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  1. 30 points
    Extracts posted last week on closed thread: The other part of the equation is the seasonal transition within the stratosphere from its winter default vortex position to its summer state. This is bound to increase -ve momentum (easterly) zonal wind activity across the pole and manifest blocking tendencies at high latitude which adds further to NWP vicissitude...….. ...….Mitigation of HLB sustaining too long also probably aided by a weak El Nino forcing which acts to help the ITCZ further north in late Spring heading into early summer sooner than under low angular momentum La Nina conditions...... Forthcoming prospects? ….. assuming active tropical >extra tropical forcing sustaining angular momentum tendency through the greater part of May c/o weak El Nino circulation and aligned with w/QBO, increasingly inhibiting Atlantic and Greenland blocking heading towards the important seasonal wavelength setting as Spring turns towards Summer, then whilst such a pattern will inevitably sustain backwards and then forwards once more- its not unreasonable to hypothesise further re-setting of the Atlantic trough and downstream W/European ridge and re-cycling of increasingly warm patterns from an ever warming continent as the days keep growing longer. ---------------------------------------------------------------------- The most recent post following these extracts spoke of fine margins in respect of much of the wider discussions ongoing in these summaries. Categoric underestimation in that analysis, no doubt, of the vast amounts of vertical heat transfer generated into the pole by the recent Scandinavian height anomaly - - which has further augmented the final warming and thus created the "dynamic" response to the final seasonal warming of the stratosphere that has made the difference between a more conducive Branstator (mid latitude) ridging arrangement to late Spring warmth and the highly anomalous Greenland block verifying instead. The result being the polar vortex splitting and leaving a core cold element to our NE which is set to spoil the B/H weekend temperatures and increasingly also looking set to usher in a southerly tracking procession of lows from midweek. So one might assume such a reverse polarity outcome has also scrambled the polarity of the whole analysis, and left credible extrapolations of cool cyclonic conditions for weeks on end in its legacy instead? No, not really. The fundamentals remain that the seasonal stratosphere/troposphere transition might well be simply masking the direction of travel to an ultimate destination that sees transport of the end of season cold vortex back across the pole c/o the reverse polarity, helping to converge a mid term cyclonic mess in the process right over our heads, but with the Greenland height anomaly also fading and backing west towards Newfoundland and Canada with the result that something of a west based -NAO allows pressure to rise from the south and starts to draw up warmer air in the process. There are some hints of this in extended means, albeit the exact timing of this is open to question circa a few days bandwidth. Such an evolution would go full circle to re-setting the original analysis suggesting of an Atlantic trough and downstream ridge and return of something much more seasonal. As depicted by the sharply defined edged red anomaly in the Hovmollers plot below, this pattern evolution also draws on the significant westerly wind burst about to be set in motion in the West Pacific as the strong tropical CCKW related MJO wave propagates further east (and ultimately engages the standing wave at the Pacific dateline) - -and hopefully keeps a borderline Nino signal going into the start of summer and which assists in choreographing a rossby wave pattern suitable for downstream mid latitude ridge building (as the wildcard -ve easterly anomalies at higher latitudes fade out to summer transition of the stratosphere/troposphere state) As previously outlined, the importance of this is vast - because seasonal wavelength changes from Spring to Summer would lock in this type of default for periods during June, and possibly July in much the same ways as, by way of a few examples, during 1994, 1996 (to some degree) and 2006. Most of those years also had some Nino upstream forcing attached to them - and 2006 perhaps closest in this respect with an establishing and growing +QBO phase which helped supress sustained higher latitude blocks and facilitated low heights over the pole to follow the blocking of seasonal transition. The most recent post discussed some of the elements that could make things go wrong, and which also would encourage Atlantic blocking mechanisms to become the default instead - and which would persist or follow on from the upcoming unseasonal supressed jet stream conditions. So of course there is nothing inevitable about such repetition in 2019 However all three of the aforementioned years (1994, 1996 and 2006) saw highly underwhelming May's with a supressed jet stream and plethora of Atlantic/Greenland blocking prior to very good June and July's - but summer variants followed this in each case centred around extended dry very warm/hot settled spells and some spectacular thundery breakdowns and re-loads of the Atlantic trough and European ridge pattern. 1994 was especially notable for the thundery variant during both June and July.
