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Tamara

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Tamara last won the day on February 10 2017

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  1. The first and most important thing to say is to enjoy the spoils of some excellent weather in the 7 to 10 day period. After a warm week ahead, it could feel quite tropical by the Bank Holiday weekend with hot sunshine for many and some thundery downpours for some....then clearing to let hot sunshine out again. Rinse and repeat for a few days The last post gave some background as to how the early season warm spells have evolved since mid April. The highlighted sections of the above extracts from that post last week then went on to try to anticipate a likely crossroads ahead. This crossroads now broken down into basic suggested pathway scenarios : Changing seasonal wavelengths from Spring to Summer > leading to either, Low atmospheric angular momentum retrogression of the wavelength - North Atlantic/Greenland ridge and downstream trough or, High(er) angular momentum greater retention of downstream Scandinavian/European ridging and a troughing profile in the Atlantic to our west or, There is actually a third scenario that involves a lapse around the 12 to 15 day period into the Option 1 but a bounce (and likely a sustained cyclical bounce) back to Option 2 thereafter. That is I freely admit, covering all options *and sounding like a lot of back covering on her part* but two things here: The aim is, and has never been to give long range predictive forecasts - there are plenty of guru's around who like to do that anyway without adding any more. Secondly, the balance of factors, as I see them, are very finely balanced, so it seems eminently sensible to pitch any summary suggestions to embrace all the spectre of possibilities within that envelope. So I have my own little ensemble suite most of the time, which seems to work for me anyway Speaking of ensembles, NWP has indeed started to take the suggested pathways under the radar as we start the new week. The retrogression spectre started to appear in some low resolution GFS output late last week and now the EPS clusters have started to pick up on this signal. However, the background signals in relation to the tropics, extra tropics and subsequent consequences for atmospheric angular momentum remain uncertain. Based on some more recent historical precedence (and also a seemingly increasingly inherent longer term climate trend, but that is not for this thread) it would be easy to see start of summer and yet another collapsing angular momentum regime as somewhat predictable with a string of summers in the last 10 yrs following this same pattern.... Spring warmth leading to another indifferent cool and damp summer.... But back to basics - where are we with things this since time last week? GLAAM has slumped back below average, losing the gains of the recovery earned since mid April However, as likely commented to be the case last week, relative angular momentum tendency has been holding higher again in the present low cycle ebb than the previous low tide marks in the global wind-flow cycles of mid March and then early April. The inference of this, extrapolated longer term, is that the atmosphere is trying to resurrect itself longer term from the La Nina state that has, mostly, been in evidence for the last two years. Convection in the tropics in reflection of this, is continuing to imprint the active periodicity (recurrence) cycle of the last 90 days. As bolded in the captioned post above, what is very important as we hit June is that we see clear signals that MJO forcing wants to embrace eastward shift to the Pacific as represented by an evolution to Phases 6,7 and 8. This, as demonstration that the upcoming cycle represents a further move away from La Nina with accelerating westerly wind inertia in the atmospheric circulation sustaining the priming of downstream summer warm ridges rather than sustained lapse into downstream summer chilly trough. The deterministic tropical convection forecasts have been proving, not unusually, a bit too progressive with trying to break down amplitude of the latest cycle. There is a conceivable chance this time around that modelling may overcook -ve AAM downside, and hence any blocking in the North Atlantic and/or Greenland may be overblown. Either that, or of it does verify, it does not sustain. Just this side of the Spring/Summer wavelength changes, in the short term the recent fall back of AAM has done no harm at all. Indeed, the upstream deceleration of the jet has/is helping our downstream ridge hold sway with a moribund Atlantic. The deceleration and amplification of the jet upstream in the Pacific clearly represented here by the -ve mountain torque over Asia - with the consequent vacuum created to fill as momentum is lost from atmospheric wind-flows Such a negative AAM regime, however, not recovering as we arrive at imminent changing seasonal wavelengths also assists further retrogression of the longwave pattern and is not desirable longer term. So its important that momentum upstream has some impetus heading into the new month so that any retrogressed ridge to the W or NW (should it evolve) is shunted back east by the jet stream increasing from upstream and as a consequence LP being re-set in the Atlantic. This scenario would suggest a pre-cursor to some further, sustained warmth into the meat and bones of official summer - even if the initial burst of momemtum flattens the ridging initially and allows a (likely brief) more unsettled westerly pattern for a time. Some of our best summers have displayed this sequence of events in early season, so the retrogression scenario of the extended period, should it come about, should not be treated as "summer is over before its officially begun" . It could well prove to be the opposite. On that basis, the present and upcoming spell of weather may well be just a taste of what is to come. So best not fret, just yet anyway, about the new month (and new season) breaking the weather down - it might not be for too long if it does happen Have a lovely week and Bank Holiday weekend
