occasionally moderate snow today and especially Monday evening mostly north of the U.S./Canada border but also in the western Adirondacks and northern Green Mountains, with milder daytime temperatures approaching near or just above freezing in lower elevations. An arctic front will bring a snow squall to areas along and northwest of the Appalachians, followed by quickly falling temperatures. It will also be quite windy for most Monday evening through Tuesday morning. Another clipper will bring more widespread snow on Wednesday before the coldest air mass of the season arrives on Thursday. There could be a storm next weekend, but whether it brings a snowstorm, mixed precipitation, or not much precipitation is uncertain. That storm could finally be the start to a stormier weather pattern in our region.

 

Meteorological discussion:

 

Two clippers going to the north bringing light to moderate snow in northern areas through Monday night, ending in snow squall

 

With a positive NAO but with the subtropical jet rather inactive, the next 5 days will be characterized by fast-moving clippers alternating with arctic high pressure systems in the large-scale, fast, and deep west-northwesterly flow. A clipper going by to the north has produced snow showers since last night mainly north of the U.S./Canada border and in upslope regions of the western Adirondacks and northern Green Mountains with the stiff westerly to southwesterly flow. As is typical of moisture-starved clippers going to the north, the Champlain Valley and areas southeast of the Appalachians are getting downsloped and are struggling to see any snow, with milder daytime temperatures approaching near or just above freezing.

 

After drying out tonight, another stronger clipper will pass by way to the north over central Quebec tomorrow evening. Despite the low-pressure center being so far away, the strength of the low-pressure system and broad warm advection with strong west-southwesterly flow will lead to light to moderate snow, more than the first clipper, for the same areas as those getting snow tomorrow: areas north of the U.S./Canada border, western Adirondacks, and northern Green Mountains. Meanwhile, the Champlain Valley and areas southeast of the Appalachians get downsloped with almost no snow again, with daytime temperatures reaching near or just above freezing. For most, snow totals will be limited by the moisture-starved nature of the clipper, as usual for clippers, and the fast movement. However, the western Adirondacks will also get lake-enhanced snow off Lake Ontario with both clippers, with a total of up to 10" (25 cm) possible with the two clippers. Also, this second clipper will bring a strong arctic cold front with a very strong convergence zone and winds shifting from west-southwesterly to northwesterly that will lead to a snow squall quickly traveling southeastward Monday night, possibly dropping a quick 1-2" (2-5 cm), even into the Champlain Valley as the wind turns to northwesterly and downsloping ends, though areas southeast of the Appalachians could still miss out as the northwesterly wind is also downsloping there. The strong winds will also lead to blowing snow.

Source: TropicalTidbits

Source: Climate Prediction Center

Third clipper brings widespread snow on Wednesday

 

After a brief break on Tuesday with quickly falling temperatures behind the arctic front, another somewhat weaker clipper will move into the region on Wednesday, but farther south than the previous two clippers. It is projected to move through northern New York, Vermont, New Hampshire, and then exit just off the Maine coast by Wednesday night. This means winds will be weaker, terrain effects will not be as pronounced, and the swath of snow will be farther south, leading to a widespread light snow (likely 1-4" or 2-10 cm) for our region, likely mostly from Montreal on southward and perhaps still slightly more for higher terrain. With all the clippers, snow to liquid ratios are expected to be relatively high (15-20:1) given the cold, dry air, though the strong winds with the second clipper Monday evening could lead to more snowflake fragmentation and lower ratios.

 

Source: TropicalTidbits

 

Very cold late week, potential storm next Sunday into Monday

 

The coldest air mass of the season for most arrives on Thursday, behind the third clipper. Unlike the cold air mass last week which was muted due to a subtle disturbance in the Great Lakes turning the wind to west-southwesterly in our region, this time, the cold air will come straight from the northwest, leading to minimal moderation of the cold air. Thursday night will likely be the coldest night of all, though it depends a bit on the evolution of various little disturbances/weak clippers in the northwesterly flow, which we won't know the details of for another few days. At this point, a cut-off low in the Desert Southwest U.S. will be ejecting northward, and this is when the details become critical for determining the weather in our region next weekend and beyond. It is also clear that an upper-level trough will be approaching the North American West Coast at around this time, promoting downstream upper-level ridging in western and central North America, though the strength and orientation of both are uncertain. This uncertainty is partially due to uncertainty in whether part of the upper-level trough will cut off in the central North Pacific and get left behind, leading to a weaker trough entering the North American West Coast. One possibility is for the arctic-high pressure to move offshore the U.S. East Coast on Friday and allow the building ridge in central North America, accompanied by a surface low-pressure to the northwest, lead to already mild Pacific air being downsloped off the Rockies (Chinook winds), making it even warmer, and advect into our region in westerly flow aloft ahead of the ejecting cut-off low. In this scenario, the cut-off low would move northeastward and not re-connect with the jet stream until eastern Canada, perhaps weakening and getting stretched out in the process. It would also mean precipitation will be not snow given the warm air aloft, though residual low-level arctic air could lead to freezing rain, especially in the St. Lawrence Valley and east of the Appalachians due to low-level cold air channeling and dammed respectively. This appears unlikely as of today. However, if the central North American ridge is beaten down by additional disturbances diving southeastward, it could allow for additional arctic high pressure systems to sneak colder air in again from the north before the cut-off low arrives, which would make it more likely for precipitation to fall as snow and also for heavier precipitation due to the enhanced thermal contrast and wind convergence. There would even be a chance of the storm being suppressed to the south. Whatever storm would likely arrive next weekend.

 

Source: TropicalTidbits

 

Source: TropicalTidbits

Storm likely finally start of stormier weather pattern

That storm might finally mark the beginning of the long-awaited stormier pattern that does not appear to be delayed any longer. A persistent signal for upper-level troughiness in western or central North America and ridging near the Southeast U.S. coast (neutral or slightly negative PNA), along with a still plentiful supply of arctic air in Canada with arctic surface high-pressure systems, helped by Alaskan ridging (-EPO), favors an enhanced temperature gradient and a storm track generally from the southern or central Rockies into our region along the battle zone of air masses, a setup that tends to bring rich Gulf of Mexico moisture into our region as well as potentially many storms, perhaps some with mixed precipitation in parts of the region. This is a setup not seen yet this winter; we shall see how this materializes. Whether any one location gets a lot of snow depends on details we won't know for at least another week, but the weather pattern appears to generally favor a snowy February from the Northwest U.S. to southeastern Canada and northern New England with not much snow in the southern U.S., the opposite of this winter so far.

Source: TropicalTidbits