  2. 25 points
    Greetings to you all! A glistening new thread for the month of May and early Summer! As we head deeper into Spring and into Summer (though I guess for some, May could be classed as a Summery month), a number of us hunt for warm weather with sunshine, thunderstorms and plumes. For some, you may be after some cool and wet, or cool and dry weather instead. That time of year where trees become thick of yellow, green and purple foliage, and flowers burst into life all over the place! A little glance at the models and you can see, using the GFS 18Z as example, that it's painting a chilly picture over the UK later this week with a cool flow developing from the North. This is thanks to High Pressure to the South-West of the UK linking up with the high heights over Greenland with a trough dropping down to our East from Scandinavia. But before that happens, a puny Low Pressure system to the West of Ireland, currently sandwhiched between both the High Pressure to our South West and the High Pressure over Greenland, will track South-Eastwards to join up with the Low Pressure to our East later this week. The Low will fill as it does so and become a wave feature. This helps out with High Pressure amplifying to our West in the Atlantic. That little cyclone will bring some showery rain over the UK today as it makes its journey South-Eastwards, with further rain and showers on Thursday. With regards to that Northerly following after (see charts below), the best of the driest conditions would most likely be over Western UK closest to that High Pressure. Chiller conditions likely further North and East you are with a chance of showers, possibly with some longer spells of rain and hill sleet and snow. Probably not much precipitation about, but some of the showers may have a wintry flavour to them. Most likely over Northern high ground and maybe to lower levels over Scotland. The 850 hPa temperatures the GFS shows below could certainly be cold enough to support some wintriness over Northern areas. Could be quite windy too, especially towards Northern and Eastern coastal districts. Did feel back in April that one or two of the chily outbreaks the models were showing would have been the last shot for the cold and snow enthusiasts. Nevertheless, this would very likely be the last chance to squeeze out some wintriness for the cold fans before next Winter. Their may also be enough room for the Northerly to back a little further West allowing lower heights from the East to become more influential and increase the instability for more widespread, potent, (wintry) showers. Equally, the Northerly may just get shoved further East with the High Pressure over Western UK giving the Scandinavian troughing a bit of a kick - more of the UK ends up staying dry and bright. There is a risk of some night time frosts later this week and into the weekend, which may cause some disruption to plant growth and farmers. Perhaps, though, nothing too servere and hopefully not much damage is caused. Still looks as though it would be a fairly dry period overall, particularly again over Western UK spots. Later on into the outlook, and it looks as though Low Pressure to the West of that Atlantic and Greenland ridging will try to take over. (Quite possibly with ridging over Southern UK hanging on): At 192 hours, the 18Z GFS, 12Z ECMWF and 12Z GEM generally show the UK under the Atlantic and Scandinavian's troughs spell! Some strong heights over Greenland maintained with Atlantic Lows directed over the UK. Could stay quite cool, especially over Northern UK areas, and maybe become more unsettled during this period next week. Since it is 192 hours away, things may still improve for those wanting to see more in the way of warm, settled, weather (including myself). However, it would be fair to say some rain is likely needed in some places still, considering how mostly dry its been for some parts, especially for the South East of the UK. Both the 6 to 10 day and the 8 to 14 day CPC/NOAA 500mb mean charts following similar ideas as the above operational runs with blocking continuing over Greenland and Low Pressure in the Atlantic. Perhaps some ridging influencing Southern areas of the UK at times (especially with the higher than average heights over Western Europe), so probably nothing majorly unsettled. Maybe a possibility some of the operational runs, such as that 12Z GEM, over-doing Low Pressure over the UK. https://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php https://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php I suppose it will be interesting to see how the models continue to develop things. Wanna Be Good? Whatever