40/70 Benchmark

Block looks better relative to 00z....lost that silly ULL W side of Hudson's Bay.

Active Mid-December Pattern Poised to Take Shape Book-End Threats to Begin & End the Work Week As we begin to approach the all important holiday period, the more active pattern post December 10th appears poised to begin as advertised late in the month of November. The first of two winter storm threats is slated for Monday. In the annotation below derived from the 00z Wednesday ECMWF ensemble mean valid late Thursday night and early Friday morning, it is apparent that the shortwave is careening to the east and towards a compressed flow between the fledgling NAO block to the north, and mature southeast ridge to the south that is in response to the deep west coast trough. In fact, that southeast ridge is so pervasive early on that it initially causes the fledgling NAO block to conjoin with it, which both acts to negate the influence of the negative NAO and cause a very compressed flow. This compressed flow acts as a source of deconstructive interference for the shortwave that is very reminiscent of this past December 2021. Towards the end of the week, the shortwave continues to struggle in the compressed flow and attenuates to an open wave over the Ohio valley by late Friday night and early Saturday AM. Note the absence of a notable gap or area of lower heights between the south east ridge and NAO block. However, by Monday AM, the southeast ridge begins to relax as the west coast trough matures, which creates separation and falling heights in between the two ridge nodes in a more traditional configuration. This in conjunction with the strengthening NAO block that is becoming better positioned to exert enough an influence to reduce the compression to the flow allows the storm to quickly begin to re-amplify and close off as it exits the coast. The trend began to emerge yesterday, as the NAO block began to distinguish itself from the southeast ridge and exert more of an influence, faster, which allowed for quicker re-amplification of the exiting wave. Just how quick this system is able to amplify and produce the first significant winter storm of the seasons for the region is dependent on two factors: -Just how close is the major storm over New Foundland. It is is too close, the coastal storm will not b able to amplify as far to the north, and may skirt southern areas of the region. -How strong is the NAO block and where is the ridge axis in the plains located. A weaker NAO block allows the ridge axis to progress further to the east, which will force the redevelopment of the storm later/ downstream and further off of the coast. However, a stronger NAO block will tend to slow the flow down, which causes the plain ridge axis to be further west, and accordingly, the downstream coastal also amplifies further to the west/closer to the coast. The Newfoundland low dictates to a large extend how far north the system does or does not get and the NAO block determines whether or not the flow is too fast to allow the system to amplify close enough to the coast for the northern extend to matter. OPTION 1: One possibility is on the benign end of the continuum of possible outcomes. If the Maritimes low near New Foundland on Monday ends up slightly closer to the region (further south) and the NAO block weaker, then the developing coastal will be develop later (further east and off of the coast) and not allowed to amplify (squahsed to the south). This represents wither no storm of a very minor impact. OPTION 2: However, if the Newfoundland low is slightly further to the north and the NAO ridge stronger, than the storm develops faster and amplifies more to the north. This would represent the first major winter storm of the season. It a blocked pattern like the one that is developing, it is likely that whatever happens next Monday will impact what happens further upstream, on Friday. Double Jeopardy There is the potential for the development of another major coastal storm (get used to this) on or around Friday, December 16th, which, is signaled well via teleconnector convergence. Thus the degree to which the Monday system can amplify and just how quickly it can do so will have a large impact on how much resistance it can provide to the Friday system taking an inland track. OPTION 1: A more intense and slower to exit first storm acts as a "50/50 low" to work in tandem with the resistance provided by the NAO block to induce a more rapid and proficient transfer of energy from the primary tracking through the Great Lakes, to the secondary coastal development. This results in (another) major winter storm with a potpourri of mixed precipitation that would produce major travel headaches to end the work week. These type of systems are referred to as SouthWestFlowEvents (SWFE) due to the prominent southwesterly flow aloft that results from warm air advect in he mid levels of the atmosphere due to the dying primary low. OPTION 2: The first storm is less and intense and faster to move out, which while this is still likely to force the ultimate development of a "triple point low" at the surface near the coast (limits low level warmth), most of the precipitations falls as rainfall after perhaps a very brief bout of wintry precipitation near the onset. Travel impact is limited. Clearly given the state of the Pacific pattern, the key to an early and aggressive onset to winter here in the eastern US is heavily dependent on just how pervasive a force the NAO block can become and thus how proficiently it can offer up resistance in the flow. While the result is likely to fall somewhere in the middle of the continuum of potential outcomes, the trend is to increase the risk for a more noteworthy initial onslaught of winter 2022-2023 next week. Stay tuned for a potential Friday issuance of First Call with respect to Monday-

Models won't accurately portray a very blocked flow until it sees the whites of its eyes, no pun intended.

Still trending IMO.

Before 12/20? Nah...

I'll probably miss that to the southwest, then the Friday deal is good for NNE.

https://easternmassweather.blogspot.com/2022/12/active-mid-december-pattern-poised-to.html

Yea, that is what I focused on instead of the ridge location that Brooklyn did.

Nobody can get enough of those...keep 'em coming

Hopefully it misses, but is still strong enough to alter 12/15

Yea, formidable showing of the movie Groundhog Day.

Stunner.

Just unreal.

You are correct. I missed that.

Its not about the amounts it showed, but the overall conceivable trend.

Nuts sheared to shreds by female confluence? Bravado out to sea?

You know my weak spots hahahaha That would eat my soul away in short order

I love 33 and snow in Chatham and 19 and IP in Tolland

We may end up with an inverted trough on Monday, too (yay)

Main difference I see is that the low near NF is a bit further away on the GEM, which maybe allows for faster amplification of coastal.

Triple ninja

SouthWest FlowEvent.......its when the storm in the mid levels cuts west, causing winds aloft to scream southwest and advecting warmer air ne. But when when there is confluence and cold air in place, the surface low is forced to redevelop off to the se and the warm air advection causes snowfall. There tends to be a transition to sleet for many spots due to mid level warmth

Not directed at anyone in particular, but I recall a few posts to the effect of "nothing else shows it", blah, blah.....I mean, a 2' blizzard....unlikely, but a plowable snowfall for a portion of the region is a totally viable outcome. I'm guilty of it a lot, too, but its tough to sometimes not view a solution through a biased lens due to the reputation of the model.....all else equal, its not a huge leap of faith that an exiting coastal trends less progressive in the face of a large block.

I think he was probably basing that off of a presumed unfavorable storm track....just broad-brushing the longer term.

Yea, we are in the timeframe now where any warmups would be shorter term due to wave-breaking from unfavorable tracks, rather than a hostile overall longwave pattern. The latter is done for at least about a month.