Finally after weeks of boredom we may actually have something of importance occur weather-wise. The jury is still out this storm but the potential for is there for a long-duration precipitation event across the Adirondacks, Green Mountains, and White Mountains from Friday through Saturday night. While track and storm strength are still up in the air, I have high confidence in at least some accumulating snows across the mountains of northern New England and northern NY.
Here’s the synoptic overview: Late this week, as an upper level trough digs through the Ohio River Valley, the baroclinicity caused by the cold air and low pressure of the trough to the west and the mild air with higher pressures to the east over the western Atlantic, will cause a surface low pressure system to form off the mid-Atlantic coast. It will track up the eastern seaboard and will likely get captured by the big upper level trough that takes on an obscenely negative tilt as it reaches the northeast. The interaction between the upper level trough and the surface low along the eastern seaboard will determine where and just how much precipitation (in both liquid and solid forms) will fall. At this time, it appears that the upper level low, which slows and cuts off from the flow at the base of the upper trough, will be strong enough to yank the surface low back NNW into ME after it passes Cape Cod. This track will allow for marginally cold air to work into the system on its western side and cause rain to change to snow first across the Adirondacks on Friday, the Greens on Friday Night, and eventually the Whites on Saturday.
This potential storm will have two phases to it with regards to precipitation: 1) Synoptic scale precipitation and 2) Meso-scale upslope precipitation. Synoptic scale precipitation is caused by the interaction of large areas of low and high pressure systems and occurs over a wide spatial area. Meso-scale upslope precipitation occurs on a much smaller scale and in our neck of the woods only effects localized mountain areas, particularly across the northern Adirondacks, the northern Greens, and portions of the northern Whites.
The synoptic precipitation will likely be mostly in the form of rain as the low works its way up the coast and a moist southeasterly flow off the Atlantic pumps in mild, maritime air ahead of the storm. Actual rainfall amounts are going to be hard to pin down because most of the computer models don’t show this coastal storm getting its act together (and getting captured by the upper level low) until it is physically passing Cape Cod and moving into the Gulf of Maine. This causes a couple of concerns… if the storm is even a few degrees of latitude too late in developing, it could miss us all together synoptically speaking (the Canadian GGEM has been showing this as a possibility) but would still bring some upslope snows to ski resorts like Whiteface, Jay Peak, Stowe, and Bretton Woods. However, the majority of the global models including the GFS, the European ECMWF, and UKMET do show this tracking close enough to the coast to bring us rain on Friday, then mountain snow Friday night and Saturday as cold air wraps around the western side of the storm. Accumulations from the synoptic portion of the storm look minimal with maybe up to 3” above 2,500ft by very early Saturday morning.
By Saturday morning, the low will have passed our latitude, hopefully bombing out in the process. The term “bombing” out refers to rapid deepening of a surface low in a very short period of time. In truth, the term “bombogenesis” is for a storm that deepens by 24mb or more in 24hrs and while we won’t see that sort of explosive development, we could witness a quick 12mb drop in 12hrs on Friday night. This will tighten up the pressure gradient around the low and the wind field at all levels will increase markedly. As the low tracks into the state of ME or the Canadian Maritimes, winds will pick up across the summits out of the NW. H85 (~4,500ft) wind speeds on all models increase to 40-50kts out of the northwest, while advecting cold air into region. Our low pressure system is now vertically stacked from the surface to 500mb (~20,000ft) up in southern Quebec and this is allowing it to cyclonically wrap moisture from the Atlantic back into northern New England. This moisture when combined with colder temperatures and strong NW winds will produce upslope snow across the northern Adirondacks, northern Green Mountains, and northern Whites. I have decent confidence in at least a moderate upslope event for the Green Mountain spine ski resorts north of I-89. I am not sold on the Adirondack or White Mountain resorts quite yet because they are a little more fickle when it comes to upslope (ie. The planets need to align just a little more than they do for the Greens to get upslope) but regardless they should both see at least some accumulation on Saturday.
Given the overall look to the synoptic pattern and with the potential for a decent upslope event on Saturday, I think there is a moderate to high risk of 6-12” falling across the northern Green Mountain spine including Bolton Valley, Stowe, Smugglers Notch, and Jay Peak by Saturday night or early Sunday morning. Elsewhere, I’d say that Whiteface in the Adirondacks, MRG and Sugarbush in the Greens, and Wildcat, Cannon, and Bretton Woods in the Whites stand a moderate to high chance of seeing 3-6” of snow with locally higher amounts. I’m a little uneasy about throwing numbers out still 4 days away from the event, but that’s the type of system I’m looking at right now. It might not be prolific but it’ll likely be the first widespread snow of the season for the ski resorts.
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