happens, please keep things friendly and on topic in here. Some banter, including the odd bit of off-topic chat, is fine as longs it doesn't cause the thread to come off its tracks. The Netweather team will moderate this thread from time to time to keep it focused on the models and stamp-out inappropiate nonsense! Bad and rude behaviour will not be tolerated! Any issues with members, please use the Private Message system. Should you be naughty and disobey our rules, you may either get a warning, have your post removed or, if you've been very naughty, you may have your keys to the door of this thread taken away from you. Alternative Threads: To chat more generally about the Spring weather, please head over to the spring thread: https://www.netweather.tv/forum/topic/91223-spring-2019-moans-ramps-chat-etc/ The Summer one: https://www.netweather.tv/forum/topic/91676-summer-2019-moans-ramps-chat-etc/ And to post tweets about the models (although you're still welcome to use the Model Output Discussion thread), please see this thread: https://www.netweather.tv/forum/topic/87130-model-tweets/ For the Met Office outlooks, please use this one: https://www.netweather.tv/forum/topic/64157-meto-uk-further-outlook/ Model Output And Charts On Netweather: GFS GFS FV3 (Parallel) GEFS Ensembles ECMWF ECMWF EPS NetWx-SR (3km) NetWx-MR (9km) Met Office (UKMO) Fax GEM GFS Hourly Model Comparison Golbal Jetstream Stratosphere Previous thread: Thanks a lot all!
  3. 24 points
    This convectively coupled kelvin wave (CCKW) I have continued to reference over the last week or two has been of such strength heading through the Indian Ocean that it had much to do with the development of the devastating tropical cyclone Fari which sadly crippled the Indian state of Odisha in recent days. It has now passed eastwards through the Maritime continent through to the Western Pacific and in terms of the feedback processes from upwelling warming across the ENSO zones (see below tweet for illustration purposes|) has possible significant future implications to downstream patterns in terms of the ushering in of summer wavelengths - and when the dynamic response to the final warming of the stratosphere eventually starts to fade from influencing tropospheric responses. The bright red - intense white colours in the Hovmollers plot pick up the strength of the WWB heading through the W Pacific. On the VP200 anomaly chart depicting the CCKW tropical convection, notice the eastward progression of the CCKW in the first half of May to engage the dateline in the Pacific - and how suppression (yellow, orange. red colours) of convection appears in the wake of the tropical wave across the Indian Ocean and then Maritime continent respectively These westerly winds in the Equatorial Pacific propagating eastwards, tend to migrate poleward through the extra tropics with time, and programme swathes of downstream amplification. Where this amplification sets up is dependant on the longevity of the more transitional seasonal downwelled -ve easterly zonal winds across polar latitudes. The question is - how sustained are they likely to be? Any collapse in angular momentum caused by increase in easterly winds across the Pacific has the effect of transferring the amplification wavelength upstream to the Pacific and create a downstream ridge>trough>ridge trough response. The final ridge trough response being that in the Atlantic and European sector respectively. On that basis it could be seen that any Atlantic or Greenland blocking default created by a -ve ENSO atmospheric circulation feedback is a natural extension of any pre-seasonal higher latitude blocking such as we presently have. If the ocean/atmospheric standing wave is held back across the Western Hemisphere because of the effects that easterly trade winds have on supressing tropical convection in the Pacific - the consequential stable atmospheric environment is conducive to High pressure in the Pacific and a downstream blocking response also in the North Atlantic.. That is why the setting of a +ve ENSO wavelength in the Equatorial Pacific is useful for warm air advection patterns in our part of the Northern Hemisphere in summer because it encourages MJO related and associated separate induced cyclonic activity in that part of the tropics - which in turn helps promote a downstream Pacific trough/ridge pattern, and replicated Atlantic trough and downstream European ridge In this way, the CCKW is a very important event in reducing the risks of a more la Nina like atmospheric response generating sustained easterly trades winds heading into summer and also therefore less chance of any Atlantic blocking configuration