Isotherm

Great call - I don't think anyone else forecasted the month correctly w/ that level of detail. Regardless of our differences in reasoning, this was a great call for December.

It's clear by your response that you do not understand long range forecasting. It's isn't a linear A+B+C. There are multifarious factors examined pre-season, and those indicators provide a general landscape of what will transpire for the winter. The exact timing as far as progression is more guesswork. The important part is if the forecast correctly ascertains the season overall, bearing in mind the apposite indicators. I will not be drawn into the trap of impugning the CPC's work. However, their method of forecasting is probabilistic, and they typically err warm. Your post is non-scientific and provides no substantiation for your claims regarding the PV split.

Report post Posted just now I concur that it was easier to see from about the middle point of the month, once it became ostensible that the MJO would continue intensifying further beyond low-orbit. However, my contention is that this was not easily foreseen from the pre-season period in November, and but for the stratospheric induced MJO amplification, December would have finished less warm, and likely with more snow in the Northeast than it did. The literature demonstrates a trop-->strat-->trop pathway, whereby heightened tropospheric induced stratospheric perturbation, climaxing in a sudden warming event, can operate on a dual pathway, with the stratosphere thereupon modulating the intraseasonal signal and further amplifying it. This significant, anomalous amplification of the MJO, in my opinion, as a consequence of the major stratospheric event, was the curveball. A low-orbit MJO would not have ruined late December, in light of other background signals, which favored cooler December. I believe the argument has merit, further, as December was cooler than average through the latter point of the month, at which time the intraseasonal signal amplified materially, driving trough after trough into the Western US. There are numerous cases historically in which the MJO amplifies significantly contemporaneously with a significant stratospheric event, and this is not a coincidence in my view, due to the dual feedback pathway. We saw it last year, for example, wherein the MJO amplified quite strongly prior to the sudden warming event. So, when I say, curveball/largely unforeseeable, I'm referring to from early/mid November, not a couple weeks ago. Yes, canonical Nino analogs supported a warm December, but we were not following the canonical Nino playbook as far as how we arrived at the result in my opinion. The primary reason for the decline of the pattern late December was the amplification of the intraseasonal signal, brought about largely by feedback from stratospheric modulation. So, Ray, we'll have to agree to disagree on how the results arrived the way they did for December - as in my view, background signals supported a normal or cooler December. My initial winter forecast included a non-SSW year, so again, the resolution of it is immaterial to the rest of the winter, but I strongly believe this trop-strat->MJO interference aided significantly in hampering winter chances in the Northeast in late December.

@CoastalWx @40/70 Benchmark This is in response to both of your inquiries. I concur that it was easier to see from about the middle point of the month, once it became ostensible that the MJO would continue intensifying further beyond low-orbit. However, my contention is that this was not easily foreseen from the pre-season period in November, and but for the stratospheric induced MJO amplification, December would have finished less warm, and likely with more snow in the Northeast than it did. The literature demonstrates a trop-->strat-->trop pathway, whereby heightened tropospheric induced stratospheric perturbation, climaxing in a sudden warming event, can operate on a dual pathway, with the stratosphere thereupon modulating the intraseasonal signal and further amplifying it. This significant, anomalous amplification of the MJO, in my opinion, as a consequence of the major stratospheric event, was the curveball. A low-orbit MJO would not have ruined late December, in light of other background signals, which favored cooler December. I believe the argument has merit, further, as December was cooler than average through the latter point of the month, at which time the intraseasonal signal amplified materially, driving trough after trough into the Western US. There are numerous cases historically in which the MJO amplifies significantly contemporaneously with a significant stratospheric event, and this is not a coincidence in my view, due to the dual feedback pathway. We saw it last year, for example, wherein the MJO amplified quite strongly prior to the sudden warming event. So, when I say, curveball/largely unforeseeable, I'm referring to from early/mid November, not a couple weeks ago. Yes, canonical Nino analogs supported a warm December, but we were not following the canonical Nino playbook as far as how we arrived at the result in my opinion. The primary reason for the decline of the pattern late December was the amplification of the intraseasonal signal, brought about largely by feedback from stratospheric modulation. So, Ray, we'll have to agree to disagree on how the results arrived the way they did for December - as in my view, background signals supported a normal or cooler December. My initial winter forecast included a non-SSW year, so again, the resolution of it is immaterial to the rest of the winter, but I strongly believe this trop-strat->MJO interference aided significantly in hampering winter chances in the Northeast in late December.

