A mild reprieve of the past few days will be a distant memory in short time as a well-defined Eastern United States trough will take hold. In time, this may result in an accumulating snow event for much of New England by the middle of next week, but that's a long way out, and remember what this Sunday prospectus is - just my view of the weather that lay ahead from a relaxed, big-picture, Sunday spin-up perspective. The week will bring the need to get down and dirty with the details, some of which will clarify and some of which will muddy the view, meaning it will be necessary to rely on this big-picture perspective for clarity.
The water vapor loop shows a very active continent this evening, with a couple of well defined shortwaves spinning east toward New England - one set to cross the region overnight Sunday night into Monday morning, and another likely to pass on Monday night. Each pinwheels beneath a strong upper low spinning across extreme Southern Canada, and each will deliver slightly cooler air to New England. Farther west, a strong upper low is evident moving across the Four Corners region of the Southwestern United States, while a series of strong upper level disturbances are racing into Western Canada from the Northern Pacific. The Southwest U.S. low will dissipate but move over New England on Thursday as a vorticity lobe with warm and moist advection, and a substantial chunk of Aleutian Low energy will move through New England next weekend.
The short-term forecasting challenges will come from the most immediate shortwaves, and the cold air that follows them. With cold air streaming east, lake effect snow will begin off of Lake Ontario, and though this often means only limited consequences for New England, indications are we should get a decent spray into Northern VT on Monday. The challenge will be boundary layer temperatures, which appear to stay too warm for snow - at least for appreciable snow - in the valleys, including and especially the Champlain Valley. The mountains, however, and the higher terrain from Montpelier north to Jay Peak, should find upslope flow with a west wind enhancing the lift, and cold enough air above about 2000 feet during the day Monday, then lowering to about 1000 feet Monday night, to produce accumulating snow. Total amounts won't be blockbuster, for sure, but a few inches are likely in places like Jay Peak between Monday and Monday night. Elsewhere, a westerly, downsloping flow will limit precipitation chances, keeping scattered instability produced showers the most likely precipitation form both Monday morning with the first vorticity axis, then again Monday night with the second.
Confluent mid and upper level flow takes over for midweek, ensuring subsidence and therefore surface high pressure will dominate. Cool temperatures but dry conditions are expected. Meanwhile, another impressive storm will take shape from the Northern Plains to the Upper Midwest, though it won't be anything like the last blockbuster blizzard of this past week, largely because an abundance of Gulf Moisture will remain untapped, with the southern stream shortwave remaining just a bit too far south and a bit too progressive to interact. Instead, that southern energy rides into New England later Thursday, with quickly increasing clouds from Wednesday night into Thursday and a good chance of at least some rain developing in the southwestern half of New England by the time the day is out Thursday. At first I was somewhat skeptical of this - and to be completely honest, I think this timing is one that still could change as we near it and the details become more clear - but the 850 mb warm advection is pronounced at the same time the vort max moves through, and this shortwave does have a history of Pacific moisture with some weak Gulf interaction, so some showers seem like the wise way to go for now.
Next weekend the trough associated with the Midwest energy really digs, and this ejects Gulf of Mexico moisture and energy northward so that after a break early Friday, heavy rain is likely Friday night into Saturday morning. Rain is likely to exceed an inch for many spots, with some two or three inch amounts possible, at least given this cursory glance. One thing that may alter this is if the system progresses a bit quicker, as the energy aloft will start piling east, and will shift the moisture axis east, too, by late morning or midday Saturday. Thereafter, cold air surface and aloft means some drying but also some instability for scattered rain and snow showers as another shot of cold comes on.
What I find the most intriguing of this week's cursory glance, however, is the setup for midweek next week. A series of strong northern shortwaves dig across the Upper Midwest and Great Lakes, and this not only keeps shots of cold air coming at the Northeastern corridor, but also gradually shifts the mean trough axis on the longwave pattern just a little farther west with time. By next Wednesday, this takes a similar baroclinic setup to what we have coming up next weekend, but moves it slightly farther east and thereby introduces the possibility for at least weak coastal storm development with much of New England (interior) on the cold side of the system. We're talking a week and a half out here, so we'll see what verifies, but the pattern does look favorable. Additionally, the Ensembles are showing signatures I usually like to see to support such a scenario, including cold 850 mb temperatures (-4 C anomaly), baroclinicity along the coast and just east of New England, and, though not nearly as important but still an important signal, a moderate swath of precipitation in the means, on the cold side of the storm.
So, plenty to watch - and what does seem likely is that the Northeast remains colder than normal at least until around Thanksgiving, while warmth will build in the west with time.
Matt
