Tamara

Yes there is certainly some truth in some of this. Paraphrasing, I have written what (to me) amounts to be a book on the perspective of this since returning to posting for the summer. Its always easier to discuss and explain these things when the weather preference is reflected by the macro scale weather pattern translating the desired observed surface conditions on the ground. Then the perception is that these drivers "work". and the people who are hardest to please are willing to appreciate the value of them The rather large snag in all this, is that these diagnostic wind-flow aids are not intended to be magic bullets to fitting to meet the needs of idealistic weather preferences - they are there to try to help find the correct solution (which may or may not include the preference solution). I find that the use of these highly valuable aids to the atmospheric circulation and wind-flow inertia, providing clues as to how the jet stream may be influenced by them upstream and downstream, to be wholly incompatible to the hopes and expectations of them from some quarters (not all by any means). It is a smaller scale version at this time of year of the much larger disconnect that exists in winter and creates the total circus when the "science" only matters and "works" if it makes it snow... Problems also arise when the diagnostic credibility becomes reliant on numerical model forecasts using that diagnostic data. In the same principle as NWP interpretations of the atmosphere, these AAM forecasts are estimating calculations of tropical and extra tropical phenomena which are prone to forecasting revision when such numerical interpretation of them changes. The actual diagnostic (not numerical forecasting) modelling which includes the wind-flow phase plots (GWO) and angular momentum and wind-flow torque plots help decide if the numerical models are on the right track or whether change in their estimations is possible. These, plus other various proxies are aids to this. It is necessary to know the consolidated starting position of the atmosphere wind-flows as accurately as possible to account for how numerical modelling biases may extrapolate forecasts ahead and produce results that risk deviating outwards in time I cannot add anything further to recent summaries which have stated the probabilities of what might go right and what might go wrong - in terms of desired weather hopes. It was possible to have an overview ahead of time of what the default pattern might be heading into the start of summer (a predominant emerging Atlantic ridge) and this has duly played out so far this summer. The hardest part has been trying to identify when a-typical aspects to this may arise - such as the heatwave ridge of last week. It was also possible to identify that in good time However the task is becoming ever harder now we hit high summer wavelengths.. Some of the modelling, including the EC weekly modelling is extrapolating the African/Indian Ocean low frequency tropical >extra tropical signal outwards in time ,(that configures to the Atlantic ridge and downstream trough) and suggested the overriding of other signals (as endlessly described and discussed) that might provide dissonance to that default signal. Caution is still required with this - evidence becomes required to back these numerical extrapolations up - and at this time it is not wholly convincing (at least yet) It seems wise not to make any further attempt as means to avoid endless repetition of the same thing (and save personal time) Again somewhat rhetorically speaking , the best thing to do is simply let some days of NWP watching go by, let associated reactions to to it play out, and revise prospects then. Continuity, irrespective of weather preference and any non allegiance Mother Nature adheres to them, is always possible,. In truth that is all that matters to me personally. Continuity provides the space for future clarification and the space to find answers as part of that process. It compensates for any frustration of the weather itself. In my humble opinion of course. All those things are possible. But in summary - if anyone expects guarantees and magic bullets, at any time of the year, then there will inevitably be disappointment (and disillusionment) at some time or other. More often than not as well.

Probably a good time to recap on where we are (and why we are where we are) to try to bring back perspective to this thread, as the morning time period tends to lose perspective at times - and can be a difficult read when it is wholly focussed on the worst aspects of selected operational outputs and misses out so much of the bigger picture. From mid-June and during the lead up to last weeks hot spell, c/o downstream ridging, I commented that the Global Wind Oscillation, a plot depiction of wind-flow inertia in the atmospheric circulation, would reflect as a barometer for endurance of our down-stream ridge. GWO Phase 4 indicating that enough forward momentum remained to prevent the upstream pattern amplifying too much to flatten the downstream pattern - and hence keep a ridging profile for longer. The fact that the ridging collapsed when it did is indicative of the slow crawl into only GWO Phase 3 last week - indicating insufficient momentum to keep the downstream pattern amplified for longer. However, despite this, quite a few of us managed a quite glorious week - overshadowed by the rapid weekend breakdown and the weather since then which has taken all the focus instead. For all the bad press that June received, whilst it was clearly not a classic summer month, it still managed an above average CET return - which rather illustrates how it doesn't take much for a month to be dismissed as poor by various members on this site. There have been much poorer June months than this one, under quite similar regimes as June 2020. With a CCKW imprinting the relocated standing wave low frequency tropical signal across Africa and the Western Indian Ocean as indicated by the blue shaded anomaly on the velocity potential convection plot (note the extensive orange shaded convective suppression across the Pacific) - - then this maintains negative extra tropical torques and ensures that the GWO will be re-orbiting during this week back towards Phases 1 and 2 . The response, as we have been seeing modelled in the extra tropics, is to re-enforce the Atlantic ridge and downstream trough across NW Europe and Scandinavia into this week and explains why the weather is struggling at present to resemble anything properly summery. Little point in taking the recent extended term deterministic MJO forecast at the forward amplitude suggested at face value - the trend is what matters here. Suffice to say, the signs are still there heading through July that this CCKW related high frequency MJO event will cycle eastwards onwards from the Indian Ocean and the imprint of the low frequency wave will be mitigated sufficiently to increase chances of bolstering anticyclonic wave-breaking and allow the Atlantic ridge to move further downstream less erratically. What has been problematic is determining how far north and west this can extend based on the background AAM budget being quite changed since May. It is, however, important to also take some of these AAM forecasts that get posted on here into context. They do certainly point to the innate tendency during this type of regime for ridging to tend to ebb and flow to our west and south west and hence this will inevitably lead to variable conditions - cooler and most unsettled during the most retracted phases. However, there is continued absence of stratospheric interference on the polar field to lock in unsettled cooler spells and rule out sub tropical ridging potential, This, as well as the tropical forcing as discussed in terms of when the low frequency signal (that suppresses the influence of the sub tropical ridge into our part of Europe) can be muted at times, and leads to outcomes that are not cut and dried In short, there remains at least the capability, if not the cast iron certainty, to deliver realistic improvement as the month progresses - and with time, less of the ongoing phantom movements of the ridging eastwards that has (so it seems) evidently frustrated NWP watching over recent days or so. Dwelling on operational output that is always erratic with trends is not the most helpful way to observe proceedings - it requires a constant overview reminder of the larger factors driving the pattern and which the ensembles and upper air pattern anomaly charts will evolve much less erratically (overall) than, especially, any individual GFS output. These seem to get the most coverage for some reason - and even NWP as a whole, due to being prone to error when reading these signals, is better measured over a day or two at a time rather than drawing instant conclusions often laden with a sense of inevitable foreboding, sometimes up to two to four times a day.

As suggested previously, there is no straightforward axiomatic x=y correlation with this, as is the case with many global drivers. Solar forcing has different implications provided for, depending on the relationship between the tropics and the pole, and specifically here in terms of whether the given QBO/ENSO phase interaction augments or detracts from Brewer Dobson circulation and propagation of ozone between the tropical stratosphere and tropical stratosphere. This. an indicator of prevalence to blocking or to a stable stratosphere/troposphere layer. The adjustments of the sub tropical ridge have been in accordance with reduced wind-flow inertia upstream which periodically amplifies the upstream pattern and forces a downstream trough - not because of the action of stratospheric forcing on the troposphere due to low solar forcing allied to a stronger La Nina and properly down-welled e/QBO. Such as happened in 2007 for example - and which had occurred already by the time that summer had started. Such a full combination has not, yet at least evolved. So whilst it is conceivable it may evolve in future, it cannot be attributed to the here and now. How else did such a downstream sub tropical ridge evolve only last week otherwise - and no conclusions at all can be drawn from present NWP that the relationship has, yet, changed in terms of any downwelling within the stratosphere to affect the troposphere - just a few days into this next changeable spell. To reinforce that point, and as repeated so often, an abstruse e/QBO state transition has prevailed for some time and there is high lack of confidence how this will evolve during the remainder of summer and into the autumn. The outcome of this still has quite separate consequences in terms of weather pattern wavelengths as influenced between the stratosphere and troposphere - as linked to solar state. With weak La Nina-esque low frequency tropical forcing in place, and equal uncertainties as to how off equator forcing may continue to apply some dissonance between the tropics and extra tropics, then quite a choice opens up according to whether to the QBO transition finally bumps forward and strengthens, or whether the eclectic stand-off persists and even matches 2016 style failure. Should the latter persist, or go even further and abort the easterly transition, there is every chance that sub tropical ridging will prevail alongside a (relatively) stable polar field. This mitigates the extent of sensible weather fall-out at the surface and leads to a relatively better case scenario within the limitations of a pattern to achieve sustained downstream ridging. Not a great summer pattern - but still some room for fine, warm spells in between changeable and cooler spells such as earlier in June, and again presently.. For all the reasons given of late. And irrespective of the solar signal which would be overridden in such a scenario. However, should there be signs of closer union between a deepening e/QBO and La Nina forcing towards retracted sub tropical ridging attaining more of a polar aspect, then a trend towards an increasingly negative Annular Mode becomes more inevitable which sustains low pressure and attendant suppressed temperature anomalies at mid latitudes - this the result of a "constructive" relationship created between the stratosphere and troposphere towards blocking and also allowing a "constructive" relationship to low solar phasing. Constructive in the sense of assisting the potential dynamic relationship between the drivers, not in terms of how the outcome is viewed by a given audience as to weather preference outcome. Indeed confirmation bias as means of seeking a weather preference outcome can lead to error as a consequence of trying to fit given drivers to those particular sought after outcome(s)