  2. Hi - yes, some very relevant points made A favourite period of the year for me with the long hours of daylight. Autumnal weather set in comparatively early in September last year (no summer extension on this occasion) so the recurrent warm spells arriving following a cold and wet first half of the Spring have been especially welcome in my opinion with natural hopes of plenty more to come in the many weeks ahead of us. These warm spells are a good point to begin the starting analysis. Why have they happened, and why is it important that the factors behind them sustain to allow seasonal wavelengths to augment them, rather than increasingly detract from them as happened last summer for example? The tropics have been active in respect of MJO convection for several months. Everyone knows of the spectacular tropical cycle which helped engineer the SSW in February - but what has happened since. This is a layered profile of the atmosphere from top to bottom for the opening months of 2018 - which tells the story well. The classic down-welling series of the negative zonal anomalies evident from the stratosphere to the tropopause layers as triggered by the massive SSW - a series of higher latitude easterlies which persisted into the first half of April. Rather accounting for the weather type seen through the first half of the Spring with a supressed Jetstream and persistent -AO/-NAO pattern A change quite suddenly appeared in the middle of April with the polar field switching +ve in tandem with the Atlantic profile to +NAO. If we take a look at the trends of total and relative atmospheric angular momentum we can see a pattern reflective of the changes across the polar field and the tropospheric pattern. Seasonal wavelength changes heading into Spring in tandem with falling atmospheric angular momentum following the SSW locked in the longwave pattern to -AO/-NAO . However, during this time with the tropics remaining active, a series of +AAM anomalies propagated poleward over time in accordance with this activity and c/o co-operation in the extra-tropics in the form of repeated +ve mountain torques over Asia creating a jet extension across the Pacific and adding westerly winds to the global atmospheric circulation. (Notice also the corresponding peak in +AAM tendency in the plot above in the second half of April along with the recovery in GLAAM reflecting those additions of westerly winds). These westerlies aided a recovery in atmospheric angular momentum tendency and the poleward +AAM wave train eddies manifested anti-cyclonic wave breaking with anomalous mid latitude ridges bubbling up downstream which have assisted the jet stream north and warm air advection patterns replacing the dominant cold air advection and troughing of the supressed jet stream -veAAM/SSW legacy. Another way of looking at the attempted ocean/atmosphere steer away from La Nina type forcing is the -ve trending of the Southern Oscillation Index (SOI) downwards from persistent +ve numbers in March (signifying a Nina-ish tendency) to much more neutral figures in the last few weeks https://www.longpaddock.qld.gov.au/soi/ So, we have continued to reap the benefits of the lagged effects of these westerly additions through the much better surface conditions (overall) in this second half of Spring - the periodicity (timeline recurrence) of the MJO has shown its influence in this respect of large contribution towards determining longer range weather patterns, and the possibility of using these intra seasonal phenomena for assisting longer range prediction. This overview of the seasonal evolution since the end of the winter, provides us with clues as to trends to look for ahead as another summer rapidly approaches. We also have the La Nina legacy hanging over us in terms of how things evolved from this time last year, which after all also provided some early season warmth and sunshine before, ultimately going downhill by mid summer as easterly trade winds surged repeatedly and retrogressed the fine warm anticyclonic early pattern into an Atlantic height and downstream UK trough anomaly. The standing wave pattern of La Nina which has dominated everything for the last 2 yrs, (despite a few notable "destructively acting" disconnects of relatively higher AAM such as in February this yr leading up to the SSW) really needs to be unshackled over the coming 4 to 6 weeks to ensure that a reasonable chance that the jet stream shift seen since mid April and the presently highly enjoyable fine weather continues. As of the here and now, we see westerlies being scrubbed from the atmospheric circulation as easterly trade winds increase in response to kelvin wave activity in the I/O These easterlies propagating across the Pacific and with both total and relative tendency of atmospheric angular momentum snapping backwards. The Global Wind Oscillation, which is a plot depiction of total wind-flows in the tropics and extra tropics, has largely been orbiting between Phases 0/4 ( signal for downstream mid latitude ridging) since mid April and is falling back into La Nina territory Phases 1/2 in reflection of the tropical signal rooted in the Western Hemisphere At the moment, being still in Spring, the significance of easterlies being added upstream amplifying the Pacific pattern and decelerating the jet downstream remains a benign enough one ( @Singularity analysis is very good here). However, (assuming for just one moment the atmospheric circulation remains close to where we are at present in light of latest drop backwards) seasonal wavelength changes heading into the summer which is fast approaching increasingly suggest a retrogressive pull of the long wave pattern with the spectre of that Atlantic ridge and downstream trough returning if the ocean/atmosphere relationship cannot fully break down the legacy of the La Nina standing wave. This (in this scenario) would mean that despite the ENSO regime "technically" returning more neutral in association with many forecasted expectations - there would still be a -ve adjustment/disconnect to the atmosphere which inclines the AAM budget within the atmosphere being pre-disposed towards greater easterly wind-flow inertia and hence high pressure in both the Pacific and Atlantic - rather than a longwave more Nino-ish pattern of, the reverse profile, of Pacific and Atlantic troughs and respective downstream ridges. The trough in our locale under summer type +AAM/El Nino type forcing being repeatedly focussed/re-set to our west in the Atlantic and the ridges over Western Europe and Scandinavia. There is of course every possibility that