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Showing content with the highest reputation since 19/08/18 in Posts

  1. 35 points
    Evening All - Its been a long long time since I opened a thread - So I will try to make it interesting... The first dip of the toe into Autumn is for many of us the change in mindset away from summer heat & into the ever shortening days & colder weather... Traditionally as we head through September & especially October the vortex & westerly jet increases to a point where the probability of southerly warmth is significantly reduced in probability- Notable dates in the diary for this is around the 10th of October onwards where the winter time Stratospheric vortex is ~ half of its winter peak speed @ ~ 16-20 M/S Westerly. Shapes of high pressure through 40- 50N should be flat & the mode of the AO / NAO historically reads as a positive... There is one other important Teleconnection that I never hear anyone ever mention but Ive kept revisiting it each winter for about the last 5 / 6 years is the POL ( the polar eurasia pattern ) The loading pattern for POSTIVE PHASE is measured across Northern Russia down to about Mongolia & is a similar measure to the NAO - The more POSITIVE the phase the lower the geopotential heights are over Norther Russia supporting a westerly circulation So + AO + NAO + POL all indicate a traditional zonal flow. To emphasise this the 90s was where the jet was roaring & the AO & POL certainly in autumn months peaked heavily positive So all said & done taking into consideration natural variation between occasional stronger & weaker years & of course ENSO phases we generally see a uniform process to our weather through Autumn which decends into 'westerlyness' - & this years Autumn forecast would seemingly be very straight forward if you wanted to pluck out things like matches from ENSO state & QBO phase & of course they 'could' still play their part however ENSO will be solid Neutral for SON & QBO will be dwindling Easterly - Anyway- What changes do we see potentially impacting our weather & the imposed 'Westerlyness' ... Pattern Induced Climate change is probably a phrase thats not bantered about to much but it certainly will be in the coming years- The globe is warming however the poles are warming much faster than the average annual rate - this is creating a NEW ( circa 2007 onwards ) feedback loop over the polar cell & * SOME * of the mid lattitudes - It is causing autumn tropospheric decoupling from the stratospheric vortex & it occurs in the low sea ice areas ( or more specifically the areas with the biggest negative anomaly to the norm ) What we have seen since 2007 is not only the decadal average of sea ice decline ( especially August / Sept & Oct ) but also focal points of significant negative anomalies in areas close to where the POL teleconnection is measured. The Barents / kara & laptev seas have all been in the 'ice news' for the wrong reasons & the graphs below show how this summers ice coverage has taken a real beating - The 3 above are in Anticlockwise order from Scandi Eastwards - Notes being * Barents melting out early like the decadal Trend * The next in line Laptev taking a further hit this year - being probably the worst on record * Kara as well - under the decadal ave & close on record lows - - Its also worth noting how far away they are from the 70s / 80s are - imagine how far they would be from the 50s & 60s ! The net fallout from this is the amount of residual latent heat in these areas through Autumn & *Possibly* now Early Winter & what the net fall out is - the creation of a new feedback loop of Positive heights In Northern Russia. This is also probably the net reason 'globally' why there is a reduction in the overall jet speed & depth of negative geopotential heights because of the reduced Thermal Gradient.. This illustrates well if you chunk up Sept & Oct 500 height anomalies charts for 1948 -1990 The base period 1990 - 2006 a fairly significant 16 year phase of ice loss 2007 -2017 the last 10 years in ice loss creating this new feedback loop & pattern change. We see a CLEAR Modal change in the height field over the pole - especially concentrated over the 3 weak ice areas. Lets reintroduce the POL teleconnction to include the last decade The mode has swing to a very sharp -POL especially in Autumn but not exclusive. The data indicates ftp://ftp.cpc.ncep.noaa.gov/wd52dg/data/indices/poleur_index.tim That 2007-2017 Sep / Oct / Nov 20/30 months have been negative with 9/9 on the last 3 Autumns !!! 100% Its also about the 'negativity' of the mode as well - going off the scale more recently.. So Bringing that back to this Autumn & NW Europe the net effect is that the eastward propergation of the atlantic is expected to be weaker & weaker - so for Western Russia we could be promoting an earlier signal for Colder weather developing - This signal fades as we come SW towards Norther & Central Europe, however the extent of the high promotes higher probability of early warmth from the south but again later into Autumn could also promote Colder air filtering through - The UK sits as ever at the end of the blocking - & whilst its immediate impacts may be slightly tempered its still expected to impact us ... but how? I would consider the following in terms of probabilities !!! NOT forecasts... * Higher probability of warmer phases in Sept Oct in particular from the south & East * Higher probability that the atlantic jet will be displaced further NW towards Greenland ( although occasional split jets towards Spain & portugal as well ) * Rainfall - Probability should be that its drier however we could up in the unique scenario where the westerly jet runs out of puff over the UK & its very wet ( the weather becomes stationary ) - this would be very unlucky. Also short periods of very high rainfall could occur * Whilst the probability remains high that it will be warmer than usual - the locality of that blocking high means that as we transition through Oct & Nov the chances of early season chill & cold could also