Can I ask , was the PV in part to blame ( in a good way if you like long dry periods) for the unprecedented dry sunny weather as soon as lockdown started right up to latter June bar two rainy days in April. What enable such huge high pressures almost encircling the globe at mid latitudes especially towards and over the UK for Such a long period of time ? Another question which I have always pondered, do you think there is any correlation between the inner workings regarding metals under the core and certain large strong high pressure cells ( Hadley I think ) that make them tremendously difficulty to shift at times ? One of note often seems one off the Portuguese coast and extends over Spain although this year Spain doesn't appear to have this but instead a constant slack low pressure producing many thunderstorms over the country this year. These are good questions, and they relate completely to how and why there has been pattern shift since the summer began. . The excerpt taken above from yesterdays post gives some answers in terms of the relocation of the low frequency tropical signal further upstream to Africa and the Indian Ocean - which essentially also re-configures the rossby wavelength further upstream as negative torque mechanisms increase easterly trade wind inertia - and amplification in our part of the Northern Hemisphere takes place across the Atlantic, more often than NW Europe - which was the case during the Spring. As far as the PV is concerned, this was very strongly influenced by the westerly QBO phase during winter, and a strong lag effect persisted through the Spring - also aided by the fact that there has been no progressive transition to the easterly phase which would assist stratospheric downwelling of negative zonal wind anomalies and increase pressure over the pole. What we are seeing is the increased La Nina forcing c/o the relocated tropical signal steering the pattern away from the persistent downstream ridging of the Spring to the more retracted ridging seen under much lower angular momentum conditions than up to just a month back in time. This type of regime often favours countries like Portugal and Spain - at that latitude clearly on the opposite flank of the Azores ridge and immune to the cold fronts and incursions of much cooler maritime air that cut short fine and very warm spells in our part of NW Europe. One aspect someone like me has in her dreams for the future... This 90 day plot tells the story in terms of the changes between spring and summer for this part of the world however: Momentum fell below average on cue at the start of June and summer. It is no coincidence we have seen much more mixed conditions since then My own view though is that, taken in the round, we have actually done better than might have been anticipated - thanks to the off equator diffusing of the effects of the relocation of the low frequency forcing and kelvin way characteristic high frequency tropical forcing providing some further temporary ridging as we have seen. Also the enigmatic QBO transition has prevented a much worse outcome developing c/o higher latitude blocking. As suggested, attempts to switch the Annular Mode have proved to reverse due to countervailing westerly inertia playing peek a boo in the stratospheric echelons. As long as something of a disparate relationship persists between the tropics and the extra tropics, and the polar field doesn't tank negative, then the story is the same one. Next week is a test of the off equator forcing helping a more eastward displaced ridge and further high frequency tropical forcing assistance. Much as discussed at length in recent posts. This is why I continue to recommend not being too reactionary to each and every operational model suite. There is some bandwidth in solutions here according to how the upstream wind-flow inertia plays out. In simple terms this translates to timing and extent of Azores ridging eastwards - meaning there is an envelope of a few days for its arrival and there is also room for either reduction OR increase in extent of this ridging. That sounds like covering all bases to be proved correct whatever happens. However, being correct is secondary to monitoring a very interesting fine margins as far as I am concerned and the truth is that a favourable or rather less favourable outcome are both highly conceivable at this time. We are simply under an different overall regime to that of the Spring and whilst we readily saw prospects for ridges upgraded in nearer timeframes , the re-configuration of the pattern since then simply makes it harder to achieve that favourable outcome each and every time However, we are (relatively) fortunate to still have the real chance to see some shorter warm spells amidst the more changeable and cooler periods. It really could be considerably worse than that as a perspective for those who continue to be underwhelmed by how the summer is panning out so far

Yes, it was good and helpful he replied You will possibly have seen some of us posting these diagnostic wind-flow plots which in essence measure the strength and path of the jet stream. Much of the wind-flow inertia, though not all, comes from propagation of these wind-flows between the tropics and the extra tropics via torque mechanisms which essentially create a turning force action on the jet stream and alter the strength and direction of the jet stream according to whether greater westerly energy (via positive torques) or greater easterly loss of momentum is weakening forward westerly momentum in the tropics (via negative torques). The inflection point of these torques is determined in large part by where low frequency tropical convection forcing is positioned in the tropics - and how active the high frequency MJO tropical signal is in terms of whether it augments the low frequency signal or creates a, usually transitional and temporary, a-typical relationship through the atmospheric circulation to the ocean base state. To deliberately greatly over simplify for purposes of not overcomplicating things - as we know, ENSO phases switch periodically in the Pacific and these phases fluctuate according to various cyclical and intra seasonal phenomena. When wind-flow inertia overall is lower than average in the atmospheric circulation, then easterly (negative) trade winds dominate across the tropics and through the ENSO zones. As determined by the laws of conservation of angular momentum, this puts compensatory forward energy into the extra tropical jet which flows downstream from the Pacific to the Atlantic. The inflection point of the negative torque usually propagates around 20N to 30N in the Equatorial Pacific and the divergence of decelerating wind-flow creates amplification and sub tropical anticyclonic responses which are amplified poleward into the extra tropics. The displaced westerly momentum in the extra tropics flows across the top of this anticyclonic response according to the downstream trough/ridge response - which is the downstream sub tropical Bermuda and Azores ridges likewise intensified and amplified in the central and western Atlantic. The downstream jet loops across N America and then likewise around the flank of the high pressure response in the Atlantic - with downstream trough signatures across NW Europe and Scandinavia. This is the kind of default scenario we saw play out at times during June, and is set to continue, at times, during July. However, as posted recently there are various other factors (already covered in some considerable detail in previous posts) which are periodically interfering with this typical low angular momentum La Nina type summer pattern response, and which allows the Atlantic ridge to adjust eastwards into the UK and other parts of NW Europe periodically. This also happened in June, as we know, and looks like it will be a theme as well during the upcoming month So this is duly playing out once more in the modelling - with the Azores ridge advertised to return eastwards into the second full week of July. Assuming that the high frequency tropical forcing aiding this shift plays out sufficiently to diffuse the low frequency tropical signal as it propagates eastward across the tropics, then the risk of the ridging being adjusted back into the Atlantic at this timeframe is reduced. During the next few days it will be possible to monitor this and report back on progress - but at this time it looks promising for summer weather to make a return, at least for a time, during the following week That means I agree with @bluearmycomment, on the basis of the above analysis, that chances of extended country-wide heatwaves are unlikely - but if one is prepared to be sanguine over a mixed pattern of relatively shorter warm spells, potentially thundery breakdowns of interest (such as end of last week) back into cooler more changeable spells when the low frequency tropical signal re-dominates, then it is a reasonable seasonal outlook

The upcoming period has been well advertised, as a changeable flatter downstream spell of weather, and for the forthcoming period at least, the pattern stays amplified across the Pacific c/o low frequency tropical forcing rooted in the Indian Ocean However, as is always the case, it is not NWP that is driving the pattern but a raft of highly uncertain signals that are not cut and dried by any means in the coming weeks and why extrapolating same trends too far out in time is likely to lead to error. There are some similarities with where we are now to 2016 in terms of tropical feedbacks and a somewhat fitful extra tropical disconnect to these, which looks likely to keep waxing and waning related to a reprise of very similar mercurial QBO behaviour, even if based on different triggers. As a consequence, unexpected results could well keep manifesting in the extra tropics. The essence of this is that amplification of the Pacific will take charge of proceedings once more in the opening part of July, but will still be prone to greater interruptions than might be expected from a regime like this - based on further off equator forcing diffusing the default low frequency Indian Ocean tropical signal that is supressing angular momentum and leading to a downstream retracted Azores ridge.. On this basis, lifting out of low pressure once more and further warm spells are quite feasible as July moves further forward. With all that is mind, and the talk of off equator forcing, this is something to watch A significant high frequency eastward propagating CCKW related MJO event programmed by this model, and gaining consensus with ECM during July which would trigger sub tropical ridge wave-breaking and provide a push to lift out the UK/Scandinavian trough of the first week or so of July. NWP in general is starting to programme the beginnings of this ridge encroachment in the extended period as well stated by Matt and others. These high frequency tropical waves are likely fast moving through the tropics until they start imprinting on the low frequency standing wave across Africa and the Indian Ocean, by this time acting "constructively" to increase trade winds once more. Constructive in terms of re-enforcing the low frequency standing wave , but clearly less constructive in terms of what it does to our downstream pattern. So it is possible therefore that a similar progression of weather as seen in recent weeks may occur through July and heading towards August - with the upcoming cooler changeable spell leading to another potentially very warm spell before, perhaps, breaking down once more from the west later one - as the low frequency signal returns to control the downstream pattern. A mixed outlook, but certainly not a completely bad one by any means with plenty of interest for more excellent summer weather in between cooler more changeable conditions