this latter hoped for scenario prevails to underpin some of the promising seasonal modelling indications. If we take a look at the above copied GWO spider graph of the on-going low AAM phase of the tropical/extra tropical cycle , the Phase 1,2 orbit of the GWO is thus discernibly shallower than that of 6 weeks back. This reflects the overall grip that La Nina has relaxed on the atmosphere - though clearly not yet gone completely. Its important that we see a willingness of persisting MJO tropical activity supporting further bounces in +ve AAM anomaly wave trains, but more important still an eastward shift of the locale of this tropical activity from the Western Hemisphere Such an eastward shift in the location of tropical activity seeking cooperation from the extra tropics in form of more +ve torque mechanisms adding further westerly winds to the atmosphere to prevent the sort of deja vu of a La Nina type summer and instead keep building downstream ridges and reinforcing the trough in the Atlantic (and not the UK and Europe). This type of persisting +AAM anomaly trade between tropics and extra tropics would see the GWO orbit more sustainably keeping away from the La Nina Phases 1,2 and 3. The present atmospheric profile, as shown at the start of this post, is conducive to a +AO profile, which even with a de-coupled -NAO would clearly be very good for warm/plume advection - though its still early in this respect and there is time for things to change if a persisting lower angular momentum regime in tandem with eQBO gained ascendency and increases heights across the pole and encourages blocking in the North Atlantic and supressed temperatures as the tropospheric pattern retrogresses. 30mb zonally averaged winds at the equator. -ve QBO phase in italics and April figure in bold. 2017 14.92 14.78 14.35 13.88 8.01 -3.18 -10.48 -14.42 -15.28 -16.79 -17.20 -18.12 2018 -19.02 -19.37 -19.77 -21.41 http://www.esrl.noaa.gov/psd/data/correlation/qbo.data Aside from any La Nina disconnect considerations as part of any downside analysis, should we evolve on the upside towards a more El Nino type circulation or even a weak Modoki El Nino state during the later summer and then further on into the autumn (i.e the eastern most Pacific zone remains relatively cool and convergence winds in both the eastern and western Equatorial Pacific focus a tropical convection signal as well as help upwell warming sub waters in the Central Pacific) then there are examples such as 1990, 1994 and 2004 to draw on. These years have all displayed the virtuous cycle nature of repeated downstream ridging at least at some stage in the heart of those summers in our locale - and bringing very warm/hot conditions (and with the exception of 1990) a fair amount of thundery activity (c/o temporary trough intrusion overspreading and destabilising the heat) for the weather enthusiast who likes some added interest to blue skies and hot sunshine as well Lets hope that this early season promise leads on to more, and not less, for a change
  3. Hello people to my west I thought I would visit and try and send some snow your way The streamer that has given the cover here is showing signs of shifting west and some of you in the eastern part of your region should hopefully be seeing some very soon Tomorrow looks good for those of you further west of your region as well And then of course there is Thursday/Friday... Good luck to all x
  4. I think too many have already become desensitised to what constitutes a 'fantastic chart' and the seasonal ailment of this thread (which is irrationally mood driven anyway by the more average synoptic charts that are customarily on offer) has taken on a latest variant of becoming superimposed and twisted on the absurd semantic that 'merely' only UK Tundra conditions are being shown and not the Canadian variety. Truly, if you cannot exercise self control in front of your lap-top by the smorgasbord of dessicating cold solutions evident on NWP, especially as we are heading right into meteorological Spring, then its maybe best that a different form of self torture is considered to spare those who take a more considered perspective. This has nothing to do with any regional bias (coming from a part of the country that relies on these increasingly rare sort of synoptic to get a snow fix) its to do with the usual fascination I have for sitting back and marvelling at watching a pattern like this unfold in the greater macro scale. If/when it snows at home, I will be less inclined to spend spare time waiting for when it is next going to snow, or when its going to end - but instead getting out, having fresh air, exercise and enjoying it. And then, when the snow and ice is over, it will be a case of seeing how the patterns evolve through Spring and into Summer - looking for the best that can be on offer for this Island, whose micro climate is fickle, elusive and overly too mobile to the sort of sustained blocked patterns that can be the deeply cold derivative as upcoming next week, or depictive of deep Azure blue skies, sunshine and warmth of the summer. Get used to this reality - it will always be thus
  5. I quite often agree with your sort of sentiment, as I'm one who opts to look at the most likely solution to fit the signals rather than the preferred one But, equally impartially and with intended objectivity (hopefully): The situation at present is a highly unusual one and the risk of some astonishing late season wintry weather is much higher than usual, certainly than often seen in these cases where deep cold pool advection flirting with the UK graces the perimeters of more 'reliable' NWP The repercussions of this SSW are going to be sustained. The clock starting ticking back in January and carried on through this month with extreme instability of the atmospheric profile with the tropics and extra tropics being subjected to opposing high amplitude states of angular momentum tendency. The impact on tropospheric global wind-flows (the Jetstream) has been significant, in addition to the detonation of some intense cold pooling over the polar field (relative to the modern day generally warmer arctic) : more especially across the Canadian arctic as multiple programmes of hot needles are probed into the polar stratosphere The result of extreme tropical momentum and stratospheric implosion implies high impact weather events on a broad-scale. Some