Thank you. One additional note is that - although in my opinion effective propagation is favored - the resolution of the stratospheric event isn't a prerequisite for the expected evolution of the winter. I created my winter outlook operating under the presumption of no technical SSW. There are other, significant indicators which favored a mean -NAO signal for this winter (weak-mod), and weak negative AO (I expected the center of the blocking more toward E Greenland rather than Arctic).

My winter update analysis, for any interested:

My winter update analysis, for any interested:

My winter update analysis, for any interested:

---The extirpation of the second half December as a paradoxical consequence of aberrant stratospheric perturbation--- 1. My winter outlook included the hypothesis that a technical stratospheric warming event (or major) would not occur, although the stratosphere and troposphere would be quite perturbed. 2. The precursor indicators suggested early perturbation of the troposphere, and there has indeed been a weakly negative NAO in December. The Southeast and southern Mid-Atlantic experienced a major snowstorm earlier in December, which unfortunately, did not progress farther northeast up the East Coast. 3. However, the stratosphere has actually been more perturbed than I anticipated. The anomalous perturbation steadily increased throughout December, the provenance of which included torque forcing / concomitant AAM increases, and felicitous tropospheric circulations which significantly enhanced wave driving. 4. My research has evinced to me that sudden stratospheric warming events often occur contemporaneously with anomalous, amplifying MJO pulses. This is not a coincidence. Stratospheric perturbation is pleiotropic. In the period preceding a sudden warming, the stratospheric forcing on tropical convection and concomitant divergence increases. The MJO, thereupon, amplifies, as a positive feedback cycle. MJO forcing can generate planetary wave driving, which aids adjunctively in SPV perturbation w/ EAMT, and other exogenous forces such as suppressed geomagnetic activity, and easterly z50 wind stress. Upon receipt of the wave driving, the stratosphere can then modulate the tropical wave propagation and amplification – i.e., intensification. 5. This is why, about a week ago, I noted that the MJO was no longer likely to quickly enter the COD, but continue to strengthen further – and it did. At this point, I realized that the prospect of any wintry event in the Northeast would likely fade. 6. The stratospheric modulated MJO amplification through phases 4-5-6, has induced spasmodic trough amplification in the West US which, concordantly, drives Lakes Cutters to the west of the I-95 corridor. 7. December was progressing largely as anticipated through mid month, with low orbit MJO forcing, and much of the northern tier colder than normal through the 17th. However, the anomalous amplification of the intraseasonal signal in the second half of December extirpated Northeast snow prospects. I am convinced that a snow event would have occurred, but for the SSW event which aided adjunctively in amplifying the intraseasonal tropical convection and resulting in the induction of trough dips in the Western/Central US, warming the East Coast. 8. This anomalous late December MJO amplification is something that would be virtually impossible to foresee, and anyone who expected a warmer than normal December certainly did not mention this evolution in their forecasts. 9. Nevertheless, I regret the error, and will attempt to rectify in prospective years, although this curveball was largely unforeseeable in my opinion. 10. Easterly 50mb QBO winters are notorious for enhanced intraseasonal signals [e.g., active MJO], which should have been a clue, which I regret not weighting more significantly in my initial winter outlook. 11. Going forward, how does all this impact the outlook? The overall ideas will not alter materially. Rather than December and February being the productive wintry months, with January warmer (my initial progression), it will be January and February as the productive winter months. 12. A significant SSW event is in progress, and this year has virtually all of the key hallmarks, from my research, as an effective propagator. The negative NAO pulse in the medium range is directly related to the stratospheric alterations. Most of the high latitude blocking through the first 10 days of January will be over the NAO domain, as the z150 and tropospheric vortices will be displaced near the north pole, resulting in lower than normal geopotential heights there, at least initially. 13. I anticipate that the ECMWF will continue to be incorrect in the rapidly decaying MJO. The stratospheric induced aid will carry the upper divergence through phases 6, 7, and into 8, albeit at an amplitude less than the GFS indicates. Nevertheless, a robust MJO signal will propagate east. 14. Low-frequency walker cell forcing engagement more archetypal of El Nino’s initiated near the New Year, which, contemporaneously with significantly increasing mountain torque, will extend the jet, amplify the Aleutian trough, and elicit PNA/EPO domain height rises for January. 15. GWO is circulating toward phase 5. The added momentum injection via EAMT and tropical convection propagation ewd adjunctively, will aided in increasing AAM yet again. The amplitude of GWO is indeterminate, however – there will be sufficient engagement to alter the Nina-esque atmosphereic regime. Conclusion: The late December amplification of the intra-seasonal forcing [MJO] as a consequence of excessive stratospheric perturbation has yielded an error in the December forecast, as temperature departures will finish warmer than normal due to frequent Lakes-cutters. Paradoxically, as noted, December would have been colder and snowier in my opinion if not for the ongoing major stratospheric event which significantly enhanced the MJO signal. Going forward, the troposphere is already responding and altering as a function of stratospheric changes. This has the earmarks of an effective propagator. The NAM won’t change significantly initially due to the positioning of the tropospheric / lower strat vortices, but I expect the NAO diminution to begin now, into January, with a negative NAO and developing positive PNA/EPO. Therefore, from my initial winter forecast values, I would simply reverse Dec and Jan, and keep February the same (+1 to +2 is now Dec, and -2 to -3 is both Jan and Feb). I have no changes to the snowfall forecast either, which continues to indicate a good to very good snowfall winter in the Northeast (not a blockbuster – which was never expected). The late December misstep is very disappointing, as I am a perfectionist / highly self-critical with impugning my own methodologies. Again, I think the reasons for the December failure could not have been foreseen too well even from November. December will not finish warmer than normal / less snow because of the typical canonical Nino reasons, but because of MJO-strat interference on the background state which favored cooler than normal December, in my view.