That is a somewhat parochial assessment if I may say so. As posted recently, these numerical model products derive data from some of the algorithms used in what is called the Global Synoptic Dynamical Model (GSDM) That is just a fancy name for a diagnostic process that assesses wind-flow inertia in the atmosphere and hence a good overview of how the jet stream might behave. The difference is that the GSDM produces consolidated data to help establish a solid basis start making forward prediction assessments. Whereas all numerical models change as theses atmospheric processes evolve, and this means they can read amplitude and timing of changing signals incorrectly at a distance. However to simply dismiss them as "rubbish" is rather short-sighted in my humble opinion. If the tropical MJO and velocity potential convection components are assessed alongside how propagation of wind-flows is occurring into the extra tropics - then it is possible to gauge if the computer model is predicting along feasible lines or not. So the AAM forecast product is still useful as a gauge to test feasibility and accuracy. No-one can second guess the atmosphere, but having some guidance as to how the jet stream may behave is surely a big help when looking at NWP - as this particular thread is devoted to it. These products are dubbed by some as pretentious technical babble. An open mind shows they have value, but also one that is prepared to accept that they are not magic bullets to delivering a given weather preference of choice. Particularly not to expect to sate micro scale weather preferences of given counties within a small island UK nation, that is in itself a very micro scale part of a large hemisphere.. These are macro scale (not micro scale) diagnostic model processes with a purpose to help decide the range of possible evolutions in the future and a good dovetail to work alongside NWP. More widely in terms of the overall pattern : There is nothing mystifying about how this current warm spell evolved, and equally nothing untoward about long it is set to last. It was possible to pin-point the chances of this cropping up from about 15 days out as previous discussions will confirm. I say chances, because as per above, the atmosphere does not work in tramlines and there is usually more than one solution at a given distance - unless occasionally there is an exceptionally compelling signal. This is why reactions to NWP need to be proportionate to the bandwidth of probabilities offered by the wind-flow diagnostic and other long term factors (e.g, interplay between the tropics and the pole that affect whether sub tropical ridging holds sway, or whether there is a trend to build heights across the pole and diminish the strength of the sub tropical high) This extensive overview remains highly pertinent to the here and now and what the models advertise moving forward. Sensible not to get too sucked in, as ever, to the errant distracting variables of operational output and instead match the ensemble means to the upper air anomaly charts and then in turn match these to the diagnostic wind-flow. and try to decide from there what the direction of travel may be. I think that @johnholmes recent overview of NWP via the anomaly charts is a good current match to the GSDM data which supports a flatter downstream pattern heading into July but still evidence of sub tropical ridging to the south. That gives something of the proverbial NW/SE split which will explain some of the dissatisfaction of certain regional members - but that is not the fault of the atmospheric forecasting, or a given computer model interpretation of them - simply more so about a geographical proximity to a large ocean which understandably changes perceptions and expectations depending where one lives. Later this week it will be possible to submit the two day lagged GWO phase plot and match the atmosphere diagnostic to this weeks downstream ridge synoptic. Based on latest two day lag last updated yesterday pm (to Saturday 20th) the GWO was circulating into Phase 3 (with associated uptick in momentum tendency) It might be remembered from previous analysis that GWO Phase 4 was the maximum doable target for downstream ridge arrangement - the way the modelling is evolving reflects a transitional orbit towards this GWO phasing but returning back to lower phase octants thereafter. I think that @Singularityassessment of the upstream Pacific pattern yesterday is a good reflection of this brief spike in momentum before falling back once more - as was matched by him comparing the ECM operational of yesterday 0z suite vs the parallel with with its higher momentum downstream signal. The way the overall modelling is panning out since then supports that flatter downstream outcome c/o upstream Pacific amplification. As identified by the return increase of trade winds west of and close to the dateline as suppressed CCKW that has been passing through the Pacific moves through to the tropical Atlantic. It is this next increase in negative inertia across the Pacific which feeds downstream and dissolves the downstream ridging by the weekend and into the start of next week. With all the amplification returning upstream then there is bound to be a downstream flatter pattern response with a trough signature in the N Atlantic extending through to Scandinavia in the more extended 10 day plus period and with the Azores High ebbing and flowing to the SW. But, even though chances of long lasting downstream ridges is certainly reduced from what we were used to leading in to the start of the summer - this does NOT extrapolate out to writing off July or the rest of the summer.....

What is always helpful with these anomaly charts is that its possible to see very easily via the contour lines where any amplification across the hemisphere as a whole is occurring and where the converse response is found - having filtered out the usual operational and intra day noise and distraction most especially of operational NWP. This is where the wind-flow diagnostic can be matched up to the upper air pattern to discern how NWP interprets how the upstream pattern dictates what happens downstream. Rising angular momentum tendency c/o rossby wave transfer in the tropics to the extra tropics alters the amplification wavelength from upstream further downstream and vice versa if momentum falls upstream - so the type of example @mushymanrob cites is where an increase in momentum has created the downstream buckle - the downstream response to the upstream pattern doing the reverse and flattening out some. This is clearly an extremely simplified and somewhat dumbed down overview of the complex processes involved but I found its not a bad starting point to getting to understand wind-flow inertia and torque mechanisms (the turning force applied to the jet-stream) as a visual to get in your mind. There are some differences emerging between how the GFS and its ensembles and the EPS are modelling the polar field profile - with the result that the former wants to supress the jet stream at our mid latitude more than the former. This is one of the pitfalls I was referring to the other day - there was a period in late May when some NWP tried to invoke a more -AO pattern but did an about turn. This related more especially to the GFS (correctly) identifying falling angular momentum into early June - but taking this a step further with some summer 2007 style stratospheric downwelling of negative zonal winds into the troposphere. With the QBO stalled once more, and continued very enigmatic behaviour of this easterly transition then a lot of caution has to be attached to any modelling trying to build heights across the arctic and parking supressed trains of lows across the Atlantic across the UK and into Europe. There has been considerable long term lagged feedback due to the remarkably intense positive AO signature of last winter in addition, - so this makes the more traditional high pressure to the south and lower pressure to the north more intuitively probable. Much as these summaries have continued to suggest in recent weeks. Tropical modelling c/o the velocity potential anomalies continues to show transition of the convective response to the Indian Ocean progressing through the summer, so there is little doubt that angular momentum trends will be (overall) negatively influenced. Note the orange supressed signal close to the dateline further developing through July and replacing the standing wave convective signal (shaded blue)that has been evident for quite some considerable time The second half of the summer holds uncertainties based on this outlook in terms of implications for changed propagation of wind-flow inertia between the tropics and extra tropics.. However as long as the polar profile remains stable, then some of the commentary this morning is very reasonable - a changeable outlook, but for the time-being at least continued room for further shorter length fine warm spells as and when the upstream Pacific profile allows (i.e when it is least amplified). In the meantime it is sensible advice to enjoy the stunning spell of outdoor weather to come this week. Deep blue skies and summer sunshine and lots of Vitamin D for well-being

The tweet from @Singularityvery good post explanation of it has been removed to preserve reading space I also re-copied my own post of last weekend because it was made in anticipation of the same events (as so well interpreted of that tweet). Rising frictional torque in the tropics impacts rising mountain torque tendency in the extra tropics - as the addition of westerly winds in the tropics changes the inertia within the greater atmospheric circulation. The inflection point at which that forward momentum is added is identified as the frictional torque mechanism itself. There is a lag period of time it takes to impact wind-flows in the extra tropics c/o rising mountain torque tendency as the rossby waves created by the wind-flow additions propagate poleward. The overall increased momentum of the turning force exhibited on the Jetstream (the positive torque) is the vehicle to increase angular momentum tendency. The propagation of these rossby waves is the means to amplify the Azores sub tropical ridge in our part of the NH. Such an increase in angular momentum tendency should register in the days to come on the Global Wind Oscillation plot. Posted below. Based on its customary two day consolidated lag, this has paused during this week in Phase 2 (the La Nina attractor phase) - and some days prior to the forward momentum that is to come in the forthcoming week period. How much deficit of AAM that is recovered from the negative easterly inertia period that started impacting the extra tropics in early June (and broke down the NW European anticyclonic domination during May) will determine how long our downstream ridge and very warm/hot spell holds together next week. Much as @Singularitydescribes well The ECM and its ensemble data looks to be suggesting that the mid Atlantic ridge might try re-asserting approaching the months end - indicating the spike in momentum reversing once more as part of a (possible) longer term negative trend to momentum in the atmosphere. It remains to be seen what diagnostic support there might be for the CFS forecast for AAM recovery sustained into the first half of July based on its known issues with amplitude propagation. On the other hand, it is also true that other proxies such as the Southern Oscillation Index point to an overall very neutral pressure differential in the Pacific that is not following the script of a descent of the atmosphere into a traditional La Nina type summer. A +ve SOI trend is traditionally a sign of La Nina establishing in the Pacific So the extra tropical forcing continues to assist sub tropical Azores ridge development downstream and something of a cap on the amplification potential in the Pacific that would usually occur in the circumstances.. As stated previously, the less amplification in the Pacific, the less chance there is of a retracted Atlantic ridge gaining a sustained foothold. The lack of any summertime stratospheric forcing on the troposphere is also helping the cause for sub tropical ridging. So suffice to say, there are a lot of pitfalls in general NWP at the moment for the extended period because relatively small adjustments one way or the other will have quite some impact on whether we stay at least part under downstream ridge influence through early July or whether the downstream trough becomes more and more dominant. I have annotated the GWO plot based on the uncertain forecast options. These are just rough and ready scribbles simply to give a very simplified guide to the calculation in play within the atmosphere. The failure to consolidate Phase 4 is the decidedly faster route to end of the very warm spell whereas a greater orbit to Phase 4 would make quite some difference and provide a ridge solution maintained for at least some days longer into week 2 (end June/start of July)

