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Tamara

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  1. My own summarisation of prospects for this season to date has been concluded, but before that happens, I cannot leave the quoted post remain unanswered as it requires 'outing' for its wholly unacceptable misrepresentation and inaccuracy of reporting. I suggest the poster reads in full the posts to which he is referring and which he clearly has not already done and furthermore should acknowledge that quoting posts, and in their full context, is the respectful and reasonable way of reference rather than this kind of exercise. The diagnostics have pointed persistently to split outcomes this season - as identified some time back in the second half of Spring. There has been more than enough repeated attempted guidance as to how the conundrum of the stratospheric final warming vs the tropical/extra tropical circulation feedbacks on the pattern may run into some major headaches for NWP modelling. Others too have clearly endorsed such views in their own attempts of assisting deciphering these complexities. There is every evidence, as already correctly documented by some in this thread that the intense dynamic blocking responses of the last 6 to 8 weeks are coming to some resolution - and some comparisons were made a couple of weeks back by myself with other years that have shown similar stratospheric/tropospheric downwelling evolution as this year. Amongst them, 1995, 1997, 2009 and 2013. Two of those, 1997 and 2009 also showed very similar low frequency tropical signals to this year. More of that later. But taking them all together, a variety of different synoptic outcomes verified through the course of these summers but I am not going to waste yet further time referring back to any of this. This year, for what it is worth, it has stayed my view as per some weeks back when these seasonal updates began, that once the -AO forcing over the polar field started to respond to summer wavelength changes (and which it is now showing quite clear evidence of doing) that the fate of the summer synoptics would then be more clearly in the hands of the tropical/extra tropical cycle and whether this shows either: A) a continued risk to adopt -ve momentum tendencies c/o of an amplified upstream Pacific pattern and associated persisted trade winds resulting in a retracted Azores High downstream and added polar jet flow keeping cool Atlantic circulation across the UK and a changeable mobile element to the greater part of the isles or B) whether the low frequency standing wave in the Pacific can hold out against any increased trade wind phases and relocation of that standing wave to the Western Hemisphere (that assists scenario A) and help sustain improvement from the less than desirable base line of the start of summer and increase the frequency and duration of downstream summer ridges. As things stand: The present situation with respect to the tropical wave and associated propagating westerly wind bursts which aid downstream ridge amplification is that the velocity potential convection anomaly charts (VP200 anomalies) point to propagation of the tropical signal to the dateline in the Pacific during the last third of June In favour of option A: In association with recent tropical suppression phase in the Pacific (shaded orange above), trade winds increased at the turn of the month and helped exacerbate the recent stratospheric/tropospheric lock in of the resident trough c/o intense Greenland/N Atlantic blocking. Wind anomaly forecasts continue to point to -ve zonal winds persisting to the east of the dateline in the Pacific, and which, potentially, presents some question mark over extent of propagation of the latest tropical wave advancing into the Pacific and currently over the Maritime Continent. Notice the muted response west of the dateline in terms of advancing westerly winds in association with the tropical signal indicated on the convection anomaly plot above. Taken at face value, the net effect of sustained trade winds against the suggested weak propagation of the tropical wave by the ECM would suggest that the tropical wave would beat a retreat towards the dateline (by or probably before MJO Phase 7) and this would be the cue for derailing downstream amplification of any mid latitude ridge and initiating a flatter Atlantic pattern with the Azores high retracted westwards In favour of option B: The GFS model forecast, below, has a clearly significantly stronger westerly wind burst advancing into and across the Pacific than the ECM forecast, even if it does retain the same sort of trade wind sequence in the Eastern Pacific. The ECM is known to exhibit some -ve tendency bias with eastward propagating tropical waves from the Maritimes to the Pacific, so whilst it is not necessarily wrong here, there is no inevitability of Scenario A. Undercooking westerly propagation plays some part in over estimating -ve easterly trade winds in terms of compensation of wind-flow inertia which cannot by nature, exhibit an inequality of vacuum within the atmospheric circulation. There has to be a compensatory wind-flow response for each and every other one that occurs - and according to the laws of the conservation of atmospheric angular momentum. Also, and with that caveat to -ve bas tendency in mind, its worth looking at the ECM's own suggestion that irrespective of -ve zonal winds in the EPAC, a low frequency tropical standing wave will remain in the western and central Pacific in tandem with a developing twin low frequency signal over Africa/Western Hemisphere. The engagement of the former supports a Pacific downstream response, irrespective of the EPAC trade winds mitigating the signal and suppression of the Pacific standing wave whenever the twin signal in the Western Hemisphere is engaged, The GFS interpretation of the tropical signal is to propagate wave eddies into the extra tropics, fully engage +ve torques and the resultant push to angular momentum resulting in a break away into the El Nino attractor phases 5 and 6 of the Global Wind Oscillation Taken at face value, this would be a red flag signal for summer in our part of the NH to spectacularly reverse fortunes with anomalously very warm summer ridges extending across large areas from Scandinavia and mainland Europe in the east, through the UK and out into the central Atlantic and with the Jetstream displaced a considerable way to the north. The GFS interpretation of the GWO needs to clearly be taken with some certain caution, but equally a careful watch is required on any suggestion of early termination of this signal c/o trade winds killing off the advancing tropical wave prematurely. To add to the mixed messaging, the extended overnight ECM suite within NWP has two clusters of more amplified downstream response solutions than the first flatter cluster the operational and control sits within by day 10. A similar pattern exists within GEFS and GEM ensemble suites. One gets some idea of which tropical>extra tropical signal these cluster solutions are representing Furthermore, usual disclaimers applied with very long range suites - but the latest EC weeklies continue the theme of mid latitude more typical flow and signs that a trough/ridge interplay will persist from June well into July. But a clear evolving northward shift in jet stream trend that becomes more evident with time is suggested by these. Based on proxy and diagnostic evidence, including the tropospheric profile comparisons, there is some intuitive support for such a summer trend and this is consistent also with some of the helpful seasonal modelling evidence based summaries given by @Mike Poole amongst others Its always possible to check diagnostics vs NWP - and unless there is a very compelling signal one way, there is more often than not more than one possible solution ahead and which does not always tie with a bias preference solution. However, with the removal of the intense blocking signature over the polar field and a more traditional tropospheric mid latitude pattern returning with some zonal type flow, the influences within the tropics and extra tropics should no longer be scrambled to the extent they have been. That has consistently been the takeaway from these summaries for quite some time, and that time has now come when the way forward becomes more and more dependant on the tropospheric influences rather than dictated by late season intense stratospheric downwelling processes. With the well meant intention of trying to be helpful, I would suggest that those of you who are interested and there are some who try to contribute to this thread (notwithstanding the ongoing difficulties in doing so) as well as those who do not post but like to keep updated), continue to monitor some of these plots and indicated possible trends to see how the rest of the summer might play out. Whatever the weather holds, best wishes for the remainder of the season
  2. There is some sense within that post and I certainly agree with the opening sentiment that also applies to a core small number who persist in ignoring any objective discussions and instead appear determined to make this thread an unhelpful and tedious read. I guess that is where the ignore facility comes in use to provide some respite, though a big shame it doesn't also block out the text when these posts are responded to. The section about "background signals" though, like I said yesterday very often is misunderstood and misrepresented at all times of year. This term, is very overused and loses its true meaning and purposes. More specifically and accurately, it is a non numerical evidence based diagnostic process to identify the drivers at any given time that NWP is making its own calculated interpretations of. This means that if used objectively, it can provide a very useful insight into the range of possibilities within deterministic solutions and identify where patterns may change (or may not change where indicated to) based on a range of recurrent intra seasonal wind-flow signals and torque mechanisms that relate to the laws of conservation of atmospheric angular momentum. The diagnostic looks at wind-flow mechanisms which steer the jet stream and give clues to where changes may occur based on a range of teleconnections and proxy data which are well identified to produce specific synoptic responses within given ranges of parameters at different times of the year. It is not a stand alone approach and combines with other seasonal factors that include stratospheric and sea ice trends and states which can alter these synoptic responses. 