My Winter Outlook 2018-19

[frd]

1 hour ago, Isotherm said:

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. 

Great update Isotherm, makes a lot of sense!   

And maybe your progression could lead to a snowy period around the holidays as we come up towards the later part of the month.  

[40/70 Benchmark]

Tom, at this point, there is nothing left to do but some celebratory post bumping in a few months.

Your grasp on the wide array of specific atmospheric processess across the globe is superior to mine, but we are always on the same page in our aggregate expectations.

[Isotherm]

3 hours ago, frd said:

Great update Isotherm, makes a lot of sense!   

And maybe your progression could lead to a snowy period around the holidays as we come up towards the later part of the month.  

 

3 hours ago, 40/70 Benchmark said:

Tom, at this point, there is nothing left to do but some celebratory post bumping in a few months.

Your grasp on the wide array of specific atmospheric processess across the globe is superior to mine, but we are always on the same page in our aggregate expectations.

 

 

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

[thunderbolt]

1 hour ago, Isotherm said:

 

 

 

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

In Tom We Trust

[Isotherm]

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.

 

 

 

 

[frd]

1 hour ago, Isotherm said:

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

Excellent update Isotherm ! Things are progressing well for December so far based on your initial seasonal forecast. 

Just a quick question, I hear some strat expert talking about the continued assault on the PV from wave 1 and wave 2.  And how if history repeats itself based on studies the current precursor pattern might really weaken and displace PV soon.  

My question is, do you foresee a possible SWE taking place as well ? And if so,  what implications would that have on your seasoinal forecast ? 

Bear in mind I know we are not dependent on a SWE for the sensible weather progression you have forecasted. Alas, I find the mention of this possibility interesting. 

I hear TonyWells@scotlandwx talking about a possible SWE at the end of December, and I also hear HM mentioning that if the PV weakens, as he thinks it, it could open the door to some very nasty winter weather at the end of December here. 

Thanks Isotherm. 

     

[weathafella]

3 hours ago, Isotherm said:

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.

 

 

 

 

•  

Great post!  I’m learning a lot here.  And as an aside, I like your writing style.

[Zach’s Pop]

4 minutes ago, weathafella said:

Great post!  I’m learning a lot here.  And as an aside, I like your writing style.

He is one of the best. Glad you took the time to read his thoughts!

[weathafella]

4 minutes ago, Zach’s Pop said:

He is one of the best. Glad you took the time to read his thoughts!

I’ve been reading hs stuff for years-he is excellent.  The writing ability is really a lot higher this year it seems.

[Zach’s Pop]

1 minute ago, weathafella said:

I’ve been reading hs stuff for years-he is excellent.  The writing ability is really a lot higher this year it seems.

Good to see the young Turks growing into such great weather experts. 

[Isotherm]

21 hours ago, frd said:

Excellent update Isotherm ! Things are progressing well for December so far based on your initial seasonal forecast. 

Just a quick question, I hear some strat expert talking about the continued assault on the PV from wave 1 and wave 2.  And how if history repeats itself based on studies the current precursor pattern might really weaken and displace PV soon.  

My question is, do you foresee a possible SWE taking place as well ? And if so,  what implications would that have on your seasoinal forecast ? 

Bear in mind I know we are not dependent on a SWE for the sensible weather progression you have forecasted. Alas, I find the mention of this possibility interesting. 

I hear TonyWells@scotlandwx talking about a possible SWE at the end of December, and I also hear HM mentioning that if the PV weakens, as he thinks it, it could open the door to some very nasty winter weather at the end of December here. 

Thanks Isotherm. 

     

 

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.

[frd]

8 minutes ago, Isotherm said:

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.

Thanks Isotherm! It certainly appears that we are firmly on the road you are forecasting strat-wise.

More amd more signs, and stronger indications as well ,that the progged events, Wave 1 and 2,  indicated several weeks ago are only increasiing in forecasted outcomes as we get closer in time.  

