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Tamara

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  1. Hi Tom Yes indeed, and coincidently I have recently also considered 2007/8 in parallel even though it wasn't part of our discussion back then! Some key considerations: We are seeing some westerly additions propagating between 30/40N and these suggest some increasing of tendency for mean zonal easterly anomalies at higher latitudes (shaded blue) to assist amplification of ridging and southward displacement of trough disruption What would be expected to follow the tropical pulse having passed through the Pacific phases that supports these westerly additions is a signal for frictional torque tendency to fall back and invoking a -ve mountain torque across the Rockies to start removing those westerlies and in tandem with a subsequent uptick in the polar jet at higher latitude. So support for a GWO response through Phases 4/ 0/8 - the former indicative of the +ve momentum transport c/o of the tropical passage and the latter indicative of a fall in relative angular momentum as the tropical cycle completes, coming from torques and rotation of the planet that favors a mean ridge solution at each opposite end of the GWO phase spectrum This extra tropical signal is consistent with the Pacific ridge re-setting the wavelength downstream with another anomalous downstream ridge in the Atlantic. Much will tie into the next phase of tropical convection in late November and December. The Atlantic blocking and -NAO scenarios being discussed and suggested as stemming from the twitter-sphere assume another round of amplified tropical forcing to boost repeated poleward fluxing But its worth noting that the seasonal cycle in angular momentum will likely (at this stage) increase in a low momentum base state during December c/o return of the GWO to Phases 1 and 2. Also its sensible/cautionary to not underestimate the strength of the seasonal vortex based on its initial uptick prior to the upcoming interruption to zonal speeds. This evolution of falling momentum allows the space for vortex re-intensification as the hemispheric wind-flow budgets reverses the tendency seen during November for westerly additions at 30/40N to that of easterlies. Compensated westerly inertia at higher latitudes simultaneously removes the propensity for amplification of ridging to higher latitudes as alluded to above . Such a hostile extra tropical circulation would negate poleward fluxing and mean that the repeated synoptic of November, and as dictated by seasonal wavelength changes as winter begins, would be less amplified than that of November. Time as always will tell. But this post is an endorsement of the momentum budget element which is one of the key components that Tom discusses in his detailed and highly objective seasonal forecast
  2. Hi Tom - you have set the optimum example of how a forensic lesson in meteorological diagnostics should be presented Your input in the ongoing pm group is always inspirational and there is so much evident from those discussions that is highlighted in this assessment to assist further understanding and appreciation. Very grateful for the time and care you have taken to bring together this excellently balanced and thoroughly objective outlook. Tams
  3. Its my own view that there is no single key area of consideration alone, when it comes to a diagnostic approach that assists seasonal analysis - and moving back and between, or switching from one to another doesn't achieve the necessary equilibrium that leads to a satisfactory assessment of all probabilistic outcomes I can wholly understand why followers of the winter season patterns will choose to attribute priority significance to a single key factor if there is a belief that such a factor increases the likelihood of a single bias outcome. However, the most coherent conclusion so far in my opinion is that ever increasing amplification of hemispheric patterns, which few now doubt has a good deal of attribution to unstable sea ice distribution patterns and feedbacks, has served to increase uncertainty of all possible outcomes rather than increase probability of any single outcome. This includes a cold air advection single bias outcome in winter that seems to have a parallel bias assumption, that thermal gradients will inevitably be sluggish because of this instability feedback and so increase the chances of slow moving and meandering blocking patterns - at higher latitudes. Its always possible to pattern-match and produce desirable results when extracting variables that are conducive towards leading to a given outcome most particularly when that outcome is steered towards, or meets any given desired end product. This applies at any season and not just winter. My opinion though is that in context of popular winter discussion on pages like these, there is no pure analogue existing these days which provides the desired clear cut tropospheric>stratospheric pathway solution with all the implications that go with it in terms of bias solution end product of potential reversal of polarity at higher latitudes, and a disrupted tropospheric pattern overwhelmed by frigid air at mid latitudes. Uncertainty remains about frequency and duration of the SSW mechanism, and this uncertainty also applies to any potential tropospheric fall-out. A cold air solution in any one place isn't a given, as much as a cold solution anywhere at all is not a given - especially as in winter there is simply less aggregate cold air to go around in general to begin with Such uncertainty is sustained through the overwhelming destabilization within the polar regions due to unchecked and vehemently pernicious warming processes. However this does not quid quo pro endorse rubber stamping of indefatigable empirical resolution of a contingent -AO/-NAO pathway relationship if an element of confirmation bias underpins it - and there is a danger that whilst it is of course highly welcome and vital that so much understanding and awareness has been advanced in this area of meteorological science, such awareness doesn't mean it is more likely to make cold spells within mid latitudes in winter occur, just because of that extra understanding. Each and every season (not just winter) has to be taken on its own merits, more especially because of the intense superimposed forcing on weather patterns/climate Equal to such consideration of the higher latitudes, one also needs to look at the tropics, and the additional anomalous warming of oceans across the tropics, which are increasingly frequently supporting stronger sub tropical ridging patterns at mid latitudes due to altered momentum transport processes created through skewed ENSO ocean/atmospheric SST distributions and resultant a-typical feedbacks. A superimposed elevated tropopause is more commonly propagated from tropics to mid latitudes due to increasingly active phases of the ferrel cell c/o warming processes - especially when tropical >polar stratospheric processes (QBO phasing) becomes aligned to further augment this. Diagnostic approach is as crucial to these vis tropical (over)heating as is the true arctic dilemma and consequent alarm over it. Tropical feedbacks are manifesting an increasing frequency and propensity for intense sub tropical ridging to propagate to mid latitudes. These are serving to bolster intense +NAO patterns, as much as any active polar destabilization, under any given conducive tropospheric>.stratospheric pathway that exists with a similarly conducive momentum transport structure, may be argued to serve to compliment a consequent -ve Northern Annular Mode. This means that one is also wise to equally apply diagnostic examination and scrutiny towards the role that slow moving, meandering, amplified mid latitude blocking patterns (so limiting cold air advection in winter and which have clearly also been seen to increase intensity and frequency of mid latitude heatwaves in summer) are playing in weather pattern distribution (and subsequent sensible weather on the ground. Based on the laws of conservation of angular momentum, such activated sub tropical>mid latitude patterns involve corresponding compensated polar jet strength at higher latitudes which is detrimental to, and to the eradication of, cold air advection processes. It is also not a given, under the wider remit of diagnostic variables present at any time, that sub tropical ridging inevitably always evolves poleward beyond mid latitudes (as it can under certain empirical rules progress towards higher latitudes, given total variables that augur such an outcome). This is where considerations to the individual components of the GSDM budget are key. These pertain to the relationship that the atmospheric circulation adopts to the ocean base state - and not ENSO per se. In a lot of communications within twitter and internet weather threads on various sites, there is an incorrect blanket link to ENSO itself without consideration of the increasing frequency with which an a-typical atmospheric relationship exists towards the macro scale base state, and which can mean the difference between poleward and equatorward flux of planetary wave activity - which in turn dictates whether ferrel or polar cell has the ascendancy. One has to also examine the atmospheric budget and break down that budget to see where the dominant aggregate wind-flows exist at any given time. Dominant inertia flow could exist within either global hemisphere - and within that given hemisphere, they could also exist at various latitudes that have a bearing on where jet deceleration or acceleration occurs. In turn determining where spatial inertia distribution permits developing blocking structures, set against compensating zonal velocities