Yes, the short answer is, "no" - it won't impact the idea that winter will be colder/snowier than normal. Certain outcomes could increase the ceiling and severity of the winter, however. Now for the long answer incoming...[cross posted on other boards] Re: the more abstract / academic / non-sensible weather related discussion of wave 1/2 forcing and attendant stratospheric warming events... While wave-2 vertical driving is typically a hallmark of splitting events, we have seen examples of primarily wave-1 forced splits, often with wave-2 "preconditioning" a couple weeks prior. Typically, there is some adjunctive aid via intraseasonal tropical forcing as well [aka MJO]. Here's an example: February 11th, 2001 split event. Wave 1 dominated - and it wasn't even as potent as the present burst.  However, interestingly enough, the MJO at the time of the split on February 11th was located in precisely / almost identical location to the forecast for the present event -- mid-octant phase 5. This certainly aided constructively to the warming, as we have all discussed. Point being, a split can occur without significant wave-2. Note the wave-2 preconditioning, last week [2018] which aided in significantly weakening the vortex. Note that the status of the vortex pre-SSW attempt is critically salient w/ respect to subsequent tropospherically generated pulses of energy. Bottom line: I wouldn't write anything off yet regarding the outcome of this event. The bifurcation leads us to three primary outcomes: 1) SSW-reversal, no destruction 2) SSW-vortex destruction or 3) Failed resolution / no SSW. To me, option #2 is truly the pathway that elevates the ceiling of severity of high latitude blocking this winter, and by extension, sensible weather impacts. Numbers 1 and 3 are fairly similar in my opinion, though number 1 could lead to a more significant interval of anomalous blocking. My winter forecast was predicated on the notion that no SSW would occur, but the lower strat and troposphere would be very perturbed w/ higher than normal blocking. So the outcome here is largely irrelevant as it pertains to whether we enter a colder/snowier than avg pattern. However, certainly the specific timing and severity could be different. In other words, a vortex destruction could "up the ante" for a protracted [50 day] period of anomalous HLB. Regarding latest model variance, I've seen discussion noting that GEFS is more robust b/c it doesn't extirpate the MJO signal as much as the GFS, but then why is the ECMWF more bullish on the warming? The more I research into this topic, the more I believe there's a dual feedback pathway here. The MJO constructively amplifies wave driving, but stratospheric patterns and perturbation also appear to feedback and aid in more effective ewd MJO propagation. The wave 2 preconditioning and EAMT elicited wave 1 initiated the domino effect, and the MJO is further aided by the strat. I now believe there's a chance the MJO wave propagates right through phases 5-6-7-8 at a solid amplitude . Historically speaking and data wise, we've been checking all the boxes for a precursor pattern to SSW. [I would not look at RMM plots as others have noted - the MJO chi 200 signal will be in a felicitious phase for maximum wave convergence on the SPV around December 28th +/- a couple days]. Will be interesting to track.

