High pressure will build across New England on Wednesday before another disturbance moves through New England Thursday, then cold air floods the six-state region for the weekend. Another storm is in the offing for late Sunday through Monday, before a shot of somewhat prolonged cold air arrives next week.
There were some surprises for this meteorologist in the mountains of Vermont Tuesday night with the passage of a weak cold front and an upper level disturbance that teamed to produce a swath of mountain snow showers and squalls. These squalls were enhanced as a strengthening northwest wind pushed up against the western slopes of the Green Mountains, and the result was a quick half foot of snow in a few isolated spots like East Montpelier, and a couple of inches in the high terrain of the Greens and also the White Mountains of New Hampshire. Though this much snow was a bit surprising for me, it's certainly not unheard of or unprecedented, as the Northern and Western Mountains can and do occasionally funnel incoming wind upward as that air pushes against the mountains, resulting in recurrent and persistent snow squalls that are stubborn to move from those localized areas that most favor their development.
With the departure of the jet stream disturbance and the passage of the weak cold front, moisture in the lower altitudes of the atmosphere began to decrease and snow showers diminished, leaving clouds that have also been evaporating in most spots to allow for sunshine, excepting some mountainous terrain that remains favored for cloud development and also in the immediate vicinity of Lake Champlain were cold air gently streaming over the lake has left patches of lake effect clouds floating around the southern shorelines. Elsewhere, New England will see sunshine mixing with a few high altitude clouds, but a fair day will come courtesy of the eastward sliding high pressure cell that will also allow winds to diminish through the afternoon. Wednesday night will begin with the same conditions the day left off - quieting wind and cirrus clouds - and this will allow temperatures to drop relatively quickly early in the night, falling into the 20s and teens north, and 20s and 30s south. As the night wears on, the center of the high pressure cell and its clockwise flow of air will slide east of New England, allowing a southeast wind to develop.
While the evolution of the weather pattern will be rather gradual at the surface here in New England, the quick changes occurring aloft should be an indication that the weather pattern remains active. As mentioned here earlier in the week, the jet stream winds aloft that steer our storms and disturbances are racing across the country, dipping into a broad and slowly deepening trough over the eastern two thirds of the United States. The nature of this trough, and the fact that is slowly sinks southward, means cold air gradually settles south, as well, and each time an energetic disturbance drops into the trough it holds the potential to strengthen on its trip across the Eastern United States, and to deliver another shot of cool air in its wake. Though these disturbances are moving aloft, there is certainly a reflection of each at the surface, as well, either as a surface trough (wind shift), a series of fronts, or a developed storm center. With Thursday's disturbance, a cold front will be draped from north to south over the Great Lakes Thursday morning and racing eastward with a weak developing wave of low pressure along it.\, beneath the heart of the energetic jet stream disturbance. The result of this front and developing counter-clockwise swirl of air along it will be a mild flow of strengthening southerly wind on Thursday, bringing temperatures into the 40s for many of us and perhaps
near 50 in far Southern New England. This influx of warmth and gradually increasing moisture, and its collision with our cool air in place, will bring increasing clouds and a period of midday and afternoon rain showers with the passage of the
attendant cold front Thursday afternoon. In Northern New England, however, colder air will be far less willing to relinquish control of the weather playing field, meaning snow is more likely, especially in the higher terrain. It appears as though north-south oriented valleys are likely to find enough warm air moving in for a mixture of rain and snow, resulting in a wet coating on grassy surfaces. Above about 2000 feet, however, the precipitation is likely to fall as all snow Thursday afternoon, bringing as much as 2"-4" of snow Thursday afternoon and evening, and in favored locales where westerly winds will favor continuing snow Thursday night (especially the favored areas of the Western Slopes of the Greens) up to half a foot of snow is possible by Friday morning!
With
New England remaining on the northern side of the jet stream, this will favor
deeper and more potent shots of cold, and chilly air is expected
Friday, though the approach of yet another energetic disturbance will prompt a west to perhaps even southwest wind in the lower few thousand feet of the atmosphere on Friday, keeping deep cold just north of New England and bringing the likelihood of more mountain snow squalls Friday afternoon and night. Behind this disturbance, the floodgates to deeper cold will open and a cold, windy Friday night will give way to an intensely cold Saturday for some! The chunk of air heading for New England this weekend originates where high temperatures have only been in the single digits and teens over South-Central Canada, but the cold will certainly moderate as it moves southeast. Nonetheless, temperatures will struggle to get out of the 20s in many communities Saturday afternoon, even with any early morning clouds giving way to sun. While temperatures in Southern New England may be a touch warmer, an active wind will drive the wind chill even lower!
Sunday will begin quiet after a very cold night Saturday night, but we know a pattern like this keeps us on our toes heading into the late weekend and early next week for
stronger storm development, as another digging energetic disturbance
will usher warmth and moisture into our cold dome. The result will be thickening clouds on Sunday after morning sun, with highs stuck in the lower to middle 30s, in general. This air is plenty cold enough to support snow when enough moisture arrives to New England, and I do expect widespread accumulating snow to develop from southwest to northeast Sunday evening into Sunday night. The key to determining the forecast from there is based on the track of the storm Sunday night into Monday. At issue has been whether the storm moves west of us, develops a second center that moves over us, or develops a second center that moves just south of us. The latter solution would be all snow, but as mentioned yesterday, that seems unlikely to me given the propensity for western tracking storms recently, and the departing high pressure cell that houses the cold air. This leaves the original storm center tracking to our west, though with the amount of energy and moisture available, I do think we should see some sort of secondary storm center developing. Such an evolution would still spread not only moisture but also warmth into New England as the cold air gradually lets go, and is the reason I think we'd see our burst of accumulating snow Sunday evening and early Sunday night turning to rain from south to north, then falling primarily as rain into Monday. This actually leaves a scenario similar to this week's storm that tracked across Central New England, though with colder air in place at the onset, a track more across Southern New England seems likely, meaning a colder scenario (similar setup to this week, but shift rain/snow line farther south). Still, if the western track of the primary storm center is correct, enough warm air will already have been transported north to allow only the Northern Mountains and far North Country to stay as all snow, though amounts could be significant.
