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Tamara last won the day on September 5 2018

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  1. The coming circa 10 days are fully documented in the +ve momentum sequences and timelines as described in detail. In my own words, and not your incorrect interpretation, representation of them this translated to 'highly amplified' and not 'weak amplification'. The models are duly following an amplified pattern within the 10 day time period. If you must dissect mine or anyone else post please do not put words into mouths. Thank you. Is an amplification temporary taken in context of the period under the radar within my own post evolved? Its still late autumn for another two weeks. before winter proper begins There is much one *could* reply wrt Ed Berry's presentation and your own interpretation of what you consider short-comings, but this is not the thread for it and I suspect you would not be interested anyway as your focus skews approaches you do not personally subscribe to as restricted to the attaining and sustaining of cold weather patterns. However, the GSDM is created as an all year round diagnostic tool to supplement numerical modelling, not as a mechanism to fit signals/teleconnections into the desire for cold weather patterns 3 or 4 months in a year. I personally attempt to utilise these processes during the summer and adopt the same perspective as of today of fitting them to likely patterns and not preferred ones. Hence a pros and cons approach. Plus I do not pretend to be any self appointed clairvoyant forecaster anyway - simply try to progress understanding and learning. And offer a differing perspective that hopes to avoid too much bias loading. Orbit of the GWO through the Nino attractor phases does support retrograding to Iceland, Being a long post and only so much time and space to complete it, I omitted to state it and certainly accept that could have been made clearer- However, with that said and in support of the thrust I was emphasising - the focus was ultimately questioning what happens when the amplitude tropical forcing fades and angular momentum falls back. It seems you have chosen to omit that part to try to further discredit my post, A fall back in angular momentum would imply some recovery in polar jet flow and a possible return to a more mid latitude pattern. Clearly the Scandinavian ridge has mileage to support a higher latitude pattern in the medium term, but again in that post I was, and still am, seeing this in perspective of it being late autumn still and not winter itself This is the UK and not the tundra - putting aside the likes of 62/63 even the coldest winters are not uniformly cold and allow for relaxation of the pattern, Unless you are suggesting this is the start of a protracted uninterrupted 3 month freeze? Maybe you are suggesting just that, judging from your prophecy further down. Yes I had already fully anticipated you would scour it before your post appeared. Some things can be wholly predicted ahead of time. If I was making a 'formal' LRF (which I wasn't) and detailing every single forcing variable,(which wasn't the purpose of the post) I wouldn't have posted it in this thread. And momentum processes within the troposphere can be both augmented and detracted by unstable polar temperature and ice profiles. Again not the thread for this debate. Your own priority is to lead a charge for cold patterns and find reasons to support them both now and in the future. Different priorities, and also your own somewhat skewed (and incorrect) understanding and perspective of the GSDM, does not make the diagnostics wrong even if as a willing interpreter of the GSDM I am not bullet proof like anyone else when it comes to making forward suggestions based on them or any other method. Whether those are based on numerical models, or other approaches. Maybe you might include yourself in that bracket as a mortal who can (and does) get things wrong as well?.... .....Or perhaps not. You are to be envied and possess a certainty of the future that surpasses anyone (professional or amateur and regardless of contributory approach) and so there is nothing left to discuss And as stated previously, I'm heading back to my planet anyway So just let it snow.. See some of you maybe next year
  2. This quoted statement strikes quite a chord - looking in as I am from the outside of the thick panelled window of this particular utopian world The METO are professionals and interpret numerical model data, as well as utilising the considerable investment they have in tropical modelling - and make their own conclusions. As such they are completely divorced from any hysteria attached to weather preferences. One can of course dispute their own findings and conclusions based on other collective/ individual professional or amateur analysis and many rightly do this. Assuming that is, that such alternative offerings remain credible in themselves and designated such that the signals are derived from applied meteorological science, and so fit a realistic range of probabilistic solutions, and not merely as given lip service to try to fit an idealised one Sensibly, the Met are quite right to state things as they see them - and not instead on a regular basis feel obliged to please (and equally reassure!) their public of any perceived preferences they may have through making extemporaneous interjections in the interests of satisfying bias neurosis. Therefore as a consequence making a skewed mockery of probabilistic solutions (and making them redundant as a credible service provider at the same time!) On that basis, the idea of them trying to inject a little calm into the proceedings takes on a highly absurd quality if one stops to consider that the "hunt for cold" thread world is a very different planet - objectivity and non pre-occupation with ice age synoptics being deemed boringly alien and kill-joy because it spoils the entertainment and threatens a tribally protected species. So, with that in mind, some one-off attempted analysis before vanishing back to my own planet of Venus. Process of +ve momentum transport c/o CCKW driven tropical convection has been progressing through I/O and has spiked frictional torque tendency +ve with associated westerly wind burst anomalies representative of this around 30N (orange shading) The frictional torque response reflects the inflexion point of where additional westerly winds are added to the atmospheric circulation through progression of advancing organised MJO thunderstorm development - and convergence of macro scale wind-flows creates a turning force on the Jetstream and changes the direction of travel of relative angular momentum. So this increased +ve momentum transport and associated +ve frictional torque response registers immediately as a fairly significant spike in atmospheric angular momentum tendency - - A mechanism that leads towards programming the highly amplified pattern as advertised by numerical models within the atmospheric circulation, as according to the spatial poleward propagation of those +AAM anomalies over time. It is the lagged timescales according to this progression which provides the lead for further +ve mountain torque tendency in the extra tropics and sustains the amplified pattern through the majority of this momentum accounted for over the Himalayan ranges, setting up an extended Pacific jet and supporting phasing of energy into sub tropical flow (of which the models are presently balancing the equation over the medium term) The 'however' that is coming is that the adage is "what goes up must come down". Catalysts as they are for major pattern changes, there is no indication (to me at least) that the present tropical convection cycle matches those that have been a prequel to some of the classic early to mid winters. Meaning by this that the tropical signal aborting and losing amplitude sooner as seems currently likely than on those occasions implies a faster reverse scrubbing out of more sustained +ve momentum to follow that may, in turn, prevent the upscaling of the switch to an ever colder and colder pattern as some of the extended numerical model fantasy, filling the cracks of these pages, panders to. So a complicated sequence in terms of the lagged +ve momentum propagation which impacts the tropospheric/stratospheric pathway in the second half of November and reverse sequence to follow reflecting loss of the tropical signal which suggests greater polar jet flow in relative terms to the generally weak vortex and some relaxation, at least for a time, of -ve AO. This makes making any prediction moving forward sensibly erred towards caution this side of the glass window, and irrespective of any personal preference. Unfortunately the link to the consolidated Global Wind Oscillation plot has been down for some time to confirm precise position, But taking into account the relationship existing between an atmosphere co-operating well with an establishing Nino standing wave in the Pacific, as reflected by GLAAM retaining generally around a +1SD to parity... ….is suggestive and supportive of the GWO progressive into the El Nino attractor phase 5 (illustrative of +ve extra tropical momentum poleward propagation as discussed above) to be followed by an orbit through the Nino phases and depending on how far AAM falls thereafter, possibly returning to Phase 8/0. These phases within the tropical>extra tropical "mini ENSO cycle" being in simplest terms indicative of a 'waning' sequence during the major long term evolving +ve ENSO phase This forcing sequence roughly translates to the possibility of Scandinavian ridge and euro trough morphing into mid latitude Atlantic /UK ridge as the Pacific pattern re-amplifies somewhat (GWO Phase 8/0) following the relaxing of the +ve momentum phasing, switching some energy back into polar jet flow There is also a notion of argument to subscribe to, that the +ve QBO transition has already passed its optimum tropospheric/stratospheric disruption potential as it continues to downwell further, and moving ahead the onus becomes increasingly further on active amplitude tropical forcing resuming to re-stock +ve poleward +AAM transport processes and keep the tropospheric/stratospheric boundary unstable in the face of ever colder mid and upper stratospheric layers- and so manage to sustain blocking mechanisms at higher latitude. This occurred during early/mid winter 2009/10 under an emerging El Nino, bottom rung of solar forcing and being within -ve QBO phase and away from advanced westerly transition - but, notwithstanding polar stratospheric ozone distribution and concentration is (presently)elevated indicating the Brewer Dobson circulation between tropical and polar stratosphere is at least (currently) buoyant, the variables are not aligned the same this year. Any shortfall in all these respects renders the chances of a closer struggle between the upper and lower atmosphere, and a 'less warm' tropopause boundary which alters the complexion of the establishing Nino pattern evolving more towards a mid latitude European blocked one rather than one sustained long term between vectors at higher latitude to the NE and NW. Following what for some off us, away from the sole priorities of this thread, is a very pleasant and highly welcomed mid November week of weather to help save unnecessary heating bills, its certainly a cold outlook with perhaps some equally cold rain to match it and possible marginal wet wintry mixes for a few But whether it morphs into the freeze frenzy that is the utopian paradise the other side of the glass from where I am sitting, remains (at least in my humble opinion) yet to be seen.