Yes. Based on the upstream signal, the surface conditions are, and have certainly been, better than one might expect for a pattern of a retracted ridge and relatively lower pressure downstream. Low angular momentum conditions heading towards high summer wavelengths can lock in a more amplified upstream pattern, and, as a consequence, a deeper trough anchored close to and over to the NE - with winds predominantly between a N and W vector. So below average temperatures, sunshine limited to early and late in the day followed by unseasonally chilly nights - and temperatures taking an extra knock back during the day during periods of rain or downpours. After an anomalously warm Spring in 2011 similar to this Spring, unlike this year that type of very cool and unsettled polar maritime regime set in quickly in the lead up to summer (and lasted, mostly uninterrupted, though the bulk of the summer) No chance in 2011 to see trough re-set in the Atlantic and even the chance to see warm air advection from the south.. Such as we see next week for example. Perspective. The lottery of the weather on a small island with a big ocean one side, and a large continental land-mass on the other, means that all of us at some time don't share the lions share of any goods - or bear the brunt of the more inclement conditions. I expect if (hopefully) I ultimately succeed in relocating to Portugal I will still remember this principle with the different weather expectations to be found As per pervious updates, unfolding NWP links to recent suggestions of keeping an eye on the tropical signal during this second half of June - angular momentum tendency should rally somewhat as a convective signal edges east across the Maritimes towards the West Pacific forcing a reversal in the extra tropics of a long lasting on-going negative mountain torque across the Himalayas - which results in an upstream Pacific jet extension and forward momentum downstream and greater trough solution in the Atlantic. The initiation of tropical>extra tropical wind-flow data to the AAM product from the CFS that gets posted on here requires to be checked with the relevant proxy data to assess reality vs forecast. That is where velocity potential charts, as posted above, that identify tropical convection anomalies, plus the wind-flow and torque budget plots as well as the consolidated GWO data can help match reality vs model forecast. Often enough a signal identified by a model is correct, but it can either make an error of the amplitude of the signal or it can be overly progressive with the timing. However, for purposes of the direction of possible travel, it is still a useful product as long as it is not taken too literally at face value at what it shows from one update to another. Much the same as NWP. The handling of the advance of the trough to the west, in the extended period, to the humid plume advected northwards c/o the downstream sub tropical ridge - provides a watch for hot sunshine and scattered thunderstorms, at least for some, to follow this weeks warm and showery interest. It also carries a caution against assumptions of what follows any subsequent breakdown from the west. Whilst long lasting summer anticyclones look unlikely - further sub tropical ridging seems reasonable. As long as the relationship between the tropics and the pole remains tilted to the former rather than the latter then there is less chance of any Atlantic ridge getting locked in towards Greenland by rising pressure across the polar field that consequently weakens the propagation of sub tropical ridging from the tropics to mid latitude. There is a long way to go yet, and this requires a constant watch, but some of my own caution a few weeks back as to what might have already evolved has been pleasantly surpassed so far at least.

NWP duly investigating the possibilities suggested in the previous summary. Its the same story as detailed over the past 10 days - the requirement for tropical support to supply sub tropical ridge extensions to mid latitude and most especially to attain the eastward displaced Azores ridge that allows the sort of advection processes from the south envisaged in that previous post. There continues to a signal for a cyclical re-bound in angular momentum, irrespective of the long term trend - the question is where the floor is and where it can re-bound to - based on the extent to which angular momentum has fallen already. Atmospheric angular momentum now reflecting a distinctly Nina-esque forcing on the atmosphere with the Global Wind Oscillation into a higher amplitude Phase 1 - based on the standard two day consolidated lag. This represents this weeks synoptic pattern of an Atlantic ridge and slack low-ish heights across much of NW and central Europe. There is fortunately no polar cell forcing on the pattern c/o the mercurial and rather a-typical very weak e/QBO signature - hence the slack pattern is of the warm variety with a pleasing mix of lovely summer sunshine and convective enthusiasm. Set against the suppressed momentum, as repeated previously, there is off-equator forcing strengthening the Azores sub tropical ridging, along with the lid being kept the on e/QBO stratospheric/tropospheric forcing and is preventing an authentic summer low angular momentum response which would involve a more pronounced Atlantic/Greenland ridge and a trough stuck across NW Europe and Scandinavia. On that basis there would no chance of any eastward ridge extension splitting to a downstream ridge element and allow, at least the possibility of a plume or very warm advection from the south - the predominant source of air would be from North Atlantic polar maritime and arctic maritime sources. It is interesting that the EC seasonal model suggested the traditional Nina summer pattern for July - as initialised at the start of this month. However the EC weekly updates have moved in the opposite direction and along with the CFS modelling have reasonable agreement for anomalous ridging to persist across Scandinavia - with trough influence ebbing and flowing to the west. This does reflect quite significant differences in QBO and associated tropical forcing expectations. The last two summers have shown it is possible to arrive at hot continental solutions under falling angular momentum in June - the key is maintaining influence from the tropics and attendant sub tropical ridging alongside the AO staying at least neutral. What will matter, ultimately, is with the arrival of July and how the atmosphere couples with high summer wavelengths. That will decide whether the CFS/EC weekly modelling is accurate or, should momentum stay supressed and the polar cell start to become less favourable, the seasonal modelling is closer to what happens.

It is sensible, at any season and an any time, not to try to fit any weather preference to numerical model output interpretation of the diagnostics that drive them. The NOAA charts are a best guide to numerical weather modelling guidance though it has to be remembered that these are also snapshots in time of the overall numerical model interpretation of global diagnostic wind-flow inertia. On that basis they will also evolve and are subject to change as that interpretation of tropical>extra tropical wind-flow inertia becomes consolidated in agreement in the nearer term. I think the fourth quote is an accurate assessment well pitched between the opposing boundaries of operational output orientated reactions in the quotes that precede it The continued interventions from the NW of trough features are indeed converging, taking into account all NWP, as to how progress of the Azores ridge is suggested to ebb and flow. This has been the focal driving factor, since the broad-scale pattern change away from the dominance of anticyclones at the start of the month. Often referred to quite appropriately as an "envelope" by some on here, it seems to me that this envelope of possibilities is more blended, and less black vs white than some of the omnipresent views on this thread. There are continued uncertainties and some contradictory implications, at present ,with regards to tropical forcing as @Singularityhas recently emphasised on here. The outlook remains sensitive to events upstream in the Pacific and how much amplification, or not, takes place there. For downstream summer hopes - the less amplification upstream in the Pacific, the better. It is complex, but there seems to be some link here between how the tropics and extra tropics are acting in something of an disconnect with the notion that off-equator forcing c/o anomalous warmth and moisture across the tropics as a whole (aside from the cooling of the ENSO regions) is mitigating what would be the expected pattern of a growing La Nina and e/QBO transition signal.. The off Equator forcing is creating a stronger downstream sub tropical ridge response which off-sets the opposing attempt to raise pressure across the extra tropics in the Pacific and create a deeper downstream trough response (than the weak height transferences that we have been seeing) due to La Nina-esque falling angular momentum. In short, the tendency for a downstream trough led by an amplified Pacific wavelength is being watered down (to a degree) by the sub tropical ridging (Azores High) being influenced through strengthened tropical wave propagation. Such a development makes the Azores High more influential across NW Europe than otherwise would be the case. It is a case of seeing whether this gains traction or is just a temporary disconnect. But it does rather echo, so far at least, what happened in summer 2016 - which turned out (relatively) better than was originally suggested, more especially the latter part of the summer (and into some glorious September weather as well). That year also featured a very enigmatic QBO transition to easterly, which was ultimately curtailed. There is uncertainty this time around, but there seems to be a link allied to keeping the polar cell more stable due to dampening of any stratospheric disturbances caused by absence (so far) of pronounced e/QBO downwelling. Such a scenario would also lead assistance to deepening of La Nina forcing and greater upstream amplification So irrespective of the mixed moods on this thread, an upper trough over Greenland in summer is not necessarily a bad thing to have, and even with the trough influence ebbing and flowing from the NW there always remains a much better chance of classic summer weather quickly appearing whilst this remains the case. It would be more dubious if there were signs of that wholesale drop of pressure at mid latitudes and pressure rising across the pole and extending a block into the N Atlantic. This is still not the case, and while things can and sometimes do change, I am personally encouraged by the lack of appearance of this so far. Musing here to an extent, but for what it is worth, should the tropical signal align further c/o that anomalous warmth in the tropics and the polar cell remain stable - irrespective of what extended ensembles and associated cluster data suggests currently as a snapshot in time (yes, that phrase again) - look for that trough to the NW to start align itself in such a way to allow some hot and potentially thundery conditions from the south later this month