elsewhere according to the amplifying/de-amplifying proxy of change of (+ve or -ve) wind-flow torque mechanism that dictates the turning force within the atmosphere circulation and controls angular momentum tendency. If tropospheric momentum transport is a-typically skewed by sustained and unchecked artificial superimposed forcing, then one cannot make analogous linear assumptions about poleward transport of wave eddies through torque mechanisms that will perturb tropospheric layers. Large lessons were learnt last winter in this respect, when such assumptions were made that a tropospheric>stratospheric pathway existed, and permitted through the macro scale atmosphere>ocean signal vs arctic instability to create the conditions to trigger a cold-air advection brand of stratospheric disturbance. Stratospheric disturbance indeed occurred but its arctic>mid latitude distribution of expunged polar airmass was very much restricted vs expectation - and despite its very local intensity on the micro NH scale, it was out-stretched by the predominance of sub tropically derived warm anomalies. This is also an unbalanced relationship existing intra seasonally and not applicable alone to winter. In this respect and again in reference to this year, despite prolonged fall-out from a highly dynamic final warming of the stratosphere, and which continued to have quasi-permanent lag influence on a good part of the summer season - this did not result in a uniformly supressed jet stream sustained at mid latitude. A predominance of intense sub tropical ridges were often present alongside any propensity for enhanced summer easterlies at higher latitudes - the latter more especially in early summer however. Intense heatwaves were still very much a feature despite any spasmodic blocking at higher latitudes and the first of these appeared remarkably fast even when the higher latitude Atlantic blocking c/o of the final warming was starting to pass its peak. So a seamless intra seasonal approach, and appreciation of the role that changing wavelengths play alongside the timelines of intra seasonal phenomena, is required to be adopted to objective diagnostic approach, and not a truncated one dimensional approach that pertains to one season alone and omits consideration of what has preceded it. In conclusion of all the above, I welcome the paper dissemination posted on this page, which illustrates the open mindedness that David @Bring Back 1962-63 rightly alludes to above. This invites examination of all possibilities to advance the science without attempting to fit the science to any given bias outcome - at any time of year and not just in winter.. With respect to the here and now and moving forward : Its not a surprise to be seeing the amplified Atlantic ridge programmed over coming days underpinned by some -NAO troughing. This, in accordance and in tandem with advancing autumnal wavelengths, advertised through torque momentum now falling from its 'peak' and +ve momentum westerlies getting scrubbed once more from the atmospheric circulation. The recent momentum rally has cut the -ve GLAAM deficit to -1SD prior to probably renewed descent. The failure of the GWO to engage the transitional phase space 4, outside of the La Nina attractor phases, also of note in terms of the tropical/extra tropical cycle. Much of the tropics, and the Pacific now controlled in the days ahead by increased easterly inertia. Based on assessments for the season made in the first part of September, the pattern vs the atmospheric feedbacks are progressing close enough to what has been anticipated. It gets more difficult to decipher as winter seasonal forces start to align, and in some cases clash with one another, but for my own part there is no reason, yet anyway, to alter expectations looking ahead. Caution therefore remains for my own part about any early cold air advection scenarios c/o amplified Nina-esque ridges and what this might mean looking too far ahead. Wholly typical for the last third of autumn under low angular momentum regime wavelengths, and still relatively early for the tropospheric vortex in terms of timing for starting its traditional annual attempts to couple with the strengthening upper stratospheric vortex and organize within the polar field Objectively and to mitigate as bias adjustment (as is prudent and sensible at this of year) - then based on the discussed atmospheric budgets, replying on walker cell/ WPAC typhoon activity as a means to garner planetary wave disruptive elements is not likely to be enough to prevent vortex intensification impacts extending into the tropospheric winter - and it would require a sufficient push from within the mini ENSO high frequency tropical signal and also a signal that the QBO transition is becoming more progressive. There is no clear indication yet of the latter either, at this time. In my opinion.
  4. The key thing about the 62/63 unusual anomaly case (and not too different from late 2010 in this respect) was that +ve momentum transport processes preceded cold air advection/blocking and the GWO orbits in the Nino attractor phases in late autumn/start of winter 62 confirm that those +ve torque processes lead to the early season tropopause instability with poleward disruption within the tropopause taking place. Post SSW is indeed when a low AAM pattern (sluggish momentum) can serve to hold a higher latitude blocking pattern in place if the polar field is conducive to this. Quite the opposite though to a -ve AAM pattern pre-SSW where the increased westerlies at higher latitude run flat and fast and increase the polar gyre. Which was the gist of my earlier post. The GWO in autumn 2010 similarly responded to +ve momentum processes and a departure in terms of atmospheric /ocean de-coupling, temporarily, from an impending strong La Nina regime. So its very true that -ve momentum processes following poleward surges in momentum can 'lock in' slow moving blocking patterns. as happened in 62/63. The usual dominant polar branch of the jet that occurs with low angular momentum regimes - gets instead diverted/split by stratospheric>tropospheric downwelling which creates a shut down far greater than the residual polar jet momentum created by -ve AAM forcing within the tropics. Also, seasonal wavelength changes into late winter further prolong such pattern locks - much as also happened in late winter and Spring 2018 when the La Nina standing wave had been temporarily reversed by the +ve momentum transport processes in late January that led up to the SSW. But a subsequent return to low AAM and the GWO returning to the Nina attractor phases locked in the blocking, and according to those end of winter and start of Spring wavelengths Tropical/extra tropical forcing through +ve momentum processes create a poleward fluxing pathway to break the stability of a cold stable vortex - any resultant higher latitude pattern suddenly blocks any return to -ve momentum like a huge boulder in a stream, and returning polar jet energy is instead forced around the pole with the result that warm advection suddenly floods into channels that previously were cold zonal vorticity energy parcels. Of course, so many decades later, its necessary to factor in background warming trends and so many altered states between both the tropics and the pole before assuming any composites/analogues - especially where any fsvored outcome is involved. But diagnostics such as stratospheric/tropospheric interplay and GSDM momentum budgets vs computer model interpretation of these variables lack any such human attachment to weather type preference anyway - and Mother Nature does as she will despite how we interfere. alas, too much
  5. Yes indeed For what it is worth, the tropics and extra tropic are as far away from any co-operative Modoki El Nino atmospheric>ocean coupling as they could be at this time. The Global Wind Oscillation, a plot depiction of aggregate wind-flow inertia within the atmospheric circulation is rooted deeply at high amplitude within the La Nina attractor orbit phases 1,2 and 3 - and representative of total relative angular momentum at -ve 3SD as sum of aggregate wind-flow momentum budgets at this time. Notice the persistence of anomalous easterly momentum around 30N as identified by the blue shading on the plot supplied - and mirrored equally in the SH. Notice also that this regime corresponds with the Western Hemisphere and I/O high frequency tropical blueprint in evidence of the previous weeks. This extent of -ve momentum represents a firmly retrogressive synoptic pattern - but with the laws of conservation of angular momentum meaning that the easterly momentum being added from the tropics - is being compensated by increased westerly momentum at mid and higher latitudes. With stalled QBO transition, and of which uncertainty exists at this time (imo) in terms of speed of continued transition towards -ve phasing at a level compatible with BDC assist to potential stratospheric destabilization - this added momentum leans with time over the upcoming weeks towards coupling of developing seasonal stratospheric polar vortex with the troposphere heading into the first part of winter at least, without any significantly abrupt change to the global wind-flow budget and a very strong rally in AAM to ladder the GWO away from the Nina attractor phases via robust increase in tropical and extra tropical frictional and mountain torques. Factors such as solar minimum, low Barents sea ice etc discussed eloquently and with excellent insight across most twitter and international forum zones only become influentially meaningful in any forward plotting of events as I see it - if higher latitude westerly gyre is interrupted enough for these to start to create cold air advection feedbacks that most