to follow on from final warming HLB and then stick for any length of time. Ultimately, the current MJO wave will return, naturally as part of the "mini ENSO cycle" to the Western Hemisphere - note the suppression arrive in the Pacific as the signal returns from Africa back to the Indian Ocean in the last third of the month Based on the fact that the latest wave is already likely to adjust the Pacific SST pattern favourably, as detailed above, and help tip the balance more towards a summer ridge pattern downstream, then the return of the tropical wave pattern to the Indian Ocean later this month might well see a higher floor to the fall-back in angular momentum likely later this month - and that usually always occurs at the end of each MJO cycle. Currently globally averaged atmospheric angular momentum (GLAAM) is about +1SD above average which is a quite good place to be in ahead of the upcoming passage of WWB's associated with the CCKW. CFS and other model products are picking up on a possible further CCKW event heading into June. Its early to have high confidence in this, but its one to keep an eye on. . This watching brief then also ties in with what happens to the polar field pressure pattern in terms of the remnants of the final warming. Some current NWP extended products are hinting at wanting to try and retrogress the poleward amplifying sub tropical ridge that evolves through days 7 to 10 again and sustains the block to the north in the more extended period. This then potentially inviting another swathe of troughs to have the potential attrition to undercut from the west and promote further cool unsettled weather How credible is this? Assuming that longer term prospect chances have been improved by upstream tropical developments sustaining a supported angular momentum regime heading into summer, then the lifespan of dynamic fall-out from the final warming has limited sustainability heading into summer period, with a combination of seasonal wavelength changes, +ve momentum forcing from an El Nino type atmospheric feedback and assistance from the +QBO phase to also underpin this. So whilst a further round of attempted Greenland blocking cannot be ruled out in the medium term, then this might give way to a warmer mid latitude ridging pattern as Spring heads to early Summer. Though the sustained anticyclonic conditions of last summer seem less likely this year, and a potential thundery element exists which many would welcome on the basis of a reloading warm pattern and to add some interest to conditions. May 2007 was a generally +ve AO regime which gave way to higher latitude blocking through June and the rest is history. It was also a year where angular momentum collapsed heading into summer at the same time as an easterly -veQBO assisted downwelling of -ve zonal winds into the troposphere to align with weak sea ice and produce a very poor summer. The previous year, as documented in a post last week, had the opposite configuration with a higher latitude blocking in May followed by mid latitude heat ridges as soon as the calendar turned into June. This year the chances of more sustained relapse have not gone completely yet, and it will require a close watch on both the ongoing blocking patterns and angular momentum/tropical wave trends during the remainder of May heading into June - but latest events should have at least reduced the risks vs what was beginning to seem increasingly possible in recent weeks and create a better chance that this summer evolves closer to the better variety than the likes of 2007, 2011 and 2012. So that improvement from the south comes as suggested of late by the weekend to follow what looks a truly dismal week - albeit due to the persistence of the higher latitude blocking signal it looks now to set up initially further west than ideal to cut off the cooler air staying close by. However, the depth of cold air compared to this weekend is not there and liable to mixing out further with time. Its also not the end of the world if it morphs into attempting to retrogress with further fall of pressure undercutting it. It doesn't mean summer is destined to be over before it has begun. Such an evolution is far from certain anyway at this stage and some fine weather, albeit not a heatwave, still looks likely heading into the following week. But should this month continue to struggle to follow through on any recovery promise, the philosophy of ice in November and sludge and muck to follow comes to mind with its opposite counterpart in May. It remains the case that what follows afterwards matters much more in terms of hopefully disposing of the Greenland and higher latitude blocking..