Yes, the Nino-esque structure will resume fairly expeditiously in my opinion near the end of December with phase 5 GWO resumption, and enhanced walker cell forcing in the CPac. as the MJO signal begins to dampen and propagate through the CPAC at z200 as well. This should ignite a more classic PNA approaching the 30th/31st. It will be "Gradient" / countervailing -NAO until then.

Just to clarify, in case my statement is misconstrued - I'm not guaranteeing that next week's event will be conducive for NYC, simply elucidating the significance of the flux which has been ongoing w/ respect to the EPO and NAO domain corrections as a function of the forcings noted. I'm more confident that the 27/28 could become an energy transfer w/ resultant favorability for New England, lower probability for NYC but it cannot be ruled out either.

Well, since you inquired, here's what I posted on another board a few days ago. Very little change from previous thinking. Transitional period 21-22nd with neutralizing temperatures, followed by a sufficiently cold pattern to produce winter threats thereafter. There will be a temporary suppression of heights in the W US via the diminutive -MT/FT pulse in the 24th-28th period, but it will be countervailed by higher heights in the NAO domain, yielding a zonal flow (i.e., no significant ridging in the East). Note recent runs continue to correct w/ higher heights in W North American and the NAO domain, and this will continue, as a function of momentum alterations and vertical wave driving/strat changes. By the end of December, changes continue will a more Nino-esque Pacific structure developing. The medium range pattern in late December is multifactorial, and the provenance of the depictions seen on model data are as follows: 1. There will be a relatively insignificant extratropical contribution of -MT in about a week, which aids in an ephemeral Pacific jet retraction. 2. The intraseasonal/MJO signal currently in phase 3, precluding full-entrance into GWO p5 right now, will be in the decay/coherency loss phase in late December, but will also aid adjunctively in the ephemeral jet retraction ("Nina-esque" interlude) 3. However, contemporaneously, the ongoing tropospheric forcing/MT/AAM induced stratospheric displacement event is inducing severe model volatility and rendering NAO/AO domain geopotential height forecasts quite inaccurate. Note the robust blocking signal in the NAO domain on the 23rd/24th (not detected a few days ago), which is rapidly lost by Christmas on the EPS. This is apocryphal in my opinion. The z150 vortex will be pushed into Siberia by the 23rd-24th w/ significant height rises in the southern AO/NAO domains. So, this correction will continue. 4. The diminution of the MJO signal as we approach Christmas, and the concurrent reinvigoration of the walker cell induced CPac. forcing, will force the GWO back toward p5 toward very late December. And as the strat. event realizes, all the putative dominios align, with a more classic Nino-esque Pacific structure near the end of month/New Year. What does this mean sensible weather wise? I'm sensing quite a bit of worry regarding late December. There will be a transient momentum loss induced jet retraction which retrogrades the mean trough axis in the CONUS, but, concurrently, the AO/NAO domain geopotential heights will be more positive than currently progged. And therefore, the SE-ridge will not be as robust as some modelling indicates 25-28th. The flow will go more zonal for a period of several days (if you want to call this "gradient", but I dislike the word) as the momentum flux alters. Nothing else has changed regarding the "transitional period 21st-22nd", with the pattern conducive for a threat thereafter.