Many people feel that the incorrect SPV displacement could yield the coldest and snowiest sensible weather towards Europe and Eurasa. As seen this AM on MichaelVentrice's  Twitter feed. 

From your previous reply below , in regards to displacements ,  you indicated that displacement favors North America. Yet, I still hear some folks stating the opposite. 

I imagine there might be confusion over a tilted , or partial displacemrnt versus a SPV displaced completely away from the NA continent. ( As mentioned below ) 

I will be closely following to see how things play out, very fascinating stuff going on right now.     

19 hours ago, weathafella said:

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.

      

[Isotherm]

4 hours ago, frd said:

Thanks Isotherm! It certainly appears that we are firmly on the road you are forecasting strat-wise.

More amd more signs, and stronger indications as well ,that the progged events, Wave 1 and 2,  indicated several weeks ago are only increasiing in forecasted outcomes as we get closer in time.  

Many people feel that the incorrect SPV displacement could yield the coldest and snowiest sensible weather towards Europe and Eurasa. As seen this AM on MichaelVentrice's  Twitter feed. 

From your previous reply below , in regards to displacements ,  you indicated that displacement favors North America. Yet, I still hear some folks stating the opposite. 

I imagine there might be confusion over a tilted , or partial displacemrnt versus a SPV displaced completely away from the NA continent. ( As mentioned below ) 

I will be closely following to see how things play out, very fascinating stuff going on right now.     

      

 

 

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.

 

 

[40/70 Benchmark]

I wasn't crazy about the idea of a SSW this season, but I don't think it will matter much in the end.

[Damage In Tolland]

Any updates on the final 15 days of Dec and heading into January or status quo? 

[Isotherm]

23 hours ago, Damage In Tolland said:

Any updates on the final 15 days of Dec and heading into January or status quo? 

 

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.

[40/70 Benchmark]

I don't think it will matter a ton....we both composed our outlooks under the pretense that there would not in fact be a SSW...do the math lol

It may not be quite as cold if it doesn't, but I don't think its a huge deal....but Tom can answer for himself.

[frd]

48 minutes ago, 40/70 Benchmark said:

I don't think it will matter a ton....we both composed our outlooks under the pretense that there would not in fact be a SSW...do the math lol

It may not be quite as cold if it doesn't, but I don't think its a huge deal....but Tom can answer for himself.

Thanks Ray.

I was also thinking about the relationship too, outside of just temperture, regarding the implications for EC storm tracks, and SE Canadian vortex placement and even HA events. I guess my thought was, whether correct or not, is a major warming with proper tropospheric response could up the ante on storm intensity, maybe surpression too could be an outcome as well.  

[Isotherm]

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.

[frd]

1 hour ago, Isotherm said:

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].

This is awesome information, Thanks, much appreciated. You really do take this strat area to a new level.  

[Typhoon Tip]

Just FYI ... general reader 

A critical correlation metric between these stratospheric warm intrusion events and the AO relates to whether they are downward propagating. 

Currently the GEFs cluster suggests so, but the verification may demo more in the way of that specific behavior over the next ten days.

If so ... the lag is two to three weeks from first onset. ... which is now; a historic inference lands a would be PV morphology in the ides of Jan. 

Also as others have noted… Negative AOs do not always distribute cold in the middle latitudes evenly, should this all lead inexorably to -AO; it may favor one side of the hemisphere

 My present hypothesis is that with the modest warm ENSO correlation favoring (perhaps) positive PNA back end Winters that may actually parlay/prone Rosby positioning ... establishing a cold conveyor over the Canadian Shield if those two statistical behaviors play out according to their majority historical precedence. 

[Isotherm]

---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 17^th. 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.

[512high]

1 hour ago, Isotherm said:

---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 17^th. 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.

well written.....

[40/70 Benchmark]

6 hours ago, Isotherm said:

---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 17^th. 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.

