Springlike roller-coaster temperature pattern this week; perhaps one last snow chance around 10 days from now before return to spring

Plain-language summary:

A springlike roller-coaster temperature pattern is expected this week, with a chilly Sunday, milder Monday and Tuesday, cooler Wednesday in northeastern areas, warmer Thursday, and cooler afterward. Despite this, little or no wild or severe weather is expected. A few rain showers, except snow north of the St. Lawrence River, on Monday, will be followed by a dry Tuesday and then a rainy Wednesday and Wednesday night, especially in northern areas with freezing rain possible at the onset north of the St. Lawrence River and in northern Maine. The warmup Wednesday night to Thursday will be most pronounced in southern and southwestern areas, with it turning cooler and drier for Friday and likely the weekend as well. There is late-season snow potential for beginning to middle of the following week, albeit it will likely be a tenuous and elevation-dependent setup as is typical for April. With spring likely returning afterward, it would likely be the last chance for widespread accumulating snow at lower elevations until late fall.

Meteorological discussion:

After a chilly Sunday, temperatures will rise for Monday with a clipper passing to the north, despite increasing clouds, due to southerly flow ahead of the clipper. The clipper will be moisture-starved and will bring little or no precipitation south of the U.S./Canada border, a few showers for the St. Lawrence Valley, and some snow for the Laurentians to the north. Then, the clipper’s cold front will gradually bring a modified low-level Arctic air mass into the region, especially north of the U.S./Canada border, though it will still be a bit mild on Tuesday before the colder air mass settles in briefly. The upper-level pattern of a deepening trough in the eastern Rockies and a building ridge in the eastern U.S. will halt the southward movement of the cold air mass. 

Source: TropicalTidbits

As the storm in the Rockies ejects northeastward into the U.S. Midwest, warm air will surge in aloft by later Wednesday, accompanied by warm advection precipitation, especially in northern areas, while the low-level cold air attempts to hang on, especially from the Green Mountains on northeastward. This could lead to a brief period of freezing rain north of the St. Lawrence River and in northern Maine, somewhat unusual for April. However, eventually warmth will move in through the entire column, with the warmth modifying as it moves northeastward due to it fighting the antecedent low-level cold air, deep snowpack, and relatively cool maritime air mass advecting from the western Atlantic chilled from winter. This modification means that the severe weather outbreak expected in the Ohio and Mississippi Valleys is unlikely to reach the Adirondacks on northeastward. A few strong to severe thunderstorms could make it into eastern Ontario, where the warm and moist air mass will have the least resistance and will arrive in the evening, right before the cold front arrives and just after daytime-induced instability is maximized.

Source: Storm Prediction Center and PivotalWeather

Source: TropicalTidbits

 

Another modified arctic air mass moves in on Friday and will penetrate slightly farther south than the previous one, as the Rockies trough/eastern U.S. ridge pattern slowly breaks down. The temperature roller coaster will end for a while, as there is no sign of a big warmup soon afterward. There has been some suggestion of another wave moving along the temperature contrast, leading to a colder storm for next weekend, but ensemble and deterministic model support has mostly disappeared with an unfavorable west-northwest to east-southeast upper-level flow. 

 

Source: TropicalTidbits

Then, there is unanimous ensemble agreement on an amplified upper-level ridge building over the western U.S. early the following week, which probably has not occurred since October! This will lead to a deepening trough in the eastern U.S., though it is unclear if it will pull down true arctic air or not-so-cold air from central or southern Canada. This will have implications for late-season snow potential, since it is quite difficult to get accumulating snow in April without a notably cold air mass, especially in lower elevations. Nonetheless, there is potential for a weaker version of the mid-March Nor’easter, and if it pulls down enough cold air from Canada and does not cut-off too quickly, a wet snowstorm would result, with snowfall amounts being elevation-sensitive as they almost always are in April. I am skeptical that the western ridge/eastern trough will last long given how the winter went and the ocean temperature anomalies going against it, and indeed, most ensembles are showing a return to a western trough/eastern ridge pattern by mid-April. This should end chances of widespread accumulating snow at lower elevations until late fall.

 

Source: TropicalTidbits