2018 to 2019 alone has been a powerful example of this sort of complex blend of factors, which sometimes have a-typical and countervailing aspects and make deciphering aspects of weather pattern modelling highly challenging for the best professional minds - let alone the enthusiastic student with the curious mind at home. So the likes of the Global Synoptic Dynamical Model (GSDM) is a diagnostic supplement to purely NWP driven investigation, but NOT a silver bullet with sole purpose to endorse human weather preference from one season to another - though clearly there will be times when given factors will combine to include such a preferred solution within the overall diagnostic which may point to more than one possible solution in addition to the bias solution. The problem with threads like these, and its especially poor in winter with the huge volume audience all baying for one popular outcome, is that the bias preference overwhelms everything and people will latch onto the "background factors" if the diagnostic happens to suggest a percentage probability of the desired solution...but will choose to ignore any other solution. Other times, members will migrate to any NWP which may be following a signal that doesn't even exist within the diagnostic - and that is a time to not bother posting otherwise because such analysis would be considered being a "killjoy". Of course whichever route is taken, the end result is the same when the desired solution doesn't verify (which tends to happen more times than not when any selective process is undertaken). Irrespective of the reality, it will the be the "background factors" which are to blame - not the consensus bias of people who took the NWP model(s) at face value. And so it goes on from one season to the next and from year to year, with some none the wiser. So I don't accept its the diagnostic "background signals" that are wrong - its the human interpretation and applied bias use of them that inevitably increases error rate. So what is new today, away from the flurry of intra day reaction and overreaction to specific NWP outputs? This is interesting in terms of where convergence of tropical convection may be adjusting in the Pacific, at the same time as changing the Indian Ocean Dipole signal. Redolent of a semi quasi centrally based neutral/ El Nino type signal or very weak "Modoki". To try to put this into simpler language - This comes about through the effects of trade wind increases in the central and eastern Pacific, augmented by suppressed phases of MJO convection such as currently being witnessed as the active MJO passes through the I/O resulting in increasing cooling of the surfaces of the eastern ENSO Equatorial zones through upwelling. However, at the very same time, there is an opposite eastward moving current to observe in the Western Pacific which creates a convergence zone of maximum downwelling and consequential surface warming in the W/C Pacific. This convergence zone consequently spawns an ideal site for tropical deep thunderstorm convection development n tandem with a similar trend in the Western Indian Ocean where downwelling currents also create favourable cyclonic convection sites. Putting the two opposite co-existing signals in the tropics together, the net result of this is to create an a-typical Nino atmospheric imprint (La Nina like) on the rossby wavelength whilst the MJO imprints the warmest zone in the I/O but then defect also to a constructive coupled response in the Pacific when the wave phase propagates this region of the tropics. Why does any of this matter this far away? It matters because the tropical phase will be induced to produce the type of downstream response we are seeing at present with a downstream trough when the I/O low frequency signal engages, but with a tendency to contrasting signal of Atlantic trough and downstream ridge when the Pacific convective signal engages - and hence the opportunity for warm and settled spells maximised at this time. Its yet another of the factors that could be shaping this summer and why numerical models may be subject to curveballs due to a twin aspect tropical>extra tropical wind-flow signal. Something else to chew on while the rest of the previous analysis remains consistently on course at present. So, still cuing up some kind of mid month onwards shift : With the SOI still in negative territory reflecting the continued presence of a weak El Nino signal despite the destructive action of the supressed phase of tropical convection : and relative global atmospheric angular momentum still above average and with the active phase of the tropical cycle set to approach the Pacific from mid month... ..reflected by associated further rise in angular momentum tendency at precisely the same time as westerly wind bursts replace the supressed phase and easterly trade wind uptick.. ...then the pressure is growing for NWP to start reflecting a more downstream high pressure outlook and some kind of trough response in the Atlantic rather than the UK. But with the principle of the diagnostic in mind as discussed above, there is likely to be associated risk probabilities to continue to observe. The fly in the ointment remains the very stubborn -ve zonal flow at higher latitudes which continues to negate some of the more favourable warmer and especially settled aspect to the pattern, but this too should come under increasing pressure with summer seasonal wavelength changes as long as the I/O tropical signal does not start to dwarf the Pacific and become the more default response The latter will have to be continued to be carefully monitored, but plenty to observe as antidote to NWP derived swerves in temperament.
  3. So much going on right now that renders over scrutiny of NWP, especially each and every operational output, even less sensible than is usually the case. Yet another occasion therefore to attempt to supply some analysis of drivers, for those who at least might be interested in reading between the lines a bit and looking at some causes and effects, rather than simply wading through a diet of a cacophony of intra day spasmodic gloomy reactions. First of all, if we take a strong westerly phase of the Quasi Biennial Oscillation (QBO) aligned with solar minimum conditions - plus added to that a stratosphere > troposphere profile that has a lot in common with years like 1995 and 2013, then the summer in terms of broadscale height anomaly pattern *should* be on destination to something like this during this summer : If a weak El Nino atmospheric circulation forcing is added to the melting pot which engages extra tropical propagation of planetary waves from tropical convection located within an Pacific standing wave, then something akin to this becomes the framework destination as summer wavelengths really start to engage the closer we head towards July: The former anomaly chart to the one just posted has some similarities at face value to those we have become accustomed to. One highly crucial stark difference is that the emphasis has been for the longwave trough wrapped within that arc of height anomalies to be displaced towards the UK and locked in over us rather than westward placing in the Atlantic and which would make a massive change to warm air advection adjusted our way rather than stuck to our east. Some post analysis, from those that read them, discussed a week or so back, why the trough was displaced in our vicinity, and what it would take to displace it westwards to more closely the blue print composite anomaly that reflects what some will coin/overdub the "background signals" as identified above. The cause, for another further reminder is a combination of persistent override from a dynamic element to the final stratospheric warming, later than usual in Spring - sustained further by a "destructively acting" phase of the tropical cycle on the El Nino standing wave (suppression in the Pacific) which skews the blueprint of the above expected anomaly towards a greater emphasis of Atlantic/Greenland ridge, rather than Scandinavian and European. Furthermore, and most crucially it places the trough further east towards us than the suggested composite. This is redolent of an a-typical La Nina type adaptation of the template pattern that has the crucial effect of making a vast difference between sharing the heat over the nearby continent, and instead being stuck in a cool and unsettled envelope. That struggle clearly evident within NWP - with heat locked in to the east, and despite hints from some NWP ensemble suites, unable to advect far northwards or westwards due to the propensity of ridging to the west and northwest. Hence the upper trough has nowhere to go, but stay in situ, with more and more surface troughs being bred at its base and being pulled northwards within the upper cold pool created. Frustration with the deadlock is understandable, but objectively it is more rewarding, ay least in my opinion, to identify causation though diagnostic approach and probability assessment, look at what is required to change the rossby wavelength, and then once again through the use of diagnostics (beyond the face value identification of the upper air and surface patterns), the probabilities of change occurring to what remains actually a finely poised pattern based on the drivers in play than the computer models might appear to suggest moving forward Its worth looking at that height anomaly cross section and where we at vs the most recent of the years mentioned above - 2013. As we know, putting aside the anomalously much colder first half of Spring than 2019, nevertheless the profiles of the atmosphere this year share some noteworthy similarities in terms of slow speed of strong downwelling into the troposphere - and which continued to scramble the pattern of late Spring and first part of summer in 2013. Now lets take a look at the representative QBO values for both years: Both firmly westerly by this time, and to very similar strength. 2013 -6.07 -1.23 2.85 8.39 12.64 13.38 14.27 14.66 13.12 11.69 12.45 12.55 2019 9.02 9.25 11.82 13.36 14.59 (May to date) QBO Calculated at NOAA/ESRL PSD 30mb zonal wind at the equator, zonal average For info https://www.esrl.noaa.gov/psd/data/climateindices/list/ units=ms-1 Next up lets look at that -ve disconnect to the tropical cycle to the El Nino standing wave and latest EC weekly forecast of propagation timing of the MJO back to the Pacific - returning a more constructively acting relationship to the Nino standing wave and hence re-configuring the downstream pattern to more of an Atlantic rather than UK trough The risk to persistence of the Atlantic and Greenland pattern becoming the default remains failure of the propagation of this MJO wave and what difference it would make not just to any June improvement but how it might alter the progress to a more mid latitude pattern deeper into summer as the template Nino/wQBO low solar combination suggest. But the present forecast from a much more reliable velocity potential component forecast to tropical forcing than RMM modelling, continues to suggest eastward propagation into the Pacific, albeit on a slow time envelope for realistic timing being from third week of June. I'm not sure the MJO RMM deterministic forecasts are especially helpful here, and which underestimate eastward progression - especially around the Maritime Continent and where models tend to try to "stall" the topical wave and interpret loss of signal. This bias tendency will also skew NWP perceptions - hence another reason to treat models with caution who, as is well known, have a capacity for apparent consensus to extrapolate a signal for indeterminate periods of time, and then catch on what is happening and head into reverse. With all of the above analysis in mind, there is good reason to discount the upcoming period as unlikely to change until that disconnect tropical phase is complete - but a lot of evidence and added research to show, that as 2013 suggested into July, it is baseless to extrapolate an apparent persistence factor out across weeks of a whole season, let alone a whole season. Evidence base reasoning is always a more constructive (and enjoyable) method and pastime, and which can always be sensibly monitored for progress and revision according to any further departures from the template - than just pessimistic frustration which offers no objectivity other than based on previous worst case scenarios.