  3. Yes I stated the other day that August had featured a cancelling out process of the tropics vs the extra tropics, but one that still appeared to be cuing up very nicely for the re-start of the next atmospheric circulation to resume the progress up to late July. Which up till then had beautifully read the script and meant that not just was the weather itself lovely to savour, but also there was satisfaction in seeing the difficult processes and explanations play out and provide personal happiness and enjoyment of attempting to oversee developments as well. Humility is indeed a vital quality, and one of the first we should all should try to eschew - but on the other hand no-one earns a salary to take time out to post on this thread and on that basis it should be a personally enjoyable and rewarding experience at the same time as one shouldn't be beholden to expectations of total clairvoyency in terms of suggestions made ahead as to how the patterns may evolve. On that basis maybe not too many apologies should be issued for not reading the weather patterns correct 100% of the time should be made - the likes of the METO as a professional institution would not provide a service at all if they had to issue apologies and explanations for every time Mother Nature didn't follow the best measured expectations. Additionally, the complexities of the atmosphere defeating human attempts to study them, does not justify those minorities who always seem to appear at these times to suggest the 'teleconnections don't work'. They almost certainly do work - its just the hardest task to try and understand them, relay and explain them - and those that don't try but criticise first and foremost instead - should practice their own humility first Such sentiments of humility within these contexts become even more important as the audience no doubt starts increasing and changes ahead of yet another autumn>winter chase for cold patterns. Its my experience that whilst most on this thread, and large parts of the site as a whole, consider the busy season the most exciting and absorbing, it is also the time that unfortunately humility is usually least evident. With all the above in mind, this is the last post on this thread of the sequence of summaries since May covering this wonderful summer season just ended ( a small few at least will no doubt be relieved and delighted to see the back of the never ending length posts) and it has been a wonderful summer despite the relative disappointments of August and the now apparent stuttering of developments for any further sustained warm and settled conditions in this month also. The starting point of discussion far back in May was whether the step change to a contrasting much warmer second half of the Spring from the first half would successfully negotiate the hurdles of previous years where warm late Springs have only led on to a downward path to cool and more unsettled conditions. The pros and cons revolved around stubborn persistence of La Nina type circulation lag set against the suggestion of gradual changes to more Nino-ish patterns in later summer>autumn and hence trying to 'risk assess' mid Atlantic ridge propensity for preventing warm air advection building sustainably (and more especially from the south) or, whether a greater eastward extension of ridging would prevent this happening (again) and instead , over time, encourage development towards trough activity to our west in the Atlantic and further assist plume like activity from a southerly vector to take over from the Azores High. As it turned out the ocean signal indeed continued to build towards an El Nino standing wave, whilst the atmosphere in terms of the extra tropics rather lagged the vestiges of the La Nina regime with low angular momentum and easterly trade wind patterns evident during June. The Atlantic pattern in the first half of summer was in many ways was not too dissimilar to a traditional La Nina summer pattern with the core heights centred around an intense sub tropical Azores ridge,and one which occasionally waxes but mostly retracts westwards due to the effect of upstream amplification c/o easterly trade wind domination in the Pacific However, this time around, the the unusually north and eastwards displacement of these core Azores/Atlantic ridging heights means that the downstream trough that is usually reserved for the UK and NW Europe was erased quite some distance towards NW parts of Russia So instead of customary low pressure upper cold pool - to the much greater extent and by way of total contrast, home grown heat build in situ from these ridges with the NW of the UK first to benefit from this. As the summer progressed, and as the Pacific pattern started to couple the atmosphere towards the steadily warming ocean signal, the pattern did indeed start to signal a gradual transfer of core heights NE - culminating in (what turned out to be) the one and only real plume scenario of the whole summer in late July with the much anticipated and discussed Scandinavian heights and Atlantic trough. More of these plume scenarios into late summer and early autumn were envisaged and commented on several times.This late July Pacific forcing passage has however unexpectedly proved to a brief culmination of steady development since Spring What was subsequently envisaged some four weeks back was a res-set of the late July pattern through the middle part of August to repeat the sequence during the last third/last week of August. As we know, and as has been reasoned and explained, this sequence was delayed and August turned out to be more changeable and cooler for longer than seemed likely. So to September, and the modelling expectations of upturn once more in angular momentum remain present, but seem to keep remaining in real time at the end of arms reach. This not just applying to the CFS and its well know biases (those starting to re-appear here for winter attendance should beware its tropospheric>stratospheric modelling) but the ECM is also proving culpable to its own biases much as the GFS with its own -ve tropical biases. *So famous last words of hers when she said that seasonal modelling of AAM had been proving reliable* Ha-ha! Another example of freely given humility.. Extrapolations of re-engagement of the Pacific standing wave have stayed around the equivalent of chasing optimum synoptics at day 10 with NWP. Instead we see a return to Western Hemisphere engagement of VP200 tropical convection anomaly at the expense of the Pacific. This renders suggestion of recently rather void that the opposite seemed likely to prevail in the Pacific instead. At the same time no surprise the African wave signifies greater hurricane activity transferred from the Pacific back to the tropical Atlantic. An echo closer to September 2017, and against wider earlier expectations for September 2018 The greater -ve tendency in the atmospheric circulation sees transfer into -ve Asian mountain torque tendency in the extra tropics This is the signal to amplify the Pacific profile through deceleration of the Jetstream there, and downstream retracts the sub tropical ridging in the Atlantic. This ends the recent attempts for Scandinavian heights to prevail along with the suggested longer settled spell some days back and also means that the attempted re-set of the ridge from the SW is more supressed from the weekend allowing the jet further south and greater trough intervention It had been envisaged the GWO might hold ground in weak signal and then resume progress to higher AAM orbit sooner. However, eventual capitulation in the extra tropics (as discussed above) has been sufficient to re-engage the Global Wind Oscillation and end the long period of resistance in weak and incoherent orbit with a move into low angular momentum Phase 1. This definitely precludes any immediate re-positioning close to the opposite end of the spectrum in El Nino Phase 5 (as briefly achieved in late July at 'peak' of the Nino standing wave development). Its now about revising expectations in relation to how the eventual natural upswing in the tropical>extra tropical pattern can recover angular momentum back to a lower amplitude Phase 4 This reduced orbit expectation wavelength is indicative of the faltering of development of the progress to the expectations of weak El Nino through this autumn and then into winter. Its not a preference of mine at all, but not a surprise either in the 10 day period to see the models move away from warmer and more settled solutions as the re-engagement of higher angular momentum tendency keeps being put back in time. Instead the mid Atlantic ridge is being programmed in most modelling at the moment to engage a greater balance of polar maritime air, keep the jet stream straddling close to the UK and prevent it lifting further north and allowing sub tropical warmth to approach from the south and build back an Indian Summer. This said, the GEM has been suggesting that some cut off may occur in the jet stream to our west and provide a break on advancement of the migrating Atlantic ridge and a loop of the jet to our S and SW to engage something of a plume scenario through next week. This is not an uncommon scenario based on past similar situations, and would be lovely to see emerge - though at present it remains a low chance probability. Something will give with this situation at some stage, as natural tropical.. extra tropical cycles dictate but essentially the low frequency signal in the Pacific has gone more AWOL since August at precisely the time that it was set not just to allow August to repeat the feats of 1976 and 1995 - but quite conceivably surpass them with a marvellous September as well. 'What ifs' and 'could have been' aside, its still been a fantastic summer and thanks should go to the regular contributors on this thread who have taken time to provide model sum ups and also enjoy the positivity of the weather suggested by them, at least until relatively recently taking the season as a whole. A long way it seems from now until next summer, but time never stands still
  4. The initial estimates, have proved to be a little on the extended end of the envelope ( and hence the fate of the last week or so of Augusts prospects less inspirational than hoped). But overall the pattern has progressed reasonably well in terms of expectations as expressed initially some 3 weeks back. The one part of the jigsaw remaining, and which has been proving slower still to appear ( up to now) than envisaged is an upper trough showing signs of diffusing energy underneath any of the blocking. This element is actually now materialising in NWP, however the suggested difference to the early analysis is that it might manifest itself amidst more of a -AO regime rather than the long prevailing +AO regime. Taken at face value, this implies quite a possible difference in surface conditions to those envisaged in the captured quote because a less +ve NAO set against a still prevailing +AO infers a mid latitude Sceuro block with upper trough in Atlantic disrupting to the SW to provide late season influx of humid air northwards (as per early August assessment) On the other hand, and purely at face value (which is an important thought to retain) a -ve AO profile suggests the type of smorgasboard on offer from elements of latest NWP - with cooler upper air seeping around the blocking re-positioned at higher latitudes and a hard to pinpoint array of shallow troughs appearing in the upper cold pools of these troughs, at the same time as the direction of approach from troughs approaching from the Atlantic suggests possible fusion with these shallow features to erode the higher pressure regime further and further northwards. But, as implied, this is getting way too far ahead in detail at a range that is still open to question in terms of why the broadscale changes are being suggested - and of course how likely and to what extent might they might verify. On that basis, probably best to do some analysis of events since early-mid August. to try to make sense of it all moving forward This period has been frustrated by some contradictory signals between the tropics and the extra tropics. The former attempting to resurrect something of a Nina flow with increase in easterly trade winds amplifying the pattern upstream (Atlantic/more supressed ridge and greater trough influence) and the extra tropics which have retained much of the westerly wind inertia of the tropical signal in late July (with the Scandinavian ridge and Atlantic trough that concluded the final days of that month) The tropical>extra tropical cycle is looking to set to resurrect this sequence again through September (as stated at the beginning, slightly later than first thought a few weeks back) and its no surprise to see the Scandinavian heights programmed accordingly. Total global angular momentum is currently broadly neutral... ..., despite the on-going lull in the low frequency tropical>extra tropical cycle and has been largely dictated by micro scale tropical activity to a small degree in the Atlantic but more especially the Pacific as one might expect with an El Nino standing wave erratically implementing itself. This balance of activity has helped support westerly wind inertia in the extra