A quick-hitting snowstorm to affect most of the region tonight into tomorrow; modestly cold through Thursday with some snow showers on Wednesday; dry Friday into weekend before potential uncertain storm and likely mild weather

Plain-language summary:

 

Unseasonably mild weather and rain will come to an end tonight, with rain changing to snow for most outside New Hampshire and Maine, and a significant snowstorm ensuing for the Adirondacks, Vermont, and southeastern Quebec, with light snow to the west and heavy rain to the east. Tuesday will be seasonably chilly and dry, and Wednesday will feature scattered snow showers and squalls especially over higher terrain and along and west of the Appalachians. A brief cold shot follows behind it for Wednesday night into Thursday, but it will quickly warm up through next weekend while staying dry. A slow-moving storm could bring mixed precipitation early the following week, but the timing and location is highly uncertain. A brief cold shot likely follows, but it otherwise will likely be rather mild afterward, though perhaps not as mild as farther west.

 

Meteorological discussion:

 

It is currently unseasonably mild, though not record warm, southeast of the St. Lawrence Valley, due to southerly flow to the west of a strong high pressure system in the western Atlantic and southeast of a low pressure system over James Bay. However, a deep trough is carving down to the Deep South of the U.S., and a southern storm is forming in the Carolinas and will quickly strengthen as it heads northeastward up to Maine by tomorrow afternoon. Without a -NAO and high-latitude blocking, it will move rather quickly, limiting total precipitation amounts, but the rapid strengthening will cause rather heavy precipitation rates for several hours, with a frontogenetic snowband likely forming tomorrow morning over Vermont or southeastern Quebec. The Hudson Bay storm will also remove any cold air ahead of it. But cold air is coming in on the back side of the storm, enhanced by the storm’s own cold air generated by strong ascent and heavy precipitation as it quickly strengthens. We are finally about ready to nail down the snowfall forecast. It was an incredible turn of events, given that it was poised to be a strong, torchy Great Lakes cutter that would bring a widespread heavy warm rain just a few days ago. The north-northwest flow and storm track will favor the spine of the Appalachians and just to the northwest, including northern Vermont and southeastern Quebec, with 8-12” (20-30 cm) likely away from the broad Champlain and St. Lawrence valleys. It will start as rain everywhere, but slowly change to snow, first at higher elevations, and then at lower elevations. Farther west, the heavy precipitation will never really enter, with 4-8” (10-20 cm) over the Adirondacks and 2-4” (5-10 cm) or less in the St. Lawrence and Ottawa valleys west from Montreal on west. Farther east, over most of New Hampshire and Maine, heavy rain will fall instead, possibly changing to a brief period of snow at the end.

 

Source: TropicalTidbits

 

 

Source: TropicalTidbits

 

 

 

The storm quickly moves away by Tuesday, leaving a seasonably chilly but dry day. A weak disturbance will bring snow showers and possibly squalls on Wednesday due to instability created by the not-so-cold low-levels and very cold air aloft. The higher terrain and western slopes of the Appalachians are expected to get the most accumulation, though even there, few places will get >2” (5 cm). A brief cold shot follows behind it for Wednesday night and Tuesday. A huge, broad high-pressure system over the eastern U.S. follows for Thursday and Friday, leading to almost all of eastern North America being dry and mostly clear! The very strong upper-level ridging over central Canada and westerly flow on the northern side of the surface high pressure will transport mild Pacific air into our region by next weekend, though it will be dry with no Gulf of Mexico or Atlantic moisture involved. 

 

Source: TropicalTidbits

 

However, a cut-off low pressure system will be sitting in the southern Plains and Deep South of the U.S., underneath the central Canadian ridge. The low-pressure system will slowly move eastward, and then perhaps move up the U.S. East Coast early the following week. However, the timing is highly uncertain due to its slow movement. The timing will also determine the later track and intensity. If it waits until the central Canadian ridge moves all the way to northeastern Canada and gets replaced by a trough, the trough could link up with the southern storm and strengthen the southern storm if the trough is deep enough. But if the storm is too far south, it could just remain cut off and never come north to affect our region, though that appears somewhat less likely. With mild Pacific air dominating at this time, if the storm comes into our region, precipitation would probably at least initially be non-snow, though the storm will likely produce its own cold air on its northwestern side through precipitation and height falls, and if the northern trough brings in cold air, there could be snow on the back side of the storm. However, this is all very speculative at this point. Afterwards, there will likely be a shot of cold air, but that will probably be brief as the strong Pacific jet will keep sending mild Pacific air into North America, though with a slightly positive PNA, most of the warmth could be in western North America, very much unlike last winter, allowing for occasional cold shots to sneak into our region this far east.

 

Source: TropicalTidbits

 

Source: TropicalTidbits

 

 

Source: Climate Prediction Center