Here's an example of a displacement event that pushed the SPV into Eurasia -- late January 1987 February 1987 was colder than normal in the Northeast (as an example: -3.2 departure in New Brunswick, NJ, 17" of snow, and snow cover the entire month). Just to underscore the fact that winter can still occur if the SPV is pushed into Eurasia. To be honest, I do not believe we will see a technical SSW this month. I think it'll weaken significantly with an off-pole displacement for a time, but not official wind reversal at 10hpa/60N.

Thanks, all, for the kind words. Frd, it all depends upon the potency of the EAMT --> MT --> Rossby wave dispersion into the stratosphere. I think it could be a close-call, but the SPV will be displaced, even if not technical SSW, for awhile. If there is a technical warming, but no destruction of the SPV, I don't see any material impacts to my forecast. The SPV would probably reorganize by early/mid January in time for my progged thaw period. If, however, the tropospheric forcing is so strong that it actually induces a total displacement - destruction event of the SPV, that could potentially yield a 40-60 day period of potent high latitude blocking conditions, taking us right through the heart of the winter. If that were to happen, I could see January featuring more impactful winter weather than February. This is all speculation for now, but my confidence is high on the above post and December's progression.

An atmospheric cascade of events is about to unfold over the coming weeks. While the angular momentum tendency plots have a slight time-lag, AAM is now reaching a minimum, as reflected by the cessation of the FT diminution, and onset of gradual rises. MJO divergence signal is rapidly progressing into the eastern hemisphere, and will lose coherency over the coming 7-10 days as it's signal declines in phase 2-3. We are about to see a rather impressive mid-latitude rossby wave induction event with a robust extratropical contribution to the angular momentum budget, via a potent EAMT in the medium range. The MSLP plots are redolent of this, and the z200 response is apparent with an impressive jet extension in the Pacific as we approach December 10th. The resultant rossby wave induction and further enhancement of wave-1 energy via the tropospheric pattern Dec 7th-13th will release a substantial amount of energy, vertically and poleward, up through the stratosphere. The 10-day forecast plots do not detect it yet, but there will be a potent wave-1 attack on the SPV in mid December, thus completing the wave 1, wave 2, and wave 1 "triad" impact over the multi-week period. Contemporaneously, the dampened intra-seasonal signaling will acquiesce to re-invigoration of the low-frequency Nino-esque/walker cell forcing, and elicit retrogression of the mean z500 action centers in the December 15th-20th period, while incipient high latitude blocking elicits geopotential height rises over the Arctic and NAO domains. The model data is already detecting the deceleration of 60N/10hpa zonal winds around Dec 17th. This is in fact a veridical signal, and the zonal wind deceleration forecast has its roots in the train of events, provenance of which is the momentum budget alteration and potent extratropical torque forcing / concomitant RW generation. Sensible weather wise -- no changes from my initial post on Nov. 23 which postulated the retraction/reset period in Dec 10th-16th, and thereupon, rearrangement of features with a rapidly improving hemispheric regime shortly after the mid month point +/- three days. I maintain that notion. The week period of December 12th-18th will likely feature warmer than normal temperatures; however, heights should neutralize in the East by the 17th-18th already, with normalizing temperatures. The retrogression of the GOAK trough will be occurring concomitantly in the December 14th-18th period, and as we approach the 20th, all disparate domains will be increasing in favorability (e.g., PNA, NAM, NAO), such that the final third of December is interesting winter weather wise. The 9th period remains a distinct threat as well, as originally noted on the 23rd to monitor the 7th-11th period. As an aside, a displacement event favors North America (compared to Europe) for "winter" weather, and even if the SPV is displaced away from the continent, that does not implicate "all the cold air" will be taken with it. Quite the contrary, actually, as the geopotential height structure would be conducive for tropospheric, high-latitude blocking.