tropics whilst the easterly trade wind inertia in the tropics c/o -ve South Pacific Oscillation influence (SPO) and also weak phase of the low frequency signal since the start of August has been represented by -ve frictional torque tendency which is now starting to trend more +ve (ahead of likely changes upwards in angular momentum tendency through September as discussed later) The propagation of those -ve easterly winds in the tropics and subsequent degree of amplification in the Pacific has been negated of late in the extra tropics through the continued presence of the developing Nino standing wave and high levels of accumulated cyclonic energy (ACE) in the Pacific. Hence any -ve Asian MT tendency, which serves to help decelerate the jet in the Pacific in response to the lead set by -ve frictional torque tendency from the tropics, has shown a much more muted response to the previous (much greater) trade wind response that propagated to the extra tropics in early summer and prevented total global angular momentum from repeating the falls to the low point indicated of 8 to 12 weeks previously... ...and which at this time of year would be manifested as a very different outcome not just to the conditions of early summer, but to what we presently see nowcast synoptically according to the growing shift in seasonal wavelengths since then Kind courtesy of @Snowy Hibbo if we look at an ECM plot of forecasted angular momentum tendency,the advertised rise through September as mentioned earlier on, is in evidence. Backing up the CFS seasonal expectations (of which has proved a little progressive with the Nino standing wave) Note that both of these plots are overall tendency plot forecasts which have to be set against where total global AAM currently sits close to parity. The upward trend in tendency imminently commencing from the current 'low point' (and as indicated by the rising frictional torque tendency plot as above) helps bring about the re-set return of extended heights to the NE and the suggested approaching trough from the west to replay the sort of sequence seen late July. So this leads to the question of the suggested difference to late July in terms of the switch of heights from mid latitude orientation to progress to higher latitudes. A large part of the complex global blocking picture is the effects of a northwards recurvature of super typhoon Jebi through the North Pacific (with ominous threat to Japan), as part of a tropical>extra tropical interaction creating a knock-on anticyclonic wave breaking pattern which shakes up the NWP picture in term of trying to fit the precise positioning of these blocks set against the broadscale factors already outlined. There has been uncertainty as to the speed of downwelling westerly phase of QBO looking ahead through autumn (and then into implications for winter). This appears, to be now rapidly advancing through 30mb as is often the case when phase switches are becoming increasingly imminent Much the same principle as stratospheric vortex switch regimes, the advancement of +ve westerly winds starts flushing out the existing -ve easterly phase winds to the surface and these manifest themselves as they exit into the tropospheric surface level as +ve height anomalies. So on the basis of so many factors in play, then a lot of caution is needed in terms of NWP and how all the cards in the air fall to the deck. The background trend in angular momentum tendency to be rising through September well supports the overall continued evolution to an Atlantic trough and one which looks increasingly likely to undercut where the blocking mechanisms ultimately position themselves. The higher AAM potentially climbs through autumn then the more sub tropical jet energy seems likely. In terms of detail this is obviously almost impossible to gauge, but suffice to say and as per some previous analysis during August, the more unsettled conditions perhaps further south and south west and more settled the further north one heads. But with the suggested changes in latitude orientation of the high, this makes interpretation less reliable than was envisaged with a more mid latitude block. Nonetheless, with residual summer heat to the south, the track of any meandering troughs could have big local impacts in terms of boundaries of temperature and rainfall anomalies from one place to another. But I suspect based on the presence of troughs appearing more and more to the west and south west that any cool air filtering around these large ridges further north and north east is going to have a hard time this early advecting far south and west enough to the greater part of the UK and the potential remains for very warm unstable and humid air, (especially with SST's still close to peak from the summer) to be some influence furthest south.
  5. The best answer, in my opinion, lies within the bolded section of the first post extract made earlier this week. So no garden path exists so long as every operational and ensemble NWP set isn't taken at face value Latest angular momentum update c/o the Global Wind Oscillation continues to show the support from within the extra tropics to add westerly winds to the atmospheric circulation which essentially are helping to neutralise attempts to make AAM fall more substantively through easterly trades currently added within the tropics. This means a slumbering stalled orbit is in evidence reflective of latest weak low frequency tropical forcing signal rather than any orbit fall-back. This limits the degree of persistence of an Atlantic ridge as previously suggested and explained. . This willingness for the extra tropics to support angular momentum shows that the atmosphere is going along with the on-going slow and erratic movement towards a weak El Nino through the coming autumn. The presence of a further convectively coupled oceanic kelvin wave developed in the Pacific is, as Mr Ventrice describes, of a greater amplitude event than the one that helped propagate warmer waters across the Pacific during Spring and bring La Nina to a close in early summer - and should further help develop the Nino trend in the coming few months. This suggests further support for angular momentum in the longer term and also the prospect of a sharp upward surge in AAM tendency as soon the tropics spring to life again across the warmest waters of the central Pacific. With this in mind, many of these post summaries have anticipated an atmospheric response to ocean CCKW signal by way of an amplitude MJO wave, and this continues to be the case. Seasonal modelling maybe inclined to be progressive with this signa in the last couple of weeks, and I will happily admit my own weather pattern enthusiast wish to see this happen is hard to contain and not resist over anticipating. However, it still objectively looks to be a correct signal and should have impact repercussions for the global pattern this coming autumn based on timeline recurrence - and also quite possibly also for the development of the seasonal stratospheric vortex looking even further ahead on the basis of a perceived strong Brewer-Dobson circulation between the tropical and polar stratosphere this autumn/winter. In the meantime, latest ensemble means (ECM,GEFS and GEM) indicate (on the above proviso that one reads between the lines a bit when viewing them) there is nothing untoward at all suggested in my opinion. Further fine and warm weather still seems very probable into the new month most especially further south and east - and despite the expected changeable look to the weather heading through next week its notable how the Atlantic ridging of the more immediate term has been put into the more transitory perspective suggested in summaries of the past week to 10 days. Mostly a trough/ridge arrangement advertised and no sustainable ridge/trough - so with time a return to generally above average conditions for the time of year and still the opportunity for troughs to dig southwards to our west and inject greater humid warmth northwards and for mid level convective thundery features to occur - and that are not uncommon at this late season. These events are never especially well modelled and tend to come into full focus at relatively short timescales - but as long as the jet axis is generally SW-NE, rather than W-E or NW-SE - there is always a good chance for some extra amplification to inject some of the warmest air advection northwards September looks set for the time-being to continue to follow the long term dominant +NAO profile - but should that Pacific amplitude low frequency signal come into focus sooner than later - then this suggests the sub tropical Jetstream waking up a bit which would further upgrade late season plume and thundery prospects initially as the NAO becomes less +ve and encourages lower pressure to develop to the SW.
  6. Overall there is little I would change from any of those excerpts from the previous post. First the matter of the programmed Atlantic ridge as explained and discussed in previous post and now well within the modelling radar. It remains the case that the cool air Atlantic ridge sequence is a snapshot in time set against what has been and what is still likely to resume thereafter. It has to be said though, those of us wishing for a summer bank holiday to reflect the stunning overall quality of the season - that the weather looks set to certainly not read that particular script and the timing is quite unerring indeed. It is looking increasingly likely that the upcoming Bank Holiday, at least for many southern and south eastern parts who have been fortunate to see the best of conditions, will be the most underwhelming for a few years, Last year featured a fast track to early autumn conditions both prior to and immediately after the Bank Holiday, however the whole holiday weekend period itself was very warm and sunny for many at least further south, echoing that of 2016 and also 2015 which were both fitting for the end of season. Some enjoyable mid level plume conditions and evening lightning displays also added an extra element in 2015, and 2016 went on to feature these conditions well into September itself Another way of measuring related analysis to the programmed Atlantic ridge sequence, is the short term tropical convection VP plots that identify the loss of signal and meandering track to the Maritimes and emerging there by the closing days of the month. This is sufficient, in the shorter term, to be amplifying the upstream Pacific pattern and also pull the ridging pattern westward downstream and invite cool air advection from the NW. Much as described in the last post. However, the emergence of the tropical signal from the Maritimes (and then subsequent track back eastward into the Pacific) is what is a key to reduced trade winds serving to de-amplify the upstream pattern once more and help return to warmer and hopefully also more settled conditions downstream in our sector with time This links on to the updated zonal wind analysis below used as focus for those who wish to welcome in autumnal type weather and which reflects the interim short term loss of tropical forcing in addition to transitional CCKW across the tropical Atlantic (which was covered in last post). I think the particular point has been made before that taking these wind anomalies plots in isolation of the broader picture associated with it tells one part of the story but not the complete picture As hinted at above, it also means that any autumnal flavour to the weather is quite likely a temporary feature with further summer-like weather delaying the eventual seasonal changes that happened faster last year. This doesn't 100% guarantee any heatwave, though still plenty of time for one to develop in the new month, and still plenty good enough to continue to enjoy outdoor life for a while yet despite the B/H spoiling things for quite a few. The bigger picture, beyond the short term analysis, remains one of trying to assess the present lull phase in the tropical cycle and associated increase in trades against a larger atmospheric/ocean trend that has been heading in the opposite direction to any La Nina type forcing through the latter part of this summer. Albeit, with erratic progress which is now proving perhaps a little slower and more frustrating than seemed to be the case (hence the window for end of official summer plume that seemed possible in the last week of August has been put back a bit as just discussed) Its worth reading the attached link which discusses the role of the South Pacific Oscillation (SPO) in regulating the strength and influence of easterly trade winds (to which the immediate post under reply reflects with the short term zonal wind anomaly forecasts) The link was provided originally kindly courtesy of @Blessed Weather https://www.climate.gov/news-features/blogs/enso/look-south-enso-forecasters A +ve phase SPO suggests a weaker South Pacific subtropical ridge and weaker trade winds reducing the cold-water upwelling in the eastern Equatorial Pacific and allows for easier propagation of the warm waters from the Central Pacific to the Eastern Pacific. This is consistent with speeding up the development of an El Nino circulation and associated high angular momentum regime. However the