places are going to get bitterly cold and some weirdly warm. In this day and age fewer parts of a hemisphere can get cold with less to go around than used to be the case maybe. But this programme of events strongly favours the European sector to become bitterly cold from what looks to be an impressively large breakaway cold pool for the time of year from Siberia. While its true that the envelope of this cold has boundaries that shift in intra suite modelling, the focus of the BI being impacted in inclusion, is much higher than other situations where lesser broad-scale drivers have been in evidence Ramping indeed requires a justification - I think this situation fits that criteria. Areas of land mass infrastructure most at risk aside from weather impacts (hopefully with least human welfare risk), the synoptic blocking pattern and its associated reverse polarity from one side of the Northern Hemisphere to the other - is not something seen on an every day NWP menu
  6. Posted February 10 Irrespective of what the ECM goes on to show shortly and irrespective of what my head keeps telling me of how the effects of this SSW could be mitigated, I am not sure I have seen anything programmed quite like this thing. Polar easterly reversals are often enough mitigated at least to some degree by other tropospheric drivers, but I am beginning to come to round to thinking this may not be one of them where that happens so easily and its going to take over a lot of the NH for some time. it could be the case that it would start to be more prudent not to underplay the SSW, than place caveats as to what might mitigate it. On that basis maybe its me who should have a bit of a ramp, and not others who should restrain themselves However it plays out in terms of what comes out of the sky in the coming weeks - and despite the fact that the actual phenomena of SSW's is not new, this is quite a significant specimen indeed we are watching unfold ............................................................................ A week on, and a crazy amount of pages later, what has changed? Well I haven't had another ramp, and the deepest cold is still 9/10 days away But what has become clear in the course of a week is that the first stratospheric break-down salvo is set to verify for certain this week - and that day 9/10 day period marks Phase 2 and the time when the Canadian vortex to the NW should finally back off and the down-welling process of -ve zonal wind anomalies really start to make themselves felt in out part of the Northern Hemisphere On that basis we can give credence to the shape of the mid and higher latitude pattern and emerging block alignment with the deep cold backed up like a dam waiting to be unleashed I am amongst the most sceptical of day 10 UK deep cold in NWP and very often based on the realistic signals, barely take a second glance, if even much of a first glance at all But this SSW is a significant specimen indeed, and no further deep analysis is needed. On that basis I will be taking this particular day 10 deeper cold rathe more seriously as a contender The fact that Phase 2 marks the time when the strongest sibling vortex lobe starts to finally cave in after its winter rule, increases the chances of deeper cold air advection at that time-period not just because the block to the NE can start to orientate in ideal position as polar jet energy is finally being squeezed out, but because the chances of retrogression are also much higher so that at some stage re-loading deep cold has a heightened chance of finding out even this little Island. Probably the most simplified basic principle post you will get from me - but less is more sometimes and nothing else needs to be added
  7. You are quite right As was Captain Shortwave observation at the same time about the amplification in the Pacific sector. And that remains the clue, despite suspending usual thought yesterday for good reason. We can all think we are missing something when there are extraordinary things happening at all levels of the atmosphere. But seeing as I have returned to my head attempting to be in control over what is happening, then as previously suspected - its the case that falling angular momentum since the MJO induced Scandinavian ridge of last week, is meaning that -ve zonal easterly winds are lining up again from along the tropics at 30N As repeated a bit like a stuck record by me this season (sorry about that but its based on intended good reasoning) the effect of a return to more La Nina-like type forcing (for the time-being)is to re-boot the sub tropical ridges aligning along 30N. The classic configuration of this forcing this winter has built up the signature traditional default pattern of amplified North Pacific ridge which locks in the Canadian vortex, with increased polar jet energy and further sub tropical ridging downstream pushed to mid latitudes across Bermuda and to the Azores ridge. The -ve zonal wind anomalies supporting these ridges underneath, with the polar jet flow across the top. Very much a +NAO regime. However much members dislike it, that is what the ECM operational keeps modelling each time at the moment into the medium term, and its not hard to see where it is coming from - based on its interpretation of the recent very high amplitude tropical forcing concluding its cycle - and with those -ve zonal winds returning across the 30N as angular momentum falls back ...ahead of the next tropical cycle retuning to the Indian Ocean. If one thinks that the deep amplitude low angular momentum GWO pattern of January helped cement the Canadian vortex at a time when the polar field is typically at its most organised, then as suggested in posts at various times through January (and in anticipation of the latest MJO forcing) it was always going to be a big ask (initially) to change an entrenched tropospheric base state pattern - which in turn frameworks the polar field. I think a weak El Nino forcing, in tandem with eQBO would have created the stratospheric pathway that does not favour amplification restricted upstream in the Pacific and does not teleconnect to a strong Canadian vortex lasting in latter winter and being more resistant to any poleward wave flux that does come from phases of tropical momentum Under a feedback pattern that produces steady background poleward +AAM forcing, and unlike a La Nina regime not relying wholly on tropical