be higher- We could see drastic swings in the weather from extreme Mild & warmth to Cold as the jet flow will be buckled... - Also there could well be some overlap into December in these conditions - Highlghted below-- The transition from Autumn & Winter this year will see the usual array of teleconnections to measure up- Currently - ENSO appears to be Neutral out to December, possible low end El Nino, critically here the lower we stay the weaker the impact will be - QBO - decending Westerly at the moment, whilst this isnt great in the long run the effects of the 'westerly' are unlikely to impact until the late part of winter perhaps reducing the prospects of a SSW ( other factors like MJO activity may support either way ) - Sunspot activity continues to be at a low point in the cycle which is a huge positive- - The troposheric disconnect that may well run through sept > Oct could Extend to Nov > Dec for 2 reasons * The feedback from the ice anomalies is so significant that if on average the signal in the last decade is muted out mid Oct - then how long will the new record low take to mute out ?? Another 4 weeks ?? Plus the wildcard this winter may be that theres support for the feedback from greenland in the form of more warmth due to record low ice here as well Plus the stratosphere is being modelled to be weak- The mean of the all the CFS runs should be taken with a pinch of salt - however its modelling significant weakness as we head through Oct & Nov - Further delaying the onset of the westerlies... So there we go as I see it - Autumn - Blocking to the East supports weaker westerlyness - although the UK could sit on the periphery where the jet holds stationary - ( worst case scenario ) Best case scenario >> Jet up to iceland & warmth Winter - Everything is in place to positively support a blocked winter - however the last peice being the strat will only become clearer in another 8-10 weeks ... Best S
  2. 34 points
    Yes I stated the other day that August had featured a cancelling out process of the tropics vs the extra tropics, but one that still appeared to be cuing up very nicely for the re-start of the next atmospheric circulation to resume the progress up to late July. Which up till then had beautifully read the script and meant that not just was the weather itself lovely to savour, but also there was satisfaction in seeing the difficult processes and explanations play out and provide personal happiness and enjoyment of attempting to oversee developments as well. Humility is indeed a vital quality, and one of the first we should all should try to eschew - but on the other hand no-one earns a salary to take time out to post on this thread and on that basis it should be a personally enjoyable and rewarding experience at the same time as one shouldn't be beholden to expectations of total clairvoyency in terms of suggestions made ahead as to how the patterns may evolve. On that basis maybe not too many apologies should be issued for not reading the weather patterns correct 100% of the time should be made - the likes of the METO as a professional institution would not provide a service at all if they had to issue apologies and explanations for every time Mother Nature didn't follow the best measured expectations. Additionally, the complexities of the atmosphere defeating human attempts to study them, does not justify those minorities who always seem to appear at these times to suggest the 'teleconnections don't work'. They almost certainly do work - its just the hardest task to try and understand them, relay and explain them - and those that don't try but criticise first and foremost instead - should practice their own humility first Such sentiments of humility within these contexts become even more important as the audience no doubt starts increasing and changes ahead of yet another autumn>winter chase for cold patterns. Its my experience that whilst most on this thread, and large parts of the site as a whole, consider the busy season the most exciting and absorbing, it is also the time that unfortunately humility is usually least evident. With all the above in mind, this is the last post on this thread of the sequence of summaries since May covering this wonderful summer season just ended ( a small few at least will no doubt be relieved and delighted to see the back of the never ending length posts) and it has been a wonderful summer despite the relative disappointments of August and the now apparent stuttering of developments for any further sustained warm and settled conditions in this month also. The starting point of discussion far back in May was whether the step change to a contrasting much warmer second half of the Spring from the first half would successfully negotiate the hurdles of previous years where warm late Springs have only led on to a downward path to cool and more unsettled conditions. The pros and cons revolved around stubborn persistence of La Nina type circulation lag set against the suggestion of gradual changes to more Nino-ish patterns in later summer>autumn and hence trying to 'risk assess' mid Atlantic ridge propensity for preventing warm air advection building sustainably (and more especially from the south) or, whether a greater eastward extension of ridging would prevent this happening (again) and instead , over time, encourage development towards trough activity to our west in the Atlantic and further assist plume like activity from a southerly vector to take over from the Azores High. As it turned out the ocean signal indeed continued to build towards an El Nino standing wave, whilst the atmosphere in terms of the extra tropics rather lagged the vestiges of the La Nina regime with low angular momentum and easterly trade wind patterns evident during June. The Atlantic pattern in the first half of summer was in many ways was not too dissimilar to a traditional La Nina summer pattern with the core heights centred around an intense sub tropical Azores ridge,and one which occasionally waxes but mostly retracts westwards due to the effect of