converse holds true with a -ve phase SPO and this means that propagation of the warmer waters from the CP to the EP are slowed and retarded. This is reflected in on-going ENSO zone profiles. It doesn't automatically mean that an El Nino won't develop at all - it just makes it likely to be slower to develop in this instance and also much higher margins to be on the weak end of the spectrum and more centrally based. This summer the SPO has been in slightly -ve phase and this has been a factor in the erratic progress of the development of the Nino standing wave as just mentioned. The relevance of a -ve SPO to this thread and the synoptic upstream and downstream pattern is that the relationship that the atmospheric circulation acquires to the ocean base state is one that features a more amplified Pacific pattern with stronger sub tropical ridging in the Pacific when the tropical>extra tropical set-up allows it. Stronger sub tropical ridging in the Pacific in turn regulates the development and orientation of the Azores/Atlantic sub tropical ridging in our sector. When the trade wind effect is greater, -ve frictional torque around 30N (and associated falling atmospheric angular momentum tendency) creates the mechanism for amplification to occur upstream to retract the Azores ridge westwards and means that cooler incursions and trough influence from the NW is greater. As soon as the trade wind effect reduces, then the developing Nino standing wave Pacific pattern has chance to regain more influence as soon as tropical convection patterns create westerly wind bursts to de-amplify the Pacific pattern as AAM bottoms out and then rises back up - and in turn return the downstream ridge eastwards and reduce the influence of polar maritime airflow with the jet axis SW-NE rather than W-E or even NW-SE. Such a more "Nina-like" sequence with the jet pattern switching to a more looped southern track occurs later this week before the pattern attempts to return to the flatter more cyclonic Pacific pattern that allows greater downstream amplification of the Azores high in the UK/European sector rather than to our west. This is yet another further element to the GSDM diagnostic process. Knowing how the upstream pattern is affected by factors such as these is a help towards determining how jet flow and trough and blocking features may also behave further downstream. So how much is the developing Nino standing wave likely to be "destructively" affected by any interim trade wind anomaly? With a new CCKW presently passing though the Pacific, easterly inertia is likely to be mitigated in the short term and then developmental to resumed progress in the medium longer term Additionally to this, the presence of a further CCKW in the Pacific also adds weight to the expectation of that low frequency amplitude MJO wave to develop across the Pacific as part of an atmospheric response to this. Signs of this starting to happen are discussed above. Furthermore, the CCKW passing through the Pacific also supports development of "non low frequency" activity in the form of cyclones. The tropical modelling (up the page) is starting to reflect the following on upstream pattern change more clearly on a shortening time period and this helps start to increase confidence that NWP will carry the signal forward more consistently and with better continuity. Both types of tropical activity, low frequency and non low frequency, are conducive to supressing trade effects and replacing with westerly winds that add an Asian jet extension across the Pacific, de-amplifying the upstream pattern - and, downstream from this, reversing the ridge/trough pattern in the Atlantic and returning the jet northwards once more - that is, following the loop south over the short medium term. NWP has kept the signal stubbornly beyond day 10 in recent days, but cluster and ensemble data should start to read better developments and though next week may still take a few days to settle down beyond the cool and changeable holiday weekend - things still look reasonably set for more fine and warm summer-like weather to return at the turn of the month and heading into September Latest 0z ECM clusters and GEFS ensembles continue to reflect these much improving prospects by the end of the month. With all the above in mind, there is much to agree with this third highlighted post. I would question the first and second lines though. From my own point of view there is no need to be silenced by any NWP currently (or indeed at any other time for that matter) and as based on attempted forward looking assessment. The end of week and B/H has been well anticipated in recent days and continues to not require any further reaction beyond what it is. An autumnal interlude as a snapshot in time that is best put into perspective of what preceded it and also the longer range likely perspective of which your final sentence quite reasonably assumes Personal optimum preference would certainly prefer ridging setting up just to the E/NE to invite a quicker route to plume scenarios and southerly winds. Up till recently this seemed quite possible. Though cautionary reality now suggests initial position of ridging my be a little further west ridging into the UK and across mainland NW Europe as dictated by the Azores ridge. Which in itself is not an unwelcome prospect by any means
  7. The ECM difference you illustrate as measured by the Global Wind Oscillation in reality being in "transitional" Phase 8 as of yesterday 14 August.... .....rather than heading through low angular momentum La Nina Phases 1 into 2, (as suggested at face value by those operational outputs a week out) which models a sharper Atlantic ridge and hence greater cool air advection from the NW than has been the reality The reasoning as so often discussed in these posts being the degree of upstream amplification in the Pacific which serves to retrogress the high that is downstream from this in the Atlantic - and with the polar jet pulling troughs around the top of the high c/o of a more NW/SE axis. If the model overcooks the upstream amplification, then it overcooks the polar flow and looped jet axis Looking at the Pacific we see an increase in trade winds (covered in last post) following the passage of westerly winds c/o tropical activity which is now in end/re-start cycle - simply a natural pause in the tropical cycle and coinciding with CCKW towards the Western Hemisphere. Its this that modelling is jumping on and gunning for as pattern evolution to Atlantic ridge. This actually mirrors the sequence during the first half of July - the difference being that the trade wind increase is set to be weaker this time (albeit seasonal wavelength changes since then mean that the polar Jetstream is rather naturally adjusted further south according to this latest global wind-flow position than earlier summer). Notwithstanding that, the significance of the trade wind increase being weaker compared to back then is that in related terms, global atmospheric angular momentum is significantly higher than it was in early-mid July - - so extrapolating an establishing mid Atlantic ridge ahead on this basis needs some care and caution and none of the usual MOD discussion premature declarations in terms of an early autumn (beyond a possible transitory cooler interlude) This isn't 'teleconnections' saying "No" to an Atlantic ridge either - its an attempted diagnosis as to how likely a wind-flow pattern is to assist it developing and lasting for any meaningful time. Compare current AAM establishing closer to parity to the more -ve longer term establishing pattern of August/September last year c/o the persistent easterly trades and La Nina standing wave. N.B Its seasonal wavelength changes that are the essential importance here which heighten the Atlantic ridge synoptic response to -ve AAM conditions from mid summer increasingly into autumn This on the other hand looks very much like a transitory phase and certainly not a shift regime phase such as was seen during late July and August 2017 where a persistent signal for a mid Atlantic ridge in late summer and early autumn was well supported. The summaries since May have been covering this aspect and fully anticipating it and stressed the differential as to mid summer crossroads *should* a La Nina type signal persist (which it hasn't) and force the first half of summer Azores ridge eastwards extension to retrogress and force a homogeneously distinctly cooler, showery and unsettled second half of summer countrywide - such as seen in 2017. This clearly has not happened and instead we have seen a more traditional UK summer pattern emerge, still largely warm or very warm at times further SE and most changeable and average conditions further NW. The jet axis favouring tropical maritime, mostly, rather than mostly dominating polar maritime influences Compare a one year snapshot of tropical activity imprint of summer 2017 to summer 2018 A stark difference - and emphatic evidence of the role that tropical>extra tropical momentum transport has played in sustaining programmes of amplified late spring/summer ridges, whilst the standing wave regime of last year and associated lack of activity allowed a much more repressed Azores ridge to take over semi-permanently the closer high summer approached and Atlantic/polar maritime regimes increasingly prevalent Its also clear from this year how the mid to late July low frequency signal has transferred to the Pacific rather than defaulting back to the I/O and the relevance in that sense as to where we are in the current tropical cycle to early-mid July this year is very similar. Its this benchmark that the remainder of the summer and heading through September is best assessed in my opinion. This means that, overall, we should expect an Atlantic trough (not ridge) to prevail) and a case of looking for signs of the next Pacific low frequency engagement to re-emphasise a sharper trough to the west and south west and downstream European/Scandinavian ridge CFS vs 2 seasonal modelling identifies the next Nino standing wave engagement with associated surge in angular momentum tendency and tropical momentum transport beginning around the last week of the month and especially into September. Such a surge sharply reversing any interim easterly trade wind burst, and with it, any intuitive reason for mid Atlantic amplification to prevail too long Anticipating ahead comments about CFS capabilities here - these daily updated angular momentum forecasts have been consistently flagging this next upturn - and proving highly reliable and useful guides since becoming available c/o Victor Gensini maproom. Dr Gensini is co-working on developing further this maproom faciility to include further and larger data-sets with Ed Berry (former NOAA scientist and co author of the GSDM) Based on NWP behaviour since mid summer, then confidence in picking up extended signals in good time and then carrying them forward consistently is pretty low to say the least. Much as the mid July period, the models were as suggested at the time blind-sided and over pre-occupied by the tropical phase lull and were programming a mid Atlantic ridge and downstream trough to take over from the sustained heat of early to mid summer. This clearly didn't happen and instead over the ensuing days the path to a plume c/o Atlantic trough and Scandinavian ridge and a reload of heat into early August came into focus instead. In conclusion, in my opinion anyway, best to perceive any Atlantic ridge programme as a temporary blind-side to the bigger developing picture and no permanent feature- should it evolve to any extent in the medium term. Focus looks very much on an extensive ridge adjusting east with time (if it doesn't evolve more quickly from within the circa 10 day modelling) ahead of a defined Atlantic trough. As so many recent updates have suggested, this keeps prospects of further plume scenarios very much alive if nothing for a pinpoint micro scale island such as this can be guaranteed by anybody But as late winter 2018 starkly showed, it makes little difference to the weather if a season changes, it will do what it sees fit regardless