analysts are making their starting forecast assumptions hoping they will be. We all know that fitting drivers to bias outcomes, however well intentioned and thought out, still nevertheless creates margins for error when probabilistic analysis can (and often enough does) point to other possible long term solutions that are less palatable than the bias outcome and may exist in tandem with, or stand=alone isolating the bias outcome. I do not make forecasts within any season, and will not be attempting to make one this season either - but I do believe that something is going to have substantially give over the coming weeks for some of the analogue assumptions expressed on this very acquitted and informative thread and elsewhere to become reality. This may or may not be the case, but from my own point of view, whilst I subscribe to caution with seasonal modelling, there are times at least when these models reflect at the very least some compelling starting conditions that are being extrapolated forward and require a large catalyst to alter their expected destination. It will be interesting, either way, to see if these change in coming weeks and( trying to take a neutral position) I am open minded to this. However- at this time the seasonal modelling has some credence and can't be dismissed because it doesn't reflect sensible weather of choice, in my own opinion of course Just to add, as I should - the GSDM plots are restricted access only @OceanSnow I will send a pm in reply when I have time
  6. In the nicest way, things haven't turned out yet for this storm It is still subject to modelling that is set in the future, and subject to extremely sensitive and fine margins in terms of infrastructure risk vs probabilities of landfall (where and when) Anyone living in the SE US will remain on the highest alert right up to nowcasting situations with a highly dangerous and volatile storm such as this. Based on the life threatening risks of such a storm it will never be deemed a non event....until it is as certain as possible to know where impacts are most likely to be focussed. Indeed it only becomes a 'non event' when the storm has passed and it is known that impacts have been next to minimal. The NW Bahamas will certainly not be viewing this as a non event. This looks extremely worrying for them especially if Dorian stalls anything like suggested. The overnight EPS 'cone' has shifted to a solution that (as of this time) reduces the risk of Florida landfall..... . ….but as one who likes to pay attention to suggested diagnostic evaluations first and foremost, numerical models are always snapshots in time and are evolutionary in prediction and not face value absolutes. Its far too soon to suggest that the models will not shift back to a Florida solution, however much the trend may appear to moving way from it at this present time. Until, or if, the risk becomes zero in any given place, then the very high impact risk remains the crucial assessment vehicle. The suggested stall could prove quite a pivotal sequence in terms of the fate of the Florida east coast, (as much as it could prove a most unfortunate fate for the NW Bahamas - one can only hope for them) However, clearly most especially for those whose homes and livelihoods are most at risk from Dorian (including Floridians) its eminently sensible and wise that ears avert attention to overly premature declarations based on suggestions of intra day modelling suites who will continue to struggle with initiation data within a storm that, quite typically, will always be one step ahead of the number crunchers Notwithstanding any of that, eyes and ears should be spot welded towards forecasters. of whom there are many. who assess risk probability based on diagnostic evolution of modelling unfolding with time and not based on single snapshots of time Edit: The updated Euro model evolution rather illustrates the points made
  7. I think that some separation between GSDM data and proxy supporting data is useful to read between the lines a little to help distinguish between natural ebb and flow of momentum budgets and associated torque mechanisms as they can play quite different roles in determining short and long term variations as contextualized within the broad-scale ENSO cycle. Short term loss and gain momentum transports certainly impact sensible weather over relatively short term periods in terms of whether they decelerate wind-flow patterns and create associated -ve torque mechanisms or accelerate wind-flow patterns and create +ve torque jet extensions. But attempting to extrapolate these forward in respect of trying to correlate wind-flow to surface patterns is soon fraught with error as the atmospheric circulation is always in constant flux and one momentum budget 'transaction' alone doesn't inextricably alter the macro scale ocean>atmospheric relationship and associated sensible surface weather on any permanent basis. Such exchanges requiring monitoring of persisting trends over weeks at a time, not through one specific wind-flow event which has it its own limited wavelength or lifespan With that in mind, the -ve NAMT of the other week did/has created by its nature of deceleration of wind-flow, a regressive pull on both relative tendency and total angular momentum as part of a legacy of persisting trade winds across the Pacific during the first two thirds of June. But this is where its necessary to differentiate between the cyclical MJO 'mini cycle' and the low frequency walker cell signature with also the passage of convectively coupled kelvin waves which create separate upwelling and downwelling sequences which alter the composition of the SST ENSO zones over longer timeframes and also interfere with the budget wind-flow exchanges according to whether they act constructively or destructively on the base state. If we take a look at the low frequency signal, the CFS continues to advertise the persistence of convergence close to the dateline through July. Longer term ENSO forecasts should be precepted against shorter term proxies, as the former tends to be reactive to the latter, rather than necessarily proactive in themselves These dovetail with the z850 zonal winds on the Hovmollers plot, in the shorter term, that clearly depict this low frequency convergence Adding this together with the recent/ongoing passage of the convectively coupled envelope of the MJO, ( and associated tropical activity c/o Barbara as an artefact of that in the EPAC), one gets an understanding of why the trade winds have been dampened. This doesn't, however, account for the lagged effects of any wind-flow deceleration within the extra tropics that has scrubbed out westerly momentum within the extra tropics and is still working through its timescale feedback. When we consider the momentum budget, the tropics and extra tropics can exhibit periods of relative disconnect where contravailing wind-flows are present in each. Hence why care is required when extrapolating how the total budget may behave over a future period. So whilst the MJO is an engine room catalyst for accelerative and decelerative wind-flow propagation, it is not the only driving mechanism of z850 wind-flow in the Pacific - and fluctuations of wind-flow and propagation of momentum between the tropics and extra tropics that influences the orbit evolution of the Global Wind Oscillation should be assessed from broken down proxy analysis. In this respect any decline into the less +ve echelons of the neutral GWO octant phases does not automatically imply long term quasi permanent decline As alluded to above, torque events have a wavelength (lifespan) and as also impugned previously, they cannot, on their own, determine longer range atmospheric circulatory and reflected surface patterns in isolation, and it cannot be presumed that they are definitively part of a longer term trend in angular momentum tendency associated with macro scale ENSO shift. It is highly concurrent with any minor or major ENSO event, for interim waxing and waning phases to occur. Personally on that basis, but also as one who does not make definitive forecasts anyway, I would be highly cautious of extrapolating ahead through the rest of summer, let alone the coming two seasons. But for what little it is worth, I am not sure that a Nina//wQBO low solar combination,(if it hypothetically evolved) is necessarily a good thing for those already resting their hopes on NH winter in terms of upper polar vortex development - but this is clearly highly speculative at this range anyway, and open to considerable margin of outcome with uncertainties apparent within weeks, let alone months. Plus based on the downwelling sequences of the +ve QBO wave vs the waning late season dynamic warming into the troposphere, the coming few months looks to have an increasingly less blocked structure at higher latitudes. For now, a waning oceanic phase to warm/neutral is palpably apparent - but notwithstanding that, until, or if, the convergence zone Nino-esque walker cell breaks down (and there is not evidence of that within a forthcoming period that some are making assumptions to formulate forecasts built upon a more La Nina-ish feedback) what matters here is the relationship that the atmosphere adopts to the ocean base state, and not the base state per se. Taking into account the periodicity of the MJO cycle which is up to between 60 to 90 days for active amplitude cycles, and with the last active amplitude Phase through the Pacific in May, then assuming the Nino walker cell prevails, a further active phase, based on background proxy parameters becomes increasingly possible in the latter half of the summer. That, and a downwelling CCKW phase due (as opposed to the early summer 'destructive' upwelling phase) wrt ENSO zones, will be something that seasonal forecasting will not be 'seeing' very clearly at the moment. The rest of the year remains finely balanced, but whilst El Nino has clearly struggled to sustain its late winter 'peak' strength and has weakened further, other years like 1997 and 2009 for example have shown that twin standing wave straddling seasons (African and Pacific) which exert -ve destructive and +ve constructive action respectively on any +ENSO state, can achieve further waxing regimes after apparent mid year decline - and with renewed atmospheric/ocean co-operation coming into the final third of the year. Its far too soon to discount such an event at this time Edit: As a backing supplementary, this animation c/o Ben Noll illustrates how the Nino walker circulation created a sink in the Atlantic Ocean due to downstream wind shear during June The GFS is predicting an uptick of easterlies c/o the African standing wave across the Equatorial Atlantic, destructively interfering with the Pacific wave and ending the downstream wind shear across the EQA. In contrast to the Euro model.- as suggested above More reasons not to place too many bets too soon Tams