  4. Hello there - yes that represents the favourable outcome This is a very tricky and finely balanced period, with a myriad of possibilities suggested across the spectrum. Many of them are indeed at least reasonably favourable - but from a personal point of view, based on the distance involved and on what I can see within the non numerical modelling diagnostic elements that are putting a few nagging question marks in my own mind over previous assessments of how this summer might progress, I would ideally like to see any NWP solution from any computer model that has an element of a persisting Atlantic ridge within it, dropped completely in the coming days. Its perfectly possible this will indeed happen, but for purposes of being wholly objective and honest it has to be monitored. Its been interesting, though not especially at all welcome, that the EC operational has kept representing some kind of Atlantic ridge type of solution to the day 10 period, and hence persisting with some of the coolest solutions vis its ensembles and some of the other computer models,. Taken at face value, such persistence of an element of Atlantic ridging rather than downstream would suggest that any subsequent improvement in the time under focus heading to the mid month period was more questionable, certainly in terms of recovery of temperatures to levels many of us would like to see at this time of year. I think its worth reiterating the key points previously detailed in terms of progress: 1) The coming 7 to 10 days of this month are well documented, and so I think any daily re-packaging of the obvious negative aspects of it isn't sensible or helpful. Better I think to continue to remind of the causes instead and which put the further outlook into context of the possible outcomes. Those causes relate to an a-typical (La Nina type) forcing from supressed phase of convection in the Pacific resulting in uptick of trade winds responsible for the upstream amplified pattern (Atlantic ridge leading to our downstream longwave trough) The very strong tropical convection suppression in the Pacific causing the upstream amplification from us is circled here: The associated uptick in trade winds (blue shading in the wind-flow anomaly plot below) to the supressed convection phase are circled accordingly - the contrasting westerly winds (yellow/orange shading) associated with the current MJO wave are also part included within that circle to the east of the -ve zonal wind anomalies across the Pacific - representing the westerly winds heading across the Indian Ocean to the Maritime Continent to meet the wall of trade winds across the Pacific 2) Which brings us precisely to that further outlook and what the possibilities are for de-amplifying the upstream ridge, lifting out our resident trough, and presenting a downstream ridge profile in our vicinity instead The improvement is predicated on the suppressed phase of the tropical>extra tropical cycle completing and a return to a more active convection phase across the Pacific. The effect of this to replace increased trade winds across the Pacific with further westerly wind bursts, such as seen earlier in May. This sequence re-configurating the rossby wavelength and blowing a hole in the Atlantic ridge and implying a better wavelength for amplification of the sub tropical ridging (Azores high) further downstream instead The VP200 tropical convection anomaly forecast above ^^ above gives some kind of indication as to how quickly this might proceed. The week 3 chart correlates to the start of the time of hoped for improvement as the orange shaded suppression starts to ease away in the Western Pacific, suggesting angular momentum tendency starting to rise once more and the cue to de-amplify the pattern upstream and instead re-amplify downstream as momentum transport propagated from the tropics to the extra tropics starts to feed across to our side of the NH. What is vital in this process is that the tropical convection phase does indeed propagate back to the Pacific, without beating a retreat - and we see no sign that some longer term shift in the default position of the tropical wave from the Pacific to the Indian Ocean is underway. This would be a sign that a more fundamental longer term breakdown, rather than merely just a natural suppression phase within the "mini ENSO cycle (aka MJO) was in process. With that in mind, that is why whilst the EC ensemble suite continues to look promising for this more favourable change back to summery conditions , I would ideally like to see over the coming days the operational, and any associated cluster it represents, stop producing cooler spectrum solutions and start to follow the ensemble pack pulling the other way - rather that see any opposite trend to this. These cooler soutions indicative of reluctance to break down that Atlantic ridge and/or shift its mean position closer to us and replace it with the trough backed west into the Atlantic instead. At the distance we are discussing, and with the diagnostic approach pointing to two different possible outcomes - one favourable as discussed in considerable detail for some days now, and one less favourable - its important that all NWP (not just the ECM) sings from the favourable hymn sheet c/o the more favourable diagnostic solution gaining traction with persistence, at least for a time, of the very borderline El Nino standing wave in the Pacific. To illustrate the influence of the Nino standing wave since the winter, its position in the Pacific and its representative 500mb downstream synoptic pattern of Atlantic trough and ridging mostly placed downstream, I have borrowed these composites from twittersville - as I think they well capture what any shift in that low frequency signal would imply in terms of a reverse Atlantic ridge AND downstream trough Signs that this Pacific standing wave is succumbing to further pressure and that a shift in the low frequency signal is set to head back to the Indian Ocean would suggest something of a re-assessment of prospects for the UK looking further ahead. We are certainly not there quite yet anyway, and reason for the moment at least to keep looking at that hoped for improvement in the time period you suggest. Hope that helps
  5. Thanks for your customary posting of the latest ensemble means and which is much appreciated by many I am sure - I know you provide these for the right intended reasons and without knowingly trying to create reaction from others or mislead anyone As you know, from my point of view the diagnostic approach to the outlook has stayed consistent with pros and cons as to how the pattern may evolve beyond the unsettled phase next week. It continues to be a case of having valid reasons to suggest improvement beyond this time - mindful as previously stated in equal detail what could alter such an improvement. The ensemble members can give a broad numerical modelling view, as a snapshot in time, of how each model perceives the signals influencing the synoptic pattern, but changes to these can occur over a period of days rather than necessarily from from one suite to another in a single day period. NWP can be prone to reversing trends as much as accelerating them based them on changing interpretations of signals - so the diagnostics prove highly useful in terms of trying to identify when such changes might happen and/or point to the likely outcome(s) within that given time. I also think that the continuing reference to operational outputs, even less of a reliable snapshot of time for obvious reasons, is proving especially unhelpful in distorting perception (and not helping stabilise mood swings) according to the particular modus operandi of the poster on each occasion As I see it, the GEFS has been a little progressive in terms of creating the impression of the pattern improving as soon as later next week and I think the potential advection of heat from the east has rather helped create this illusion as well in what has remained an unstable pattern surrounding the longwave trough. The real improvement chances have always been beyond this time - any heat equation injected into the unsettled pattern has always been an 'add-on' to create a little interest. But all the main model ensemble suites (ECM,GEFS and GEM) all point to this improvement beyond this to varying but quite reasonable degrees. The VP200 tropical convection anomalies clearly show up the suppression phase over the Pacific and active phase in the Indian Ocean that is responsible for the step up in trade winds which is creating the La Nina-esque type pattern downstream to the Atlantic and European sector in the coming period - the distinct amplified Atlantic ridge and longwave trough response over the UK. Quite the change there from the sustained and robust array of westerly wind bursts associated with the recent convectively coupled kelvin wave progression through the Pacific earlier this month The eastward progression of propagation of this activity, is on the slower side of the envelope. This is in contrast to the fast propagating CCKW related phase of tropical convection in recent weeks. Hence why it is unlikely that the trough solution will lift out properly until the supressed phase in the Pacific starts to fade out in advance of the convective zone proceeding through the Maritime region towards the West Pacific. This sequence changes the rossby wave response further downstream with the result that amplification responses also shift further downstream to assist pressure rises in the wake of the trough.at the same time as allowing the heights to the east to link up with this pressure rise and improve conditions. Present estimates do not suggest this evolution advancing sufficiently till towards the mid month period - so the extended ensemble suite reflection of improvement are not too far away from the diagnostic guide. The timing of associated rises in angular momentum tendency, as the tropical signal propagates, also clearly coincide with both the tropical>extra tropical diagnostic and the extended ensemble suite suggestion The caveat, as before, is that the tropical cycle retains some progression to allow that rise in momentum tendency - the diagnostic equally shows that any lack of verification of propagation implies a greater struggle to change the downstream pattern. Answers to that question however simply cannot be properly answered immediately, by anyone - and require a watching brief to check progress. On that basis, any gloomy prognostication bases on snapshot modelling is as counter intuitive and misleading as any, allegedly, over optimistic one. Mindful of these cautions and caveats, which in truth once provided as balance and information to help the thread, should not thereafter require to be endlessly inserted and repeated with every post as means to try to ease the truly tiresome battles of attrition on this thread that persist, there nevertheless continues to be, at the very least, reasonable evidence to back an improvement towards, or by mid June. Especially as stated in recent posts the background to global relative momentum is set more favourably than other years at this specific time of seasonal change and should help the process of the trough lifting out in tandem with the shift in rossby wavelength re-configuring the pattern.
