Winter 2025-2026 Offers Return to Normalcy

[Baroclinic Zone]

Nice write ray.

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Plowable Snowfall Still Favored Sunday

Devin In Details As Considerable Model Uncertainty Remains

Rainfall Likely Tonight

Regardless of the ample supply of cold throughout the first third of the month of December, the storm system approaching the region today still looks to fall as primarily light rainfall for the majority of the region.

 

 

The rising temperatures throughout the overnight period last night were the first indication of this outcome, as an innocuous looking wave over the Ohio River Valley manages to phase in enough with a lobe of the PV to amplify and track through southern Canada, which has already turned the winds out of the southwest across much of the northeastern CONUS.

 

Although some light snowfall is possible across the higher terrain of the Berkshires, this particular system will prove more met than white. This is a very easy forecast since the system is traveling so far to the north, however, when that is not the case, modeling will be very sensitive to any subtle change with respect to phasing attempts is an extremely fast flow. This will be on full display with regard t the weekend forecast. 

Complicated Weekend Scenario Unfolding

As of this morning, there were two more distinct parcels of energy over the arctic that are modeled to be on a collision course over the Canadian prairies late this week.

 

The system over the Arctic Ocean, and the one entering Alaska are forecast to rapidly funnel SSE in the flow between the PV and west coast ridge, before ultimately coalescing in the vicinity of Alberta, Canada on overnight on Friday.

 

 

The system will then careen around the southern side of the PV on Saturday, at which point guidance diverges concerning the precise nature of this crucial interaction. 

 

 

The European cluster of ensembles favors a scenario in which there remains enough space between the PV lobe and the developing system to allow to amplify sufficiently as to eventually impact much of the region with a plowable snowfall on Sunday. The GFS camp, on the other hand, keeps the PV in close enough proximity to greatly impede the development of the wave to the south by largely shearing it apart, which results in little if any snowfall across the area.

 

The version of the EURO guidance that is derived from Artificial intelligence (AI) is even more aggressive than the traditional model, and implies a warning event of 6" or greater throughout at least a portion of the area.

 

The Eastern Mass Weather hedge remains in favor of a plowable snowfall for at least a portion of the forecast area on Sunday given previously discussed analog support and teleconnector convergence, in addition to robust AI support in addition to a death of high latitude blocking at present to pin the PV slightly further to the south. First Call is likely either Thursday or Friday.

 

[40/70 Benchmark]

Festive Light Snowfall Likely Sunday

Plowable Possible South & East

Compromise Solution This Weekend

On Wednesday, Eastern Mass Weather discussed subtle differences between the GFS and European suites, respectively, with the latter favoring a plowable snowfall for  large portion of the region and the former merely flurries. 

 

 

The preference was for the European blend, which entailed a significant snowfall for most of the region; however, as is often the case, it appears as though a compromise will ultimately be in order.

 

Synoptic Overview

It appears as though a rather modest parcel of energy congealing over the prairies of Alberta, Canada later today and tonight will race east-southeastward and begin interacting with a lobe of the polar vortex (PV).

 

This particular randevu will be a complex, and somewhat noncommittal one, at least initially. The two pockets of energy will initially flirt with one another in that they will reman in close enough proximity to hunter the amplification of the smaller system.

 

 

However, any phasing will occur at a rather lethargic pace owed to the shallow amplitude of the western ridge, which will lack the depth to trigger a more aggressive and committed union.

 

The end result will be a light snowfall, which a some moderate totals likely well to the south, where plowable amounts remain possible. 

 

 

Anticipated Storm Evolution

Light snowfall will begin to break out after midnight Saturday night, during the predawn hours on Sunday from south-southwest to north-northeast.

 

 

The "peak" of the storm will occur in the vicinity of dawn on Sunday, when low pressure will begin to slowly strengthen south of Long Island, and snowfall becomes more steady and even moderate at times the southern and southeastern third off the area.

 

 

Snowfall will begin lighten up later in the morning and during the midday hour, but just as that happens, the energy from the polar vortex lobe to the west will begin to drop in to initiate phasing as the system exits.

 

 

This will likely serve to protract light snow across especially the eastern half of the area through the afternoon, which will entail the potential for very light additional accumulations before ending during the early evening hours.

 

 

Stay tuned for important updates on the holiday period to be issued early next week-

FIRST & FINAL CALL

[rimetree]

I was curious about previous winters around here when Washington had significant December flooding. Using Concord, seems all over the place but some good years in there like '07-'08, '77-'78, '70-'71 and '55-'56. Looks like some of these were mentioned in Ray's write-up.