  8. Hi James - yes, I think that use of proxy data provides a bit of extra reading between the lines when apparent contravailing macro scale factors are present. In this respect good reason not to too directly correlate GSDM diagnostics to NWP synoptic patterns and instead focus closely on the "grey areas" There is a continued rossby wave train c/o the remaining weak Nino standing wave in the Pacific and it can be seen how the forward speed of the current eastward moving kelvin wave can be determined by the filtering of the velocity potential wave bands The SOI evidences the persisting wave trains c/o consistently recording -ve values and this has been determining frictional torque at 30N close to parity based on the momentum budget of the backdrop of globally averaged angular momentum remaining a little above average as is consistent with weakly +veENSO Capacity of any +ve torque response is proportional to the existing +ve wind-flow inertia that already exists in the greater atmospheric circulation. This means that the higher the macro scale inertia present is, the higher the extra additional supply of the same wind-flow is required to be added to create a greater still tropical>extra tropical momentum transport response. On that basis, it is loss of westerly momentum due to tick backs in angular momentum c/o trade wind bursts which would register greater downward fluctuation in frictional torque tendency. But unless the whole tropical>extra tropical circulation decouples as part of a longer term shift, too much shouldn't be read into such short term torque differentials attached to the "mini ENSO"/ aka MJO cycle. (Also see Hovmollers plot further below identifying continued weak westerly wind anomalies). Additionally, CCKW activity passing through the EPAC is responsible for helping dampening the trade wind burst east of the dateline, breaking down wind shear, and allowing the spawning of the first tropical activity of 2019 in the Eastern Equatorial Pacific. As per Mr Klotzbach : If one takes into consideration the persistence of the "destructive" suppressive phase on the Nino standing wave from late May and during the first two thirds of June, up to the recent resumption of Pacific +ve forcing from west of the dateline and eastwards - than one can conclude that both total and relative trend angular momentum have held up well. A clear sign that the atmosphere still remains receptive to wanting to retain some semblance of "westerlyness" to wind-flows rather than let that period of relative destructive -ve forcing totally re-configure the standing wave to the WH and I/O. A twin forcing regime has rather developed, which dictates active and suppressive tropical activity based on whether the Pacific or newly developed WH wave is engaged as part of the intraseasonal MJO cycle.. Other years like 1997, 2006, and 2009 saw a similar twin standing wave regime I think that ENSO forecasts and some tropical/oceanic commentators have exhibited a surfeit of Nina bias in this respect since late Spring. Its understandable though of course that a few eyes perhaps look well ahead to the Hurricane season and are keen to assess SST's in the tropical Atlantic and what presence (or otherwise) of wind shear might be evident depending on whether some degree of Nino forcing persists, In the more advancing mid summer centric focus, the evolved and evolving diagnostic proxies I think help assess the risk probability of amplification c/o -ve forcing in the Pacific as "restricted" and to take any amplified Pacific and Atlantic indicators from NWP as not sustainable on that basis. This would require a clear signal of shift in ocean>atmosphere regime and the Global Wind Oscillation, a key tropical and extra tropical indicator of global wind-flow, losing traction towards the lower octants of transitional/neutral phases 8,0,4 - with evidence of greater Phase 8 transitions which would suggest ever higher losses of momentum within the atmosphere as greater and greater amounts of westerly inertia is scrubbed out at the expense of growing -ve frictional torque at 30N in the tropics leading -ve mountain torque tendency at 50N in the extra tropics. However, the persisting pattern is one of the GWO maintaining a very tight knit orbit within the more +ve sections of the "transitional" wind-flow phases - and this is indicative of insufficient -ve wind-flow existing within the momentum budget to create any sustainable Nina-esque regime. There is no evidence, beyond natural fluctuation ebb and flow of wind-flow and torque mechanisms within a weak momentum budget, this is going to change much any time soon. With all this in mind, its sensible in my view to assess NWP cautiously against proxies and look at how they are reflected within the GSDM momentum flux and torque budget than attempt direct diagnostic > synoptic pattern matching. As interesting as that may be of course On that basis, extended ensemble and weekly outlook products require a regular updating watching brief based on diagnostic budgets first - rather than attempting working assumptions of how the diagnostics seem set to evolve according to whatever the numerical models might suggest.. Numerical models have biases, are characteristically prone to error reading the tropics at a given greater than 5/6 days ahead - and so therefore cannot always read wind-flow changes and fluctuations ahead which means they can be prone to change direction like shoals of fish in mid stream. As we all know, signals leads models. Models do not lead signals With that said *she reflects a little further *, I think that James assessment of the most recent EC weekly suite correctly identifies the Atlantic anomaly as part of a typical weak Nino pattern. I am also somewhat cautious in respect of the future modelling of the polar field and think that Tom's seasonal expectation of "spasmodic blocking" remains consistent with the medium and longer term - and with continued expectation of this to have a retreating tidal trend as the summer continues to mature. Tams Edit update : I think its worth me adding something wrt the GWO/AAM budget and the limited boundaries of ebb and flow I referred to. In the immediate term its true to say we are seeing something of a temporary divergence of this. The recent quite robust EWB in the EPAC has created an inverted wind-flow as momentum suddenly drops and a significant -ve NAMT has occurred this week. The two day lagged mountain torque budgets identify this clearly The extra tropical Global Wind Oscillation has responded with a jump out to -ve tendency transitional Phase 8 in response to the upstream wind-flow momentum drop This upstream vacuum creating extra amplification of the downstream omega block stretching from the Atlantic into Europe - with the Atlantic section of the block assuming dominance as a result of the temporary retrograde pull of the pattern. This has allowed the unusual situation of cool air advection being pulled around the strong upper ridge with a long fetch across relatively low northern Atlantic/Icelandic SST'S to the UK sharply undercutting an intense plume of hot upper air which by contrast is creating record breaking heat at the lower boundary layers across many parts of mainland Europe this midweek. EC map Atlantic/European view as of yesterday. A classic example of one occasion where macro scale wind-flow changes, which can be identified within GSDM diagnostic AAM/torque budgets, can be accurately pinpointed onto associated synoptic responses and produce micro scale contrasts owing to geographical location relative to the positioning of placement pattern features Based on the erasing of this -ve momentum wind-flow phase as the trade winds are ended across the EPAC c/o CCKW passage - the result looks to be a fast return GWO orbit back to the default prevailing wind-flow pattern. Hence NWP advertising the intense Atlantic amplification to cease the end of this week as momentum upstream recovers - and the ridge to edge back east and retreat through mainland Europe. At the same time the low level maritime cool air flow over the UK is cut off and due to be replaced by the residual hotter continental air for tomorrow and the first part of the weekend Further update based on above suggestion as quoted yesterday: Based on the erasing of this -ve momentum wind-flow phase as the trade winds are ended across the EPAC c/o CCKW passage - the result looks to be a fast return GWO orbit back to the default prevailing wind-flow pattern Evidence for this suggestion now apparent in latest European model trade wind forecasts with CCKW enabling WWB's across the central and eastern Pacific to replace the recent -ve forcing trade wind burst So this supports re-stabilization of the weakly +ve GWO orbit phasing as hypothesized previously