Well, in truth it is the strength and trajectory of wind-flow inertia of the jet stream - which determines the turning force exhibited on the jet stream. That turning force of the jet stream is manifested by a torque mechanism and impacts whether angular momentum increases (positive torque) or decreases (negative torque).So this is why diagnosis of AAM trends, and where specific wind-flow convergence or divergence is occurring across the hemisphere is highly useful in assessing how well NWP interprets jet stream calculations Latest NWP is at the same fork in the road that led up to the week just completed. It is sensible to interpret the latest suite and representative of clusters as a snapshot in time and see how the overall modelling converges on this over the weekend and into the start of next week The suggested outcome for this week (which didn't come off) whereby there is downstream ridging ahead of a sharpening trough in the Greenland tip and Iceland region. As we know, the trough has disrupted through the UK into the continent rather than staying integrated to the NW and helping to amplify the downstream ridge across the UK into Scandinavia with the trough despatched further away to the west or south west. A quick look at the Global Wind Oscillation plot, based on consolidated lag time, supplies the answer why the trough didn't back west and the ridge stayed more retracted rather than extend across to Scandinavia. Phase 8/1 is on the perimeter of low angular momentum La Nina attractor phases - which advertise amplification wavelength set from the Pacific and adjusting the downstream amplification wavelength accordingly. The GWO plot reflecting global atmospheric angular momentum fallen below average As previous posts have documented, the recent slide in angular momentum has shown that getting to the downstream ridge scenario we came so used to seeing rinse and repeat with ease during the Spring, has more stacked against it under our new summer wavelength whereby a tropical signal is adjusting the rossby (amplifying) wavelength on a more retracted regime. As described in detail in various posts.. So it is worth re-posting this GWO plot from the other day as a gauge as to where it needs to orbit to match the scenarios that GFS and UKMO (up to now) are indicating. Phase 4 GWO indicates the upstream pattern de-amplifying as momentum increases and sends the amplifying wavelength much closer to NW Europe at the same time as a trough sharpens in the Atlantic. The further that momentum falls in the very near term (i.e slides into the lower momentum GWO phases 1 and 2) then Phase 3 becomes more likely as the maximum uptick response rather than Phase 4 and this would indicates a very weak and transitory downstream amplification response before the upstream wavelength resumes the Atlantic ridge and downstream trough back in place. It is the question that NWP overall is calculating at the moment. Suffice to say the ECM is erring towards a low amplitude orbit to GWO Phase 3 scenario whilst the GFS and UKMO, to date, are seeing greater downstream amplification. Given the fact that the modelling has tried to start reflecting a deepening e/QBO and coupled Nina-ish signature during June to the overall polar and tropospheric pattern but now pulled back to a +AO/NAO regime there is some short/medium term indication to be gained from that how the ongoing mercurial QBO behaviour might be instrumental in maintaining a stable pressure profile across the arctic for the time-being. As long as this continues to be the case, and it needs to watched for change, then there is support for the provision of more opportunities for sub tropical ridging to play its part and, overall, maintain seasonal average to fairly warm temperature anomalies.. It could be a worse outlook, albeit quite changeable, and one that with upside momentum to sharpen the downstream ridging could quite quickly became a very good one and invite some of the warmest air in from the continent. Its worth keeping in mind though the niggle of the upstream pattern re-amplifying again however instead - and the less exciting scenario of another nuisance trough splitting too close to NW Europe. These CFS AAM forecasts for late June and into July require evidence from the Global Synoptic Dynamical Model diagnostic (GSDM) to back them up as a clear signal that the atmosphere doesn't want to go a whole hog to a La Nina coupled signal - or confirm that it is modelling too high an amplitude signal in the tropics to sustain such an uptick in momentum. As can be seen the prediction trend ensembles oscillate with each update much like any numerical evaluation and prediction of atmospheric parameters. But it is nevertheless a source of interest to keep watching as June moves forward because the direction of travel will help determine which longer term fork in the road is taken with the weather pattern

I am sorry you think that. No expert in my case - just an ordinary member trying to apply some balance whilst at the same time also trying to delve a bit deeper into the science. Which isn't always an easy thing to do. Mistakes however, are the best way to learn.. Irrespective of assumed knowledge, everyone makes mistakes. This is a good thing, and is rewarding for the next time. It is true though in my opinion that it can be helpful to step back from reactive judgements stemming from responses to NWP at face value - and instead let answers to questions evolve in their own time. This is a good way to starting to understand the (apparent) curveballs that occur with NWP output.- and in turn leads to greater evenness in the nature of response. That is intended as a helpful suggestion, albeit as constructive criticism, but in no way undermines the contribution of anyone Back to the modelling itself, and more especially the diagnostic process (as I keep referring to it) The deterministic tropical convection forecasts are steeping the convection signal in the Indian Ocean. Calculated tendency of angular momentum refers to an aggregate of torque responses within the atmospheric circulation. Wind-flow torques are created by the turning force applied to the jet stream due to deflections in wind-flow speed and trajectory within the atmospheric circulation. These can decelerate (negative torque) or accelerate (positive torque) wind-flow according to where they occur in the tropics and extra tropics. The diagnostic plot shows considerably tanking negative torque inertia propagating from the tropics to extra tropics - as manifested towards the active convective signal across the Indian Ocean and the suppression of convection across the Equatorial Pacific Ocean The tropical signal rooted in the Indian Ocean will continue to promote easterly (negative) inertia across the Pacific with the standing wave relocated further upstream in the tropics - and this in turn re-configures (retrogresses) the amplified rossby wave response further downstream. In both summer 2018 and 2019, momentum actually fell during June and this is not uncommon as linked to the Indian monsoon season which typically begins around this time . What matters is how the Walker cell behaves as interpreted as differential between the low and high frequency tropical signals. Both those summers also saw a convection convergence signal within the Pacific which interfered with the low angular momentum forcing within the atmosphere and assisted greater eastward ridging of the downstream sub tropical (Azores) ridge - most especially of course in 2018 which saw a steady progression from a weak La Nina to warm neutral ENSO by July. Last summer saw a warm neutral/very weak El Nino dovetail with a w/QBO and both these neutralised the a-typical (to El Nino) low angular momentum trend and effects of the very dynamic final warming of the stratosphere in late Spring 2019 which had developed a high latitude blocking response this time last year - but was largely overcome by late June. Last summer angular momentum trend here as identified on the 365 day plot: The takeaway from all this is that falling momentum during early summer on its own per se, does not automatically imply "summer is over" each and every time. However, it does require some a-typical tropical>extra tropical proxies to be present, to alter the traditional summer La Nina low angular momentum response which blighted summers such as 2007, 2011 and also the second half of summer 2017. Just as a few examples.

The fall-back of pessimism and what can go wrong will go wrong is a very simple option any of us could choose, but it isn't scientific. The first caption from a previous post on Monday is a reminder of realistic expectations and cuts through the very easy option of trying to be wise after the event NWP has duly evolved down the path of juxtaposing the divergence of those two signals as suggested in that post the other day. It makes comparing and contrasting the blends of solutions being advertised a very precarious process. On that basis there is little value or constructive purpose, as ever, demonising one model or another - there have been leads in ECM modelling that have deviated at times, as much as the GFS operational. No numerical model is (ever) bullet proof and that extends to the UKMO et al as well.' Furthermore, guidance from ensemble and cluster data can also be culpable - it is possible to have good agreement for a wrong solution as much as sometimes a less favoured solution can gain support with time. It is the diagnostic that matters and which ultimately decides and in that sense it doesn't matter which model is proved "correct". My own position is, as always, less interested in the computer model "hugging" and more interested in seeing how they resolve the diagnostic. This is a process that takes longer than 6/12/24 hours on an intra day basis but too often evolves over a few days at a time. Since the highlighted post was made on Monday, they have indeed started to "see" the fork(s) in the road according to the wind-flow momentum budget and the truth, as anticipated, remains very finely balanced. Global atmospheric angular momentum since the end of last week has slipped into slightly negative territory and wholly consistent with the change of weather as discussed in detail for some time it is worth looking at some other diagnostic proxies. Irrespective of lower angular momentum, one of the leading atmospheric proxies, the Southern Oscillation index, which gives a guide as to pressure differential across the Pacific, remains very neutral and no uptick in sustained positive indices to suggest fast and progressive coupling of La Nina in the atmosphere. There is not the kind of negative PDO signal upstream suggested to "lock in" a retrogressed pattern. Nonetheless, it is becoming clear that something of an upstream switch is occurring that looks like it might make it more difficult to achieve downstream ridging with the sort of ease that was demonstrated during the Spring Furthermore however, the QBO continues erratic progress and only very weakly negative easterly - and continues to show little enthusiasm for rapid down-welling of easterly phase such as happened in a summer like 2007,..and deepen such attempted coupling and stratospherically induce an unstable tropopause layer (higher latitude blocking). In that sense, the suggestion of a more traditional westerly pattern in the further outlook is not necessarily a bad thing in terms of the Azores High relationship with lower heights towards Greenland. However, any retracted Azores ridge is not going to lead to classic warm summer weather, albeit relatively better than polar blocking and southerly tracking lows. QBO Jan to May 2020: Jan -2.51 Feb -3.20 Mar -4.36 Apr -5.03 May -4.86 . Very weak and erratic at present. The pattern is re-set as suggested some 10 days back. However, the full re-set to Scandinavian High and the trough backed comfortably west was achievable under the May (higher angular momentum) wavelength. A further switch into early summer wavelength and less forward momentum in the atmosphere to assist downstream ridging is proving to make this more difficult to achieve in June. A resurgence of the Azores ridge across the UK in the extended period is subject to a rise in angular momentum tendency and the GWO re-orbiting accordingly back to (rising tendency) Phase 4. This remains quite possible but again, subject to change not just based on the uncertain fulcrum of the medium term, but also to the susceptibility of keeping Azores ridging held back and pressure lower downstream if momentum stays flat and the GWO doesn't arrive back at Phase 4. That particular question is beyond the first corner. The fence for sitting on is moi But objectively, that seems intuitive at present. .