  6. Reference paragraph 1 : Clearer signs have emerged from NWP related to this suggestion - one that previously had first been flagged up last weekend related to possible tight margins of error related to this dividing line between the cooler Atlantic air and the increasingly hot and very humid air consolidating over the continental mainland. Hence the reference, however clumsy it might have been to interpret, to the void where low pressure 'seems' to gravitate no further eastwards. Remaining paragraphs: The final outcome of this scenario remains predicated on the technical factors outlined already in considerable detail - under the pros and cons influencing it. I think some are perhaps getting sucked too far prematurely into the 'against' argument rather than keep an open mind at least about the 'for' argument, or perhaps they have other reasons for the apparent pessimism for no obvious reason - other than using thesnapshot of an unsettled spell being extrapolated outwards for concocted periods of time by specially selecting NWP operational charts to try to prove the points. Operational charts which so often chop and change each and every 6 to 12 hours. However, whatever the motive, this is a perilous stance to take based on the fact that the doom-saying summers listed of 2007, 2011 and 2012 (and one or two others maybe such as 2010 which featured a -ve PDO and low angular momentum La Nina state which correlate to a -AO) have some considerable ostensible differences to this summer. One thing this summer does have in common with those years is the perilous arctic ice situation (and even more perilous than since any of those summers) . But we have also seen other summers in this period, such as from July 2013, some parts of summer 2014, the latter part of 2016 and most especially of all of course last summer where the pressure state of the Arctic has had no influence at all in contributing towards blocking patterns that are detrimental to some highly ideal spells of summer weather. Therefore it once again reinforces the message, and one that I fully subscribe to, that each season should be sensibly taken individually on its merits. How else can one be objective? One key difference to all those poor summers listed is that this one is being ushered in by a higher than average angular momentum regime feedback circulation. 2007 featured sharply crashing AAM based on a fast emerging strong La Nina (nowhere in sight this year) aligned with the very low sea ice and a strong eQBO to help reinforce the blocked patterns in the Atlantic and over the pole. Likewise both 2011 and 2012 featured low angular momentum Springs heading right into the start of summer - - with the former never recovering from this state during the summer at all until early September (which coincided with some of the hottest weather of the 'summer' during autumn 2011.... and the latter with a brief rally in angular momentum in late June 2012 into the early part of July which accorded with the spectacular plume seen close to the end of June and hence otherwise associated poor synoptics. No coincidence that both 2011 and 2012 both featured, like 2007, extensive periods of blocking in the 'wrong' places and a trough that refused to lift out properly due to the location of the tropical standing wave being in the 'wrong' part of the hemisphere and according with long periods of amplified Pacific and Atlantic ridges and downstream trough.. This summer begins featuring a weak El Nino, w/WQBO and overall we have been seeing a neutral to slightly +ve PDO. I have seen suggested by a very respected and knowledgeable forecaster in another place as something of a cross between 2002 and 2006. In terms of the UK, the former was not especially good though a few short bursts of warmth occurred, but the latter featured some wonderful weather throughout June and July and then a very impressive Indian summer from early September into October 2006 was also a w/QBO year like this year - a good antidote to any -AO patterns. There are other observations to make in terms of SST's and solar forcing here too in respect of both those years - and so again another argument for taking each season on its own merits. This summer also starts with a supressed phase of tropical convection in the Pacific, temporarily altering the PDO state a little, and already dealt with in huge detail - and which lends itself to some a-typical Nino forcing (aka more La Nina-esque) Hence the displaced and amplified Atlantic ridge and trough axis steered south on a very unhelpful longwave in our vicinity. But until, or if there are signs this is to become the default, signal (i.e through crashing angular momentum as part of a a longer term change of atmospheric circulation such as happened in the aforementioned poor years) it remains sensible to be suspicious of any NWP which appears to try to match some of the commentary on here by sticking the boxed in pattern for inordinate amounts of time. It remains to be seen how far any heat advection from the continent might advect this way - but whatever happens in that respect, the chances are higher of this trough lifting out much sooner than in any of the pessimist years. And even if the greatest heat doesn't arrive, there is no reason not to expect a general improvement in conditions more widely SE>NW in the more extended period. If its not good enough for the likes of someone like me to say this, then look at the METO updates, which essentially are saying the same thing as someone ordinary as me on a weather enthusiast page. Based on the fact that the polar field is now resembling a state adjusting from the fallout of the strength of the final late warming of the stratosphere, and assuming that angular momentum remains close enough to where it is at present, the pressure will grow according to summer wavelength changes to keep backing the pattern very slowly westwards the further June progresses and most particularly from midmonth towards July. Keep the pros and cons list handy - but try to remain objective about the possibilities of both, and not skew opinion according to other motives and reasons.
  7. On the first comment, you didn't unfortunately include the relevant part of the post that showed it was a comparison between a model ensemble suite and a diagnostic (GWO plot) as a way of trying to helpfully and objectively assist readers in matching up where the pattern might evolve vs the movement of that diagnostic. The post yesterday fully explained the context of the "void" but the impression I get is that you knew this when you nevertheless felt compelled to want to create an illusion of error. More generally, in view of the continuing snap reactions to individual NWP operational outputs which maybe not unexpectedly and somewhat predictably have persisted since observation was made of them - it might be worth looking at how the extended ensemble clusters incorporated within on the EC ensembles and follow on immediately after that 0z mean chart are picking up on the possible GWO vs NWP evolution to reduce the influence of the trough, which is being extrapolated forward with inevitability by some, and return some influence of higher pressure building from the east and north east Clusters of that EC 0z ensemble suite reflects the steady trend of atmospheric angular momentum tendency, todays update now posted, staying very buoyed in association with that development As stated in the previous post, this is worth watching to see if it gains traction for the reasons given - but notwithstanding the cases for and against improvement probabilities provided in attempts of neutral objectivity - it at least provides some scope to stop writing off weeks of early summer before it gets here officially. It goes without saying that of course people can comment on all kinds of aspects of NWP - but surely its better backed up with more than just deliberately pessimistic hunches that have no foundation up to weeks ahead and seem purely designed to create reaction. This issue pervades this thread most often in winter, but clearly is present at this time of year as well and rather seeks to discredit any attempt at taking out time to try to be objective and helpful as various posters who are enthusiastic about their spare time here try to do. No-one is attempting, or believes themselves to have wisdom or is some kind of elite over anyone - such an attitude would be anathema. There are all kinds of ways to contribute. But ways which are respectful and manage to drop the need to be either sarcastic, discrediting and/or are reaction seeking.