convection forcing to boost westerly winds in the tropics as a means to amplifying the extra tropics downstream (the Atlantic and European sector) then this SSW would have taken route 1 - as last weeks +AAM spike produced in terms of the Scandinavian ridge and less upstream energy waiting to return c/o the Canadian vortex. .The SSW would be more likely dealing in those circumstances with a sibling Canadian vortex and parental Siberian lobe - rather than the other way around as we see at the moment, and as very well described by @lorenzo on the stratosphere thread today Its a case in my opinion of the tropical cycle re-setting from the Indian Ocean and angular momentum rising once again. Also I think that March will see the Pacific profile change and warmer sub waters changing to mean that a more sustained +AAM cycle will evolve as a signal that this La Nina is going to fade though the Spring into early summer. So an extension of 'winter' and a cold March does look intuitive on that basis at this stage Before then, however and notwithstanding all said in intended sense as above - its still very much the case to watch this bag of tricks called the SSW . As soon as the parent Canadian vortex shows weakening and the models factor in better the constantly new starting conditions based on the Krakatoa evolving from the highest levels of the atmosphere downwards, then the stubborn tropospheric pattern c/o (weakening) low angular momentum forcing should become less dominant and more easily overridden - especially as wavelengths shorten and assist cold air advection heading into March
  8. Irrespective of what the ECM goes on to show shortly and irrespective of what my head keeps telling me of how the effects of this SSW could be mitigated, I am not sure I have seen anything programmed quite like this thing. Polar easterly reversals are often enough mitigated at least to some degree by other tropospheric drivers, but I am beginning to come to round to thinking this may not be one of them where that happens so easily and its going to take over a lot of the NH for some time. Its one of those very occasional cases in point where referring to the direction of travel of the GSDM is certainly not the whole story when it comes to tropospheric forcing and the placement of the jet stream, set against such a considerable reversal of zonal wind anomalies coming into the troposphere. So on that basis, putting aside what my head has been telling me, it could be the case that it would start to be more prudent not to underplay the SSW, than place caveats as to what might mitigate it. On that basis maybe its me who should have a bit of a ramp, and not others who should restrain themselves However it plays out in terms of what comes out of the sky in the coming weeks - and despite the fact that the actual phenomena of SSW's is not new, this is quite a significant specimen indeed we are watching unfold
  9. The decent orbit was the GWO 5-6-7 part. It changed the upstream profile and enabled the door to be shut on the Atlantic that has been fed for so long by the low angular momentum combination of increased polar jet c/o Canadian vortex and bumped up sub tropical ridges due to enhanced easterly trade winds. Its proved brief - a jab around the edges as I described it might be about 10 days back. The heading to GWO Phase 8 part has curtailed the Scandinavian ridge and returned greater polar flow with angular momentum falling back once more as the vigorous tropical momentum phase c/o MJO comes to a conclusion as it arrives at final high latitude destination. The fall back in AAM now entails looking at the 'back door' Atlantic ridge route to height rises over the arctic c/o the SSW. We have seen plenty of these scenarios many time before. The height rises across the arctic are not in question. Self evidently as I said yesterday the highly impressive reversal of zonal winds will effect the higher latitudes into the troposphere through a quick response. But as other SSW events have shown, that does not preclude obstacles occurring as a result of legacy of tropospheric default patterns at mid latitudes. An SSW is only effective 'in ones back yard' if there is clean cold air advection that is unhindered by 'left over' vorticity and also any legacy of sub tropical ridging pattern c/o low angular momentum... which, in my humble and less swashbuckling opinion anyway, doesn't make an -AO/ -NAO 'impossible to escape'. The record breaking SSW of Feb 2009 was seen as a 'dead cert' to a cold pattern - and it fulfilled that initial part of the bargain no question at all. But in terms of longevity, which you dismiss with ease as 'irrelevant' on this occasion, it flattered to deceive in terms of its undoubted long life being a quite unremarkable slow release valve - rather than any reloading deep cold nirvana. La Nina forcing on that occasion interfered with the mid latitude pattern which effectively cut off the -AO from sustained re-cycled lock-ins of cold due to the rossby wave train pattern from upstream c/o tropical forcing being scrambled by too much easterly inertia to allow a more typical +AAM signature southern stream to engage the higher latitude blocking and back the pattern substantively south and west. Once again this time, there is no doubting the size of the tropospheric >stratospheric momentum signal coming to fruition with this SSW. In my own un-exuberant way I have been a part of its evolution like very many others - albeit I admit and concede without ramping headline making It could indeed well be that the -ve zonal wind anomalies downwelled to the troposphere are strong enough to override La Nina seasonal inertia. I can see that for myself and could easily enough empty away the dregs of my glass and fill it up much higher instead and re-write this post to reflect the (obvious) upside All good then as you say. But as one who has looked closely and discussed in detail for several weeks ahead of this scenario the mechanisms that require the essential mid latitude dominoes to fall, I will be forgiven, for the time being at least, for taking much less for granted on the basis of preferring the polar field and the tropical cycle to have been, ideally, in better harmony The best forcing has just been and gone - its a pity the polar vortex wasn't sliced open then. Hopefully as you say that is an irrelevance and this post is long forgotten.