Will Noah visit Chipping Sodbury, or *insert town of choice* with his ark (?) Mood driven invective often results in loss of clarity and perspective, so some further retrospective analysis might help to we know why we have arrived where we are, and then what is set to happen over the coming days as processes keep evolving. Apologies, I admit much of this has been exhaustively dealt with previously, but operational output "model hugging" can mean that objective facts c/o the diagnostic can get buried in translation So, as previously suggested during last week, there is uptick of trade winds (shaded blue on the Hovmollers plot) towards the dateline in the Pacific as convective suppression occurs in wake of the convectively coupled kelvin wave (CCKW) returned through the Western Hemisphere to the Indian Ocean. This the cue to scrub westerly inertia from the global atmospheric circulation. The uptick in easterly inertia across the Pacific creates a negative mountain torque response (Pacific jet retraction) across the Himalayas. Indicated in red on the Global Synoptic Dynamical Model (GSDM) plot. This has set up the much anticipated retrogression of the hemispheric pattern from the Pacific and a subsequent re-configuration of the downstream signature and switch from the fine warm sunny weather that stretched in to the first couple of days of June c/o our downstream ridge - to a retracted Atlantic ridge, slump in pressure across NW and central Europe and winds of polar origin. Hence the unpalatable June conditions since the end of last week that are set to continue into this week as the retrogression process continues. This allows the Icelandic trough, midweek, to slip down the eastern perimeter of the retrogressed Atlantic ridge and disrupt into the continent. The retrogression is then completed as the Atlantic ridge amplifies over the top of the trough and extending eastwards into Scandinavia. By the weekend, the trough is re-set to our west and south west and warm humid air advects westward and chilly rain is replaced by a much more seasonal convective variant and less by this time in terms of dynamic rainfall. Caveat for those in environs of Chipping Sodbury *she says jokingly*. (In seriousness a quaint and charming English town) x The outlook continues to revolve around where angular momentum finds its floor and how much returning upstream momentum helps reinforce the re-set trough just to the west and south west . If momentum stays somewhat suppressed then this might invite the trough to phase from the Atlantic to the thundery heat lows close to the UK and the continent and then for another retracted amplification of an Atlantic ridge to force the humid thundery set-up further into central and eastern Europe and cooler air to arrive from the NW. However, should there be some momentum uptick this will reinforce the re-set trough to the west and help prop up downstream high pressure to the north east and every chance of a renewed plume scenario from the south. .....? This is the watching brief for the extended period, but certainly a warm-up later this week and through the weekend especially into the start of next with a mix of summer sunshine, most particularly away from influences of the trough to the south west (parts of Scotland look well set for this perhaps as one example) and also with so much moisture left around in the atmosphere, the instability triggering probable development of thunderstorms particularly where and when the sun does get to work for periods of time. Not a settled pattern, but certainly one that is more seasonal than what we currently have and also one to please weather enthusiasts

If I may interject here - that assertion might prove somewhat problematic...I don't post here in winter.. NWP starting to "see" the return of the trough to the west and south west around the mid month period as suggested earlier. This is not looking to be a settled period, the emphasis is on humid conditions and thundery potential. With that in mind it is helpful re-iterating because "reasonable weather for this time of year can span both warm and settled and also the more "tropical" type. Hope people enjoy the rest of the weekend and stay safe and well

Any atmospheric shift towards La Nina (if it occurs) following the cooling ocean lead would likely have lag period of a few weeks, so in terms of weather patterns it wouldn't likely have much impact on the modelling for a while. For my own part I have been careful to caveat the first third of summer (i.e June) as holding reasonable opportunity for further warm, probably humid and potentially thundery weather. There is in my view high uncertainty, either way, thereafter. There remains above average off-equator heat content across the tropics in general aside from the Pacific, which is and has been conducive for sub tropical ridge development - and until or if there are signs of negative tendency within the stratospheric layers inducing tropospheric blocking transferring to higher latitudes (rather than simply amplified sub tropical ridges to higher latitudes), then both these factors should present angular momentum falling too far too soon. It becomes trickier heading into July when seasonal wavelengths may become more conducive to coupling towards an atmospheric La Nina. These seasonal CFS velocity potential (VP) convection anomalies (shaded blue) hint at subsiding air (shaded orange) across the central Pacific leading into this time, replacing the more El Nino like convective convergence signal that assists downstream ridging and instead tends to re-configure to amplification upstream where the inflection point of subsidence (stable air) occurs. In this latter scenario, the downstream ridges are retrogressed more sustainably under such an arrangement rather than the temporary arrangements we have been seeing c/o the MJO "mini ENSO cycle" when the tropical wave passes the Western Hemisphere and into the Indian Ocean on a transitory orbit basis when the low frequency standing wave still exists in the Pacific I posted this plot below fairly recently. Worth posting once again. Take a look at the symmetry of global atmospheric angular momentum which represents the previous lull momentum periods (and the peaks) of the tropical cycle on this 3 month plot Also take a look at how the Global Wind Oscillation, a phase plot depiction of momentum wind-flow, has seen negative tendency in momentum |(GWO Phase| eight) at the bottom of those lull cycles. The indicated arrow depicting downward (negative tendency) momentum and the 3 small squiggly circles in different colours (excuse the artwork!) depict and reflect the associated descending same phase orbit each time. So from these diagnostic plots it can be seen that late March, Late April and now the start of June have imprinted the lull phasing of monthly mini ENSO cycle very neatly - and if one look at the synoptic pattern for each of these periods there has been retrogressions and associated incursions of polar origin as ridging has temporarily taken up residence across the Atlantic and a trough very close to our east or over Scandinavia. This before momentum has rapidly risen once more and the downstream ridge has returned. Note the large upswings in tendency to the other side of the GWO phase plot and to the GWO El Nino attractor Phases 5,6,and 7 which have represented the peak momentum periods and each has renewed the propagation of the lovely Spring-time sub tropical ridges we have enjoyed To conclude: Taking into account the transition to any such coupled La Nina arrangement, (if it was to happen) and the incipient lag time, then there is no reason to believe that June will be too adversely affected beyond the capricious machinations that are currently playing out - and as stated earlier in the post also it remains the case that the extended summer period is still subject to other uncertainties, not least the effect of the enigmatic QBO on the stratospheric/tropospheric relationship. In short, "summer is not over" at this time.

The commentary on here is poorer to be honest than anything that NWP suggests Far too much absurd overreaction to this trough cutting off and disrupting south through the middle/latter part of the coming week. It has already been pointed out more than once that this theme has ebbed and flowed since early in the week (i.e at least 4 days) so it is hard to know why so many are acting surprised and/or disappointed about it. Especially as it was something of a note of interest initially in terms of possibilities thereafter! Quite bizarre! From my own point of view little has changed over the week, other than yesterday it did seem possible that a faster track to warmer air might have been possible with the Atlantic ridge splitting and allowing a downstream ridge to develop ahead of the trough - thus allowing the warmer air to back westwards more quickly. However, from the outset, about three posts back, some doubts were expressed about the eastward progression of the Atlantic ridge prior to mid month and hence the full retrogression and re-set route always seemed more likely.. The diagnostic - i.e the balance of the completion of the retrogressive phase (as detailed to exhaustion already) and when momentum from upstream might start to return - thus re-setting a trough in the Atlantic vs ridging across Scandinavia was always going to be a fine margin and this margin is far from decided yet - following the trough heading north to south through the UK. That theme is still advertised - it is simply that the numerical models have not decided where the new trough wavelength sits vs the warmer continental air to the east. Better not to agitate over intra day operational details, and most especially surface details, which frankly are a particular lottery up to 5 to 10 days out at the moment and from my own perspective seems like a complete waste of time as well as quite unnecessary and self inflicted stress, That includes any "demonising" of any computer model which are simply making calculations around a broad theme that has actually been consistent for several days - it is simply micro scale details which are determining how the process evolves and for a small island like this one these make subtle but quite significant short term variations from one output to another and from one numerical model to another. Rather than trying to see too many trees in the wood, stand back and cast an eye generally around the wood first, and then pick out the trees one by one. One corner at a time rather taking on the next three at once and expecting immediate answers. In summary, and based on attempted objectivity (not optimism) still no reason at all not to expect a warming trend once this sinking trough equation is dealt with. In fact the mid month period onwards holds a lot of interest for low pressure to finally end up sitting to our west and south west and sending up some very warm and humid air as it pushes up against omnipresent high pressure to the NE. That, representing the point where the retrogressive phase completes and the trough is re-set to the west. Really seems counter intuitive to let this sinking trough overtake the greater perspective and then just extrapolate outwards c/o baseless pessimism. It isn't actually about being either optimistic or pessimistic - just trying to stop believing that is the models that lead the signals....