upstream amplification c/o easterly trade wind domination in the Pacific However, this time around, the the unusually north and eastwards displacement of these core Azores/Atlantic ridging heights means that the downstream trough that is usually reserved for the UK and NW Europe was erased quite some distance towards NW parts of Russia So instead of customary low pressure upper cold pool - to the much greater extent and by way of total contrast, home grown heat build in situ from these ridges with the NW of the UK first to benefit from this. As the summer progressed, and as the Pacific pattern started to couple the atmosphere towards the steadily warming ocean signal, the pattern did indeed start to signal a gradual transfer of core heights NE - culminating in (what turned out to be) the one and only real plume scenario of the whole summer in late July with the much anticipated and discussed Scandinavian heights and Atlantic trough. More of these plume scenarios into late summer and early autumn were envisaged and commented on several times.This late July Pacific forcing passage has however unexpectedly proved to a brief culmination of steady development since Spring What was subsequently envisaged some four weeks back was a res-set of the late July pattern through the middle part of August to repeat the sequence during the last third/last week of August. As we know, and as has been reasoned and explained, this sequence was delayed and August turned out to be more changeable and cooler for longer than seemed likely. So to September, and the modelling expectations of upturn once more in angular momentum remain present, but seem to keep remaining in real time at the end of arms reach. This not just applying to the CFS and its well know biases (those starting to re-appear here for winter attendance should beware its tropospheric>stratospheric modelling) but the ECM is also proving culpable to its own biases much as the GFS with its own -ve tropical biases. *So famous last words of hers when she said that seasonal modelling of AAM had been proving reliable* Ha-ha! Another example of freely given humility.. Extrapolations of re-engagement of the Pacific standing wave have stayed around the equivalent of chasing optimum synoptics at day 10 with NWP. Instead we see a return to Western Hemisphere engagement of VP200 tropical convection anomaly at the expense of the Pacific. This renders suggestion of recently rather void that the opposite seemed likely to prevail in the Pacific instead. At the same time no surprise the African wave signifies greater hurricane activity transferred from the Pacific back to the tropical Atlantic. An echo closer to September 2017, and against wider earlier expectations for September 2018 The greater -ve tendency in the atmospheric circulation sees transfer into -ve Asian mountain torque tendency in the extra tropics This is the signal to amplify the Pacific profile through deceleration of the Jetstream there, and downstream retracts the sub tropical ridging in the Atlantic. This ends the recent attempts for Scandinavian heights to prevail along with the suggested longer settled spell some days back and also means that the attempted re-set of the ridge from the SW is more supressed from the weekend allowing the jet further south and greater trough intervention It had been envisaged the GWO might hold ground in weak signal and then resume progress to higher AAM orbit sooner. However, eventual capitulation in the extra tropics (as discussed above) has been sufficient to re-engage the Global Wind Oscillation and end the long period of resistance in weak and incoherent orbit with a move into low angular momentum Phase 1. This definitely precludes any immediate re-positioning close to the opposite end of the spectrum in El Nino Phase 5 (as briefly achieved in late July at 'peak' of the Nino standing wave development). Its now about revising expectations in relation to how the eventual natural upswing in the tropical>extra tropical pattern can recover angular momentum back to a lower amplitude Phase 4 This reduced orbit expectation wavelength is indicative of the faltering of development of the progress to the expectations of weak El Nino through this autumn and then into winter. Its not a preference of mine at all, but not a surprise either in the 10 day period to see the models move away from warmer and more settled solutions as the re-engagement of higher angular momentum tendency keeps being put back in time. Instead the mid Atlantic ridge is being programmed in most modelling at the moment to engage a greater balance of polar maritime air, keep the jet stream straddling close to the UK and prevent it lifting further north and allowing sub tropical warmth to approach from the south and build back an Indian Summer. This said, the GEM has been suggesting that some cut off may occur in the jet stream to our west and provide a break on advancement of the migrating Atlantic ridge and a loop of the jet to our S and SW to engage something of a plume scenario through next week. This is not an uncommon scenario based on past similar situations, and would be lovely to see emerge - though at present it remains a low chance probability. Something will give with this situation at some stage, as natural tropical.. extra tropical cycles dictate but essentially the low frequency signal in the Pacific has gone more AWOL since August at precisely the time that it was set not just to allow August to repeat the feats of 1976 and 1995 - but quite conceivably surpass them with a marvellous September as well. 'What ifs' and 'could have been' aside, its still been a fantastic summer and thanks should go to the regular contributors on this thread who have taken time to provide model sum ups and also enjoy the positivity of the weather suggested by them, at least until relatively recently taking the season as a whole. A long way it seems from now until next summer, but time never stands still
  3. 24 points