  8. Yes that is right, the GSDM is essentially a diagnostic tool to both assist and check the NWP interpretation of global wind-flow (the jet-stream) as measured in both the tropics and extra tropics. As a checking mechanism, it is used in a direct practical reality - and is therefore much more than mere theory I think that separating the tropical element (MJO) and extra tropical element (GWO) as a means to try to debunk the rationale shows an inherent lack of understanding of the actual purpose of the GSDM itself. The GWO, as the extra tropical element of the GSDM takes account of the momentum transport of frictional eddies in the jet stream caused by changes in direction, convergence, speed and velocity of wind-flows, and then the subsequent propagation of these frictional eddies via mountain torques leads into rossby wave dispersion in the extra tropics - that links global >regional scale circulation anomalies. Putting all this into less presentational and simpler terms, it becomes possible from this process to match up the identified circulatory anomaly framework from the diagnostic approach (global and/or regional anomalies) with the one identified by the commonly recognised numerical modelling systems. Hence some extra insight into NWP performance and accuracy. The purpose of the GSDM is not in any way to replace numerical modelling but it is a highly important diagnostic supplement to it. Such a circulation anomaly as above, is a sum of all its parts. With such a critical link in mind, discounting the influence of upstream signals in the Pacific as only having any influence on the US and not the Atlantic /European pattern appears to pre-suppose that the jet-stream ribbon (as measured by GSDM diagnostic) gets off a train at Myrtle Beach and boards a disconnected line somewhere off the Eastern seaboard of the US Its also clear that accuracy and correlation will not be obtained alone through the use of MJO composites, because this is just one element of the GSDM and leaves out extra tropical responses as described above. Rossby wave dispersion from tropical convective activity propagates to the extra tropics according to its wavelength - (i.e how far east and at what amplitude it propagates within its usual 30 to 45 day periodicity cycle) and as "a mini-cycle" in itself that is where the ENSO link is made as determined to where the base standing wave signal exists which the low frequency MJO signal attaches itself to. The relevance to this particular summer is the slow transition that has been underway from La Nina base state towards, of late, a very weak fledgling El Nino state and how the ocean>atmosphere link would evolve according to this. As you correctly say @Singularity much of the focus has been around how fast the transition between Nina towards Nino would occur, but again to re-state, the talk here is not about the base state per say - but about how would the atmospheric relationship to the ocean base state play out in terms of the tropical/extra tropical interactions as described above to link global and regional circulation anomalies. And we think of the Atlantic and European regional circulation anomaly as being as much linked as the Pacific/US regional circulation anomaly is to the global circulation as a whole 'Teleconnections' has become a very overused and over applied word. The diagnostic process of the non numerical model is much more than mere indices teleconnection play-matching. The GWO composites, as a mere end product of that diagnostic process, are made up of the tropical and extra tropical element aggregate of global wind-flow according to the ocean/atmosphere relationship relative to the base state. Whilst its true that these composites can be used more reliably towards a pattern guide than any MJO composite - for the reasons clearly given the emphasis remains firmly on diagnosis rather than pattern match and theory. Certainly for someone like me who isn't at all interested in being any competitive forecaster, but simply looking at what might supplement/influence the direction of NWP and making suggestions according to this. Interpretation is required according to any given number of variables that might be present at a given time - and as such any rolling assessment of a given pattern or change in pattern is taken on its own merits rather than relying on any analogue. Less theory and more reality. I think that any emphasis on this type of model approach being theory rather than having any direct practical approach can be behind the attempts for a few, usually the same few, thinking (wrongly) it is easy to discredit. But, hopefully that is the very last time, any of that needs to be repeated... ….To the present day modelling: The last post on Friday GSDM raw data identified the GWO in Phase 4. Phase 4 of the GWO identifies westerly wind bursts being added to the global wind-flow circulation which start increasing momentum flow across the Pacific and a split-flow occurring downstream of this energy which separates a downstream trough and subsequent ridge. The amount of amplification of this ridge is determined by the degree of split of the flow coming from upstream that determines sharpness of the pattern. In this type of scenario, according to the current seasonal wavelength, increased upstream amplification (lower AAM) will produce greater amounts of directed polar jet flow downstream and provide initiative to the trough and produce a flatter ridge response further downstream from that. The converse holds true. Subsequent update of that raw GWO data (two days + consolidated) has identified the initial calculation as too progressive in upstream momentum (and hence too much downstream split-flow amplification) and the GWO has remained at a lower amplitude and more indiscernible signal Phase 0 than initial raw data suggested. We can only work with the date we are supplied with - that is the same for any computer supplied data. Working ahead from this changed starting data to assess ahead, this will account for the apparent continuing stubbornness of NWP to not amplify the ridging more than seemed logical from the former data The present GWO amplitude is also reflective of the fact that the tropical cycle in late July was the first one to engage the newly developing Nino footprint in the Pacific and it served mostly to wipe out the greater excesses of easterly wind inertia accrued through two years of La Nina lag which has been taking its time to be eradicated completely from the global atmospheric circulation.This is accordingly set against total global atmospheric angular momentum levels which are reflective of the GWO orbit position and has been hovering either side of parity. The GWO vs GLAAM position at any time is an excellent barometer to gauge perspective of how much the tropical cycle may serve to change and evolve the global vs regional anomaly patterns (linked to above discussion) Relative angular momentum tendency has recently stayed buoyed up through the persistence of tropical activity in the Pacific (non low frequency signal). This has been keeping angular momentum in a holding position till the next low frequency tropical cycle arrives as catalyst to boost the extra tropical circulation via another surge of poleward momentum transport and boost amplification of the pattern. Further poleward momentum being a signal for another rise in both relative and total angular momentum and reflecting greater advance of the atmosphere in embracing the growing El Nino signal in the Pacific. A fly in the ointment over the coming 10 days is the passage of a convectively coupled Kelvin Wave traversing the tropical Atlantic (dampening the Pacific storm signal temporarily and providing a window for Atlantic developments) at the same time as the low frequency MJO signal is ending latest cycle in readiness for the next. This will possibly see a short phase of greater trade winds keeping the lid on angular momentum briefly(and facilitating Atlantic tropical storm development before suppression occurs once more). This also means the broad-scale downstream pattern is unlikely to amplify sufficiently in this time to shift the Jetstream further north to encompass the greater part of the UK. It seems this is also combatting a greater temperature gradient relative to late summer polar vs summertime tropical cell Taking all into consideration, not too bad an outlook overall at all further south bar a few days, but something of a frustrating spell for those further north with support for the flatter changeable pattern and the north/south split into the last third of August, It looks to me as if the ensemble data continues oscillating around the position of the jet relative to the restricted amplification equation (for the time being) within a narrow upside/downside pendulum. The 12z giveth and the 0z taketh away etc. . But the lack of faith in NWP picking up signals coherently with poor guidance and continuity in extended data (and professional extended forecasts flip-flopping accordingly), the lack of pay cheque involved in making any suggestions ahead of time (whatever they they may be), and just the plain old devils advocate in me still clearly sees the potential magnitude of the next tropical signal cycle into the Pacific (echoing the synoptic passage of late July) and setting up an end of season plume scenario as discussed in the last post
  9. Scattergun ensembles do not mean this, as expressed in a typically over dramatized and extrapolated ahead context as given here Which leads on appropriately to a rather more objective, helpful and considered post: I think your analysis sums up well why there is no reason to over dramatize or extrapolate ahead the present pattern for the whole of this month. An examination of latest EC clusters play with the continuing theme of Atlantic trough and downstream ridge and the truth is there are only modest adjustments required in the solutions that dig the trough further south to put a subtly different complexion on the pattern. This does, its true, mainly apply further south at least to begin with but ramifications over wider distance still apply and have support. Mindful of the fact that the GWO has quickly returned to Phase 4 after a full orbit previously into Nino Phase 5 in late July …. . ….as reflection of how angular momentum is embarking on a long term trend to different territory than the previous two years, then its a matter for the tropical signal to add that small extra bit of extra downstream amplification to accentuate the trough/ ridge pattern and adjust the ensemble suite pendulum onto further support for the greater warmer advection solutions that already exist and reflect the readiness of the anomalous warmth that remains very close to our shores throughout this more changeable spell to spread back across the channel. The degrees of adjustment here are really quite small to make subtle but quite real differences within how the macro pattern affects the micro UK pattern. A good example of why this type of non numerical modelling diagnostic approach is a macro scale guide and not intended to try to second guess detail at distances which is always highly unwise anyway when NWP itself has a spread of solutions within a same theme. Hence just one real expression and interpretation of ensembles that are scattergun - but better explained than simply taking one solution as influential for weeks ahead for the sake of the pessimism attached to it, or just simply plucked out of the air for the pessimistic gut feeling associated with it. Even as it stands, taking a look at the graphical spread of solutions from the EC 0z, these are not exactly a terrible spread of London ensembles for what is the least underwhelming passage of weather in a summer that has been truly remarkable for its absence of anything like it, Yes, it is London representative for the UK which looks set to see regional varieties abound in the coming days, but it does look like the operational, even within its own cluster may be rather too aggressive with the greatest influence of the trough later next week. And that suggestion also allows for the temperature gradient issue correctly pointed out. Usual caveats anyway here with ensemble suites exists - based on them being merely snapshots in time. The "worst" solutions here are also evident within the GEFS suite, and which take the upper trough furthest east - are based on the very lowest angular momentum side of the envelope which has the tropical signal furthest west. Much as discussed recently. Even if this did happen, it would simply be a delay to recovery and hence why some professionals will rightly currently be hedging bets in terms of their extended forecasts. The effect of any suggestion of delay in some quarters on this forum however, seems to take on more magnitude than reality - simply because we are coming close to the final two weeks of official summer and some kind of irrational "time is running out" extravagancy takes over But the weather does not eschew the enchanting human habits of a weather forum that has self imposed cut-off dates - and if it wants to, then September as in reality we know, may quite easily be a further extension of what has largely preceded it in overall weather type this summer. Much as last September, in contrast, ushered in an earlier feel to autumn than accustomed to in recent years. The Global Wind Oscillation will be the best guide here to gauge the progress of the tropical signal and the subsequent impacts on jet stream wind-flow in the extra topics. Based on its current evolution and associated AAM parity, and based on likely future tropical>extra tropical evolution, that continues, until of if any evidence to the contrary appears, to suggest that some model correction to some of these coolest and most unsettled solutions lasting longest - will see them outed as the more counter intuitive. That doesn't mean the current changeable spell isn't supported within the 10 day period, but it does mean that distinct regional variations may well occur within this time and it also means any extrapolative negatively worded suggestions out to the end of the month (and even beyond) do not, at this time, have any justification - beyond taking opportunity of some less favourable weather to over agitate the closer perspective... -and of course the thread itself.