  8. If I might interject at this point. It might well be worth adding a bit more flesh to proceedings and come at this yet another way in terms of objective diagnostics vs model "hugging" hunches and speculative extrapolations of individual operational outputs For this purpose, lets take the updated ECM 0z ensemble at day 10 - which is a reasonable estimate of where we are likely to be based on current state of affairs. It also rather illustrates the points I was trying to make yesterday in terms of the pressure void to our east. Lets then compare it to how it might be reflected by the diagnostic Global Wind Oscillation plot, which is a phase depiction of wind-flow patterns in the tropics and extra tropics and shapes the jet stream patterns which carve out placement of pressure systems. Described here in deliberately simplified parlance. For this purpose we take the latest GWO plot, based on its typical consolidated lag time - at present time of typing to 25 May. This reflects a very low amplitude signal which has ebbed and flowed around a weak phase 0,4,5,6,7,8,0 type orbit for some quite considerable time - identifying the pale pink warm neutral/weak Nino signal standing wave circulation feedback in the Pacific. So once again in deliberately simplified terms - the predicted phase correlation for that EC ensemble plot is,very roughly speaking, around a Phase 8,0 position - according to month and seasonal wavelength. This phase progression is reflective on the GWO spectrum of some loss of angular momentum tendency having taken place upstream early next week which has amplified the Atlantic ridge to our west, and, downstream of that ,digs the longwave trough close to the UK. What is important here is how the GWO is likely to progress as we head through early June. Based on the supressed phase of tropical convection across the Pacific as the MJO has retuned to the Indian Ocean, then some increase of trade winds, as identified yesterday, is behind the upstream loss of momentum as -ve frictional torque mechanisms scrub some of the recent strong westerly inertia from the atmosphere. This trade wind uptick visible, shaded blue, in the Western and Central Pacific towards the dateline here But this is far from the whole story. With relative global atmospheric angular momentum comfortably above average (though still to account for some slight downward adjustment c/o the Pacific suppression phase)…. …..this will still likely leave the AAM budget of the atmosphere with a supported floor, ahead of the next uptick in the "mini ENSO cycle" as the low frequency tropical signal in the Pacific is allowed to re-emerge and add further westerly inertia to the atmosphere and re-boot angular momentum tendency. AAM forecasting still, steadfast on this Such support and uptick having the effect of re-orbiting the GWO back through Phase 4 towards the Nino attractor Phase 5....the signal to lift out the trough and pressure rise from the south (likely as suggested yesterday that the boundary of the heat will still be fairly close by and conceivably ready to advect back northwards and westwards). It remains something to keep watching in ensemble suites in the coming days, as this story is far from complete.... What could go wrong? The importance of re-energising of westerly momentum across the Pacific to neutralise the trade increase is a vital key here to support AAM and prevent a deeper slide. Any shortfall would add incentive for a more durable trough solution and retain a more amplified ridge profile in the Atlantic to lock the longwave trough in. What can quite conceivably go right (aka AAM forecast) Its also true though that if the atmosphere just stays as it is, then summer seasonal wavelengths on their own should work in our favour and increasingly means that just a persistence of the present GWO orbit regime inclines the trough to edge back westwards the closer we get towards the later part of June and into July. Any ideal scenario of repeated vigorous westerly wind bursts however, that pushes the GWO into higher phase Nino attractor orbit 5,6 and 7 starts to flag up the possibility of 2006 and 1983 type scenarios with prominent Western European heat ridges duelling with thundery cut-off lows to our west and south west....But that is for another time perhaps...
  9. Aside from the daily commentary of updated model suites, from a regular few and which proves a useful, helpful and pleasant antidote to mood swings, unfortunately far too much typically absurd and unwarranted overreaction to the inherent erraticism of numerical modelling is omnipresent as usual on here from the usual suspects - and which serves no useful or rational purpose at all. This, much more of a nuisance than what NWP (apparently) most lately suggests itself So, by way of most recent example of this - we arrive at the point that sections of NWP, about a week back (including long term EC monthly!) was mapping out a good 10 to 15 days at least of cool and changeable weather with a trough anchored very close over and to our NE, phasing with further disturbances arriving across the Atlantic on a supressed jet stream. Instead we look at this to end the coming week and the weekend Its not, and was never likely in my opinion to be a long term sustainable ridge - but what it does do is represent a likely recurring pattern in the opening weeks of summer based on the detailed discussion of parameters discussed in the previous post, and many preceding it. As suggested in that post, this is not likely to be another 2018 type summer with weeks of blazing anticyclonic ridges and so expectations should be adjusted accordingly in my opinion. If not that, then at the very least learn not to flinch with each and every output, or better still, wait a period and see what emerges over a period of a day or two rather than every 6 to 12 hours! On the basis of a diagnostic, rather than purely wholly numerical modelling approach - for the opening period of summer (at least) it does look to me to be one punctuated by an Atlantic trough and downstream ridge pattern that breaks down and then re-programmes. Rinse and repeat. In that sense, the above snapshot of the expected weather pattern to end the week (and very pleasant conditions) conforms quite closely with those prior expectations. And its not a bad place at all to be at the very start of summer - irrespective of whatever else is currently suggested to follow. Looking ahead from this time, personally I am very sceptical of any NWP trying to break down the weekend pattern sustainably by, yet again, suggesting a repetition of a week or so back with a same extrapolation of breakdown into equally sustainably cool and changeable conditions in the extended period. Operational NWP shouldn't be taken at face value at any time, and that includes ensemble data at long range as well - which is equally quite prone to change direction like a shoal of fish in midstream, when they exert a bias signal and appear unable to "see" beyond the that signal to the next. After all, it gets forgotten on this thread by some - but its not the computer models that drive the signals....but its... So NWP in the last 10 days or so has been particularly poor, and is likely to continue to be unreliable which means that human reaction to every output should be adjusted accordingly. This also means that whilst upper air noaa anomalies do represent a best guide as an overview of NWP - they too still remain just a snapshot in time and will also change as computer models evolve with signals. So a good idea to adopt a cautionary word here also at not taking them too much at face value. Relative global atmospheric angular momentum remains comfortably above average and with a fair degree of westerly wind inertia in the atmosphere and more to be added as another MJO wave begins its course through the Indian Ocean to arrive in the Pacific later in June.. This to help programme further downstream amplification in this sector of the NH heading through the month. AAM forecasts continue as before to advertise this supported trend. Whilst the natural interim supressed phase of convection over the Pacific (shaded orange) temporarily creates some upstream amplification and a little extra downstream polar jet energy, -as cautioned above, the risk of overreaction to this shorter term signal is clear and questions any attempts by NWP to try to effectively "crash "AAM and as a synoptic response send sustained increases in polar jet energy over the top of a retracted and amplified Atlantic ridge such as the ECM operational is currently trying to do. As long as the tropical signal resides as default in the Pacific, and angular momentum therefore remains sufficiently buoyant, then an upstream ridge and UK trough remains counter intuitive on any holding basis. . Look at where the low frequency tropical signal resides close to and just west of the dateline in the Pacific It supports an El Nino type standing wave, even if not a "pure" basin type El Nino. In fact, the standing wave due west of the dateline is better than any east based signature which would supply too much of a southern stream (as unhelpful for warmth in our sector as too much polar jet energy) So its not the pure ENSO base state that is important at all here, it is the relationship that the atmosphere adopts to the base state - and this is one that drives a programme of rossby wave trains that should keep punching breaks into the downstream jet and filling them with the sort of ridges that are advertised this coming weekend. With that in mind, there looks to be a very slack downstream void setting up in quite a bit of the modelling beyond next weekend where the attempted phasing of the jet coming across the Atlantic (trying to bump up the strength of low pressure) hits the buffers. A very large percentage error exists here - the European mainland having already become anomalously hot by this time. A ridge, or at least relatively higher pressure is always most likely to reside here, on the basis of the above wave train analysis - so any modelling trying to fire up huge lows and ultra progressively sweep this continental airmass aside should be viewed as just one main source of suspicion. The UK is always likely to be on the cusp of the Atlantic vs European airmass difference, and so no surprise that a uniformly settled picture cannot be guaranteed in any way and is not likely (unlike 2018) - but also no surprise that some NWP will come up with solutions that produce over deepened lows where the phasing of the lows on the downstream jet, clash with hot and humid airmasses. But though it alas takes centre attention due to the vicissitude of NWP, this is simply the noise that masks the default, which will (for the time being at least) be to restore a trough/ridge pattern - rather than progressively try to usher in a low angular momentum jet stream scenario where pressure falls over both UK and Europe and pressure rises sustainably instead upstream over the central and western Atlantic. Please note the deliberately persistent italicised and/or bolded use of word sustainably in this post.