Thanks frd and Ray. Should be interesting to see how this pattern evolves.

I wrote an "update" post here (which hasn't changed at all from my thoughts last week) regarding the December pattern progression:

When one steps back and poses the inquiry: if I were to remove the modelled EPS z500 progression from the equation, and the GEFS for that matter, how would I anticipate the hemispheric/global pattern to progress in light of the apposite physical forcing mechanisms; namely, AAM tendency progression, GWO/MJO, among other factors, etc.? For those who believe a protracted pattern break-down is ahead, ask yourself: am I thinking this principally because a volatile snapshot on the day 15 EPS suggests so, or is the belief grounded in reasons separate from modeled z500 pattern? Given the relevant factors to which I allude, I wouldn't alter anything regarding my pattern post several days ago. The BDC continues to intensify, quite strongly actually, as ozone transport increases; angular momentum is falling, and the MJO will cycle through 8-1-2, thereafter becoming incoherent and dampened by the resumption of low-frequency forcing which will reinvigorate the Nino-esque WGOAK/Aleutian Low signal. The follow-up wave 2 hit to which I've mentioned in past days is now being detected on the guidance; notice the progged wave 2 geopotential heights forecasted to increase rapidly by day 10, concordant with the auspicious tropospheric precursor regime. So we have a potent wave-1 peaking now, and will follow up w/ subsequent wave 2 around December 10th. Thus, again as noted in the post several days ago, while the Pacific jet retracts, reflective of the ephemeral suppression of angular momentum, the Arctic/Atlantic signal will countervail with a prevalence of higher geo-potential heights. This pattern will be imprinted most notably in the December 10th-16th period, wherein the Pacific has lower than normal favorability while contemporaneously, the Arctic/Atlantic have higher than normal favorability. The result will be a muted, short-term warm-up in the Northeastern US. The Pacific thereafter, improves, in concert with the weaker than normal tropospheric vortex, as we move into the second half of December. The snap-shot one sees at the end of guidance, once it comes into view, will be more accurately reflected as the short term alteration that it is. I will not use the words "Relaxation" or "pattern break" because those are subjective, imprecise parlance depending upon one's viewpoint. But more accurately, the Pacific will temporarily worsen while the Atlantic improves (Dec 8th-15th), followed by an improving Pacific and continued conducive Arctic/Atl. The Euro guidance is over-weighting and too aggressive with the MJO impact. Below -- the 00z ECMWF and 12z ECMWF valid 00z December 7th. Notice the significant alterations in the NAO domain especially. There are changes in the NPAC, too. This is what I'm referring to regarding the undermodeled Arctic/Atl response in the extended. Quote Edit Options

Thank you, frd. And yes, I wouldn't be concerned with the weeklies, and high model volatility is expected, especially in the Atlantic. Note the large error bars on ensemble means for the NAO/AO D10-15, similar to what we experienced in November. The vertically propagating wave energy via wave 1 initially with some subsequent augment from wave 2 will reinvigorate the -NAO in the second week of November. The pattern progged is actually similar to what I forecasted for December w/ PAC NW-NE US colder than normal pattern courtesy of a -NAO and Nina-esque Pacific/Aleutian ridge. The Pacific will begin to transition more Nino-esque in mid month.