  10. Almost a week on, and against the efforts of the models to progressively remove the signal as described in the caption extract, the signals have been fighting back. It remains sensible to view NWP from outside the inner circle. Cluster and ensemble data also hampered by inconsistency and erratic perceptions. Current steer from the Global Wind Oscillation is a slow low amplitude orbit underway circa Phase 8/0 which acknowledges the degree of re-amplification there has been upstream in the Pacific (as outlined in the most recent post ) through this week and injected just enough energy into the polar jet downstream to edge the heat into the nearby continent. But the models have been blind-sided by the tropical activity in the Pacific that flares up in addition to any low frequency signal - and which they are often slow to respond to. Hence the out and out trough solution suggested in recent days for the weekend ahead of an amplified Atlantic ridge, has been watered down and greater downstream ridge persists instead. This in turn has altered the apparent evolution for that once depicted upstream ridge to move eastwards and try to settle things down into next week. However, this is far from the end of the story. Worth taking a look again at the implementing standing wave pattern in the Pacific and seeing how the July pattern started to adopt to that in terms of position of tropical forcing. Which @Singularityhas already alluded to. The outlook remains focussed around the difficulties NWP is having related to this regime - in the short term, the flare-ups of more micro-scale cyclonic forcing in the Eastern Pacific which adds positive wind momentum upstream and cancels out this weeks attempting amplification (upstream). This activity is superimposed onto the moving on of the cyclical low frequency MJO signal before re-starting its new timeline eastward cycle. The Hovmollers wind anomaly cross section also depicts this positive momentum in the Pacific clearly close to 180W This means that resolving troughs and ridges downstream within an apparent upper westerly flow into the medium term is not straightforward and subject to further amendment within closing timescales. Then into the medium and longer term itself the re-engagement of the low frequency signal itself with the Nino standing wave which is highly likely to repeat the sequence of late July once again. The re-entry point heading east from Maritimes within last third of August. There is little point in posting deterministic modelling of this that far out at this stage - as progress of developments with the usual 5 days, let alone beyond it have not been reliable. This ultimate destination of the low frequency tropical convection signal in later month involves, downstream, the re-implementation of a substantive ridge to the NE, likely overspreading an amplified upper trough that is perhaps more likely to dig southwards and become slow moving to the SW as opposed to the more progressive west>east solution in late July. The ramifications of this are highly interesting indeed for those of us who want summer extension to take us through to conclusion and beyond : More settled, but most especially the further north once heads and always a good chance of mid level convection and thundery potential showing up due to destabilisation c/o of the stalling trough to the SW spiralling up some embedded features in the humid airflow from the south to keep folk entertained with some light shows in the darker mid evenings - and still plenty warm enough for many to keep sitting outside and enjoying themselves In that sense, it could well be the summer officially finishes not too dissimilar to how as it was ushered in during late May. There is credible evidence and reason to support such a scenario, which also is not also unnoticed by the professionals in the extended outlook over and above any weather enthusiasts of this site - so on the basis that none of us are paid to make suggestions or predictions, then what the heck, lets have some fun and see how it unfolds Finally to complete the post and in relation to the continued process that underpins its logic and conclusions: I think, yet again, some further repeated correction needs to be given to a few posts made since the one under update consideration - in respect of the El Nino (standing wave) and its alleged lack of effect on our downstream pattern in summer, or at any time. The emphasis of this continues not to be the base state itself as I see repeatedly still keeps being incorrectly misrepresented regarding these summaries, but the changing relationship the atmosphere is adopting to on-going slow shifts in base state and which do impact on synoptic changes from upstream. One cannot deny that changes in jet stream profile upstream in the Pacific will not impact on the downstream pattern - and in this sense it is not wise to take NWP at face value where there are complicated and sometimes contradictory signals occurring upstream. This principle applies such as it does currently in summer as much as it does in autumn, winter and Spring. This atmosphere/ocean relationship is not linear as this year has proved so emphatically - with the east based La Nina providing a very different winter (also relative also to the stratospheric state prevailing back then) than commonly seen under "traditional" La Nina's where the tropical signal is much less eastward. than it was. Similarly there are a-typical El Nino's where the most common atmospheric responses expected are altered in state. But the point is we can take each on its own merits and then identify how the atmospheric relationship may, or may not be altered from this state and then see how other factors may also augment or detract from them The whole purpose of this kind of GSDM analysis is to widen the parameters and hence open minds to possibilities within NWP, not straight-jacket them into x+y= *one size fits all boxes* based on any given base state supposition
  11. Data/substance to validate the workings of the Global Synoptic Dynamical Model is readily updated and available each day. Here is a current example to show it working in real-time and how it becomes interpreted by NWP from upstream To do so, its necessary to return to the frictional chart plot posted the other day and use a grab from weather satellite imagery in the Pacific to illustrate the development of -ve frictional as shown in the GSDM plot around 20N. The plot clearly also shows the last -ve frictional torque wind anomaly (in blue) that occurred around the similar location during the bigger trade wind burst in June. I'm not sure that the satellite image will show when posted beyond a still image (?) but the full real-time moving image can be seen from the main link. Anyway, from the imagery the storm cloud is depicted heading north westward from the tropics in association with a current uptick in trade winds which are scrubbing out some of the westerly wind bursts in association with recent passage of MJO activity. Also visible is Hurricane Hector south of Hawaii. The poleward fluxing of the activity in the Western Pacific is driving the -ve frictional torque where it meets the westerly winds on the poleward side of the jetstream. The result of the fluxing of energy is to amplify the Pacific Jetstream and drive disturbances downstream across North America. Further downstream in the Atantic, the pattern manifestation is an Atlantic ridge. The effect of the -ve tendency fluxing in the tropical Pacific is is for atmospheric angular momentum tendency to register it as a fall - due to greater net easterly winds being added to the atmospheric circulation than westerlies at the given time Taking into account the lifespan or wavelength of the frictional torque, then extra tropical lag will entail the Atlantic ridge pattern and trough solution next week as greater energy is directed into the polar jet downstream from North America.. However, with the El Nino standing wave developing in the East Pacific and associated low frequency tropical signal defaulted there, total AAM (allowing for the fall in tendency) in the global circulation remains close to average with much less scope to fall back than June/July - ahead of future further rises it is a matter of time before the tropical signal re-emerges to scrub out the trade burst, de-amplify the Pacific and return to the pattern that continues to further establish the El Nino configuration across the Pacific - and the return of the Atlantic trough and downstream ridge beyond the mid month period. So the whole point of this analysis, and all other analysis before it is the breakdown of the tropical and extra tropical interaction within a changing ENSO regime that has bearing on evolving synoptic patterns through ocean/atmosphere coupling - and not the ENSO regime itself in isolation.
  12. A raft of data (GSDM data as produced by its author Ed Berry from NOAA) has been posted and explained in detail that correlates tropical momentum spikes to synoptic responses taking into account the timelines of propagation of rossby wave eddies from the tropics into the extra tropics. That does not constitute waffle.- at least not in my own world. The reproduction of a composite for ENSO region for a given month does not account for the tropical>extra tropical cycle that exists as a "mini ENSO cycle" within the principle base ENSO state. It is this that fluidly alters the synoptic response - and any smoothed out composite is going to completely obscure those distinct variations according to the MJO and other variations of tropical cyclonic activity that actually often account for more than just the MJO itself. So as a means to dry to dispel the point I was making it is meaningless and ignores the devil in the detail. Such devil in the detail means each situation taken on its merits. I would take any composite also within the GSDM model with the same reading between the lines - which is why I often do not post them beyond very occasional rough illustration purposes and try to attempt some individual human interpretation. I didn't directly link the SSW with summer conditions - what I said was that if the troposphere>stratosphere link via tropical momentum can lead to an SSW (and which you have previously not accepted despite what you say in reply here ) then the tropospheric link wrt momentum transport also exists in summer.. On that basis, the two reanalysis charts you produced for April and May are at cross purposes to what I actually said. I was referring to the switch from -AO/-NAO profile post SSW to mid April and the sudden switch to +AO/+NAO profile from mid April at which time there was a further eastward MJO cycle which perpetuated a blocking regime in mid latitudes (as distinct to the higher latitudes in late winter and early Spring). The point was that tropical momentum processes played a part in both the SSW and the synoptic response in April- in quite different ways. So of course the geopotential charts for April and May are different as a whole - and again they smooth out the distinct change that happened in mid April which was wholly different to the first part of the month and I happen to know I fully documented at the time. Using data of which I have no plans to waste further time re-posting now to satisfy some cross purposes Neither have I said that AAM defines circulation at any time or anywhere today or in the past. I have consistently said though that changes in tropical momentum are responsible for torque mechanisms in both the tropics and extra tropics which cause changes in angular momentum responses. Identifying changes in trends in angular momentum tendency also therefore identifies that a change has happened to global wind-flows due to tropical/extra tropical momentum changes - and this in turn implies that regional global weather patterns may be impacted to some degree or other. In acknowledging the work of Lorenz, Ed Berry is able to rubber stamp the GSDM model as a means to augment medium and longer term modelling as diagnostic to NWP using exchange of momentum within both the tropics and extra tropics c/o an AAM budget to define how synoptic changes may occur. So cross purposes have, again, been created by your response in relation to NWP. I am not going to supply data from months and months of posts previously made and would consign such a discussion to the teleconnection thread if there was anything to be gained by doing so - which in this case there clearly isn't. The smoothed out analysis you have provided does not disprove my own position - its merely an aspect of cross purpose from a different approach to try to debunk it as waffle.