  4. 23 points
    In view of the provocative game-playing (that I had gladly escaped during the winter) and the absurd quick fire reactionary responses attributed to NWP operational data, attendant with not enough attention instead to ensemble data (which in itself is simply only a snapshot of time in evolving patterns) its probably a good time for some more analysis. Signals after all lead models, models do not lead signals The seasonal demise of the polar vortex, amplified by tropospheric heat flux forcing as described in an earlier post, continues to dominate the NH pattern and inhibiting any late Spring build up of real warmth over the nearby continental landmass due to persistent feed of cold air advection from a displaced and rapidly dissipating area of leftover vortex broken away from the the eastern arctic into Scandinavia The persistent height rises to the north - a manifestation of the symmetry between the tropics and the pole and differentials between them which enhance tropical convection activity (MJO) and the resultant wave train in turn triggers equatorward flux in the Southern Hemisphere (i.e subsidence away from the Antarctic) and a +ve pressure signal (+AAO). At the same time in the Northern Hemisphere, the engagement of the eastward propagating tropical wave at the dateline teleconnects the opposite way to the SH with a -AO/-NAO - the latter attendant with upstream jet extension across Asia and the Pacific and greater flow into the southern stream. The Southern Oscillation (SOI) in response to the eastward propagating MJO signal has trended sharply negative in the past few days - an indication of -ve Outgoing Longwave Radiation anomalies ( OLR) and associated deep clouds and thunderstorm development close to the dateline - also as illustrated by the intense and sustained westerly wind burst continuing across the Pacific to the dateline https://www.longpaddock.qld.gov.au/soi/ As well anticipated in recent posts in advance of this WWB, angular momentum tendency, subject to 2 day lag, is significantly ramped upwards. The +ve AAM anomaly depicted around 30N in tally with the proxy data in the Pacific as depicted in previous plots The Global Wind Oscillation, a plot depiction of wind-flow additions and subtractions as supplied by frictional and mountain torques and other related mechanisms, has responded with a leap into high amplitude Phase 4 as these large amounts of westerly additions are supplied to the atmosphere. This is the kind of repeated GWO pattern which, with repeated westerly wind additions c/o tropical activity, would return the GWO to El Nino attractor phases 5 to 7, and would accord with seasonal wavelength changes and start to build further anomalous mid latitude ridges close to and just to our east during June (and possibly July) at the same time as height rises to our north start to fade out.. More on this uncertainty further below. So for this, and all the other repeated detailed reasons given in previous posts, it continues to be premature and pointless in equal measures to extrapolate assumptions of the resultant -AO led pattern into the early stages of summer (and in some cases evidently even beyond!). A lot could, and quite conceivably will happen over the coming few weeks at such a time of seasonal pivotal change. In the medium term, its worth watching the developing low heights towards Iberia and Biscay - these could play a role in providing a stark thermal temperature boundary between the cold air advection to the north and a much warmer humid circulation becoming ensconced around the low heights to the south and south west. How far north such a boundary might set up is uncertain at the moment, but some NWP is playing with this scenario in the extended period and its conceivable that another round of retrogression of the heights to the north could lead to a similar evolution to this week, but this time with less of the deeper upper cold air around to tap into further to the north and east and any warm air advection adjusted further east into Western Europe With that type of subtly adjusted wavelength evolution in mind, if (as discussed above) tropical convection patterns and angular momentum tendency can remain conducive, and this still isn't a given and needs to be watched for a while yet, then seasonal wavelength changes and gradual ascendency of the Hadley/ferrel cell heading into new month and new season change could flip a stubbornly (relatively) cooler pattern into something more sustainably warmer. Such as happened in some of the aforementioned summers in previous years that featured May's that seemed reluctant to embrace a substantive warm-up All that said, and returning to the opening theme above, some proper perspective is needed here - next week still looks to feature a much more pleasant spell of weather after this weeks anomalously below average temperatures, with some welcome sunshine that will lead to warm feeling days out of the breeze, especially in the north west and away from eastern coastal districts where low cloud could be a nuisance. In that respect not an unusual pattern for mid May and nothing untoward whatsoever to lead to writing off swathes of a season that is yet to begin and remains too uncertain to call (either way).