See my latest update post in my outlook thread. The Height restructuring is a function of the tropical momentum loss and should reverse in the middle part of the month once intraseasonal forcing is dampened and resumption of more Nino-esque forcing restarts. During the jet retraction period, HLB will develop in the ATL/ARC (8th-15th).

Was just noting my station history and I've recorded 17 nights sub-freezing this cold season already (Oct/Nov). I honestly can't recall that happening, before December even begins.

I posted my pattern thoughts/update in last post of winter outlook thread if interested:

1. Near-term tropospheric precursor pattern will continue to enhance vertically propagating wave-1 energy which will peak at the z10 vortex in about 10-12 days. 2. Medium term burst of wave-2 energy is likely to initiate in early December, peaking close to December 10th. This burst will not be as intense as wave-1, and thus, while the concerted assault is unlikely to destroy the upper stratospheric vortex, it will weaken in substantially. This notion is reflected in the medium term z10/60N zonal wind forecast, redolent of rapid deceleration by the second week of December 3. The Brewer-Dobson Circulation continues stronger than normal w/ enhanced ozone transport into polar regions 4. MJO wave and its concomitant udiv signal will propagate ewd through the EPAC, Atlantic, and toward Africa by D7 (reflective of p8-1 passage). The rossby wave dispersion attendant will act adjunctively in northern stream deceleration and aid in the incipient HLB signal. 5. The synergistic forcing of the above quite nicely coincide on the December 8th-10th period for the rather rapid redevelopment of higher than normal geopotential heights in the east based NAO region, which will gradually retrogress in the second week of the month. 6. Angular momentum removal in the sub-tropics via the MJO and GWO progression into suppressed AAM octants (as indicated by udiv propagation into Indian Ocean) will ultimately lead to a jet retraction event by week 2, following this current jet extension. The present negative FT will eventually manifest in the mid-latitude pattern in about 10 days. Implications are that the Pacific wave-train and jet configuration will acquire a somewhat Nina-esque appearance in the first 10 days of December. Blocking will be developing over the NAO/AO domains contemporaneously with a wavier/Aleutian ridge regime in the Pacific in the December 1st-10th period. Colder weather will return to the Northeast in the means by the second week of December due to the amelioration in Arctic/Atlantic signalling; however, the Pacific will be less auspicious initially. 7. Once the intraseasonal forcing signal fades -- which, I expect the MJO will progress to phase 2, thereupon, weakening into the null phase by the second week of December -- the predominance of the lower frequency forcing signal will reemerge, and about one week following, I anticipate the Aleutian Low/E GOA High Nino-esque regime to return. This -- by my estimation -- will occur sometime around the middle point of December +/- a few days. 8. In light of the above, the large scale pattern indicators are such that: a) December 1st-5th is likely unpropitious in the means, b) December 6th-12th - becomes more conducive as NAO/AO begins to respond to vertical wave driving and tropical forcing c) middle of December onward through the second half of the month (the cycle probably lasts until early January) becomes even more favorable as the Pacific rearranges and resumes a more Nino-esque structure 9. By extension, I anticipate angular momentum in the sub-tropics will increase as we approach mid December. Countervailing easterly momentum deposits will likewise increase in the mid latitudes and reinvigorate blocking. To me, I'm not expecting the low-AAM mini cycle (As Tam refers) to be destructive to Atlantic/Arctic blocking prospects. It will result in a Nina-esque Pacific pattern, possibly for 10 or 12 days, before the interseasonal signal returns and MJO forcing is dampened. By the time the large scale variables reshuffle again, i.e., possibly a more robust sub-tropical momentum loss, we should be into January and thus would coincide with anticipated pattern break period. Overall, everything is going as planned so far. I think the "best" part of the month for snow potential is toward mid December and onward, which is more congruous w/ improved climatology anyway. However, "best" potential doesn't preclude a threat prior. I wouldn't be surprised to see something in the 7th-11th period.