  9. A handy addition is that retrospective data That laddering upwards trend of the GWO progression through June 2006 tells the story for me - it depicts a slow steady consistent rise in +ve momentum transport through the month with a transition to the Nino attractor phases by late month. Therefore, as Tom alludes to, its not always the actual GWO wind-flow phase per se that matters 100% of the time (though it usually involves some kind of representative synoptic reflection according to time of year and associated seasonal wavelength, plus the state of the NAM) but the direction of travel of the atmospheric circulation itself. Seasonal wavelength changes play a large part with the signature Pacific amplification and downstream trough/ridge/trough sequence being most focussed at certain times of the year during primarily La Nina driven circulations. The converse holds true with the jet extension phases in the Pacific during Nino-esque +ve tropical>extra tropica torque transports where low pressure and cyclonic induced conditions tend to prevail as the upstream Asian-Pacific pattern is flatter and faster and with a more split jet aspect downstream. In summer , the Pacific ridge and downstream retrogressed sub tropical ridges underpinned by easterly trade wind prevalence as characterised by a La Nina trending atmospheric circulation peaks in July and August - so its quite conceivable to have a representative relatively higher GWO state (for example in low amplitude 'neutral' phases 8,0,4), say, in May and June - and still have an a-typical synoptic pattern produced by a misaligned tropical convergence signal matched in the Indo-Africa hemisphere rather than the Pacific - acting 'destructively' on the base state. This more WH tropical signal meaning that AAM tendency is restricted and hence the GWO, atypically, not in a representatively more Nino type phase As high summer approaches, and tendency tanks increasingly further -ve to couple with a change of location of the tropical standing wave to Africa and the I/O - the amplified Pacific and Atlantic profiles become completely defined and augmented by the seasonal wavelength - and this can lock in troughs on the 'polar side' of these upper ridges - perpetuated and sustained by the thermal differentiation of cool upper air and strong surface heating c/o maximum intensity solar insolation. Conversely a +ve trending momentum will systematically weaken these oceanic upper ridges c/o steadily reducing trade winds and the rossby wavelength starts to relocate the ridge and trough pattern accordingly - augmented by the forward moving changing seasonal wavelength. So its clear that in June 2006 there was a persistent 'constructive' trend to the larger scale rossby wave progression - and that despite the GWO being in low phase in early to mid June, anomalous circum-global Branstrator ridging was enabled at continental rather than oceanic locations at mid latitude in tandem with a definitively +ve AO mode across the polar field. This type of synoptic progression creating large amounts of atmospheric divergence as high pressure zones over large continental landmasses create huge upward spiking temperature profiles - with both surface and upper air profiles reinforcing each other in tandem dwindling soil moisture profiles and solar insolation feedbacks By July 2006 when seasonal wavelengths were most receptive to align with a +ve momentum trend, these anomalous ridges took on a particularly Nino-esque reflection and coincided with some of the hottest weather across quite a few parts of the Northern Hemisphere. In many respects this type of progression happened last year. The GWO was representative of anomalously low atmospheric momentum in the first two thirds of June 2018 - depicted by the GWO in high amplitude La Nina phase 2 However, as the momentum plot indicates, there was a sharp upwards +ve momentum transport surge at the end of June 2018 which resulted in the GWO very close to engaging the Nino attractor phase 5 by mid July. If this rally had not occurred as seasonal wavelengths dictated it to, then the anomalous ridging profiles of the first half of the summer would have re-configured to classic retrogressed Pacific and Atlantic ridges. Instead, it meant that the early summer ridging was able to peak well into July. Much s had happened in 2006. The remainder of summer 2018 indeed featured an increasing macro scale Nino standing wave influence - but the extra tropics continued to manifest mixed and sometimes -ve momentum aspects such that momentum fell back once more through the late summer - and no surprise the scale of the multi wave ridging pattern also started to break down once more - even though global relative AAM was up to 2SD higher than the low point in June 2018 Just to add to this analysis in respect of this summer - I think that judgement in respect of the Nino standing wave and longer term atmospheric angular momentum tendency trends, its sensible not to get too over focussed on trade wind shear effects,, but to watch the passage of the MJO related convectively coupled kelvin wave across the EPAC as there are already indications this may be induce cyclonic activity that proxy data identifies but is not so well identified by some of the generic modelling - and a signal that the Nino standing wave may start to re-engage in the medium and longer term. Its wise I think to differentiate between the effects of the MJO "mini cycle" and the broad-scale macro scale feedbacks which are determined by processes of upwelling and downwelling waves. It is quite conceivable that a downwelling wave in process may alter any pre-conceptions about any sustained -ve tendency returning following and which might be simply attributable to the next suppression phase in the Pacific - a quite natural part of the intra-seasonal tropical cycle. With the lagged effects of late Spring season downwelling effects in respect of final warming of the stratosphere largely extirpated, the tropics returns as a driving fulcrum within the extra tropical domain and will be more sensitive to wind-flow vicissitude and associated torque altercations and contretemps. Especially with a mercurial mix of momentum forces converging close to the dateline, and the extra conundrum of a twin standing wave in the Western Hemisphere which might appear to exacerbate mini ENSO phase -ve momentum tendency wind-flows at the expense of the wider tropical>.extra tropical ebb and flow. Very much a blurred edge and not black and white series of response mechanisms here. I am not a forecaster per se and simply an enthusiastic diagnostic and evidence based weather researcher, but too soon I think to try and make determinant judgements on the rest of this summer as there remains uncertainty about this in my opinion. Tams
  10. Hello Matt - that was a well laid out summary This profile shows the extent of the downwelled blocked -AO signature - quite the change from the late winter and early Spring +AO pattern Its interesting you mention 2012. That was a Spring and Summer that was completely the antithesis to the delights of the slow moving blocking pattern at mid latitudes that dominated from May to almost mid August last year. There are key differences this year in 2019 to 2012 however. Your very good analysis covers the +AAM regime well that has been prevalent for some months now - quite the opposite to the Spring of 2012 that was mostly low angular momentum dominated, apart from a brief attempted rally in late March, as transition from a prolonged La Nina (that had been entrenched since mid 2010) to a neutral state struggled to gain traction. Secondly, as part of the difficulty of losing the Nina standing wave, the PDO was stubbornly -ve. This Jetstream pattern manifests as increased flow across the top of amplifying ridges in the North Pacific downstream across the US to the Atlantic as a result of increased easterly trade winds in the tropics. Essentially the increased westerly energy at mid latitudes due to laws of conservation of angular momentum you discuss in your writing. The converse pattern is more likely in an El Nino pattern with Asian Pacific jet extension leading to a flatter cyclonic low pressure pattern in the Pacific and a downstream pattern that is echoed with a to further trough in the Atlantic and associated downstream ridge. Thirdly, in association with Spring La Nina forcing, the QBO phase was very easterly in 2012 - 2012 -16.07 -15.25 -16.74 -17.62 -22.04 -25.89 -27.82 -27.93 -26.60 -24.51 -18.95 -10.02 2013 -6.07 -1.23 2.85 8.39 12.64 13.38 14.27 14.66 13.12 11.69 12.45 12.55 2014 13.13 12.68 11.72 7.15 -2.81 -13.98 -19.29 -21.64 -23.24 -23.86 -23.65 -25.38 2015 -26.70 -28.62 -28.15 -24.38 -12.33 2.18 7.45 10.97 12.07 13.38 12.79 11.39 2016 9.34 6.77 3.16 0.64 2.37 3.86 6.25 10.07 10.48 12.83 14.16 15.09 2017 14.92 14.78 14.35 13.88 8.01 -3.18 -10.48 -14.42 -15.28 -16.79 -17.20 -18.12 2018 -19.02 -19.37 -19.77 -21.41 -24.23 -28.45 -29.10 -20.41 -9.91 -2.79 3.36 8.05 2019 9.02 9.25 11.82 13.36 - (April update) Calculated at NOAA/ESRL PSD 30mb zonal wind at the equator, zonal average For info https://www.esrl.noaa.gov/psd/data/climateindices/list/ - assisting the type of Brewer Dobson circulation between the tropical and polar stratosphere to help sustain blocking at higher latitudes following events like SSW in winter or final warming events in Spring. Due to the pre-disposition for seasonal wavelengths to carry on building an Atlantic ridge heading into the summer months which clearly can enhance any pre-disposition there already was to higher latitude blocking, its easy to see why a La Nina and eQBO pattern often brings cool and unsettled weather this side of the Atlantic - due to the persistence of the jet stream looping southwards around the blocking kept to the west. The washout of 2007 is probably one of the most definitive of e/QBO and La Nina summers - angular momentum collapsed spectacularly just as summer was beginning. A w/QBO often sees a relatively late break up of the seasonal polar vortex, and this year is no exception. Similar happened in 2011. But that year was in the middle of the extended La Nina and -ve PDO regime which overrode the signal for any +AO developing at the pole when the seasonal downwelling of -ve zonal winds at polar latitudes ended and kept persisting Atlantic and Greenland blocking going through much of the summer. So key differences this year that lend credence to the HLB giving way to a much more traditional weak El Nino w/QBO summer pattern. 