  10. As always, to try and take stock of NWP means instead of trying to second guess it (and its ensemble suites) at face value, it means instead attempting to step back away from it and try and do an assessment of the factors that are driving it These factors are vast and hugely complex to say the least and there is literally no-one who can make solid definitive predictions, (though some may try regardless of course), based on such an extremely loaded atmospheric profile that has been pulled in two quite different directions over such a relatively short period of time. But that loaded state still has to be assessed against the fairly recent history that has been equally as volatile as the present - and may still have a say in the way ahead in the context of the SSW. The Global Wind Oscillation plot orbit emphasises the contrasting forces that have been taking the atmosphere in two very different directions one after the other over just a ~ circa 6 week period. Two high amplitude directions - one opposing the other. . We have seen strong easterly trade winds from late December and the start of the New Year plunge the atmospheric state into a deeply low angular momentum state reflective of La Nina registering a stronger forcing relative to the official weak base ocean state. This beefed up a profile of sub tropical ridging and more enhanced polar jet flow that kept an average to milder in the south and often colder in the north zonal flow pattern flatter than otherwise might have been the case. Then, in complete contrast to this, a record breaking MJO amplitude wave has subsequently attempted to imprint on the top of the robust Nina profile of January, stretching the atmospheric profile in completely the opposite direction with a markedly +ve AAM disconnect to the base Nina state instead of a markedly -ve one . This has seen quite a change in the zonal wind profile across the Pacific with MJO derived +AAM anomalies replacing the swathe of -ve AAM anomalies (La Nina easterly trade winds) We have been seeing this tropical momentum process work poleward since the last week or so of January and the signals for stratospheric upheaval come into play to join the highly stretched rollercoaster of opposing forces the troposphere has been subjected to. I am deliberately paraphrasing and dumbing down the technical processes involved here to keep emphasis on the huge complexity and conflicting natures of the pattern. These technical processes have been discussed in detail over many previous posts anyway If we take the above GWO trace plot at the top of the post literally, then NWP to date has traced it perfectly. Flatter, faster zonal under the low AAM phases 1,2,3 during January - and then increasingly amplified in the last week as atmospheric angular momentum has shot up with the Scandinavian ridge of this week verified - viewed of late as generally as an appetiser to something better c/o SSW. So far so good. But this is where it gets very very difficult and why some caution needs to be applied in terms of trying to read between the lines of tropospheric reactions to the SSW The ying-yang of the atmosphere and its instability related to the fixed parameters that govern its wind-flow exchanges between tropics>extra tropics mid and higher latitudes>stratosphere) are working on an intricate series of different timelines that take the representative synoptic pattern in the troposphere to different places at different times. Its here that we cannot ignore December and January's past history as much as we cannot ignore the meltdown in the upper atmosphere that is up-comimg The Scandinavia block hasn't sustained (as expected) due to the brief nature of the peak of the +AAM spike above. The direction of travel is descent from here - but how much? This is discussed further down. But back to the context of the SSW for a moment, because global tropospheric wind-flows (as measured by the GWO) and the net outcome of those (flatter -ve AAM flow vs amplified +AAM poleward transport) are to be measured against the polar -ve anomaly easterly period at highest latitudes that the SSW will be yielding (over however many days it has technical reversal) There is surely no doubt that a high latitude block of some kind will emerge based on a reversal of zonal winds at the highest latitudes - it would be counter intuitive to suggest otherwise. But what is highly uncertain and questionable is how the whole troposphere profile responds based on the possible default tendency of the atmospheric circulation to default to La Nina once again as the latest amplifying poleward tropical momentum transport process concludes. We cannot assume 100% that the latest poleward forcing c/o MJO will automatically imprint a sustainable impact on the atmosphere (and hence the tropospheric synoptic pattern) based on this alone. Contrary to what is often assumed on here, MJO lags alone will not account for all this - we have to take the extra tropical reactions into account as measured by the GWO. On that basis we cannot make assumptions of sustained cold pattern verifications based on dateline convection if the extra tropical GWO is not conducive to this. Feb 2009 with its noteworthy SSW and very fast response time in the troposphere did not actually sustain anything like as long in terms of cold air advection to this latitude in terms of depth as its strength of destruction, but was instead diffused and watered down beyond the initial Scandinavian High pressure that gave the easterly and snow in the early part of February. There was something of a disconnect between the high latitude block profile over the polar field, and the pressure arrangement across our mid latitude which didn't reflect the type of classic -NAO response and undercut looked for in terms of sustaining a cold spell. Ultimately, a WQBO and La Nina profile thwarted any sufficient weakening of the +NAO profile. This winter so far, irrespective of E/QBO state, we have again seen how low angular momentum regimes when unsupported by amplifying actions of tropical MJO forcing (changing the traditional Nina profile of the Pacific trade easterlies) have easily reverted the atmosphere and tropospheric state to an unremarkable one at our mid latitudes. In many ways we are in similar place to where we were at the peak of the last tropical MJO phase in December - where the route to follow of AAM is always down - towards the return of the MJO to the Indian Ocean and start of the next phase. The difference to then, and it is of course quite a large difference, is that we have implosion forthcoming of the stratospheric vortex. Its hard to envisage absolutely nothing exciting happening isn't it? Isn't it? To take NWP into context, and why despite some charts which do suggest it will do what is expected and anticipated and yet others seem (almost annoyingly out of spite) seem to keep a stubbornly underwhelming profile, its necessary to look at how far angular momentum might fall back again at the conclusion of the latest MJO wave, however huge it has been and however imposing the SSW may look. Total GLAAM, relative to where it was at -3SD has sky-rocketed as shown in the timeline plot above - and best reflects the sheer size of the poleward tropical momentum transport that has taken it there. Another measure of the latest +AAM forcing is the Southern Oscillation Index (SOI) - spiking as much -ve now - as it was +ve during January https://www.longpaddock.qld.gov.au/seasonalclimateoutlook/southernoscillationindex/ The plot above for the GWO illustrates how rapid the orbit continues to race through the higher AAM phases - and this reflects the default reality that although showing distinct signs of decline, there still remains a La Nina signal firmly in the background to steer AAM budgets (net total global wind-flows) and suggest that an easterly trade wind bias *may* try to re-emerge around the time the SSW is trying to flex its effects in the troposphere. How much, if at all, this happens will have significance on the mid latitude profile and either offset or assist the tropospheric effects So its way too early to know, but any drop-back in AAM *might* be a factor that *could* work against effectiveness of blocking at our latitude and, such as happened in Feb 2009 under weak La Nina, with some residual splintered pockets of vorticity aligning some stubborn polar flow that scuppered sustained cold air advection furthest south- beyond the initial easterly. The significant snowfalls of that event are remembered, but what is less than remembered is that it was relatively unremarkable to follow Its hard to be sure at this stage, but set against the effects that the latest MJO will have had in terms of moving warmer waters eastwards from the Western to the Central and Eastern Equatorial Pacific, and also aiding upwelling of warmer sub surface waters (and hence limiting rather more any resurgence of easterly trades), then this, plus the legacy of +AAM anomalies scrubbing out so much previous easterly Nina inertia in the atmosphere should be enough to prevent angular momentum falling back too far. Ideally though, at least in my opinion, the best timing for the SSW would have been in the last 10 days, in tandem with the massive AAM surge and GWO in most amplified phases. All possibilities, including good ones remain, but I think its important to gauge the SSW against what has been and gone and how the cyclical nature of the atmosphere may influence (mitigate or enhance) the tropospheric effects of the implosion within the polar field. On a thread which is, alas, hyper sensitive to any pitfalls and resistance to anything that doesn't suggest cold - this is simply, as per usual, a little heads-up to the type of thing that might happen. Its because of this that so many of the key words are italicised. History always shows that such a sensitive emotional environment as this leads to all sorts of misconstrued and knee-jerk assertions further on. One cannot manage expectations and thrills and then disappointments for others for them, but it is possible to try to do ones best to tell them in advance. The rest is up to them.