  13. There are correlations made pretty much every week with evidence firmly based on tropical>extra tropical momentum processes that are (and have been on countless occasions) fully identifiable and demonstrable in real-time. That is, if one is open minded enough and prepared to accept a full diagnostic approach to global wind-flow and Jetstream behaviour that uses a phase framework to identify how accelerating and decelerating wind-flows and changes in their trajectory relate to anticipated pattern change. This process is actually relatively easier to accomplish in the summer in the absence of the traditional winter-time polar vortex - which much more closely defines a relationship interplay between the troposphere and the stratosphere that affects pressure patterns close to the ground. In that sense, upstream developments in the Pacific linked to ENSO, have less feedback interference in the summer and can be even more easily correlated. I read @Singularity post as a reasoned and measured assessment as to how the synoptic pattern might evolve - one that reads between the lines of, rather, than takes NWP at face value. I would also personally , as per usual, question any post that makes definitive conclusions about NWP and then attempts to extrapolate these forward "with some degree of certainly" to use your own words. I know your stance earlier this year was to reject any part that tropical>extra tropical momentum processes played in the SSW this year (and which in terms of the tropospheric pathway came about through the east based a-typical nature of the La Nina composition in the Pacific). However ,and alternatively if one does accept the very real part played in ocean/atmosphere feedback in winter through tropical convective imprint of such an ENSO arrangement that propagated to the extra tropics and then to the polar stratosphere via mountain torque mechanisms - then why should the relationship be different under an ENSO regime in summer where rossby wave dispersion wavelengths have evolved further towards a warmer sub water and SST ENSO imprint since the winter, and we have seen how such a process has resulted in the anomalous ridge arrangements seen since the final -AO effects of the SSW diminished during April ? Once cannot deny the timetable of events as has occurred and deny one part of an equation, yet accept the other. As much as you most certainly accept stratospheric dynamics and post as authoritatively and "with some degree of certainty" as you usually do on them - but reject as unproven the tropospheric tropical momentum>extra tropical momentum processes that are trigger to events within the polar field. These processes do not take a holiday in summer along with the winter-time polar vortex. They are intra-seasonal phenomena that are in a permanent state of flux and occur 24/7 all year round. In terms of the present pattern, as discussed in recent posts, the switch east in the locale of low frequency tropical convection is set to dominate the synoptic pattern for the rest of the summer and into official autumn. I think based on recent evidential analysis, this can said with at least a reasonable degree of confidence, if like everything else it can't ever be said with wholesale certainty. On that basis, and as @Singularity quite rightly reasons, the newly establishing El Nino standing wave as governed by this low frequency tropical convective signal in the Pacific is going to ebb and flow around downstream trough/ridge solutions in both the Pacific and Atlantic. It occurred at relatively short notice in the models after mid July and this pattern is ever more likely to recur and keep recurring the longer times goes on. While the signal does ebb and flow and is never wholly constant, it is not wise in my opinion to extrapolate an Atlantic ridge and southward digging trough solution sustainably longer term- and better to try to measure intra day NWP not as face value absolute, but as a snapshot in time. Signals dictate models, models do not dictate signals....
  14. A lot of responses/feedback about the diagnostic approach encompassing varying aspects of NWP analysis. Some misunderstandings and incorrect interpretations of the purpose of this approach continue to need clearing up - plus also some credit needs to be given for some of the very good efforts made to explain some aspects of the angular momentum budget 1) So to start with the credit first and foremost. That is to @[email protected] Poole for their attempted analysis of the GSDM budget. It doesn't matter that some of the analysis would need some amendment because its hard to understand and my own understanding is still growing all the time, despite getting a useable grasp on the principles which is very rewarding from an enthusiast point of view.. The most important thing I think, is having a go at testing out new processes - making mistakes is the way to learn and no-one should be nit-picked for failing to accurately match the right solution to the pattern every time on day 1.000 let alone day 1. Its a tough audience at times on here, though the majority always seen to welcome these posts as much as the very good general NWP analysis from various many quarters on here. But the GSDM itself is highly complex and I struggle to convey the complexities sometimes to split the technicalities into simple English and would apologise for not always succeeding in this process.Its all well and good me understanding what I mean, but that doesn't automatically transfer to every reader. To this end, I would freely admit a mistake yesterday was attempting to explain links that I had access to but did not know at the time how to copy across to the post page. I'm not known as "technophobe Tamara" to a few who know me day to day for nothing! Anyway, *I think* I have resolved this thanks to a crash course on Windows 10 screenshots - and trusting that copyright of these is ok. A couple of the images and some re-attempted explanation relevant to current NWP will follow in this post 2) @Singularity refers often to the NWP reflections of Nino and Nina type forcing that I do myself (and his back-up on this is something I highly am grateful for) In context of this summer most every post has referred to these with reference to the expected synoptic patterns they represent. Reanalysis monthly and seasonal posts are also not my technical strong point, i.e condensing the succinct pattern that has been observed vs the expected one - but suffice to say my easiest answer is not the easiest and least time-taking to complete in practice. It is to read/re-read the continuity of the summaries since May, which are deliberately quite often re-copied (under self-reply) as a means to help continuity and understanding as well as to openly check progress of expectations. Its my own layperson way of re-analysis, and as someone who doesn't profess herself to be a pro forecaster - it works for me anyway 3) With all the above in mind, then it surely mitigates any charges of having ego and/or being condescending. I think if people are going to make such assertions then they should be made with sound justifiable basis. Positive criticism is not a bad thing, but its quite reasonable to have re-course to object to unfounded personal criticism. I regularly state there is no exam to pass or best forecaster competition on here - and at times the over competitiveness and endless countering of right vs wrong does spoil the gist and whole point of the thread. 4) The purpose of the GSDM analysis is not to replace or be better than, say, analysis of the upper air pattern via the NOAA maps. This is something that crops up sometimes both summer and winter. As just said above, there is no prize for best method or best "forecaster" who uses whichever method. But it is there as a diagnostic tool to help check the movements and likely future movement of the upper air pattern. After all, the GWO is a plot depiction of net global wind-flow - which is essentially a trace of the Jetstream itself. And as we know, placement of pressure patterns is dictated by the Jetstream ribbon. Knowing when the wind-flows are accelerating and decelerating, energy is likely to switch northwards or southwards (where and when) is surely a valuable assistance check to the upper air pattern and in turn a check on the accuracy of interpretation of NWP. It is simply impossible to explain the whole modelling concept of the diagnostics in one post, but it is possible to keep putting "live" analysis of the current state of play into practice and start building a picture. Hence the purpose of the continuity analysis as a means to try to do so 5) The purpose of the GSDM is to add substance to the upper air modelling on a macro scale basis. It is not intended to micro scale pinpoint temperature anomalies within the UK and precise conditions on the ground. However, it is not possible to get any idea of the micro scale details without accurate representation of the macro scale pattern first. Attempting to criticise the diagnostic element in this respect, as one such post has done since yesterday evening, rather completely misses the purpose if its objective. Its not mere teleconnections either - any diagnostic of the jet stream itself is more focussed than just anticipation of pressure placement according to various indices tools. 6) And so back to the present position itself and a further attempt to pit the background to the NWP As stated yesterday, total angular momentum has arrived at +1SD (standard deviation) above parity - representative of transfer of location of tropical convection forcing into the Pacific and help the changing ENSO base state and atmosphere couple together in reflection of a newly establishing El Nino standing wave. The cyclonic response as indicated by the depicted tropical convective anomalies in the Pacific are evidence of shift of the tropical signal to one that is characteristic of an establishing El Nino standing wave Transfer east of the tropical signal has the effect of changing the feedback of rossby wave dispersion which adjusts the longwave response to where amplification of the jet occurs further downstream. The importance of this synoptically is the appearance of the Atlantic trough/downstream ridge pattern of late which has been distinctly different to much of the earlier summer. An Atlantic ridge with pressure drop downstream is characteristic of a more La Nina like synoptic response - due to the longwave amplification occurring further upstream in the Pacific which has the effect of bolstering high pressure in the Pacific with a downstream high pressure response in the Atlantic The effect of pulling the Azores/Atlantic ridge westwards allows the polar jet to run across the top and down the eastern side of the downstream Atlantic high pressure. Clearly this is generally not an advocate for high summer temperatures usually - and encourages cool air advection to sink south This summer has been an anomalous exception to the rule. The low angular momentum conditions seen during mid June to early July resulted in the expected Atlantic/Azores ridge anomaly, but this has been unusually northward displaced and aided by the definitively +NAO tripole in the Atlantic, and kept the polar Jetstream much further north than would usually happen under -ve GLAAM conditions. This is not the thread for a thesis to look at causes of Summer 2018 heat, but there are various aspects of relevance here to take up from this Jetstream pattern analysis As also stated yesterday, tropical forcing has now subsequently lost amplitude in the Pacific and the result of this is to weaken the downstream amplification