    Overall there is little I would change from any of those excerpts from the previous post. First the matter of the programmed Atlantic ridge as explained and discussed in previous post and now well within the modelling radar. It remains the case that the cool air Atlantic ridge sequence is a snapshot in time set against what has been and what is still likely to resume thereafter. It has to be said though, those of us wishing for a summer bank holiday to reflect the stunning overall quality of the season - that the weather looks set to certainly not read that particular script and the timing is quite unerring indeed. It is looking increasingly likely that the upcoming Bank Holiday, at least for many southern and south eastern parts who have been fortunate to see the best of conditions, will be the most underwhelming for a few years, Last year featured a fast track to early autumn conditions both prior to and immediately after the Bank Holiday, however the whole holiday weekend period itself was very warm and sunny for many at least further south, echoing that of 2016 and also 2015 which were both fitting for the end of season. Some enjoyable mid level plume conditions and evening lightning displays also added an extra element in 2015, and 2016 went on to feature these conditions well into September itself Another way of measuring related analysis to the programmed Atlantic ridge sequence, is the short term tropical convection VP plots that identify the loss of signal and meandering track to the Maritimes and emerging there by the closing days of the month. This is sufficient, in the shorter term, to be amplifying the upstream Pacific pattern and also pull the ridging pattern westward downstream and invite cool air advection from the NW. Much as described in the last post. However, the emergence of the tropical signal from the Maritimes (and then subsequent track back eastward into the Pacific) is what is a key to reduced trade winds serving to de-amplify the upstream pattern once more and help return to warmer and hopefully also more settled conditions downstream in our sector with time This links on to the updated zonal wind analysis below used as focus for those who wish to welcome in autumnal type weather and which reflects the interim short term loss of tropical forcing in addition to transitional CCKW across the tropical Atlantic (which was covered in last post). I think the particular point has been made before that taking these wind anomalies plots in isolation of the broader picture associated with it tells one part of the story but not the complete picture As hinted at above, it also means that any autumnal flavour to the weather is quite likely a temporary feature with further summer-like weather delaying the eventual seasonal changes that happened faster last year. This doesn't 100% guarantee any heatwave, though still plenty of time for one to develop in the new month, and still plenty good enough to continue to enjoy outdoor life for a while yet despite the B/H spoiling things for quite a few. The bigger picture, beyond the short term analysis, remains one of trying to assess the present lull phase in the tropical cycle and associated increase in trades against a larger atmospheric/ocean trend that has been heading in the opposite direction to any La Nina type forcing through the latter part of this summer. Albeit, with erratic progress which is now proving perhaps a little slower and more frustrating than seemed to be the case (hence the window for end of official summer plume that seemed possible in the last week of August has been put back a bit as just discussed) Its worth reading the attached link which discusses the role of the South Pacific Oscillation (SPO) in regulating the strength and influence of easterly trade winds (to which the immediate post under reply reflects with the short term zonal wind anomaly forecasts) The link was provided originally kindly courtesy of @Blessed Weather https://www.climate.gov/news-features/blogs/enso/look-south-enso-forecasters A +ve phase SPO suggests a weaker South Pacific subtropical ridge and weaker trade winds reducing the cold-water upwelling in the eastern Equatorial Pacific and allows for easier propagation of the warm waters from the Central Pacific to the Eastern Pacific. This is consistent with speeding up the development of an El Nino circulation and associated high angular momentum regime. However the converse holds true with a -ve phase SPO and this means that propagation of the warmer waters from the CP to the EP are slowed and retarded. This is reflected in on-going ENSO zone profiles. It doesn't automatically mean that an El Nino won't develop at all - it just makes it likely to be slower to develop in this instance and also much higher margins to be on the weak end of the spectrum and more centrally based. This summer the SPO has been in slightly -ve phase and this has been a factor in the erratic progress of the development of the Nino standing wave as just mentioned. The relevance of a -ve SPO to this thread and the synoptic upstream and downstream pattern is that the relationship that the atmospheric circulation acquires to the ocean base state is one that features a more amplified Pacific pattern with stronger sub tropical ridging in the Pacific when the tropical>extra tropical set-up allows it. Stronger sub tropical ridging in the Pacific in turn regulates the development and orientation of the Azores/Atlantic sub tropical ridging in our sector. When the trade wind effect is greater, -ve frictional torque around 30N (and associated falling atmospheric angular momentum tendency) creates the mechanism for amplification to occur upstream to retract the Azores ridge westwards and means that cooler incursions and trough influence from the NW is greater. As soon as the trade wind effect reduces, then the developing Nino standing wave Pacific pattern has chance to regain more influence as soon as tropical convection patterns create westerly wind bursts to de-amplify the Pacific pattern as AAM bottoms out and then rises back up - and in turn return the downstream ridge eastwards and