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Verification for Festive Sunday Snowfall

Strong Forecast But Slightly too Conservative

The season's first significant snowfall for the southeast coast of New England was identified at a very extended lead time using a combination of seasonal analogs, long range ensemble guidance and pattern recognition. In fact, forecast for the storm itself actually ended up being slightly too conservative.

 

The 1-3" forecast for the central portion of the region worked out well, however, there were two primary problem areas with the overall forecast. The most obvious issue is that the 2-4" portion of the forecast over the southeastern quarter of the area actually verified in the 3-6" range, given amounts up to 5" over southwestern, Connecticut (Norwalk) and 6" on the outer half of cape cod (6" from Hyannis to Chatham). There is also a strong argument to be made that the western portion of the 1-3" area should have been extended slightly further to the north, as evidenced by the 3" total reported in Great Barington, MA in the southwestern corner of the state. This is a shortcoming that likely would have been alleviated had a follow up map been issued on Saturday, when it had become clear that the storm would track slightly further to the north.

Final Grade: B+

 

[40/70 Benchmark]

 

Mid-Month Warm Up Arrives On Schedule

Path to White Christmas Remains Despite Friday Grinch

December Forecast Largely On Track

Thus far the month of December has behaved largely as expected, primarily owed to the similarity of the anticipated deviation from the predominate Maritime Continent forcing of the past decade, to the analog periods of December-January 2017-2018 and 2024-2025.

 

December 1-13 2025:

 

 

December 2017-January 2018:

December 2024-January 2025:

 

 The primary differences being that this month has been more extreme in terms of the magnitude of negative temperature departures, possibly owed to the extreme Bering Sea blocking (-WPO) that has been observed  (-3.48 WPO peak on 12/13). The polar vortex disruption that occurred late last month has behaved remarkably similar to the early December 2000 analog event in that it fell just shy of triggering a full  850MB zonal mean wind reversal in the arctic. 

 

 

This has afforded the vortex the opportunity to recover to something that will approach climo levels by the holiday week, as forecast last fall per research conducted Lee et al (2019), which indicates that the arctic high regime is favored for less than 20 days following a weak PV (roughly November 28th). This despite the insistence of initial modeling and social mediaologoists alike that it would remain weak through the new year. 

 

This consistent recovery following the lack of a zonal wind reversal has allowed the high latitude blocking to relinquish it's grip by mid-month, as forecast.

 

 

The increasingly hostile polar domain in conjunction with lowering heights on the west coast as reflected by a descending PNA value will allow the storm track to shift west just in time for the expected "Grinch Storm" this Friday, which will eradicate all of the snowpack throughout southern New England. 

 

 

This is event is similar to periods prior to the Christmas holiday in the referenced analog months of December 2007 and 2008, especially the former.

 

Thereafter, there is going to be a battle waged throughout the holiday period as the MJO remains shallow and variable, while the Pacific Trough regime begins to assert itself.

White Christmas Odds Perilous As Pacific Trough Regime Establishes

One of the primary assertions made in the Eastern Mass Winter Outlook last fall was that the aforementioned recovery of the polar vortex and persistent RNA pattern would team up to induce a Pacific trough pattern during the second half of the month, as a potential pre-cursor to a January stratospheric reflection event. 

 

Current long range guidance now reflects such a pattern.

 

While the forecast for the balance of 2025 would appear rather unchallenging, things are seldom as they appear in weather. In this particular instance, the caveat is an MJO wave that is expected to remain rather meager and variable after having largely dissipated over the course of the past week following its brief flirtation with phase 8 near the outset of the month.

 

 

This disjointed signal will allow an occasional element of west Pacific expression to assert itself into the pattern as a byproduct of areas of dual forcing, especially into the final weak of the month, which will allow for some potential colder intrusions into the northeastern quarter of the country.

Christmas Eve 500mb depiction per EURO Weekly product, EURO ensemble package, GFS ensemble and Canadian ENSEMBLE.

 

Having a supply of cold near by means that the likelihood of a white Christmas across the southern New England forecast area, while unlikely after the visit from the Grinch on Friday, can not be discounted since there may be some weak northern stream energy passing through in the vicinity of the holiday.

 

 

There is also some suggestion amongst guidance that Scandinavian blocking could develop by the New Year, which could represent a precursor to an episode of some Greenland Blocking prior to the development of any subsequent refection event later in January.

 

 

 

Although the pattern is unquestionably turning milder on average, it would be advisable to stay tuned for updates as the all important holiday period approaches because the devil is often in the details.