Behind the storm, regardless of whether you see rain or snow or both at your house, cold air will come streaming into New England, and I expect next week to be a cold week before we see an easing of the the cold for the latter half of December. Not necessarily a disappearance of the cold thanks to a pool of remaining cool over the Northeast for awhile, but certainly a dramatic lessening of the below normal cold as we slowly be exhaust our supply of Canadian cold for now, leaving above normal temperatures though most of North America for the second and third weeks of December. In the short term, this will have no negative impact on winter sports as temperatures will remain cold enough for natural and manmade snow in the mountains. Admittedly, the longer range consequences will depend on whether we reload Canadian cold by the end of December, though with warmer than normal temperatures expected from Siberia to the Arctic Circle in the middle of December, that may be a tough task to accomplish. That's obviously a long way out, but winter resorts should make hay while the sun shines, so to speak, and blast snow as much as you can in the coming couple of weeks.
Enjoy your Wednesday.
Matt
Matt's Technical Discussion - Updated Wednesday, November 28 at 2:20 PM
Last night's snow amounts a bit of a surprise for me in places like the 5.5" of East Montpelier but conditions were favorable for windex event so I suppose I should have been more cautious of this. Nonetheless, dissipation of clouds for most areas with dry air today and temps have been highly elevation and latitude dependent. Cold draining north wind has pockets of lake effect clouds floating around the shores of Lake Champlain while mountains hold some bands of orographically enhanced clouds. Downwind, downsloping wind is stronger that I'd have expected as high axis has been slower to move east. What are the effects on this slower high progression on the forecast? Logic says longer period of quiet wind tonight so valleys decouple and Tds in the teens suggest even Ci clouds spilling in shouldn't stop a drop into the 20s for many places with teens in valleys. Increasing clouds expected Thu ahead of next shortwave, which does a decent job of winding up en route to NewEng. Though there is limited moisture to work with when sfc reflection weak low along cold front crosses NewEng on Thu afternoon, there should be good low level isentropic lift with positive theta-e advection in esp central and northern NewEng. The northern focus of advection will also mean a northern focus of precip, and Northern neweng is where I expect heaviest precip amounts to fall - though guidance is backing off on QPF and now general good agreement on either side of a quarter inch. Ratios won't be great given low level warmth, and 925 mb temp fcst from GFS brings 0 C line all the way to the Canadian border at 18Z Thu. NMM is typically colder, and a good question to ask is which product to trust more. As of this writing, a blend may have been the best way to go for today, a morning whose 00Z runs predicted 0 C and -6 C for the same Southern NewEng locale on GFS and NMM, respectively, and a difference between -6 C and -12 C at 925 mb in Northern NewEng. This is a ridiculous difference in only an 18 hour forecast and left me scratching my head this AM at exactly what's going on between the guidance here, and diffs are evident for Thu when ptype is a factor, though diffs are not as pronounced. Nonetheless, using blend of thermo profiles yields mostly snow with dynamic cooling near Canadian border and in far north, snow above 2000 feet for rest of Northern NewEng and mountains of Southern Greens, and rain/snow combo in Northern NewEng valleys that may coat grassy surfaces but should melt on roads with warm BL temps.
Shot of cold tries to follow Thu ngt into Fri but is cut off by fast flow with next shortwave already inducing weak WAA, so will go cooler but not deep cold and keep chc mountain snow squalls with vort passage later Fri into Fri night. Deep cold should arrive on active wind Fri ngt and be in place on Sat, when MOS guidance begs for low to mid 30s but progged 925 and 850 temps on GFS support widespread highs only in the 20s even with ample sun after any morning clouds and ECMWF only slightly warmer - a solution I've followed for now given downslope flow and propensity for elevation/latitude based cold. Haven't gone highs in the 20s for everyone yet, but felt free to go below MOS in all spots and am willing to drop more if it looks like guidance falls in line with coldest GFS.
Plenty of cold in place on Sunday as next storm approaches. HUGE shift in the GFS Ensemble guidance over the last 24 hours from secondary strong SE of NewEng to primary strong west of us and perhaps weak secondary overhead. That fits the forecast I had going based on Canadian Ensembles which really have led the way this season thus far. This will mean swath of warm advection snow Sun PM into early Sun ngt but unstoppable warmth with retreating Canadian high means over to rain after a few inches of snow most spots and if a secondary cuts over Southern NewEng, northern mountains could keep snowing and make out quite well!
Thoughts on longer range are laid out in General Wx Summary but are based on idea of Ern US trof keeping pool of cool aloft after intense dish of cold behind Mon storm, and that cool pool likely lingers into second week of Dec. This can occasionally result in coastal snow storms, but once the cool pool is gone we're above normal across most of the high latitudes and that means no deep cold likely second half of December until we can reload Siberia or the arctic circle.