reduce the influence of polar maritime airflow with the jet axis SW-NE rather than W-E or even NW-SE. Such a more "Nina-like" sequence with the jet pattern switching to a more looped southern track occurs later this week before the pattern attempts to return to the flatter more cyclonic Pacific pattern that allows greater downstream amplification of the Azores high in the UK/European sector rather than to our west. This is yet another further element to the GSDM diagnostic process. Knowing how the upstream pattern is affected by factors such as these is a help towards determining how jet flow and trough and blocking features may also behave further downstream. So how much is the developing Nino standing wave likely to be "destructively" affected by any interim trade wind anomaly? With a new CCKW presently passing though the Pacific, easterly inertia is likely to be mitigated in the short term and then developmental to resumed progress in the medium longer term Additionally to this, the presence of a further CCKW in the Pacific also adds weight to the expectation of that low frequency amplitude MJO wave to develop across the Pacific as part of an atmospheric response to this. Signs of this starting to happen are discussed above. Furthermore, the CCKW passing through the Pacific also supports development of "non low frequency" activity in the form of cyclones. The tropical modelling (up the page) is starting to reflect the following on upstream pattern change more clearly on a shortening time period and this helps start to increase confidence that NWP will carry the signal forward more consistently and with better continuity. Both types of tropical activity, low frequency and non low frequency, are conducive to supressing trade effects and replacing with westerly winds that add an Asian jet extension across the Pacific, de-amplifying the upstream pattern - and, downstream from this, reversing the ridge/trough pattern in the Atlantic and returning the jet northwards once more - that is, following the loop south over the short medium term. NWP has kept the signal stubbornly beyond day 10 in recent days, but cluster and ensemble data should start to read better developments and though next week may still take a few days to settle down beyond the cool and changeable holiday weekend - things still look reasonably set for more fine and warm summer-like weather to return at the turn of the month and heading into September Latest 0z ECM clusters and GEFS ensembles continue to reflect these much improving prospects by the end of the month. With all the above in mind, there is much to agree with this third highlighted post. I would question the first and second lines though. From my own point of view there is no need to be silenced by any NWP currently (or indeed at any other time for that matter) and as based on attempted forward looking assessment. The end of week and B/H has been well anticipated in recent days and continues to not require any further reaction beyond what it is. An autumnal interlude as a snapshot in time that is best put into perspective of what preceded it and also the longer range likely perspective of which your final sentence quite reasonably assumes Personal optimum preference would certainly prefer ridging setting up just to the E/NE to invite a quicker route to plume scenarios and southerly winds. Up till recently this seemed quite possible. Though cautionary reality now suggests initial position of ridging my be a little further west ridging into the UK and across mainland NW Europe as dictated by the Azores ridge. Which in itself is not an unwelcome prospect by any means
  4. 23 points
    Eyes down - here we go. (Banter? - maybe - but the topics gone)
  5. 20 points
    looking at the 3 500 mb anomaly charts I use for trying to suggest what the upper flow will be is not easy at the moment, if indeed possible. Two suggest one thing the third shows nothing much like the other two. The odd one out is NOAA which is 'usually' nearer the mark to what the upper flow turns out to be in the 6-10 day time frame. Currently is keeps its idea of several days, a broad westerly Atlantic flow which turns S of W over the UK ahead of a broad trough close into NW'ern areas. Beneath this in the right exit of the flow it does suggest a very slight indication of +ve heights with a slight ridge from the bottom of the trough into western Europe, see below http://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php Its 8-14 version is pretty similar. So this could give a possibility of surface pressure rising in this right exit area from the upper trough. The ECMWF-GFS version is much more definite over the past 2-3 days for height rises coming out of Europe from about the meridian eastwards over the UK, especially GFS which keeps showing quite marked ridging from western Europe over the UK towards Greenland. http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html Usually I would stick wuth NOAA but as it does give the slighest hint, no more, of that idea and the similarity of the other two to each other over a couple of days then conditions may be right for some build of heights at 500 mb and beneath this at the surface over western Europe and possibly over the UK (could even be centred over the UK). If we look at the link below. UK Fax charts, scroll to T+120 first and notice Exeter show a high tending to build from the actual for today over western Europe. Scroll down further to see how thie own 500 mb prediction looks. It shows a definite change from a trough dominated chart just east of the UK to a ridge type in 5 days time. So this idea of heights building at 500 mb and subsequently at the surface may prove correct. We should all know 120 hours down the line. How long this might last or indeed how much dry and warm weather this may produce is a bit problematical as well as how far north this pattern might extend its influence. All in all a very interesting set up.
  6. 17 points
    The 21st of August has seen the first dustings of snow in Siberia And we're off......