response and aid influence of the trough in the last few days. Atmospheric angular momentum as a consequence starts to fall from its peak. The GWO in relfection of this moves from the +AAM phase 5 towards what is called a "transitional" phase 8. What this means essentially is that the pattern is re-amplifying upstream as the momentum associated with the Pacific forcing wanes and easterly trade winds start to increase. The blue shading on the zonal wind anomaly cross section indicates the uptic responsek in -ve easterly wind wind-flow. Where wind-flows change from the westerly wind bursts associated with tropical forcing to the re-establishing of greater easterly trades (however temporary) - a torque is created by the turning force of the conflicting wind-flows. This is essentially represented by change of trajectory and speed of the jet stream and comprises a frictional torque. Greater net easterly winds at this location at the expense of tropical convection westerlies creates a -ve frictional torque and is the signal for relative angular momentum to start falling back. The manifestation of the rossby wave signature of this eddy created in the Jetstream is the new site for amplification of the pattern. The greater amount of easterlies added at the expense of westerlies, the larger the fall in angular momentum and the greater the upstream amplification and downstream response. This fall-back phase in AAM is registered in various monthly seasonal suites - it is model interpretation sensitive to the tropical pattern and its depiction of thr rises and falls of angular momentum accords to how the model perceives the tropical pattern unfolding. The CFS gets criticism for its modelling, but in term of seasonal atmospheric trends it proves a worthy assist to guidance and should be trusted I think much more than its NWP interpretations of pattern evolution. Clearly, the trend is not for much downside to angular momentum which endorses the background detail attempted yesterday to suggest that any amount of retrogression of the pattern in the further outlook should be taken with caution. More to the point, sustainably. @Man With Beard cluster analysis is a good illustration to me of recent suggestions I made that interirm solutions are not necessarily end games and also why I continued to recommend taking output, including the NOAA representation of NWP with equal caution. I trust its understood that is not to denigrate the NOAA upper air assessment - but simply that precise placements of features are especially critical looking ahead as to how surface conditions on the micro scale detail play out. Attempting such detail at any distance is prone to error any time - but especially at the moment. As far as I am concerned the macro scale outlook has not changed and it seems to me that incrementally the modelling is correcting westward positioning of the pattern in the shorter-medium term and better modelling the cut-off low feature that helps determine advection of heat in the weekend and into early next week period. However, beyond this and more particularly the extended period, some of the modelling (including clustering) looks dubious to me, especially how long any retrogressive lower angular momentum element manifests itself - and its best a wait and see is adopted and for now at least, not take each and every operational and ensemble suite at face value
  15. With extreme heat gathered to the south of the UK, various extrapolations being made about how this heat might manifest itself over the coming period with some very close boundaries between hot and extremely hot and a lot of chatter today on this thread about NWP signifying a restricted and only temporary heat back up again for southern UK- then it might be a good time to step back yet again for a little further diagnostic analysis to the numerical modelling (which obviously includes the NOAA charts as best representation of consensus of NWP upper pattern modelling) Caution is always the watchword with putting total faith in all numerical modelling ,more especially at times when atmospheric imprints are in the midst of undergoing a flux of seasonal change such has started to meet some of the Global Synoptic Dynamical modelling expectations of the summer. It is these signals that are leading the models, not the models that are leading the signals. The pinnacle barometer through which this diagnostic approach is viewed is the Global Wind Oscillation which gives a day by day reflection of global wind-flow inertia - so that a check for accuracy of Jetstream strength and trajectory in the tropics and extra tropics as measured by NWP can be used as a very helpful check for macro scale accuracy looking ahead. . Pseudonym names such as the GSDM and the GWO (and associated interpretations of their use such as ordinary members like myself try to provide) are viewed as jargon, hubble bubble and pretentious waffle by a parochial and cynical very small minority -- when in truth they prove themselves a valuable assist to reading between the lines of NWP and its own reading of the upper pattern - and providing some insight into where it might evolve differently to what is suggested at any given time So, what do we see: The GWO arrived at the El Nino attractor phase 5 in the latter part of last week. This as explained in the previous couple of posts is symbolic of wind-flows in the tropics and extra tropics having stronger westerly wind inertia representative of more El Nino forcing - than that of its counterpart La Nina which identifies greater easterly trade wind strength in global wind-flow. The repercussions of greater westerly wind inertia mean higher atmospheric angular momentum is added to global wind-flow as manifested across the Pacific ocean due to the tropical convective signal moving eastwards from its La Nina former standing wave position in the more Western Hemisphere. Synoptically speaking, looking downstream from the Pacific Ocean this means that the added momentum de-amplifies the upstream pattern with increased cyclonic activity in both the Pacific and the Atlantic. Each respective trough of course is interspersed by a downstream ridge. Our downstream ridge as manifested over Scandinavia reached its maximum influence coinciding with the peak of tropical.> extra tropical momentum as measured by the GWO phase plot in Phase 5. That is not a coincidence in terms of the greatest warm air advection being felt as a result of the maximum peak of downstream amplification that occurred under the rossby wave dispersion of high angular momentum wind-flow. In the last day or two, the Pacific tropical signal driving the downstream pattern has waned and the MJO has weakened and lost amplitude. As a consequence the downstream pattern changes as the westerly inertia driving the pattern peaks and then starts to decrease - this translates in the first instance to less control/de-amplification westwards of the Scandinavian ridge and greater influence of the Atlantic trough as the ridge loses its influence to its west. The first place to feel these effects, being at the crossroads of the Atlantic Ocean and the European mainland just happens to be the UK. Hence the first real cyclonic influence felt in the UK for a long time occurs at the same time as the passing from the peak of the highest +AAM momentum transport since the temporary signal leading to the SSW in February. Again not a coincidence - its an exercise in how the atmospheric parameters move within flux boundaries which shift according to how much capacity inertia the global wind-flows can accommodate a given pattern. This comes to the more tricky part in terms of the further outlook. At least its less tricky for me because I have access to the GSDM map room as used to be freely available via the NOAA. The problem is that the map room is password secured and seems to now be just "view only" and not possible to paste the links as I have discovered. Suffice to say, minus, alas, the posted image, total global atmospheric angular momentum is measured at +1SD above parity - reflecting the latest modest GWO Nino attractor phase 5 orbit as discussed above and the trough/ridge regime. As can be seen from the spider graph further up, a fast orbit of the GWO has started to be underway as westerly winds are scrubbed from the atmosphere and angular momentum falls from its peak due to the loss of the Pacific tropical signal. The key to the outlook, both shorter and medium term, and based on the newly implementing weal El Nino standing wave, is how far angular momentum falls back until the tropical signal re-engages the ocean/atmosphere coupling in the Pacific. What NWP is constantly updating at the moment are representations of how far back it thinks AAM may fall at this given time before re-set happens. With the pattern upstream in the Pacific being less flat due to momentum reduced (jet deceleration) this means that a reverse process happens to previously and the resident ridge is retrogressed, with time, as greater overall easterly inertia is added to the atmospheric circulation. In the shorter term there is some corrective consensus to keep the ridge very close to the UK. The net effect of any retrogression beyond the shorter term obviously is to allow greater energy into the northern branch of the Jetstream in the Atlantic to flow around the ridge and affect how far north the greatest heat advection from the south can move. It only requires slight miscalculations of energy either way though, to make subtle, but in this case very large and spectacular differences in surface temperature observations. This is where some differences in the modelling start to become apparent with the positioning of the ridge - albeit the NOAA charts sticking with the more withdrawn ridge and (relatively) greater polar jet flow around the ridge. But the outlook is fraught with possibility for error - in the shorter term if the models overcook the ongoing loss of momentum then further corrections eastward, however slight, will upgrade the heat further (and further north). The converse is true of course. In the longer term, should adjustment of angular momentum and inertia be wrongly calculated - and especially if the tropical signal re-amplifies sooner, then the suggested upper westerly pattern c/o NOAA will also be overcooked because the downstream ridge will be more amplified and allow greater than currently suggested warm (hot) air advection Based on where the ocean/atmosphere relationship and overall AAM tendency is, plus continued support of global torques in the extra tropics (image again cannot be supplied) then the window and range for AAM to fall back is much more limited than it has been for a long time - and this also adds caution to the equation. AAM tendency is still supported from the extra tropics. despite the reduced signal from the tropics in the Pacific So its worth stressing, that any suggested timetable has to be realistically have flexible expectations and could be quickly scrambled if the next tropical/extra tropical momentum phase resumes sooner than later or if the modelling over estimates previous Nina lag feedbacks and is forced to adjust the pattern. With that in mind, due to the upstream base state shift in favour of El Nino (however slight), the envelope for this timetable does have a limit, so something will give either way and the odds favour added momentum prevailing longer than less momentum. So care needed with all NWP face value assumptions - very much including interpretation of the upper anomaly charts which are also obviously subject to possible change from what they might suggest in the medium term.