2006 was a classic w/QBO and weak El Nino summer very warm pattern (which also had a poor May with Greenland blocking) There are of course caveats to this year in terms of the importance that the current very robust convectively coupled kelvin wave (CCKW) can draw co-operation from the ocean thermocline and help buffer El Nino which has been something of a wane period during the Spring after its peak in late winter CCKW modelling as per Euro model as part of fast eastward propagating MJO wave across the Pacific - and associated very robust westerly wind burst profile to the dateline In respect of this noteworthy event it will be interesting to see seasonal model updates - May is often a key month here.. Should El Nino rally once more, with the standing wave engaged in the Pacific and the atmosphere reflect a coupled feedback loop with the extra tropical GWO starting to repeat orbits returned back to the Nino attractor phases, then portents are good for summer. Different to last year in respect of the likelihood of no persistent ridge for weeks on end and the Atlantic trough and downstream ridge breaking down and re-setting and allowing thundery breakdowns, and then cooler changeable interludes leading to re-set of the default warm pattern. That is not a forecast - but its quite typically traditional weak summer El Nino. There is little danger of the southern stream getting too strong as it did in the start of the "super Nino" of summer of 2015 - its more a case of avoiding increased trade winds breaking down the trough/ridge pattern and creating a more persistent downstream trough instead. Especially because this years final warming has had a "dynamic" element to it, with considerable poleward heat flux drawn into the final warming and further amplifying the downwelling -ve zonal winds to the troposphere/stratosphere boundary. This might serve to give it that little extra resistance to the natural effects of seasonal wavelength changes and advancement of the ferrel cell in the tropics as assisted by the effects of wQBO usually creating an elevated tropopause due to westerly shear in the lower stratosphere Time as always will tell
  11. Hi James - yes agreed wrt GWO analysis I also subscribe to the view that the truth is that there is a danger that too much head scratching over a "failed winter" will actually mask the fact the departures have not been as great as believed. The peak period of winter cross section pattern is actually a good fit for highly amplified Nino attractor GWO Phase 6 where the main quasi extra tropical orbit has been focussed. The "missing element" to that height anomaly retro-fit is simply a -ve -NAO - which would have lead on to this as suggested by me back around Christmas in GWO Phase 7 The final third of January came within a hair-breadth of locking in the cold pattern that was trying to establish across the NH to mid latitudes - which the GWO Phase 7 coupled -ve NAM composite advertises. So margins on a macro scale separated only by subtle lack of some upstream split flow into the sub tropical jet flow (typical Nino response) and undercutting of blocking which would have adjusted the Phase 6 composite to show a greater Greenland height anomaly. That instead of the mid latitude Atlantic ridge and too much polar jet flow over the top which proved to the case (a-typical Nino response) But whichever way - a full appreciation of the GSDM diagnostic flags up the +NAM variant among the probabilistic solutions. More philosophical slant on this further down the post. So despite the stubbornness of the NAO reflecting various disparities between tropics/extra tropics and stratospheric domains, the general NH pattern has proved highly meridional as one would expect with a large amount of amplifying +AAM anomalies within the global circulation. Ultimately however they have been manifested within a sub tropical disconnect much more a-typical than one would expect of a high global angular momentum regime. Frictional torque tendency (as a measure of jet stream flow) has, too often, persistently reflected that -ve tendency with recurring easterly -ve wind-flow anomalies at 30N that have been part of the southern Pacific domain in an a-typical Nino (La Nina type) state. In turn, this being the mechanism to force inertia into the poleward jet rather than engage the expected sub tropical Nino flow , and associated more familiar PNA state facilitating greater downstream -NAO tendency, Also very much a season where an SSW in tandem with descending +QBO has also scrambled the usual tropical/extra tropical processes and resulted in usual meridional forcing associated with an +AAM regime being restricted to mid rather than higher latitudes. The above height anomaly cross section depicts the strong amplification within the troposphere - but with disparate MJO/polar domain that negated full engagement of the poleward +AAM planetary wave transport. at higher latitude But in more general perspective and somewhat philosophical terms: This maybe the third time posting, so please accept my apologies for apparent repetition, but the diagnostics are to blame for not meeting (high) winter expectations. Its attempts to try to fit those diagnostics and forecast them into one solution based on human desire to see it verify where the problem lies. If one is prepared to believe that the bias solution is one possible outcome (that can still be reasonably justified) amongst others that might equally verify - then its much more likely that expectations will be met and on that basis no-one should beat themselves (or others) up for it. However, if the diagnostic are narrow focussed to eliminate less palatable solutions, then be prepared to be let down- or, alternatively, be grateful of course if your preferred weather type happens to coincide with a lottery ticket. But don't let the lottery ticket be a fools gold to the usual truth.... and what might happen next time The majority of sources have pointed to increased chances of -AO/-NAO domain this season - whether that be enthusiast, pro met or collective national weather bureau. This increased possibility, using a variety of different (and also interdependent) methods have all come to very similar conclusions - (and on various occasions the numerical modelling has reflected those possibilities too.) On that basis, such analysis, very much including in this thread and other threads on this site, has been a joy to read, of excellent thoughtful and insightful detail and fully justified - and therefore the GSDM diagnostic should not be dismissed based on frustration of an expected favored outcome failing to verify to the extent hoped for/ The key is that a range of probabilities always exists and the best will be gained from these highly useful tools, if the range is always reflected in analysis. This is where weather enthusiasm and science have defined boundaries and while they can overlap and make the pastime/day job all the more worthwhile doing in the first place - there is no room for human preference in the cold science. If it is to be used properly. That applies to each and all of us - even if it contemplating the less appealing outcomes might appear to spoil that enjoyment. So its much less about losing trust, but in contrast much more about keeping trust based on balanced expectations and being prepared for bias to be exposed in the diagnostic processes within the atmosphere and the way the numerical models interpret them Also, the use of teleconnection science is an all year intra-seasonal process - so no need to let one season dominate emotions in that respect either I would look forward to the next season, and then the one after that as a means to move forward and not look back too much. The spaces in between (all the options), if they are allowed to be considered and their existence not denied , leave room for growth and yet more learning - that is the optimum reward in my opinion