The body of your work is second to none, but I have a bit of a qualm with implying that the relaxation during the second half of December was unpredictable.....especially with regard to the struggles to maintain a PNA. There was a signal if you utilized the analogs correctly. This is why I didn't go hung-ho on December...in fact, were it not for the emergence of that Scandinavian ridging at the 11th hour, I would have gone for a torch December, rather than the simply unremarkable month that was predicated and verified quite well. But that riding caused me to back off because it I interpreted it as hint that the stratosphere and troposphere were going couple quite early and proficiently this season.

I will grant you that I would not have been able to identify the "smoking gun", or mechanism for the relaxation, so to speak....as I am not as skilled as you are in that regard. However sometime the cruder methodology of exhaustively pouring over the analog set pays dividends.

[qg_omega]

December was forecasted by many to be warm across the conus, CPC nailed it on their month forecast issued late November.  It was clear very early on the MJO would have a prolonged stay in phase 5.  Personally, I believe the SSW event and possible split of the PV is a game changer to most winter forecasts and not for the better.  I have a very hard time with the delayed but not denied method of forecasting.  If your forecast required A + B + C + D and A failed and B was not as expected, you can't leave C and D alone as if A and B's failure don't have an impact.

[LibertyBell]

8 hours ago, 40/70 Benchmark said:

The body of your work is second to none, but I have a bit of a qualm with implying that the relaxation during the second half of December was unpredictable.....especially with regard to the struggles to maintain a PNA. There was a signal if you utilized the analogs correctly. This is why I didn't go hung-ho on December...in fact, were it not for the emergence of that Scandinavian ridging at the 11th hour, I would have gone for a torch December, rather than the simply unremarkable month that was predicated and verified quite well. But that riding caused me to back off because it I interpreted it as hint that the stratosphere and troposphere were going couple quite early and proficiently this season.

I will grant you that I would not have been able to identify the "smoking gun", or mechanism for the relaxation, so to speak....as I am not as skilled as you are in that regard. However sometime the cruder methodology of exhaustively pouring over the analog set pays dividends.

I mentioned the bad luck we had with the early December storm back in my subforum and it was mentioned that we wouldn't have gotten that storm anyway since the MJO was unfavorable and the NAO was positive at the time.  Now, if that storm happened after the middle of January, the outcome would have been entirely different.

 

Also, in addition to it being an unremarkable December, I think we can say that for SNE the winter prior to Jan 1, has been historically low in terms of snowfall.

 

Sometimes the cruder methology works because, well in this kind of currently inexact science, in analyzing too much, we sometimes lose the forest for the trees ;-)

 

[LibertyBell]

15 hours ago, Isotherm said:

---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 17^th. 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.

Thanks, it actually seems like the stratospheric perturbation prior to the SSW that we all wanted, may have caused our short term (December) to be milder and less snowy, though it may pay dividends down the road in January.

 

[40/70 Benchmark]

1 hour ago, LibertyBell said:

I mentioned the bad luck we had with the early December storm back in my subforum and it was mentioned that we wouldn't have gotten that storm anyway since the MJO was unfavorable and the NAO was positive at the time.  Now, if that storm happened after the middle of January, the outcome would have been entirely different.

 

Also, in addition to it being an unremarkable December, I think we can say that for SNE the winter prior to Jan 1, has been historically low in terms of snowfall.

 

Sometimes the cruder methology works because, well in this kind of currently inexact science, in analyzing too much, we sometimes lose the forest for the trees ;-)

 

The fact that we did not get a significant snowstorm in early December was bad luck. The favorable pattern materialized, but there was simply too much confluence. Things like that can not be predicted from a seasonal standpoint.....entirely stochastic in nature.

[Isotherm]

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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.

[Isotherm]

1 hour ago, qg_omega said:

December was forecasted by many to be warm across the conus, CPC nailed it on their month forecast issued late November.  It was clear very early on the MJO would have a prolonged stay in phase 5.  Personally, I believe the SSW event and possible split of the PV is a game changer to most winter forecasts and not for the better.  I have a very hard time with the delayed but not denied method of forecasting.  If your forecast required A + B + C + D and A failed and B was not as expected, you can't leave C and D alone as if A and B's failure don't have an impact.

 

 

 

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.