  11. Remember reminder: Its only an island if you look at it from the water Feb 2018 : Massive poleward tropical momentum transport + tidal surge of +AAM tendency > +MT > fast orbit Phase 5/6 GWO Nino attractor in extra tropics (this weeks easterly 'jab around the edges') >stratospheric pathway dissolution/feedback from dateline convection > -AO/-NAO. Allowing for some deterministic model variations of forecast, based on the fundamental changes that are underway in the Pacific eastern and central waters, good supporting reason to 'cherry pick' the ECM to illustrate impending ultimate change downstream in terms of the state of Annular Mode I don't make forecasts as such, but lets just say the Global Synoptic Dynamical Model (GSDM) timetable is evolving very close to its defined timeline schedule from inception date ~ 22 January when the starting pistol was fired in the tropics c/o the MJO and the poleward momentum process was underway. The extent of the extra tropical +MT propagation sure reflects the huge amplitude of the tropical convection rossby wave trigger Back to a previous posted comparison made in last 2 weeks: Feb 1978: Spent most of the month in GWO Phase 5/6 c/o high amplitude MJO and led quickly to a strong -AO/-NAO combination. Differences? There was no La Nina lag underpinning an entrenched sub tropical ridge +NAO pattern and so the tropospheric/stratospheric pathway was unhindered to a much greater degree. Well, that and of course the absence of so much anomalous homogenous warming of tropical oceans which are skewing and rather neutralising the natural effects of strong tropical poleward feedbacks - in addition to the alarming atrophy of sea ice which correspondingly unbalances expected albedo feedback relationships to an increasingly unprecedented state : Feb 2018 is indeed proving to be a slower burner with, overall, increasingly less cold air relative to 1978 in the NH to share around in terms of cold air advection from the pole and which inevitably therefore favours much less dilution through continental landmasses like Canada, than downstreamacross oceans) But, all that said: There is an abundance of pretty cold air to the NW as we watch the next phases of trough disruption. Based on the spatial arrangement of cold vortices which look set to ultimately implode - that doesn't mean (by any means) that the UK and Europe won't yet see their coldest weather of the winter, as the end of official winter gets closer and closer March 2013 provided this on the Costa del Cinq Ports of the SE: It was even worth capturing some So, still very much the sort of thing that is more than possible late winter 2018, a few weeks earlier than the fun and games of March 2013 - and so there is no need for anyone to be miserable
  12. Posted this on 27 January: However, it still requires successful propagation of the added westerly wind burst (amplifying) anomalies that accompany the passage of MJO convection though the tropics, into the extra tropical mid and higher latitudes to facilitate widespread hemispheric pattern change. Its necessary to understand the lag times of frictional torque in the tropics > that lead mountain torque in the extra tropics - and then try to assimilate those conclusions as to when NWP might be impacted in the mid and higher latitudes There is then the question of how strong +ve mountain torque engagement perturbs the troposphere/stratosphere boundary I subsequently posted last week regarding suspicions of NWP and suggested that the evolution heading forward was a 'slow burner' for deeper cold which reflected emphasis of a theme of the last couple of weeks related to the eventual decline of the strength of Azores High (not yet happened as expected) and how timelines of soaring angular momentum tendency c/o poleward tropical momentum >extra tropics>stratosphere would be a key to changing this. An integral part of the 'slow burner' and necessity of turning the mid latitude +NAO La Nina forcing on its head MJO propagating eastwards through tropics>+ve frictional torque 22 January ( as posted last week) +MT (here and now)>stratosphere mid month. No links to plots from me this evening, or extravagant explanations (phew, they say). Just a (relatively) short post that keeps trust in continuity of more in depth on-going summaries of recent (and not so recent) times - and still leading towards what seems to be a remarkable consensus (across professional and amateur spectrum) of tropospheric/stratospheric meltdown. How that increasing likelihood manifests precisely in terms of 'weather' for this little Island remains to be seen of course. But my customary lack of flamboyant excited hyperbole and attempts at balance over headline grabbing doesn't disguise the genuinely growing anticipation of seeing where the 'jabs around the edges (we are currently seeing and as I described them last week ) ultimately lead to.