  10. There are no apologies for self quoting a significant extract of the post the other day because its central focus becomes more primary to how NWP evolves in the remainder of this month and into the start of June Sustainability of next weeks trough solution already being examined by NWP - despite some continued extended products having recently appeared to insist it will prevail throughout the 15 day period and perhaps beyond The low frequency tropical signal shows little sign of abating amplitude across the globe. The next wave programming a further progress of convection anomalies eastward towards the western and central Pacific during the first week of June This fully endorses the consistent signal by the CFS seasonal model for quite some time(and still further consolidating) for angular momentum to stage its next rally in tandem with this event With westerly wind inertia already in the global circulation based on weak El Nino standing wave and previous robust westerly wind-bursts from the last wave, this one looks to be following on a rapid timescale envelope and should maintain an above average level of AAM through June.. A sign that the atmosphere doesn't want to let El Nino fade at least quite as quickly as the shallow ocean thermocline wants to suggest. NWP modelling should have little choice but to follow-up these signals and continue to build poleward ridges northwards through the mid latitudes and keeping the lid on attempts for the weather to turn unsettled for too long. Summer wavelengths also increasingly suggest that these ridges should embrace wider warmth parameters, despite the apparent reluctance of -ve downwelling anomalies left over from the intense dynamic final warming of the stratosphere to fade quickly - and hence the propensity for these ridges to become higher latitude than one might desire for optimal warmth. It is this factor aligned with the vulnerable sea ice that provide the wildcard flies in the ointment, and need to be watched carefully to check they don't persist in scrambling the attempts by the tropics to send the jet properly northwards. However, based on the current PDO profile and w/QBO not the same as has occurred in some of our poorest summers (and so assisted greater pernicious staying power of a -AO profile) then assuming the atmosphere stays in the same state through the opening weeks of the summer, the polar profile should succumb to a more neutral and even slightly +ve profile with time. Though the more strongly +AO profile of last summer continues to seem unlikely in my opinion.. Only beyond this opening period, (caveat: that polar profile allowing) does the ability of El Nino and associated tropical/extra tropical patterns begin to become under the greatest uncertainty - but as the last post suggested, no reason not to suppose that some very pleasant and increasingly warm spells of summer weather await us
  11. Aside from the standard posts scattered around designed purely to enkindle reaction and usually predilected and deliberately exaggerated through baseless claims and skewed interpretations of sometimes spurious sources of information, the late Spring pattern has evolved very much akin to expectations of previous analysis. That is - the substantial downwelling of -ve zonal wind anomalies at higher latitudes vs attempts for seasonal ascendancy of the tropical/ferrel cell to assign the jet stream northwards assisted by a weak El Nino forcing pattern in the Pacific. The former strongly -AO regime making the latter much more difficult to achieve than was seen under the +AO regime of late February that ironically managed to achieve temperatures not too dissimilar to what many reasonably hope for at this time of year. The recent convectively coupled kelvin wave (CCKW) has produced a considerable train of strong westerly wind bursts across the Pacific It can also be said that whilst the -AO regime has made any heatwave elusive, this Pacific pattern has still provided some fair weather and prevented an even cooler May CET from evolving than if we had been in a low angular momentum regime under substantial higher latitude blocking As the associated MJO wave concludes and passes into the Western Hemisphere, on into the Indian Ocean at the start of the next cycle and attempts at upwelling cooler water occur in the Pacific as trade winds increase once more, its to be expected to see angular momentum tendency drop as the previous span of westerlies are scrubbed out from the atmospheric circulation The ECM wind-field anomaly identifies those upcoming trade winds in association with the lull phase of the tropical cycle as it passes through the I/O and suppression returning at the same time to the Pacific as identified by weeks 1 and 2 VP200 (velocity potential) anomalies This upstream change and scrubbing out of recent westerlies signifies re-amplification in the Pacific transferring to a downstream Atlantic ridge response exacerbating the Greenland heights signal at the same time as a wedge of vorticity is allowed to sink SW'wards over Scandinavia and the northern most Atlantic towards the UK and presents a trough solution evolving immediately after the Bank Holiday. What is problematic is that this signal is to be assessed at where globally averaged angular momentum sits relative to the orbit of the Global Wind Oscillation. These indicators show westerly wind inertia throughout the global atmospheric circulation to be higher than average - with the standing wave still echoing a weak El Nino signature in the Pacific and the GWO well away from the low angular momentum octants. This puts some question as to the sustainability of this medium term Atlantic ridge and downstream trough signal - especially as the tropical convective MJO signal continues to be active and churning across the globe - which means that further westerly wind bursts can be generated. Despite its jaundiced reputation in relation to NWP interpretation of wider signals, the CFS seasonal modelling has some value in its indicators. It has remained steadfast for the last couple of weeks on angular momentum retaining a floor relative to the Pacific signal for June at the least - with the next upturn of angular momentum tendency signalled to follow the upcoming trade wind increase, in tandem with eastward propagation of the next MJO wave On this basis at least, and as this forecast is not without support from other modelling, and notwithstanding the CFS tendency to over amplify tropical signals - and still its worth being very cautious of trying to extrapolate the 5 to 10 day trend for cool and unsettled weather to take hold c/o Atlantic ridging and downstream trough for large swathes of the month to follow. Hence ensemble mean suites needs to be gauged carefully against this over the coming days and certainly not worth taking too much notice at all of intra day operational swings that are, frankly, best avoided at any time anyway. Looking forward ahead even further than this naturally becomes very highly uncertain and even more problematic - its to be seen whether the present ocean trend to want to cool the Pacific ENSO zone succeeds in overriding the ability of the atmosphere to sustain WWB's and therefore unable to prevent a more sustainable switch to a more la Nina-esque Atlantic ridge and downstream trough scenario. Avoiding this for the greater part of the summer looks less likely than seemed possible earlier in the Spring, but it is not, yet, inevitable by any means that the first half of this summer at least won't seen some pleasant seasonal weather.