A lot of concern about the UKMO it seems. Perhaps it is forgotten that this southward cut-off low solution was what was advertised by the ECM and GFS earlier this week and at the time it was provoking a lot of interest rather than concern! Three days is a long time on this thread! An edited extract below from the previous post earlier in the week at the time the sinking trough was advertised cuts through a lot of the NWP discussion detail and agitating about whether the trough sinks ahead of the amplification ridge and then the ridge overspreads the sinking trough, or whether the ridge amplifies ahead of the Icelandic trough. But once the immediate change (and some of the worst weather) is out of the way that is where it starts to get interesting in my opinion. This retrogressive phase up to mid month is intriguing and could well end up re-setting the Atlantic trough as the ridging mechanisms back so far west that trough disruption occurs proportionately to our west .- but as stated, it could well be that the pattern retrogresses so far it re-sets the pattern to the point where momentum starts to return from upstream and a downstream Western European ridge is re-instated later in the month. That is an extended watching brief of course and will require further diagnostic data to emerge to fully back it up The relevant conclusion is that either solution ultimately should lead to the pattern backing west and increasing signs of re-setting the trough in the Atlantic. The (welcome) difference is that is looking to happen quite a bit faster than envisaged earlier this week. It had seemed such a sequence would occur after mid month, rather than (hopefully) shortly before it A "Western European" ridge or "North European" Scandinavian ridge are the same ballpark results. Increasing signs now that momentum will start to rise at the pivotal point the retrogressive phase concludes. Furthermore, there remains little sign of easterly zonal wind descent within the stratosphere to the troposphere c/o any strengthening e/QBO to adopt any high latitude Atlantic/Greenland blocking response which would force an omnipresent trough across mid latitudes. Note the difference here between amplified mid latitude ridges and ridges which are forged within the arctic and extend to mid latitudes. What we are seeing advertised is a summer tropospheric pattern where there is no polar night jet vortex and where ridges of sub tropical nature can extend considerably poleward. The net associated effect is that warm air advection is carried quite some way poleward. As long as the polar profile remains in a stable position, at least for the foreseeable future, then the first third of the summer, at least, could see some very reasonable summer weather and whilst not completely settled, there is certainly thundery potential in that warm humid air backing west . There is now a very reasonable possibility of this coming off and many will be very happy with a tropical aspect to the atmosphere Its worth looking at the 365 day global atmospheric angular momentum plot and see similar trends to momentum tendency as of the start of June 2019 . Back then we saw a warm first couple of days give way to a cool and unsettled phase before Atlantic ridging phased with increasing heat across mainland Europe and provided quite a cocktail of synoptic interest later in the month. There are at least some obvious similarities this June. As long as off-equator heat content in the tropics can keep driving the development of ridges to the extra tropics, and angular momentum doesn't fall too far as exacerbated by any uptick in e/QBO influence, then every reason to back that first third of summer possibility. This is an example of where" x=y" attempts at pattern match correlation cannot be fitted to one particular given pattern. For example, one has to look at the strength of the relationship between the tropical and polar stratosphere via the QBO phasing if any undertaking of interpretation of solar activity is to be engaged. As just one variation in terms of phase relationship, a pronounced w/QBO regime under low solar conditions in summer will tend to adjust a longwave trough generally to the west of the UK and with high pressure to the east. Summer 2006 was a very good example of this. A very different interpretation and result to the number of washout summers suggested in the 2007-2012 years. This might help answer a recent (very good) question about any developing La Nina this summer and how it may impact the season: Similar to the solar activity discussion with ENSO - there is no one size fits all correlation to the base state. One has to look at the precise relationship that the atmosphere adopts to the ENSO base state, and not just the base state per se - ocean and atmosphere can adopt an a-typical relationship towards one another instead of being tightly coupled. This bridges nicely to this brand new post A timely post Matt on the subject of a-typical forcing aspect in mind related to any Nina signal A summer like 1995 with a weak La Nina base state for example exhibited a tropical signal often routed through convection convergence zone in the Pacific which effectively produces a more El Nino type atmospheric response- hence the predominance of anomalous downstream summer ridges rather than a controlling La Nina-esque Atlantic ridge as seen under mid summer coupled ocean>atmosphere low angular momentum conditions. ENSO neutral especially can produce all variants of seasons - depending precisely on what the relationship is between atmosphere and ocean. So it is not possible to attempt to make prediction from the ENSO base state taken in isolation per se without looking at how the atmosphere co-operates with it (or not as the case may be) These examples are not exhaustive, but it serves to show that each season should be taken on its own merits and whilst it can be useful to match up given drivers present in a certain season and look at other years where such combinations were present, it is necessary to look at a whole raft of proxy data to see if and where a-typical relationships may lie - as a means to avoid x=y assumptions. It is a rationale I try to follow with up to fortnightly ahead summaries, but it is just one of a few good reasons to not attempt seasonal forecasting ! Yes - that is a good technical explanation of the tropical >extra tropical processes mentioned often in these posts and how propagation of these "rossby wave packets" carve out anticyclones as momentum fluxes between the tropics and extra tropics. It is these forward momentum fluxes which halt the influence of the retrogressive Atlantic ridge and re-instate the downstream ridge.

Thanks for your comments. I think all contributions are welcome and there is always something to take away from many collective minds. As for summer prospects - well I haven't definitively made any predictions at all, beyond an overview of the shape of the early summer and what to look out for that may evolve from there. I am not personally a "forecaster", or pretend to be. Simply produce summaries as and when appropriate that attempt to make helpful suggestions to look out for and hopefully give some balance to perspective. Sea ice as everyone knows has been an increasing factor for some considerable time - summers over such a time however have been a mix of mid and higher latitude patterns for a variety of reasons and which vary considerably from one year to another. Similarly with the other seasons in the year. The summers between 2007 and 2012 seemed to install an x+y= assumption that unstable sea ice patterns equated inextricably to an unstable polar field. Winter probably the biggest culprit c/o the snow watch. However, since this is the season we are currently opening our doors to , as many summers since 2013 have shown it is nowhere as simple or linear as this . Each year, each season should be taken on its merits with a very open mind that stays uncluttered by pre-conceptions. I do think there is also a preference/bias element in a lot of this x+y= type of approach and it tends to steer people to these types of assumptions as a form of confirmation bias. It is natural to have preferences of course, we all have, but fitting/pattern matching those preferences to selected drivers is fraught with error and doesn't work in terms of the meteorological science (as in all sciences) where bias cannot exist. Analysis of global wind-flow inertia which is the basis of the diagnostic approach that people such as me try to gain understanding of, provides a skeletal framework for deciphering jet stream structures from which it is possible to identify forward or retrograde synoptic patterns - as well as using tropical>extra tropical intra-seasonal phenomena which have scientifically evaluated cyclical timelines and wavelengths. This type of analysis is a very useful supplement to the traditional numerical modelling approaches and provided it is used objectively and not letting confirmation bias invade its use, can be a true revelation and highly rewarding for an ordinary observer. Back to the here and now: Still some agitating evident and not allowing time to look around each corner at a time and find answers. Such answers do not always come every 6 to 12 hours at times like this when a pattern many do not welcome is about to begin and require space to sit back, wait and watch However, from my own perspective there is a lot of interest growing in the way ahead. The analysis from on-going NWP is consistent with diagnostic and the ebbing and flowing of the Atlantic ridge. For fully detailed reasons given previously, this is unlikely to change significantly up to mid month and requires the day to day monitoring as discussed related to angular momentum budgets which will give clues as to when forward momentum returns from upstream. Such developments can only be attempted to be provided in timely fashion as they emerge. This is more sensible and intuitive than trying to make guesses and leading to obvious error through misleading information. But once the immediate change (and some of the worst weather) is out of the way that is where it starts to get interesting in my opinion. This retrogressive phase up to mid month is intriguing and could well end up re-setting the Atlantic trough as the ridging mechanisms back so far west that trough disruption occurs proportionately to our west . Amplification of a retracted Atlantic ridge is not always bad news for summer interest. Early summer low(er) angular momentum regimes often enough feature cut off low features sinking south to allow much warmer humid air to encroach from the continent as the ridging to the NW extends across and then over the top of these features. There remains credibility towards the end of the 10 day period of the solution hinted at on todays ECM deterministic output for this type of scenario. The overnight GFS also produced a similar idea and now the 6z GFS. NB: It is the general evolution that matters here, not getting bogged down with what each model suggests in surface detail many days away. This type of solution would be the maximum possible result to achieve within a limited regime - but as stated, it could well be that the pattern retrogresses so far it re-sets the pattern to the point where momentum starts to return from upstream and a downstream Western European ridge is re-instated later in the month. That is an extended watching brief of course and will require further diagnostic data to emerge to fully back it up The blended EC mean at day 10 indeed shows good support for the type of "shape" required for the back door route to happen with the lower heights sinking towards our south. The 12z ECM clusters indicated about a third of a majority support for this solution at day 10 The overnight clusters may well therefore probably provide evidence of what the mean suggests - that it has increased traction. Edit: Indeed they indicate that support has grown to at least a half.