  7. 17 points
    The initial estimates, have proved to be a little on the extended end of the envelope ( and hence the fate of the last week or so of Augusts prospects less inspirational than hoped). But overall the pattern has progressed reasonably well in terms of expectations as expressed initially some 3 weeks back. The one part of the jigsaw remaining, and which has been proving slower still to appear ( up to now) than envisaged is an upper trough showing signs of diffusing energy underneath any of the blocking. This element is actually now materialising in NWP, however the suggested difference to the early analysis is that it might manifest itself amidst more of a -AO regime rather than the long prevailing +AO regime. Taken at face value, this implies quite a possible difference in surface conditions to those envisaged in the captured quote because a less +ve NAO set against a still prevailing +AO infers a mid latitude Sceuro block with upper trough in Atlantic disrupting to the SW to provide late season influx of humid air northwards (as per early August assessment) On the other hand, and purely at face value (which is an important thought to retain) a -ve AO profile suggests the type of smorgasboard on offer from elements of latest NWP - with cooler upper air seeping around the blocking re-positioned at higher latitudes and a hard to pinpoint array of shallow troughs appearing in the upper cold pools of these troughs, at the same time as the direction of approach from troughs approaching from the Atlantic suggests possible fusion with these shallow features to erode the higher pressure regime further and further northwards. But, as implied, this is getting way too far ahead in detail at a range that is still open to question in terms of why the broadscale changes are being suggested - and of course how likely and to what extent might they might verify. On that basis, probably best to do some analysis of events since early-mid August. to try to make sense of it all moving forward This period has been frustrated by some contradictory signals between the tropics and the extra tropics. The former attempting to resurrect something of a Nina flow with increase in easterly trade winds amplifying the pattern upstream (Atlantic/more supressed ridge and greater trough influence) and the extra tropics which have retained much of the westerly wind inertia of the tropical signal in late July (with the Scandinavian ridge and Atlantic trough that concluded the final days of that month) The tropical>extra tropical cycle is looking to set to resurrect this sequence again through September (as stated at the beginning, slightly later than first thought a few weeks back) and its no surprise to see the Scandinavian heights programmed accordingly. Total global angular momentum is currently broadly neutral... ..., despite the on-going lull in the low frequency tropical>extra tropical cycle and has been largely dictated by micro scale tropical activity to a small degree in the Atlantic but more especially the Pacific as one might expect with an El Nino standing wave erratically implementing itself. This balance of activity has helped support westerly wind inertia in the extra tropics whilst the easterly trade wind inertia in the tropics c/o -ve South Pacific Oscillation influence (SPO) and also weak phase of the low frequency signal since the start of August has been represented by -ve frictional torque tendency which is now starting to trend more +ve (ahead of likely changes upwards in angular momentum tendency through September as discussed later) The propagation of those -ve easterly winds in the tropics and subsequent degree of amplification in the Pacific has been negated of late in the extra tropics through the continued presence of the developing Nino standing wave and high levels of accumulated cyclonic energy (ACE) in the Pacific. Hence any -ve Asian MT tendency, which serves to help decelerate the jet in the Pacific in response to the lead set by -ve frictional torque tendency from the tropics, has shown a much more muted response to the previous (much greater) trade wind response that propagated to the extra tropics in early summer and prevented total global angular momentum from repeating the falls to the low point indicated of 8 to 12 weeks previously... ...and which at this time of year would be manifested as a very different outcome not just to the conditions of early summer, but to what we presently see nowcast synoptically according to the growing shift in seasonal wavelengths since then Kind courtesy of @Snowy Hibbo if we look at an ECM plot of forecasted angular momentum tendency,the advertised rise through September as mentioned earlier on, is in evidence. Backing up the CFS seasonal expectations (of which has proved a little progressive with the Nino standing wave) Note that both of these plots are overall tendency plot forecasts which have to be set against where total global AAM currently sits close to parity. The upward trend in tendency imminently commencing from the current 'low point' (and as indicated by the rising frictional torque tendency plot as above) helps bring about the re-set return of extended heights to the NE and the suggested approaching trough from the west to replay the sort of sequence seen late July. So this leads to the question of the suggested difference to late July in terms of the switch of heights from mid latitude orientation to progress to higher latitudes. A large part of the complex global blocking picture is the effects of a northwards recurvature of super typhoon Jebi through the North Pacific (with ominous threat to Japan), as part of a tropical>extra tropical interaction creating a knock-on anticyclonic wave breaking pattern which shakes up the NWP picture in term of trying to fit the precise positioning of these blocks set against the broadscale factors already outlined. There has been uncertainty as to the speed of downwelling westerly phase of QBO looking ahead through autumn (and then into implications for winter). This appears, to be now rapidly advancing through 30mb as is often the case when phase switches are becoming increasingly imminent Much the same principle as stratospheric vortex switch regimes, the advancement of +ve westerly winds starts flushing out the existing -ve easterly phase winds to the surface and these manifest themselves as they exit into the tropospheric surface level as +ve height anomalies. So on the basis of so many factors in play, then a lot of caution is needed in terms of NWP and how all the cards in the air fall to the deck. The background trend in angular momentum tendency to be rising through September well supports the overall continued evolution to an Atlantic trough and one which looks increasingly likely to undercut where the blocking mechanisms ultimately position themselves. The higher AAM potentially climbs through autumn then the more sub tropical jet energy seems likely. In terms of detail this is obviously almost impossible to gauge, but suffice to say and as per some previous analysis during August, the more unsettled conditions perhaps further south and south west and more settled the further north one heads. But with the suggested changes in latitude orientation of the high, this makes interpretation less reliable than was envisaged with a more mid latitude block. Nonetheless, with residual summer heat to the south, the track of any meandering troughs could have big local impacts in terms of boundaries of temperature and rainfall anomalies from one place to another. But I suspect based on the presence of troughs appearing more and more to the west and south west that any cool air filtering around these large ridges further north and north east is going to have a hard time this early advecting far south and west enough to the greater part of the UK and the potential remains for very warm unstable and humid air, (especially with SST's still close to peak from the summer) to be some influence furthest south.
  8. 16 points
    Models finally working themselves into a typical early September pattern, which is lots of sunny weather - and increasingly looking like Northern areas will indeed join in. I still have a sneaky eye on developments at T144 — the GFS idea of the splitting Biscay low is not too be ruled out, and could lead to a little heatwave at the start of next week is verifies. Slight outsider at the moment.