  12. I can only really repeat what I have posted previously a couple of times already It is not possible to fit GSDM diagnostics and teleconnections in general into one bias preferred solution (at any time of year and however viable and feasible that solution may be) but especially also try to micro scale squeeze what are intended to be macro scale diagnostics into one very small region within a whole hemisphere the model attempts to represent., Error rate (and disappointment) is bound to increase particularly if all other possible solutions are discounted that the diagnostic might point to. The Global Wind Oscillation calculates changes in velocity and path of wind-flows as transported between the tropics and extra tropics, and represents them via a phase timeline plot. This timeline plot helps the observer identify the progress of momentum transport pattern between the tropics and extra tropics, and between the extra tropics and the polar field. But at this time of year, in the same way as disconnects can occur between the tropics and extra tropics, they also very much can occur between the troposphere and stratosphere when long track upper warming processes within the polar field are on their own very very slow and separate timelines to those within the troposphere. This, at the same time as poleward planetary waves c/o tropical convection activity is propagating through the extra tropics via +MT mechanisms and onwards towards the pole within their own timelines which are not mutually compatible with the downwelling processes within the layers of the stratosphere itself. This has already been covered in depth by @Isothermand others and needs no further comment. But notwithstanding any of that, its clear that the +ve torque mechanisms, and represented high state of relative atmospheric angular momentum in the GWO El Nino attractor phase 6, has already made changes to global wind-flows in terms of the wholesale changes underway c/o the very strong westerly wind additions added to global circulation (and compensating deceleration of AAM at high latitudes) . The term "attractor phase" is used to identify the full capturing of coupling of ocean ENSO base state within the atmospheric circulation that currently has excess westerly winds within the global system . NB The reverse holds true with the La Nina phases where -ve easterly trade winds are being added in the tropics and westerlies added at higher latitudes. In the current Nino pattern circulation, under the laws of conservation of atmospheric angular momentum, the surplus westerlies in the tropics and extra tropics are compensated by increasing (decelerating) easterly -ve momentum at the higher latitudes. This, in tandem with the downwelling SSW -ve wind anomalies means there is a clear retrograding element emerging to the tropospheric pattern with forcing c/o mountain torque replacing the Siberian Low pressure of previously with a Siberian high The watch during the first half of February is to see how far the SH retrogresses and links up with developing cold high pressure pooling over Scandinavia - as the Atlantic pattern starts to run out steam. *See also below related to EPS clusters for brief current suggestions offered that are related to this* So based on arriving at this position, , the GWO cannot have achieved a higher amplitude Phase 6 without poleward momentum transport of +AAM having already occurred. Its more to do in general with high expectations within various site forums and outside winter enthusiasts letting expectations of human bias preference oversee the emotion free dynamics of the atmosphere which operate according to wind-flow propagation timelines. A lot of NWP "model hugging" and a myriad of conflicting solutions present from endless operational and ensemble suites leads many observers down this path of frustration, and to consequently believe that it is the signals that are broken and not the vicissitude of numerical modelling. Everyone can of course be guilty at some time if we take the hemispheric deceleration of momentum into account as described above, then as far as the Atlantic sector is concerned, each breakaway area of vorticity from the fragmenting Canadian split lobe has been like a sprinter leaping off the blocks at high speed and then trying to maintain their speed ploughing into a deep pool of treacle.- as the poleward momentum transport processes evident of recent weeks - finally arrive at the tropopause at the same time as the downwelling processes from the SSW start to carve out upper arctic ridges Taking all the NWP caveats and caution of over-emphasis into consideration, I do nevertheless think that taking a look at the latest EPS height anomaly cluster spilt for the Atlantic and European sector approaching the day 10 period very well advertises an example of where the same processes as discussed above provide separate solutions, with different surface pattern outcomes downstream as to how the pattern may proceed - but both fully supported within the parameters of the GSDM diagnostic. Rather quaintly rustic as these plots are, I think they sufficiently depict that model calculations of the decelerating inertia of the macro scale pattern and appearance of cold ridges is being balanced by fragmenting pieces of ejected vorticity energy from West of Greenland heading into its pool of treacle in the Eastern Atlantic. The model currently shows within two distinct latest clusters a straight split between the energy being dissipated and disrupted under a higher latitude ridge expansion (amidst forward momentum running out of steam) , and the other solution showing enough energy to keep head NE with a less developed (at this stage) higher latitude ridge extension. So with this very latest type of matching outcomes with different surface interpretations in mind, from my own point of view it remains a fascinating but not a frustrating season. My my own weather preferences have increasingly become more and more separate and divorced over time from attempts to objectively learn the processes and try and find the right solution which is not necessarily always the preferred solution. There is always a long way to go with this and much to keep learning, but based on the fact that the GSDM has value intra seasonally, and is not merely a winter cold spell diagnostic assist, I am already looking forward to the coming seasons anyway, and the appreciations they can bring - irrespective of how winter plays out However, even from an attempted neutral stance I think that any "winter only" weather enthusiast waiting for what they would deem real winter weather should not be considering "throwing in the towel". and maybe seeing just how the models handle the next phase of the puzzle before they do so
  13. I think that @Snowy Hibbo has given a good and fair response to parochial interpretations of signals vs models vs outcomes. The post I made last week about the purpose of the Global Synoptic Dynamical Model continues to very much apply as always. I have snipped an extract from the pm thread that @Bring Back 1962-63@Isotherm@Singularity@Snowy Hibbo and myself pitch in and formulate some highly useful collective thoughts on the evolution of the pattern rolling forward and by means of illustrating that we are all the same page in anticipating the pros and cons of the hemispheric view as offered by the GSDM diagnostic. I think this puts in perspective that many of the enthusiasts and professionals are giving full consideration to the range of possibilities within the diagnostics and not just the bias preferred solution. Please bear in mind this section of discussion below was a week back and just as the crescendo of suggestion that evolution to -NAO was imminent and, as at the time, was gaining strong traction between the models. Very much including the EPS. My comments about the "other side" were in reference to an UK component audience elsewhere who were eagerly anticipating the -NAO and HLB as a given - when in fact other solutions, as always remained present. Tamara 308 Replied: January 14 Some different implications exist between the UK and the NE US. The thoughts expressed following Christmas wrt Canadian vortex and downstream pattern have been playing out quite closely in recent days and are arriving now at the point where the continued presence of the Azores high is defying the expectations of the masses in terms of the much touted flip to -AO/-NAO. If I had been still posting on the other side I would have given some analysis of why the Azores high is still there and why the tropical cycle is continuing to support its existence there for the time being. No time to write all that analysis at the moment. I expected something similar to 2012/13 to evolve around the festive period, and it has indeed proceeded about 70% the way there - and is currently stopping just short of it. The GSDM tells the story why.. --------------------------------------------------------------------------- I know that within the pm team others have given their own views about the NAM disconnect and rather than me quote them, I will allow them to provide their own views (if they wish to do so) as supported and agreed by myself, on the conundrums regarding the troposphere and the rather "destructive" aspect this has taken to the sustained reversal of -ve zonal winds in the stratosphere and diffuse response so far The GSDM diagnostic continues to support a very highly amplified pattern, But the diagnostic cannot account for how NWP interprets the signals. The key is to some stubborn a-typical Nino disconnect existing between the tropics and extra tropics that is propping up sub tropical ridging, in tandem with Canadian vortex that would retrogress under a more conducive Nino-like PNA pattern and allow mid latitude amplification to adjust poleward to Iceland and Greenland at the same time as the sub tropical jet stream (rather than the northern polar branch) is engaged by tropical convection imprinting the dateline. This continues to be advertised in the extended period in the same EPS suites that are referred to on this page, albeit there remains some mobility to the pattern rather than a sticking upper ridge. So the scrupulizing of models vs signals continues. But the signals lead the models, the models do not lead the signals. So a good reason to look to the models rather than the diagnostic for their own error rates of the signals when handling disparate stratospheric/tropospheric issues rather than refute the diagnostic itself. As long as minds remain open and not closed only to biased solutions, then the bias solution itself remains possible within the parameters of the diagnostic.