  13. It was well intended and well meant advice Taking NWP in the round, the stubborn persistence of polar jet energy (until now) flowing from upstream across the top of the Azores ridge has been indicative of a dominating +NAO pattern attributable to the lagged low point of atmospheric angular moment c/o La Nina forcing and stronger than average easterly trade winds since the turn of the New Year. Whilst there is not yet any undercutting -AO/NAO Feb 1978 type redux fully apparent - NWP is now, within the reliable period, adjusting the upstream energy process incrementally, bit by bit, as greater and greater downstream amplification is finally being realised. If we take another look at a yearly GLAAM anomaly, the size of the peak of the-ve GLAAM anomaly achieved is evident - which saw the La Nina strengthened trade winds ramp upwards. The atmosphere is now fast recovering from that low angular momentum regime and NWP attempting evolution of another Scandinavian ridge such as was seen in the first part of February 2017. That tropical momentum led +AAM anomaly spike, was discussed in a recent post, is clear to see again in the above 365 day chart for early February 2017 Back to ushering in Feb 2018: High amplitude tropical convection progression with rapidly rising AAM tendency has all but scrubbed out that -3SD GLAAM deficit ^^ - and still heading upwards. The atmospheric state is becoming increasingly conducive to +ve poleward momentum flux helping to amplify the tropospheric pattern more meaningfully. This leading towards a much better shaped H500 anomaly to externally destabilise the vortex. This, at the same time as internal +ve mountain torque forcing occurs - as a direct consequence of the poleward +AAM anomalies c/o tropical forcing propagating to the extra tropics and perturbing the troposphere/stratosphere boundary. To put some timelines to all this with the aim of helping explanations : If we take a look at the Global Wind Oscillation below, which should be seen as a measure of how the amplified wind-flows are progressing from tropics to extra tropics- then the initial signal fired from the tropics to start the process now unfolding in NWP was around 22nd January as can be seen by the plot (high amplitude GWO Phase 3 into Phase 4). This signal is representative of a surface +ve frictional torque which indicates the axis points where westerly winds in the tropics added by the forward movement of tropical convection start the initial process of scrubbing out the easterly trade winds responsible for the greater polar jet flow at mid-latitudes that inhibits amplification. The lag time for this +ve frictional torque and associated poleward heading +AAM wave flux anomalies to arrive in the extra tropics is ~10 days. Based on the starting pistol fired around the 22nd January, the GWO progression confirms this ETA of momentum in the extra tropics by the imminent expected orbit to the boundary of Phase 4/5 and engagement of a considerable size +ve mountain torque. See the added GWO template that confirms where these torque processes have taken place within the relevant phase progressions This mountain torque event has some highly interesting possible implications - not just for the amplification programme clearly underway in NWP into the medium term and increasing programme of cold air advection, but also in terms of the sharper NH hemispheric pattern which corresponds to assist external stratospheric meltdown. Such as stratosphere forecasts are playing peek-a-boo with. At this stage, what is interesting about the current evolution is that, *she adds with due caution* it looks slower and more sustained than Feb 2017. There are tentative suggestions of a slow burner, as the models keep adjusting the pattern further on into the medium term to one that is more meridional due to +AAM flux. It *could be* that the +ve MT delivers something of an icing on the cake from mid month. Something to keep watching out for in the longer term. Lag time for +MT >stratosphere/troposphere fall-out around 12- 14 days. This zonal wind cross section illustrates how the westerly wind additions c/o tropical forcing is impacting the rossby wave pattern upstream, with the emerging propagation of +ve shaded anomalies replacing the sustained bursts of -ve anomaly easterly trade winds evident across the Pacific since the turn of the New Year. This is another way of illustrating the switch from sharply -ve AAM anomalies to a contrasting swathe of +AAM anomalies impacting the extra tropics and as a consequence re-configuring the pattern from upstream with less strength into the northern branch of the jet stream - with more split jet flow and consequently greater trough disruption downstream - hence better mid to higher latitude amplification of ridging. The signs are emerging that the new travel of direction is gaining traction - with suggestions the models are contemplating a volte face towards a cold and blocked pattern with CAA ambush from both the NW and NE. As soon as this weekend. All rather confirming suspicions of recent days, and echoed in the semantics of the highlighted post above- that the flatter low angular momentum legacy might well be over-cooked. In that sense on-going NWP suites are simply snapshots in time to the evolution of the pattern playing out. Adopting this philosophy, it becomes more possible to watch what happens without unnecessary instinctive reactions to face value variations and swings within intra day operational modelling (and ensemble suites) I'm not sure that either of these have been especially instructive to any great distance of late. If the latest trends are anything to go by this is already obvious. Its not through it being my own model of choice based around preference, but because its the model that has been best fitting the pattern to the signals on this occasion that the UKMO has been leading the way and paving the evolution of the pattern into the weekend and beyond. NWP is starting to better matches the suggested GWO evolution of recent days and makes more sense (to me at least!) It does seem that an all-round catch-up is in progress and that might seem a (very pleasant) surprise to anyone who has taken NWP at face value in recent days
  14. Tamara

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    That's the way it should be - and you and her can have fun together about horsey things as Mum and daughter should!
  15. Tamara

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    They are beautiful. Those pictures take me back to days of mucking out at the stables, and getting ready for and then heading off to shows. I've never been riding in the snow though!
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