Spring warmth on hold for upcoming week; light to moderate snow Monday for most but lighter and changing to rain in southern and western areas; snow showers Tuesday and Wednesday, Thursday night into Friday morning; battle zone between winter and spring leading to storminess with possible wintry mix next weekend and beyond

Plain-language summary: 

 

The unseasonable warmth of the past 10 days will be put on hold for at least a week. After a cold day today despite sunshine, a little snow is expected for most late tonight into tomorrow morning, with a little more in the St. Lawrence Valley and especially Maine, where most will fall tomorrow afternoon and evening. Tuesday and Wednesday will be modestly chilly with some rain and snow showers northwest of the Appalachians with only light accumulations outside mountain summits, perhaps except some more snow in Maine Wednesday night. It will be drier but still a bit chilly on Thursday before more rain and snow showers are likely on Friday. It will turn colder especially in northern areas for next weekend, but there will be a very strong contrast between very cold Arctic air to the north and very warm, almost summerlike air to the south, leading to storminess. There is uncertainty in what the storminess entails, but there could be some snow, but perhaps also a wintry mix changing to rain. More chilly weather is likely in early April, with perhaps one last opportunity for a widespread snowfall.

 

Meteorological discussion:

 

Unseasonable warmth is gone for a week, just a little snow for most on Monday but more in St. Lawrence Valley and especially Maine

 

The unseasonably warm temperatures dominating the past 10 days are over for a while. Upper-level ridging has taken over western North America, with the Pacific jet stream more relaxed with a neutral or slightly negative EPO. An arctic air mass has moved in directly from the northwest with little modification, with the Laurentians on northwest actually having received decent snowfall in the past week with snow cover persisting even as areas to the southeast have struggled to see snow. As such, it will struggle to get above freezing along and northwest of the Appalachians today even with mostly sunny skies. However, a low-pressure system over the U.S. Upper Midwest will strengthen and then occlude over the northern Great Lakes tonight into tomorrow morning before slowly weakening. As such, the heavy precipitation will be wrung out over the U.S. Midwest, with only a short burst of precipitation late tonight into tomorrow morning associated with southerly flow induced warm advection for most of the region before getting into the dry slot. The St. Lawrence Valley will see a little more precipitation due to terrain-induced convergence of northeasterly winds channeling along the St. Lawrence Valley with southerly winds channeling from the Champlain Valley. The Laurentians will also receive more due to upslope, and they are in a more favorable location relative to the storm track. With the antecedent arctic air mass, precipitation will at least initially fall as snow, though as precipitation lightens later tomorrow and the clouds thin out slightly, many low-elevation locations west of Maine and southeast of the Laurentians will rise well above freezing, though there will be very little precipitation anyway. The exception will be Maine, as a secondary low develops and strengthens in the Gulf of Maine tomorrow afternoon, leading to moderate snow there for several hours.

 

Source: TropicalTidbits

 

Rain and snow showers Tuesday and Wednesday northwest of Appalachians, with only light accumulations outside mountain summits, possible snow in Maine Wednesday night

 

The low-pressure system will become elongated and slowly weaken and move eastward over central and eastern Quebec on Tuesday and Wednesday. There will be some cold air aloft, but it will not be arctic, and some sunshine during the daytime means that it will still get well above freezing at lower elevations on Tuesday, with scattered rain showers at lower elevations and snow showers in higher elevations and north of the U.S./Canada border, with most or all of the precipitation falling along and northwest of the Appalachians. Slightly colder air will move in Tuesday night into Wednesday, with winds switching from westerly to northwesterly, with any rain showers changing to snow showers, though due to the lack of any Atlantic or Gulf of Mexico moisture, accumulations will be light except near mountain summits with upslope enhancement. This is another lost opportunity at a bigger snowfall, one of many in the past month, with the storm maturing too early and too far north. The +NAO and +AO (lack of high-latitude blocking) is apparently keeping the storm track still mainly to the north even as the Pacific jet and western North American trough subsides, with no real subtropical jet to help storms redevelop to the south and gather more Gulf of Mexico or western Atlantic moisture. However, an initially weak disturbance could exit off the U.S. East Coast and strengthen at the last minute and swing northeastward around the base of the broad upper-level trough in the eastern U.S., perhaps bringing snow to Maine Wednesday night, though models are struggling with this, and we might not know the outcome with more confidence until late Tuesday.