  12. Hello Mike - this cross section of the layers of the atmosphere clearly illustrates the downwelling process of that final warming - quite the contrast to the +AO dominated close to winter and first half of Spring. I think that puts a perspective on this Spring and its mixed character. Aside from the anomalously very cool start to May which is concordant with the switch to -AO c/o the dynamic nature of the final warming, the CET means for March and April are fully contemporaneous with that earlier generally +AO profile - both months comfortably above average. So the capricious surface conditions of the season have rather masked the fact that this Spring as a whole (so far) has not been quite as poor as some might try to make out. Also the highly anomalous warmth of the second half of Spring 2018 is a distracting and distorting comparison perspective - even in this warming world and increasing occurrences of noteworthy temperature anomalies breaking frequent records, consecutive late Spring and Summer seasons of such homogenous warmth still represent an upper benchmark. This is the UK after all and not a sub tropical climate as much as it is not a cold continental one in winter. Expectations and preference ideals are too often asymmetric with geographical latitudinal realities Looking ahead, and striving to build on previous analysis - some further thoughts to add extra substance. There are signs a more coherent +ve PDO pattern might try to set up with come modest relative cooling in the West Pacific - and by comparison, warmth consolidating in the eastern Pacific. This accords with El Nino standing wave signature being assisted by the eastward propagation of convectively coupled kelvin wave (CCKW) MJO envelope. As such, it accords with MJO Phase 8 imprint and downstream rossby wave train amplification of the wavelength Furthermore, this contradicts the identity of Springs heading into summer like 2007,2010, 2011 and 2012 where a -ve PDO was part of either an imminent La Nina (2007 and 2010) or a long established La Nina (2011) or an even more established Nina struggling to transition to ENSO neutral (2012) If we take the globally averaged angular momentum budget, the characteristic low angular momentum state (as manifested by -ve PDO tendency) is clearly choreographed during the Springs of both 2011 and 2012 Quite different to 2019 A w/QBO prevailed as is the case this year in 2011 - however the Pacific feedback was very different and clearly much more La Nina-like than this year - and the characteristic mid Atlantic ridge and downstream UK trough increasingly played a hand as summer was arriving and seasonal wavelengths changed. Furthermore, the QBO phase does not accord with the very easterly state in Spring/Summer 2012 where some other background parameters were closer to this year than 2011. The strong e/QBO overrode any attempts made by the atmosphere to try to become less La Nina-esque during early summer 2012 and sustained blocking at the "wrong" latitude instead.. Calculated at NOAA/ESRL PSD 30mb zonal wind at the equator, zonal average For info https://www.esrl.noaa.gov/psd/data/climateindices/list/ 2012 -16.07 -15.25 -16.74 -17.62 -22.04 -25.89 -27.82 -27.93 -26.60 -24.51 -18.95 -10.02 2013 -6.07 -1.23 2.85 8.39 12.64 13.38 14.27 14.66 13.12 11.69 12.45 12.55 2014 13.13 12.68 11.72 7.15 -2.81 -13.98 -19.29 -21.64 -23.24 -23.86 -23.65 -25.38 2015 -26.70 -28.62 -28.15 -24.38 -12.33 2.18 7.45 10.97 12.07 13.38 12.79 11.39 2016 9.34 6.77 3.16 0.64 2.37 3.86 6.25 10.07 10.48 12.83 14.16 15.09 2017 14.92 14.78 14.35 13.88 8.01 -3.18 -10.48 -14.42 -15.28 -16.79 -17.20 -18.12 2018 -19.02 -19.37 -19.77 -21.41 -24.23 -28.45 -29.10 -20.41 -9.91 -2.79 3.36 8.05 2019 9.02 9.25 11.82 13.36 - (April update) Strengthening westerly phase evident. A +ve (westerly) QBO, in tandem with an El Nino forcing on the atmosphere is a more "hostile environment" for any final warming feedback to prevail than occurred in 2012 and failed as a result of too much La Nina -ve PDO forcing in 2011. Summer 2006 is that excellent w/QBO and El Nino combination example, previously referenced, where HLB in May gave away to anomalous warm mid latitude blocking early in June. In respect of the CCKW as a noteworthy event, it will be interesting to see seasonal model updates in terms of ENSO SST predictions as benchmark for how Nino might prevail. -May is often a key month here.. Should El Nino rally once more, with the standing wave engaged in the Pacific and the atmosphere reflect a coupled feedback loop with the extra tropical GWO starting to repeat orbits returned back to the Nino attractor phases, then portents are good for summer. Different to last year in respect of the likelihood of no persistent ridge for weeks on end and the Atlantic trough and downstream ridge breaking down and re-setting and allowing thundery breakdowns, and then cooler changeable interludes leading to re-set of the default warm pattern. That is not a forecast - but its quite typically traditional weak summer El Nino. There is little danger of the southern stream getting too strong as it did in the start of the "super Nino" of summer of 2015 - its more a case of avoiding increased trade winds breaking down the Nino-like trough/ridge pattern and creating a more persistent downstream trough instead. Especially because this years final warming has had a "dynamic" element to it, with considerable poleward heat flux drawn into the final warming and further amplifying the downwelling -ve zonal winds to the troposphere/stratosphere boundary. This might serve to give it that little extra resistance to the natural effects of seasonal wavelength changes and advancement of the ferrel cell in the tropics as assisted by the favourable effects of wQBO usually creating an elevated tropopause due to westerly shear in the lower stratosphere. But there are signs as previously discussed the odds are stacking against such resistance and whilst, as we know, the seasonal models like UKMET et al are not bullet proof - such general analysis as attempted here does provide some logical resonance and credence to such predictions of a warm summer pattern Time as always will tell - but much more will continue, as ever, to be gained from comparing progress of ensemble NWP suites in reading all these signals than wasting time trying to draw too many observations and conclusions from the smorgasbord of unicorns offered by intra day multi faceted operational output.at long distances All the computer models have their inbuilt biases, but the GFS continues to often display a -ve tendency (low angular momentum) response to its interpretation of tropical signal imprint on the synoptic pattern - particularly as the MJO completes its cycle and returns to the Western Hemisphere onwards to the Indian Ocean. Such timing as due later this month and where differences of modelling are already apparent with the ECM .So some further erratic output and disagreement could crop up as the coming week progresses in terms of the extended period. Good reasons therefore to particularly not overreact to operational data and also be cautious with ensemble suites and compare their progress over 2/3 days rather than 1-1..
  13. In view of the provocative game-playing (that I had gladly escaped during the winter) and the absurd quick fire reactionary responses attributed to NWP operational data, attendant with not enough attention instead to ensemble data (which in itself is simply only a snapshot of time in evolving patterns) its probably a good time for some more analysis. Signals after all lead models, models do not lead signals The seasonal demise of the polar vortex, amplified by tropospheric heat flux forcing as described in an earlier post, continues to dominate the NH pattern and inhibiting any late Spring build up of real warmth over the nearby continental landmass due to persistent feed of cold air advection from a displaced and rapidly dissipating area of leftover vortex broken away from the the eastern arctic into Scandinavia The persistent height rises to the north - a manifestation of the symmetry between the tropics and the pole and differentials between them which enhance tropical convection activity (MJO) and the resultant wave train in turn triggers equatorward flux in the Southern Hemisphere (i.e subsidence away from the Antarctic) and a +ve pressure signal (+AAO). At the same time in the Northern Hemisphere, the engagement of the eastward propagating tropical wave at the dateline teleconnects the opposite way to the SH with a -AO/-NAO - the latter attendant with upstream jet extension across Asia and the Pacific and greater flow into the southern stream. The Southern Oscillation (SOI) in response to the eastward propagating MJO signal has trended sharply negative in the past few days - an indication of -ve Outgoing Longwave Radiation anomalies ( OLR) and associated deep clouds and thunderstorm development close to the dateline - also as illustrated by the intense and sustained westerly wind burst continuing across the Pacific to the dateline https://www.longpaddock.qld.gov.au/soi/ As well anticipated in recent posts in advance of this WWB, angular momentum tendency, subject to 2 day lag, is significantly ramped upwards. The +ve AAM anomaly depicted around 30N in tally with the proxy data in the Pacific as depicted in previous plots The Global Wind Oscillation, a plot depiction of wind-flow additions and subtractions as supplied by frictional and mountain torques and other related mechanisms, has responded with a leap into high amplitude Phase 4 as these large amounts of westerly additions are supplied to the atmosphere. This is the kind of repeated GWO pattern which, with repeated westerly wind additions c/o tropical activity, would return the GWO to El Nino attractor phases 5 to 7, and would accord with seasonal wavelength changes and start to build further anomalous mid latitude ridges close to and just to our east during June (and possibly July) at the same time as height rises to our north start to fade out.. More on this uncertainty further below. So for this, and all the other repeated detailed reasons given in previous posts, it continues to be premature and pointless in equal measures to extrapolate assumptions of the resultant -AO led pattern into the early stages of summer (and in some cases evidently even beyond!). A lot could, and quite conceivably will happen over the coming few weeks at such a time of seasonal pivotal change. In the medium term, its worth watching the developing low heights towards Iberia and Biscay - these could play a role in providing a stark thermal temperature boundary between the cold air advection to the north and a much warmer humid circulation becoming ensconced around the low heights to the south and south west. How far north such a boundary might set up is uncertain at the moment, but some NWP is playing with this scenario in the extended period and its conceivable that another round of retrogression of the heights to the north could lead to a similar evolution to this week, but this time with less of the deeper upper cold air around to tap into further to the north and east and any warm air advection adjusted further east into Western Europe With that type of subtly adjusted wavelength evolution in mind, if (as discussed above) tropical convection patterns and angular momentum tendency can remain conducive, and this still isn't a given and needs to be watched for a while yet, then seasonal wavelength changes and gradual ascendency of the Hadley/ferrel cell heading into new month and new season change could flip a stubbornly (relatively) cooler pattern into something more sustainably warmer. Such as happened in some of the aforementioned summers in previous years that featured May's that seemed reluctant to embrace a substantive warm-up All that said, and returning to the opening theme above, some proper perspective is needed here - next week still looks to feature a much more pleasant spell of weather after this weeks anomalously below average temperatures, with some welcome sunshine that will lead to warm feeling days out of the breeze, especially in the north west and away from eastern coastal districts where low cloud could be a nuisance. In that respect not an unusual pattern for mid May and nothing untoward whatsoever to lead to writing off swathes of a season that is yet to begin and remains too uncertain to call (either way).
