Cold but not exceptionally cold week with periods of snow Tuesday through Thursday; drier Friday, then uncertain potential for snowstorm next weekend; cold and mostly dry for several days afterward before perhaps stormier and a bit milder for the 2nd half of January

Plain-language summary: 

 

It will be a rather cold week but not exceptionally cold for January. A mostly dry Sunday and Monday will be followed by periods of light to occasionally moderate snow Tuesday through Thursday, mostly along and northwest of the Appalachians. It will turn drier for Friday, and then there's the potential for a snowstorm next weekend, though there could just be light snow showers as well. It likely turns drier and stays cold for several days afterward, though it could turn stormier and a bit milder for the 2nd half of January.

 

Meteorological discussion:

Cold and dry today and Monday

It took several days, but the northwesterly flow of air from central and northern Canada has persisted long enough for it to finally be near or slightly colder than average. It has also been mainly dry though weak disturbances have been depositing light snow accumulations in many places, just enough to whiten the ground. A surface high pressure in Ontario is providing more cold northwesterly flow today and tomorrow, with a storm producing snow and ice way to the south over the Ohio Valley and mid-Atlantic U.S., squashed southward by a strong, broad, and almost stationary storm over Atlantic Canada/northern Gulf of St. Lawrence. 

 

Source: TropicalTidbit

Terrain-dependent snow Tuesday through Thursday 

The storm is not going out to sea quickly as usual due to strong high-latitude blocking and associated -NAO. Even more unusually, the broad storm will suck Atlantic moisture, wrap it counterclockwise around the storm, and deposit it as snow in our region from Tuesday to Thursday, mostly along and northwest of the Appalachians given the constant northwesterly flow. Since the storm is broad and occluded, precipitation will be rather light and disorganized, though warm advection induced by the northerly flow of Atlantic air ramming into arctic air trying to press southeastward will lead to some periods of steadier light to moderate snow, more likely on Tuesday and Wednesday night. Snowfall amounts will be heavily terrain-dependent given the constant northwesterly flow, with the northern Adirondacks, northern Green Mountains, and parts of the Eastern Townships of Quebec possibly receiving 8-12" (20-30 cm) over the 3-day period. The snow will be rather light and fluffy, efficiently accumulating with what little moisture there is due to the ascent in the deep, saturated dendritic growth zone (atmospheric layer between -10C and -18C) and lack of very strong winds in the vertical column to fragment the dendrite snowflakes that have a lot of air and therefore pile up quickly. This will lead to snow to liquid ratios higher than the 10:1 that the snow map below is assuming, though models sometimes overdo the liquid equivalent of prolonged, light precipitation. The persistent pressure gradient will also ensure a stiff breeze with blowing snow during the period.

Source: TropicalTidbits and PivotalWeather

Drier Friday, uncertain snowstorm potential next weekend

The storm will slowly move to the northeast by Friday, with the influx of Atlantic air brought by the storm having modified the arctic air. Also, unlike model projections several days ago, the extremely cold air near the North Pole will never get unleashed into the contiguous U.S., so while it will be cold, it won't be nearly as cold as it could have been. It will also be drier with fewer clouds, and with the fresh snow cover northwest of the Appalachians, the coldest night of the week may occur around this time. Also, around this time, a storm will be moving slowly across the southern Rockies into Texas. How this storm interacts with a clipper that will be in the Northern U.S. Plains around this time will be critical to determining next weekend's weather, and presents high uncertainty. If the southern storm, containing much more moisture, is stronger and moves just ahead of the clipper, it will interact somewhat constructively with the clipper and possibly phase into a Nor'easter along the New England coast by next weekend, though the ever-present though weaker upper-level low south of Newfoundland and high-latitude blocking will prevent any Nor'easter from advancing far to the north, limiting snowfall north of the U.S./Canada border. Actually, for now, it appears more likely for any Nor'easter to mostly confine its snow in southern New England on south. If the storm in Texas is weaker or slower, it could just get cut off from the main jet stream and get left behind, and there will be just a weak clipper. In an in between scenario, perhaps the most likely, there would be a weaker storm perhaps somewhat separate from the clipper, leading to a broad area of light to moderate snow.

 

Source: TropicalTidbits

Drier and still cold after next weekend, then possibly a bit milder with more storminess for later in January

After next weekend, it will dry out again, though there could be another weak clipper bringing light snows a couple of days after, but still no major storms are expected.Tthe weakening of the high-latitude blocking, as well as a trough entering Alaska (perhaps only temporarily), will likely cause a retreat of the cold air in most of the contiguous U.S., though our region could hold on to the cold with the mean upper-level trough axis still present over Atlantic Canada, which means that clippers diving southeastward in the deep-layer northwesterly flow and cold surface high pressure systems following the clippers will reinforce the cold air directly from the north. Actually, with clearer skies and calmer winds in such high pressure systems, nighttime lows could actually get colder than they will this week. However, this deep-layer northwesterly flow will be lacking rich moisture, with the continued lack of moisture-rich storms from the south and southwest that has been characteristic of this winter. There are signs that the overall upper-level trough axis will set up farther west for the 2nd half of January (PNA turning neutral or slightly negative), perhaps in the central U.S. or Rockies, which is a more favorable setup for moisture-rich storms to come out of the southern Plains into our region, perhaps finally leading to a stormier pattern, though this is far enough out to be rather uncertain, and it remains to be seen if there will be a strong enough subtropical jet to actually fuel those storms, whether any of the southern systems can favorably interact with any clippers in the polar jet, and how cold it will still be. Such a pattern will open the door to milder surges, though at least some remaining high-latitude blocking as well as being in the climatologically coldest time of the year should preclude any major thaw.

 

Source: TropicalTidbits

Source: Climate Prediction Center