  9. 16 points
    A real shock to the system at the end of this week as the 2c line hits scotland / NI - modified up a little bit as it heads SE but very chilly & Autumnal...
  10. 15 points
    It is just for the one day though or am I missing something. You are not the only one to 'cherry pick' charts mind you. Heaven only knows why some of you cannot give a balanced view of any particular run. new folk summer and winter must be totally confused at times.
  11. 15 points
    Today is day 1 of 2018 Winter vortex.!!! Positive 0.1M/S - An early start for the PV. Im quite excited this winter as the prospect of something very tasty coming along- Sea ice anomalies in the 2 key regions very significant in terms of worse than usual & the CFS modelling of the stratosphere showing that as we start to hit the colder months through Autumn so the strat may run much lower than usual.. Still about 6 weeks to go before we see the reality - but early excitement builds.. Great work @Mattias Todays CFS runs see a SSW mid November - similar to 1962..
  12. 15 points
    The best answer, in my opinion, lies within the bolded section of the first post extract made earlier this week. So no garden path exists so long as every operational and ensemble NWP set isn't taken at face value Latest angular momentum update c/o the Global Wind Oscillation continues to show the support from within the extra tropics to add westerly winds to the atmospheric circulation which essentially are helping to neutralise attempts to make AAM fall more substantively through easterly trades currently added within the tropics. This means a slumbering stalled orbit is in evidence reflective of latest weak low frequency tropical forcing signal rather than any orbit fall-back. This limits the degree of persistence of an Atlantic ridge as previously suggested and explained. . This willingness for the extra tropics to support angular momentum shows that the atmosphere is going along with the on-going slow and erratic movement towards a weak El Nino through the coming autumn. The presence of a further convectively coupled oceanic kelvin wave developed in the Pacific is, as Mr Ventrice describes, of a greater amplitude event than the one that helped propagate warmer waters across the Pacific during Spring and bring La Nina to a close in early summer - and should further help develop the Nino trend in the coming few months. This suggests further support for angular momentum in the longer term and also the prospect of a sharp upward surge in AAM tendency as soon the tropics spring to life again across the warmest waters of the central Pacific. With this in mind, many of these post summaries have anticipated an atmospheric response to ocean CCKW signal by way of an amplitude MJO wave, and this continues to be the case. Seasonal modelling maybe inclined to be progressive with this signa in the last couple of weeks, and I will happily admit my own weather pattern enthusiast wish to see this happen is hard to contain and not resist over anticipating. However, it still objectively looks to be a correct signal and should have impact repercussions for the global pattern this coming autumn based on timeline recurrence - and also quite possibly also for the development of the seasonal stratospheric vortex looking even further ahead on the basis of a perceived strong Brewer-Dobson circulation between the tropical and polar stratosphere this autumn/winter. In the meantime, latest ensemble means (ECM,GEFS and GEM) indicate (on the above proviso that one reads between the lines a bit when viewing them) there is nothing untoward at all suggested in my opinion. Further fine and warm weather still seems very probable into the new month most especially further south and east - and despite the expected changeable look to the weather heading through next week its notable how the Atlantic ridging of the more immediate term has been put into the more transitory perspective suggested in summaries of the past week to 10 days. Mostly a trough/ridge arrangement advertised and no sustainable ridge/trough - so with time a return to generally above average conditions for the time of year and still the opportunity for troughs to dig southwards to our west and inject greater humid warmth northwards and for mid level convective thundery features to occur - and that are not uncommon at this late season. These events are never especially well modelled and tend to come into full focus at relatively short timescales - but as long as the jet axis is generally SW-NE, rather than W-E or NW-SE - there is always a good chance for some extra amplification to inject some of the warmest air advection northwards September looks set for the time-being to continue to follow the long term dominant +NAO profile - but should that Pacific amplitude low frequency signal come into focus sooner than later - then this suggests the sub tropical Jetstream waking up a bit which would further upgrade late season plume and thundery prospects initially as the NAO becomes less +ve and encourages lower pressure to develop to the SW.
  13. 15 points
    Charts to warm the cockles of a coldies heart from the ukmo 00z!
  14. 14 points
    Wowzers..look at these uppers on the Ecm 12z into september!
