Very cold today, then major snowstorm through Monday; then cold gradually moderates with mostly dry weather except a little snow Tuesday and later next week along and northwest of Appalachians; more arctic air with storminess possibly resuming early February

Plain-language summary: 

 

Our region is experiencing the coldest air of the season just as the enormous and widespread winter storm affecting the southern and eastern U.S. is turning northeastward into our region as a major snowstorm, especially in southern areas where 8-14" (20-35 cm) will fall with locally higher amounts, a surprise compared to expectations several days ago. It will be a long-duration snowstorm with dry, fluffy snow. It will then continue to be cold, though slowly moderating, with mostly dry weather except a little snow Tuesday and later next week along and northwest of the Appalachians. Renewed arctic air with resumed storminess could occur some time in early February.

 

Meteorological discussion: 

 

Major and long-duration snowstorm through Monday with generally light to moderate snowfall rates and dry, fluffy snow

 

Our region is experiencing the coldest air of the season, with an arctic surface high pressure parked over our region. The northwesterly flow straight out of the arctic with little modification on Saturday, courtesy of the very negative AO, combined with mostly clear skies and light winds, led to some rural and cold hollows falling below -22F (-30C) this morning. Just as this is happening, the enormous and widespread winter storm affecting the southern and eastern U.S. is turning northeastward into our region as a major snowstorm. This is quite different from model solutions several days ago showing the storm staying well to our south. Even multi-model ensembles generally did not show any real possibility of the storm reaching our region. However, an upper-level trough in western Canada digging farther south and west, allowing it to interact with and pick up (even if not entirely phase with) the much more moisture-laden subtropical jet disturbance over the southwest U.S. Combined with the suppressive upper-level low over Atlantic Canada that moved eastward out of our region faster than modeled, the upper-level flow is now southwesterly instead of westerly, allowing the storm to pick up Gulf of Mexico moisture and ram it northeastward into an extremely cold air mass deposited behind Friday night's cold front. It is this clashing of rich moisture into arctic air that is producing such a huge area of snow and ice.

 

Source: TropicalTidbits

 

 

Source: TropicalTidbits

 

 

For our region, it will be just snow, and it will last longer than most snowstorms, around 24 hours or even a bit more for many. The warm advection snow will initially push into Vermont through Maine this afternoon and evening, accompanied by warm frontogenesis. Precipitation rates will be heavier to the south where the moisture will be wrung out before reaching the very cold air in our region, but light to moderate snow will encompass almost the entire region. Then, the slowly-strengthening upper-level trough still hanging back to the west will provide additional forcing for ascent late tonight into Monday, targeting an area slightly north of the warm advection this evening, with a pronounced dry slot in between to the south but staying south of our region, ensuring a continuous snowfall for our region. The long duration will make up for missing the heavier precipitation rates to the south. In addition, temperature profiles support a very deep dendritic growth zone (between -10C and -20C where the big, fluffy dendrites develop), and with relatively weak winds, the dendrites will not shred apart easily. Due to this, high snow-to-liquid ratios of 15-20:1 are expected for most of the region, producing a large fluffy accumulation of 8-14" (20-35 cm) south of the U.S./Canada border from Ontario/New York to Quebec/New Hampshire and extending into central Maine, with locally higher amounts where heavy bands form. In far northern regions, the moisture and ascent will be less, and the atmosphere might actually be too cold for ideal dendrite formation, and the ascent might not be strong enough to generate enough supersaturation in the clouds for ideal dendrite formation, which could lead to lower snow-to-liquid ratios.

 

Source: TropicalTidbits

 

 

Source: Weather Prediction Center

 

 

Cold continues for rest of the week though slowly modifying with a little snow Tuesday and later in the week, mostly in areas along and northwest of Appalachians 

 

After the storm leaves Monday evening, it will likely be much drier for the foreseeable future, with arctic air continuing to dominate though slowly modifying as the cold air mass gets cut off from any additional reinforcements from the arctic due to strong Greenland blocking (-NAO). At the same time, the Pacific jet will become a little more active, which will promote arctic air to retreat from most of the U.S. and western Canada at least. However, with the upper-level ridge in western North America continuing to dominate (+PNA), upper-level troughs with cold air from the north will still push into our region and prevent any thaw. But this upper-level trough (actually cutting off into a very broad upper-level low) position over New England into Atlantic Canada promotes a northwesterly flow cutting off our region from any Gulf of Mexico or Atlantic moisture again. A weak clipper will move into our region later Tuesday but will be weakening and produce very little snow. Interestingly, the weather pattern could be so blocked that the broad upper-level low over Atlantic Canada could wrap a little Atlantic moisture counterclockwise into Labrador and then southward into region later next week, and these situations lead to warm advection from the north, which could lead to light snows. Given the brisk northwesterly flow, the snow will likely be limited to areas along and northwest of the Appalachians.

 

Source: TropicalTidbits

 

 

Slight chance of an East Coast storm around next weekend or a bit after, but most likely missing our region, then potential for renewed arctic air and increased storminess some time in early February 

 

Next weekend, another storm in the subtropical jet will be moving eastward across the southern U.S., possibly producing snow there, but given the broad upper-level low in our region through Atlantic Canada, this storm will likely scoot out to sea well to the south of our region, unless a clipper in central Canada can be more amplified and dig much farther south than currently shown on the models and phase into the southern storm to produce a big East Coast snowstorm, a scenario that a few rogue model runs and ensemble members have shown occasionally. After that, a brief mild spell is possible as the western North American upper-level ridge tries to nose eastward into our region as arctic air continues to gradually retreat, though the -NAO and western Atlantic upper-level trough could thwart any thaw, and a clipper or two in the northwesterly flow could bring light snows. It is possible that beyond that, the upper-level ridge in western North America amplifies, retrogrades to the West Coast, and noses into Alaska again, allowing for another amplified upper-level trough with renewed arctic air to push into the central and eastern U.S. some time in early February. Given the +PNA, -NAO, and -AO continuing, and the upper-level trough position farther west, that could be more favorable for storminess and snowiness to resume in our region, though the upper-level trough could still be too far east as well.

 

Source: TropicalTidbits

Source: TropicalTidbits

  

 

Source: Climate Prediction Center