The upper level disturbance responsible for driving last evening and night's storm across New England is moving through the skies overhead on Wednesday, promoting an unstable atmosphere. Behind the disturbance, cold air will be unlocked from Southeast Canada and Upstate New York, and will stream into New England for Thursday and Friday. Our next disturbance moves across the region later Friday and Friday night, before improving conditions settle in for the remainder of the weekend, though a stormy pattern is likely to persist through the first half of March.
Last evening and night brought snowfall amounts of over a foot to some of Northern New England, and mostly rain to parts of Southern New England, with many areas in between seeing brief accumulating snow changing to rain. From an historic perspective, a number of records fell with the latest storm - namely, Boston, Worcester and Concord, New Hampshire all now have the wettest February on record, meaning the most rain and/or melted snow. Fairly impressive considering someplace like Boston has been keeping records since the early 1870s. Burlington, Vermont, meanwhile, sits at the second snowiest winter on record (December, January and February) at 91.8", while Ski Vermont reports the snowiest on record for some resorts. All the while, North Country residents have between four and five feet of snow on the ground right now.
Meanwhile, we're adding some additional snow to the higher terrain of Northern and Western New England today as the upper level energy that drove last evening's storm is moving overhead, pressing east out of New York State and finding assistance in lifting air for clouds and precipitation from the mountain faces a developing northwest wind has been encountering. Because of the properties of the jet stream - the fast corridor of wind several thousand feet in the sky that steers storms and acts as a boundary of northern cold and southern warmth - cold air has not rushed into New England on Wednesday....at least not for most spots. The Champlain Valley and western slopes of the Green Mountains have seen cold air seeping southward, but the deeper and more widespread surface cold must wait until cold air comes in aloft, too, before it can have much force to its southeastward surge. Because cold air aloft sits on the northern side of the jet stream, we must wait for the jet stream to dip southward, which will happen with the passage of today's upper level disturbance. This change aloft will set things in motion at the surface, as well, propelling the cold front southward with an increasing wind from the northwest Friday late afternoon and evening that will bring falling temperatures to some of Northern and Western New England this afternoon, create a colder ride home than ride to work for many commuters, and build more substantial cold into New England Wednesday night. In the transition, and with the upper level disturbance riding overhead, snow showers will continue to crop up through Wednesday afternoon and evening, with a few likely to linger overnight, and a few new inches Wednesday through Wednesday night in the higher terrain, especially west and northwest facing mountainslopes.
The colder air streaming in will not only send wind chill values below zero in most of New England Wednesday night, but will also hold temperatures in the 20s for many Central and Southern areas for highs on Thursday, with teens in the Northern and Western New England communities. This cold air is also dry air, though, and this brings the sunshine out after early morning clouds. Expect a very cold night Thursday night as winds abate almost entirely beneath mostly clear skies, then clouds will increase after morning sunshine Friday ahead of our next disturbance. This end-of-week storm will be cranking up across the Eastern Great Lakes, then maturing over New England, and will usher warmth and moisture northward ahead of it rather quickly. This sudden surge of new air is likely to collide with the Northeastern U.S. cold air dome and touch off bands of snow Friday late afternoon and evening that will spread from west to east. Once again, this leaves us with a question of precipitation type thereafter, however, because the storm motion will be slow enough, and its track far enough north across Central New England, that warmth really should continue to invade New England and undermine the efforts of the cold to hold tough. Further aiding this influx of warmth will be the departure of an area of high pressure - the same one that initially delivers Thursday's cold - to our southeast. Of course, the combination of a clockwise flow of air around the high and a counter-clockwise flow of air around the low means a southerly wind will be favored, at least ahead of and south of the storm track, which will include most of Southern and Eastern New England. This means a start as snow would be likely to change to rain Friday night for most of these areas. North of the storm track, however, colder air will have the help of a northeast wind flowing toward the storm center, keeping the North Country snow. As the storm gains definition over New England, then reaches the Maine coastline and taps available Atlantic moisture over the Gulf of Maine, the mountains of Maine seem set to make out the best from this storm, cranking out snow Friday night into Saturday. Closer to the Maine coast, the onshore flow may bring a change to rain, and farther south and west, the progression of the storm to the Maine coastline will probably mean most precipitation shuts off by early Saturday morning, perhaps even allowing for a few breaks of sun with a westerly wind sloping down the mountains Saturday afternoon. Keep in mind that a downsloping wind would also serve to warm the air a bit, and that I don't see a really deep well of arctic air behind this storm, so Saturday temperatures where it's not precipitating may actually turn out somewhat mild.
Another shot of cool but dry air would follow on a stronger northwest wind on Sunday, but the same pattern of northern and southern stream energetic disturbances interacting with one another would repeat again next week, with another good chance of a mixed precipitation event on Tuesday. In fact, the active stretch seems likely to continue through at least the first half of March as a jet stream trough to our west continues to favor strengthening disturbances that will have access to Canadian cold dipping across the Great Lakes to their north, and deep Gulf of Mexico moisture to their south as they round the base of the U-shaped trough over the Ohio and Tennessee Valleys and move toward the Atlantic coastline.
Here's to a great midweek.
Matt
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