  14. This convectively coupled kelvin wave (CCKW) I have continued to reference over the last week or two has been of such strength heading through the Indian Ocean that it had much to do with the development of the devastating tropical cyclone Fari which sadly crippled the Indian state of Odisha in recent days. It has now passed eastwards through the Maritime continent through to the Western Pacific and in terms of the feedback processes from upwelling warming across the ENSO zones (see below tweet for illustration purposes|) has possible significant future implications to downstream patterns in terms of the ushering in of summer wavelengths - and when the dynamic response to the final warming of the stratosphere eventually starts to fade from influencing tropospheric responses. The bright red - intense white colours in the Hovmollers plot pick up the strength of the WWB heading through the W Pacific. On the VP200 anomaly chart depicting the CCKW tropical convection, notice the eastward progression of the CCKW in the first half of May to engage the dateline in the Pacific - and how suppression (yellow, orange. red colours) of convection appears in the wake of the tropical wave across the Indian Ocean and then Maritime continent respectively These westerly winds in the Equatorial Pacific propagating eastwards, tend to migrate poleward through the extra tropics with time, and programme swathes of downstream amplification. Where this amplification sets up is dependant on the longevity of the more transitional seasonal downwelled -ve easterly zonal winds across polar latitudes. The question is - how sustained are they likely to be? Any collapse in angular momentum caused by increase in easterly winds across the Pacific has the effect of transferring the amplification wavelength upstream to the Pacific and create a downstream ridge>trough>ridge trough response. The final ridge trough response being that in the Atlantic and European sector respectively. On that basis it could be seen that any Atlantic or Greenland blocking default created by a -ve ENSO atmospheric circulation feedback is a natural extension of any pre-seasonal higher latitude blocking such as we presently have. If the ocean/atmospheric standing wave is held back across the Western Hemisphere because of the effects that easterly trade winds have on supressing tropical convection in the Pacific - the consequential stable atmospheric environment is conducive to High pressure in the Pacific and a downstream blocking response also in the North Atlantic.. That is why the setting of a +ve ENSO wavelength in the Equatorial Pacific is useful for warm air advection patterns in our part of the Northern Hemisphere in summer because it encourages MJO related and associated separate induced cyclonic activity in that part of the tropics - which in turn helps promote a downstream Pacific trough/ridge pattern, and replicated Atlantic trough and downstream European ridge In this way, the CCKW is a very important event in reducing the risks of a more la Nina like atmospheric response generating sustained easterly trades winds heading into summer and also therefore less chance of any Atlantic blocking configuration to follow on from final warming HLB and then stick for any length of time. Ultimately, the current MJO wave will return, naturally as part of the "mini ENSO cycle" to the Western Hemisphere - note the suppression arrive in the Pacific as the signal returns from Africa back to the Indian Ocean in the last third of the month Based on the fact that the latest wave is already likely to adjust the Pacific SST pattern favourably, as detailed above, and help tip the balance more towards a summer ridge pattern downstream, then the return of the tropical wave pattern to the Indian Ocean later this month might well see a higher floor to the fall-back in angular momentum likely later this month - and that usually always occurs at the end of each MJO cycle. Currently globally averaged atmospheric angular momentum (GLAAM) is about +1SD above average which is a quite good place to be in ahead of the upcoming passage of WWB's associated with the CCKW. CFS and other model products are picking up on a possible further CCKW event heading into June. Its early to have high confidence in this, but its one to keep an eye on. . This watching brief then also ties in with what happens to the polar field pressure pattern in terms of the remnants of the final warming. Some current NWP extended products are hinting at wanting to try and retrogress the poleward amplifying sub tropical ridge that evolves through days 7 to 10 again and sustains the block to the north in the more extended period. This then potentially inviting another swathe of troughs to have the potential attrition to undercut from the west and promote further cool unsettled weather How credible is this? Assuming that longer term prospect chances have been improved by upstream tropical developments sustaining a supported angular momentum regime heading into summer, then the lifespan of dynamic fall-out from the final warming has limited sustainability heading into summer period, with a combination of seasonal wavelength changes, +ve momentum forcing from an El Nino type atmospheric feedback and assistance from the +QBO phase to also underpin this. So whilst a further round of attempted Greenland blocking cannot be ruled out in the medium term, then this might give way to a warmer mid latitude ridging pattern as Spring heads to early Summer. Though the sustained anticyclonic conditions of last summer seem less likely this year, and a potential thundery element exists which many would welcome on the basis of a reloading warm pattern and to add some interest to conditions. May 2007 was a generally +ve AO regime which gave way to higher latitude blocking through June and the rest is history. It was also a year where angular momentum collapsed heading into summer at the same time as an easterly -veQBO assisted downwelling of -ve zonal winds into the troposphere to align with weak sea ice and produce a very poor summer. The previous year, as documented in a post last week, had the opposite configuration with a higher latitude blocking in May followed by mid latitude heat ridges as soon as the calendar turned into June. This year the chances of more sustained relapse have not gone completely yet, and it will require a close watch on both the ongoing blocking patterns and angular momentum/tropical wave trends during the remainder of May heading into June - but latest events should have at least reduced the risks vs what was beginning to seem increasingly possible in recent weeks and create a better chance that this summer evolves closer to the better variety than the likes of 2007, 2011 and 2012. So that improvement from the south comes as suggested of late by the weekend to follow what looks a truly dismal week - albeit due to the persistence of the higher latitude blocking signal it looks now to set up initially further west than ideal to cut off the cooler air staying close by. However, the depth of cold air compared to this weekend is not there and liable to mixing out further with time. Its also not the end of the world if it morphs into attempting to retrogress with further fall of pressure undercutting it. It doesn't mean summer is destined to be over before it has begun. Such an evolution is far from certain anyway at this stage and some fine weather, albeit not a heatwave, still looks likely heading into the following week. But should this month continue to struggle to follow through on any recovery promise, the philosophy of ice in November and sludge and muck to follow comes to mind with its opposite counterpart in May. It remains the case that what follows afterwards matters much more in terms of hopefully disposing of the Greenland and higher latitude blocking..
  15. Eagle eyes obviously present... Based on yesterdays assessment those day 10 means reflect good cross model continuity for re-set of Atlantic trough and downstream ridge and warmer air to approach from the south. Taking account of the caveats that could still alter this evolution for all the detailed reasoning also given yesterday and recently, it still pays to do some QC on NWP assessment in terms of latest suite consensus (at the very least) before reacting However, the next few weeks continue to advertise a significant westerly wind burst propagating east through the West Pacific to the dateline and providing a timely shot to keep an atmospheric Nino feedback going into early summer. We are not quite there yet, but Its worth keep repeating that this is increasing the chances of warm plume scenarios rather than cool and changeable North Atlantic flow around a mid Atlantic ridge and downstream trough response
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