  15. 13 points
    ECM continues to tout a fair old swing in pattern towards a solid -AO base state Cold air filtering into mid lattitudes may include the UK - but more so Central / Northern Scandi
  16. 12 points
    With the official stats now out, here's the Met Office chart comparing Summer 2018 with other similar years. For much of our Region 2018 was the hottest, but with some variations such as Norfolk and Kent. The second chart is a great 'zoom in' by Dan Holley showing the variances across East Anglia. https://twitter.com/danholley_/status/1036680299252510727
  17. 11 points
    Mixed messages from the anomaly charts EC is now more ridge dominated than before with GFS showing strong heights but in a general westerly flow. http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html NOAA shows smallish +ve heights over the UK and little 500 mb flow south of the country. Wil this be enough to allow any sufficient build of a surfave high in a position to allow for additional warmth from France? Hard to tell, and as S posts above it does seem as if the teleconnections that some talked of are the most likely from model outputs of various types, so well done got this linkage being shown. Way beyond my level of expertise but the 6-10 and the 8-14 from NOAA do lend a fair level of confidence in those time scales for much of the UK having generally dry settled weather, just how much sun and how high the temperature levels will be is beyond anomaly chart interpretation. What can be deduced from them is that the Atlantic still seems not to be a major player, at least away from the NW. Just one caution, we moving into the major part of the hurricane season. No model, long or short term, is vary good at predicting just where any major storm will track or its possible effects in the UK area. http://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php
  18. 11 points
    So yes, here we are, 7-10 days later than originally anticipated, getting into the continental flow regime, with the Atlantic trough well-suppressed at least for the first week of the month as the seasonal wavelengths support the ridge in our vicinity. Room for the trough to present more of a fight toward mid-month, perhaps, which could lead to some interesting results. Temps wise, low-mid 20s indeed a safe bet for large parts of the UK during the easterlies, but if the flow turns south of that, high 20s are achievable. As for a direct southerly draw, well that can bring the 30s even in the late stages of the month, so it's also worth keeping an eye on any signs of such a thing. Especially if it looks long-fetch... remember the final days of September 2011? It was pretty much the optimal setup for maximising temps, so far from something to reasonably anticipate this year, but still... it's fun to entertain what it would be like if it happened sooner in the month .
  19. 10 points
    Afternoon all Completely FI and probably completely unsupported but: This would probably bring the colour back to your cheeks !! Chilly spell following: It won't happen though.
  20. 10 points
    This mornings ECM chart would bring some incredible weather to the UK at day 8/9/10 Long may that continue....
  21. 10 points
  22. 10 points
    That was a barnstorming ECM run for a late summer special. High pressure reaches the UK by, well, 48 hours time, and bar a couple of dead fronts, that's how it stays throughout the run. Good to see northern areas looking in the mix for summery weather too, though don't tell the kids This morning's ensembles finally banished any thought of unsettled weather returning quickly to northern areas - actually a bit of a turnaround on 48 hours ago - but the overwhelming backing for UK-wide settled spell is difficult to argue against when you have two clusters so emphatically in that direction even by T192 and T240 (5th Sept and 7th Sept) So I'd suggest anyone with a UK holiday booked next week won't just benefit from cheaper prices but very good weather too, probably all week. This is the absolute earliest that we see any sign of unsettled weather possibly returning from the NW, and that's on a 31% cluster (so 70% still very settled) - and we're out to 10th September here in any case: Maximum temps - well, we're out of high summer so need to be realistic, but still some hot feeling days with Sunday/Monday up to 25C ish, low 20s for much of the week but creeping back up towards the end of the week. The only way to beat that is to see the stalling low to the SW that the GFS has suggested on occasion, which may allow us to approach the 30C mark once more.
  23. 10 points
    Despite the positive comments above it would appear to me that GFS aside there has been a considerable downgrade from the Euro and UKMO in terms of support for pressure to build for more than a day or two.
  24. 9 points
    Little change in the outlook so straight to the NH profile and the surface analysis at midnight. Most of the western half of the UK is currently cloudy as the frontal system moves in from the west and sporadic rain is already into Wales. The main wodge of rain will track ENE through the day clearing into the North Sea by early evening. The boundaries of the rain are still not clear cut but we are looking at a wet day in Wales, the Midlands and parts of the north of England. Sunnier in Scotland and the south east of England where it may even be pleasantly warm. But by early evening rain from the next system is already into N. Ireland and west Wales and this will track more north east overnight and through Sunday morning so that by 1200 the fronts associated with the main low west of the Hebrides are orientated down the north west and central parts of the UK. Thus a clearance over N. Ireland and Scotland and some showers with cloud and patchy light rain persisting around the Midlands and Wales whilst again warmer in the south east. Through Sunday evening and the early hours of Monday more persistent rain, accompanied by a strengthening wind, will effect Scotland whilst further south the fronts will slowly sink south east. thus dry with broken cloud and quite warm in the sunny intervals. By Tuesday the fronts and low pressure area that brought the inclement weather to Scotland have moved away east but a cold front trails across the Midlands and Wales which marks the boundary between the cooler air to the north and warmer to the south where it will be dry whilst showery in north western regions. A not dissimilar story on Wednesday although the front has moved a little further south but with no rain now on it. And so to the NH profile at T120 where one of the main features is the strength of the Bermuda high pressure which is keeping Florence on the southerly track.
  25. 9 points
    Surprised that it's so dead in here this morning- there's been an improvement in the op runs this morning, particularly the ECM 00z, which shows high pressure building from midweek onwards, especially for the south, and eventually nationwide. The end of the run also shows heat building again: It's not too late for another hot spell, even though autumn seems to be in the air right now. Still plenty of time for more warmth and even heat.
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