@mb018538 Thanks for posting that, it is very instructive to the direction of travel during the first half of June and fully explains current NWP That VP anomaly forecast suggests a Western Hemisphere standing wave (convectively active) and convective suppression across the Pacific - which is entirely consistent with the convectively coupled kelvin wave (CCKW), as assessed in the previous post(s) which is in the process of departing the Eastern Pacific and is headed to the Western Hemisphere over the course of this week. This is the cue for angular momentum to slump back as suppression of convection (stable atmosphere and rising pressure) returns to the Pacific with associated negative tendency to the atmosphere. The current/recent warm height anomaly to our NE is caused to retrograde through a decelerative wave feedback that aligns the downstream pattern to the developing amplified sub tropical high pressure wavelength in the Pacific. Hence the ridge/trough arrangement across the Pacific and US aligns the downstream sub tropical high well to our west in the Atlantic. In turn the fall of pressure in our domain is encouraged further. The Global Synoptic Dynamical Model (GSDM) which comprises all the diagnostic wind-flow plots is updated daily (pm) but based on a two day consolidated data lag. Currently updated to 29th May which is clearly in advance of the pattern switch. Hence still firmly above average AAM. The answers as to when we start finding a way out of the incoming spell are going to be found by inspecting the diagnostics day by day and then matching these as to how NWP interpret them. But as in previous posts, it must be stressed that face value ssumptions and conclusions from each NWP suite is not going to be useful or lead to accurate conclusions each time It should be possible later this week to post the momentum budget plots to illustrate the torque processes that will be leading the imminent downturn in momentum associated with the chnaging wind-flow inertia within the tropics as the convective signal takes root in the WH The reasoning for the breakdown has already been fully explained and assessed in at least two my own posts already (as well as others who have contribued in this respect) and is panning out according to suggestions. Possibly slightly faster than might have been anticipated. So the "background signals" have not changed - it is simply that NWP is fully advertising the cooresponding change over a 10 day period - but which is completely consistent with the diagnnostic as explained above (and assisted by @mb018538 posting the VP 200 tropical convection forecast anomaly up to mid month) This does not show how the tropical>extra tropical forcing may be evolving during this time to impact the rest of the month. We have to pragmatically look around each corner as it presents itself rather than start second guessing the next one and even a third one before dealing with first things first. I think that in general there is too much agitating happening in this thread - and despite reasons provided previously not to agitate It is still two/three days before the weather pattern really breaks down (as expected) but already there are too many posts extrapolating way out in time the pattern change based on pessimistic hunches and because current NWP doesn't show any return of ridging. It won't within the time-period under dicussion. Until the upstream catalyst to hold the amplified wave in the Pacific is removed and set the downstream wavelength accordingly, then it is highly unlikely that the Atlantic/Azores sub tropical ridge is going to have too much eastward ridging influence. It will simply ebb and flow to our west with troughs riding around its northern and eastern flanks. Precisely what NWP is generally advertising at present for the coming ten days (with a couple of days this week until that pattern properly starts establishing). How things evolve leading up to mid month will revolve around how far momentum drops back in the intervening time and how much attempt the atmosphere therefore attempts to couple with the ongoing negative tendency (cooling) within the ENSO zone. It is also a case of monitoring the e/QBO descent - which has been something of an enigma to date with some countervailing and contradictory aspects to its profile layers. Negative tendency with the troposphere and the stratosphere as contrived by a strengthening e/QBO signal is presisely what we don't want to see in order to avoid a cool unsettled spell becoming something sustained towards a default pattern. These summaries have suggested neither of these are yet apparent, beyond the fluctuation of the tropical>extra tropical cycle of which is about to enter its negative tendency phase (i.e Western Hemsiphere and Indian Ocean wavelength). if this was to become a default standing wave, in tandem with signs of negative tendency between the stratosphere and troposphere implying stronger and longer lasting Atlantic blocking mechanisms migrating to higher latitudes (aka 2007 as worst case scenario) then that would be the time to properly agitate. However it is far too early to do this - not least because proxy data for the atmsophere (e.g AAM, SOI, QBO) are much less advanced and neutral overall than the start of summer 2007 when all where strongly heading into a La Nina & unstable stratosphere/troposhere regime. The coming few weeks are going to start to answer a lot of these questions. No reason at this time to write off months at a time (or whole seasons) But we cannot fit our weather preferences to the diagnostic and have to present what we find whether it is agreeable to taste, or what we might not prefer . Answers will present themselves one corner at a time, but with the required time allowed to supply those answers..

As a brief update, this is still the case The perspective of this apparent "pattern change" requires being seen as a snapshot in time on current NWP modelling - not a prediction for the whole of the rest of June or indeed the rest of the summer to come. Extended numerical model ensemble data just starting to reflect a return of upstream momentum to shunt the retracted Atlantic ridge back eastwards sometime around the mid month period. For example here is the EC weekly update for week 3. So a good proportion of a week of very warm weather still to come as from from today, taking us into the first few days of the first week of June - and then that underwhelming cool and possibly showery northerly incursion during week 2 of June leading to a steady improvement thereafter Continued assessment of the diagnostic and wind-flow budget vs NWP interpretation of these will be required in this very early part of the summer - but there continues to be nothing at this time to suggest a prolonged cool and unseasonal washout. Enjoy this lovely weather and take in the sunshine vitamin to help wellbeing

Re-quoted this as it has become wholly relevant to the evolution into the extended period as anticipated c/o the cyclical tropical>extra tropical cycle and a useful guide as why NWP depicts an Atlantic ridge and fall of downstream pressure in the extended period. There is no reason at all to change the thinking applied in that post and especially also there is no reason at all to have any doubts at this time about the final sentence either The tropical>extra tropical cycle has shown a remarkable timeline symmetry over the Spring months and easily identified by the timing intervals of the peaks and troughs of the angular momentum budget in the atmospheric circulation. It is an illustration of how the atmosphere "remembers" from its previous ebbs and flows- and it is now useful to look at these intra-seasonal timelines and assess how seasonal wavelength changes (in this case Spring to Summer) may augment existing default patterns or alter the evolving pattern from that seen at the previous peak change-end of month periods. Both March and April saw attempted retrogressions of the longwave pattern when AAM was embarking on its down cycle with momentum being removed from the atmospheric circulation resulting in the downstream pattern backing westwards and leading to cooler/colder winds from the polar regions. Both months have subsequently seen the Atlantic ridge punctured by an advancing trough heading into the West/Central Atlantic and adjusted the pattern eastwards once more Rinse and repeat of this switch once more as May hands over to June and we say "hello" to summer. Does this reasonably mean that following any northerly incursion, should we see one, there is a return to the dry and warmer spells during June which dominated April and we are now enjoying once more at this time in May? Extrapolation of suggested new patterns requires great caution with NWP suites at extended ranges and always a good time to check back on the diagnostics that are driving the numerical models to gauge whether they are on the right track and/or whether they are over egging a new signal. As often repeated by me in the past - signals lead models, models do not lead signals. This means that at distance they often (not always) latch on to a correct signal, but then they overstate its duration and can subsequently backtrack or smooth down the prognosis. Based on the above captioned summary, it remains sensible in my opinion to keep this in mind and rather than make assumptive extrapolations out in time of more of the same, continue to assess how the atmosphere applies its "remembering" . The weather patterns are not wholly chaotic all the time as they are often believed to be. In basic weather terms - overall good reason in my opinion to expect verification of the Atlantic ridge and an attempt to introduce cooler and more changeable weather from the NW approaching ahead of the second week of June. This, not before some excellent summery conditions for the bulk of the coming ~ 7 days which should be enjoyed as much as possible without dwelling too much on the suggested breakdown approaching after this time. Also, it is not yet clear as to how this eventual encroachment from the NW pans out across the UK in terms of sensible surface weather detail and as ever, regional variations may well be the case. These numerical model forecasts of AAM are not to be taken too much at face value and often enough there is a certain degree of correction of suggested trends moving forward in time. However this forecast looks reasonable value and reflects accurately enough the direction of travel with momentum loss occurring as the CCKW now propagating across the Pacific Ocean (as discussed in previous post) leaves convective suppression in its wake and the negative wind-flow torque processes that arise as westerly winds associated with the convective passage of the CCKW are scrubbed out and replaced by increased easterly trade winds. This atmospheric induced wind-flow switch sets up up the longwave retrogression of the downstream pattern at the inflection point of where the negative torque occurs upstream.. The CCKW at that time having moved on through the Western Hemsiphere ahead of the next tropical>extra tropical cycle beginning in the Indian Ocean So this lull phase of the "mini ENSO cycle" is totally consistent with the advertised synoptics. It is during this lull phase time that the last sentence of the previous post has relevance and is the watching brief over the coming week to 10 days to look for clues as to when the next warm settled summer spell arrives and will be the subject matter for the next summary. Virtually a week of that 10 days comprises the remainder of our current fine spell anyway

Fast approaching the last week of May, it looks increasingly likely that summer won't be arriving with global atmospheric angular momentum in below average territory. This means that the direction of travel continues to be quite different to other e/QBO & ENSO cooling summers like 2007 which saw very strong coupling of atmosphere and ocean right at the time spring moved into summer. Angular momentum crashing spectacularly on that occasion. Based especially on seasonal wavelength changes to summer - stable AAM is very counter intuitive to any sustained Atlantic retrogressed ridging and downstream trough. What a slight weakening of the eastern flank of the downstream ridging, and some attempted inroads of the trough to the NW might indicate is the completion of the robust intra-seasonal convectively coupled kelvin wave (CCKW) at present propagating eastwards across the tropics and due to pass through the Pacific in the remainder of this month. It is at this completion point in the "mini ENSO cycle" that angular momentum edges back somewhat. Suppression of convection occurs across the Pacific as the convective element moves on towards the African continent and Western Hemisphere. As atmospheric stability returns to the ENSO region in the wake of the CCKW, then this leads to trade wind inertia increase and a rise in pressure which in turn retrogrades the downstream wavelength and the sub tropical highs in the Atlantic (Bermuda and Azores) NWP will be anticipating the wind-flow inertia switch at this time, but as previously, they may over-egg the fall in momentum budget tendency based on global overall parity of momentum. This means they may either overdo the degree of retrogression/ fall of pressure close to the UK and/or the time period any such indicated switch of pattern lasts. As long as heat content across the tropics as a whole, and irrespective of the cooling in the Pacific, remains anomalously warm, this is conducive to further downstream summertime sub tropical ridging and the upstream pattern allowing the ridging to adjust back towards Western Europe. The reason being that angular momentum tendency is buoyed by such an SST basin arrangement & supports further MJO related activity and westerly wind inertia continuing to be propagated from the tropics to the extra tropics and the Global Wind Oscillation kept away from the La Nina attractor phases 1,2 and 3. The GWO is this week edging through the opposite spectrum of the El Nino attractor phases - so no atmospheric co-operation at all to follow the cooling Pacific ENSO profile The GWO in the high(er) angular momentum phases is therefore good argument to support further warm/very warm weather to return - with any less settled & cooler conditions trying to edge down from the NW leading back to further rinse and repeat ridging as suggested in the previous post last week