 

Source: TropicalTidbits

 

Source: Climate Prediction Center

 

Drier Thursday, snow showers Thursday night into Friday morning

 

Broad upper-level troughing dominates on Thursday but it will be drier as the previous storm finally pulls well off to the east. It will be chilly but not arctic cold, with sunshine allowing temperatures to reach well above freezing at lower elevations. A clipper passing to the north Thursday night into Friday morning will bring snow showers to our region, perhaps even a snow squall or two due to the cold air aloft while the westerly low-level flow and late March sun angle warms the low-level air.

 

Source: TropicalTidbits

 

Colder weekend especially in northern areas but fierce battle between Arctic air to the north and summerlike air to the south yields storminess

 

Behind the clipper, there will be a true arctic air mass as a massive Arctic high pressure noses in from central and northern Canada next weekend. However, at the same time, a strong and broad upper-level trough will enter western North America, promoting upper-level ridging again in the central and eventually eastern U.S.  This ridge appears stronger than what models showed a few days ago, which could promote yet another storm cutting into the Great Lakes and into Quebec, limiting any big snow potential despite the antecedent arctic air mass, though there is model disagreement on how amplified the weather pattern becomes, which will be critical for sensible weather in our region for next weekend and early the following week. 

 

Even if warm air does eventually push in, there could be freezing rain beforehand where the low-level cold air remains stubborn, such as the St. Lawrence Valley or east of the Appalachians, especially in Maine. There will likely be a brief surge of warmth with such a storm track, given how warm the air mass pushing from the south will be, especially in southern areas. It looks to be a fierce battle between arctic air to the north and almost summerlike air to the south, so exactly where the battle zone sets up, dictating the storm track, will be critical to who sees snow, ice, or rain and at what temperatures, so this is a rather uncertain forecast. If the storm track stays a little farther south, most of the region will remain in the cold air at least in the low-levels. There could also be a weaker wave ahead of the main storm, or perhaps an elongated low-pressure zone that could bring snow, especially in northern areas, and a zone of prolonged precipitation in general, though recently, there seems to only be strong consolidated storms cutting to the north instead of the energy splitting. There appears to only be a narrow zone of snow in a setup like this, with first ice pellets, then freezing rain, and finally rain as you head south. It is quite late in the season to see freezing rain, but this battle between very warm air trying to push north and being forced above arctic cold low-level air maintained by surface high pressure to the north is the perfect recipe for producing and maintaining the low-level inversion needed for freezing rain, and precipitation and clouds will also prevent the late March sun angle from appreciably warming up the low-levels even during the daytime.

 

Source: TropicalTidbits

 

More cold likely for beginning of April, perhaps one last chance for widespread snow?

 

An upper-level ridge could temporarily return to western North America afterward later the following week into early April, promoting upper-level troughing in eastern North America, and if there is surface high pressure to our north, we would see more chilly weather then. Meanwhile, the persistent upper-level trough just off the U.S. West Coast will promote storminess to push across the contiguous U.S. If one of the storms can time itself right with a cold intrusion, which has been seemingly impossible to get over the past month or even most of the winter, there would be perhaps one last opportunity for a widespread snowfall even at lower elevations. Another scenario is that the storminess off the U.S. West Coast is just too much, spreading Pacific air and promoting too much upper-level ridging in the central and eastern U.S. for any real cold and snow, like in mid-March, though some high-latitude blocking could prevent the incredible warmth of mid-March.

 

Source: TropicalTidbits