  14. The whole purpose of the Global Synoptic Dynamical Model is diagnostic to numerical model purposes in providing a very useful cross check to performance of NWP with regard to its identification of global wind-flow trends in both the tropics and extra tropics. Changes in inertia of these wind-flows gives a very helpful indicator as to whether jet flow, hemispherically, is increasing or decelerating and whether energy of jet flow is switching poleward or equatorward according to the laws of conservation of angular momentum which alter according to whether easterly or westerly wind inertia is being added to the global atmospheric circulation. Clearly, this helps pin-point when patterns are most likely to amplify in a given part of a hemisphere if one can identify where in the tropics and extra tropics these additions or subtractions of wind-flow are taking place - according to -ve or +ve torque mechanisms that reflect subtractions (jet deceleration) or additions (jet acceleration) of wind-flow. On that basis the GSDM is an intra seasonal diagnostic model which can help spot greatest amplified patterns at any time of year, of which in winter can both help create and augment SSW processes in the stratosphere that lead to increase chances of cold spells. However, like SSW's it is not a guarantee silver bullet to anything - and clearly if the diagnostic process is not used objectively to identify the whole range of solutions that may be present at any given time and simply as a means to try to fit the given signals to a biased preference outcome without considering the other possible outcomes the diagnostic presents - then yes, it will inevitably of course lead to disappointment. Therefore I would respectfully suggest that its not the GSDM diagnostics that "don't work", it can be the human interpretation or assumption of the model that it always leads down a golden path to a desired solution that doesn't always work. Because, that it not its sole purpose. As of the present time, maybe best to try to read between the lines with NWP in terms of the complex array of stratospheric and tropospheric influences and keep using the GSDM to help do this, rather than be disillusioned with it because it appears to be not serving its assumed purpose of fitting the signal to the bias preference Amidst the uncertainty and problems NWP is having with upstream split wind-flows, there are plenty of highly amplified solutions still within model suites this morning - and these reflect and jive with the present diagnostics. Its always a good idea in my opinion not to overly influenced by the vicissitude of numerical models, but to keep checking back on the diagnostics and simply sitting and watching. Kind of being proactive rather than too reactive. Models so often change direction like a swarm of fish in mid stream when they overdo one signal and then cotton on to what is really going on. A whole ensemble suite can be wrong if the model is misreading the diagnostic. Timing clearly also something that cannot be foreseen beyond the best evidence available at any given time The diagnostic always leads to the right solution - sometimes there is also the bonus that is also the preferred one, especially if the reliable signals of poleward rossby wave +AAM momentum transport are identified. These cannot be disputed - at the the very least increasing the chances of tropospheric higher latitude amplification- more so still, with a long -track SSW in town
  15. With the above suggestions in mind, and some 3 weeks passing since espousing thoughts, its time for some more of my own style of analysis The general timing estimates of pattern change from a static mid latitude pattern to one overtaken by stratospheric diminution looks reasonable value on the bigger picture evidence. Within the pm message thread that several of us exchange views, almost a couple of weeks back I focussed on those "provisos" I mentioned in the last full thread summary (as quoted above) that the lull phase of the MJO aka "mini ENSO cycle" would see a fall back in angular momentum tendency and provide a re-set of the pattern ahead of stratospheric diminution. This re-set manifested in terms of some jet retraction amplification upstream that would facilitate momentum within the branch of Canadian vortex and temporary inflation of the Azores high due to associated -ve torque mechanisms in the tropics. The net effect of this to steepen downstream thermal jet gradient adopting negatively tilted trough disruption in the Atlantic sector and falling pressure across the European sector. NWP is now well advertising this anticipated interim passage sequence prior to greater tropospheric/stratospheric coupling of the Northern Annular Mode. I also provided a background comparison to winter 09/10 in terms of the troposphere and the stratosphere displaying a reverse position that has accounted for a restriction to mid latitudes of amplification in the first half of winter 18/9 - rather than elevating further to the higher latitude blocking regime witnessed in the former. It is not the complete story as others such as Tom @Isothermhave covered in great detail and including another very thoughtful post by @Armando Smost recently. However, on the basis that much of the tropical and extra tropical GSDM forcing and associated Global Wind Oscillation behavior has been not too dissimilar to back then within the troposphere, it provides a good illustration of how an unstable lower stratosphere boundary with the troposphere (such as seen in 09/10) is quite capable of producing elevated latitude blocking under similar +AAM conditions and in the absence of, or prior to as was the case back then, of an SSW. I think, somewhat indirectly perhaps, this also helps underpin the disparate points that Tom was attempting to make the other day about the role the SSW and its relationship with the troposphere and how this needs careful interpretative analysis when considering seasonal potential impacts This time around, evolution to an SSW, along slow timelines of maturation downwelling to the stratosphere, is proving to be the catalyst for higher latitude blocking within the troposphere as the next tranch of Pacific forcing comes into view - and such HLB that has been absent due to a stable +ve zonal wind anomaly boundary existing between the troposphere and the reversal at the top of the stratosphere, and which is now finally concluding. So therefore, further to that introduction summary - here are the relevant extracts from my "thinking aloud" post in that informal pm discussion from back then Tamara 278 Replied: January 4 , I continue to think that the optimum time of the Nino tropospheric forcing now underway to "want" to forge a cold higher latitude blocking pattern is being cancelled out by the ultra slow mechanisms within the stratosphere that are stubborn in allowing tropospheric forcing to punch through into the lower stratosphere as I certainly for one was expecting about a week back to see well advertised in modelling day 10 radar by this time As suggested yesterday, its certainly a highly amplified tropospheric pattern with a classical look to the Pacific now (Aleutian Low in strong modelled presence). In this respect compared to, say, 09/10 - the troposphere is arriving at the same state as Dec/Jan - same Nino attractor forcing - "but" the stratospheric profile is completely the other way around to then. The first half of winter 09/10 featured a distinctly cold upper stratosphere but the lower levels were anomalously warm and unstable and highly receptive to the +AAM transport mechanisms and so therefore the amplified tropospheric pattern was highly perturbed within the tropopause layers This time around the unstable, receptive to tropospheric amplification -ve zonal winds are still tucked away too high up to massage the mid latitude pattern to the higher latitude pattern it would be otherwise. Hence why I said yesterday that the Phase 5 GWO composite had (has) the right shape to the textbook composite one - its simply adjusted several hundred miles further south than had been anticipated. This situation in terms of the tropopause will change - the question is will the tropical pattern still be as conducive to supply poleward amplification in the same places. My take is that the risk is increasing, with the delayed disconnect taking longer to complete, that angular momentum may well be falling back just as the downwelling process is becoming more receptive to upper troposphere/lower stratospheric amplification. This might mean that the Pacific starts to re-amplify and "advantage" for SSW effects occurs further upstream than downstream. This might well impact the CONUS with a blast of Canadian arctic air and then a gradient induced effect downstream in terms of seeing a suppressed invigorated jet stream and a cold zonal pattern. * --------------- * (Notice that the concluding paragraph posted some two weeks back, focussed on the evolution to the mid January link to further pattern change as previously discussed in last main thread post. It was not stating the current bridging pattern as any end conclusion) * So therefore what of the way ahead from mid January? I think that the slow evolution of SSW and re-set of the pattern c/o of temporary relaxation of poleward +AAM transport is the bridge that leads to the upcoming renewal of eastward propagating tropical activity to the Pacific which will fairly imminently serve to increase angular momentum tendency once more, retrogress the section of Canadian vortex and the Pacific pattern - and allow the deceleration of zonal winds across the polar field, as stratospheric diminution to take hold. Pressure accordingly rising to fill the inertia vacuum void across the NE Atlantic at the same time as residual trough disruption forms an eastward aspect to the developing-NAO - also concordant with increases the prospects for winter risk across the CONUS as the blocking mechanisms in the NE Atlantic and Iceland/Greenland develop and tend to retrogress with time Such a description fits well enough with evolution of global wind-flows to Nino attractor phases GWO Phases 6/7 c/o +AAM momentum transport in response to tropical convective forcing in the Pacific - and this tropospheric pattern in tandem with tanking -AO profile and representative of a likely destination ahead in the extended period and further into February.
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