  5. 21 points
    Last time I looked at a calendar, there were 22 days left in this month. I think anyone writing off the next three weeks on the basis that we have had a poor start to this month and then deducing the entire summer is a write off, probably needs to take a step back and consider their expectations. 2018 was extreme if you look at historical years with both the heat and the cold. We are not duplicating that this year so far for sure, but by the same token this also doesn't mean that we can confidently say that the next three months are going to be a copy of the last three days.
  6. 20 points
    Howdy all! Just something worth pointing out - while not everyone is doing it, there has been a lot of GIFs and Memes used lately - particularly on page 27/28. Though I appreciate people are trying to add fun and humour to the thread, we would kindly ask if some of you would tone down your use of these funny animations and pictures, as it can distract from the main purpose of this thread. I know I must sound like a fun-stomper. But it’s just they’re kinda being overused now to be honest, and we may start removing some of them. Cheers guys!
  7. 20 points
    The first thing to remember is that estimating the surface temp from the 850mb is very rough and ready and is very often likely to be miles out. I don't know what you have read but it will be based on the lapse rate between the surface and 850mb. Air cools adiabatically as it rises, and the converse, and in the case of dry air that will be 9,8C/km and saturated around 5.0C/km. The environmental lapse rate is in between around 6.8C/Km So it is quite easy to calculate the surface temp, given the 850mb temp, if you assume the 850mb height as 1500m and a dry lapse rate. In the height of summer you can add two or three degrees for surface heating. But that assumes (a) dry air and (b) nothing interferes with the temperature structure between the surface and 850mb such as cloud, CAA and even subsidence and you could even include orographic features for any particular location .In practice this is very unlikely So the moral is... be wary
  8. 19 points
    What a run that was! Whatever the temps turn-out to be (25-28C will do me) a fundamental pattern-change looks more like occurring, as time goes on...Of course, it is only a model? Anyone else see something rude?
  9. 19 points
    It is indeed proving to be the case that the models have been over progressive with the eastward intrusion of the trough - too far east (and for too long) General NWP culpability evident - but just as illustration here is the ECM ensemble change even over 24 hrs representing the early part of next week @Singularityhas nicely described the tropical>extra tropical forcing in the mix which is behind some of the NWP erraticism and which also encompasses my own suggestions in the wider post (of which the selected extract above comes from) re CCKW/MJO progression that might cause the models to find something of a reverse gear on the processes of extending the trough too far east into and across the UK. The downstream ridging proving more resilient than the modelling suggesting. The other part of the equation is the seasonal transition within the stratosphere from its winter default vortex position to its summer state. This is bound to increase -ve momentum (easterly) zonal wind activity across the pole and manifest blocking tendencies at high latitude which adds further to NWP vicissitude. This cross section of the atmosphere layers clearly shows the stratospheric/tropospheric evolutionary story since the SSW of January and the equatorial flux of AAM anomalies which resulted in sub tropical and mid latitude blocking (including the spectacular late Feb "heatwave") rather than the expected high latitude cold block coming courtesy of poleward momentum of +AAM anomalies - usually seen under conditions of active MJO tropical convection propagating towards, and then through the Pacific. To follow this immediate post SSW period, the return of zonal westerlies and re-organisation of the polar vortex apparent as per the blue anomaly representation through the layers of the atmosphere during March. In turn, now leading to the relatively late final warming of the stratosphere which is also complicating the models handling of tropospheric placement of these blocks . This interaction of seasonal downwelling from the arctic with influence of maladjusted angular momentum related wind-flow patterns at mid latitude, is proving to reduce the amount of Pacific amplification that has been expected by NWP - and in turn the amount of downstream polar jet flow extending the fragmenting and decaying end of season vortex and resulting trough out of Canada and US across the Atlantic. Furthermore, and to complicate matters further, the trend of equatorial zonal winds related to the Quasi Biennial Oscillation (QBO) are slowly increasing westerly in the new +ve phase. This suggests at least at face value that effects of any "dynamic" tropospheric fall-out from final warming (easterly zonal wind anomalies) of the stratosphere into the troposphere should be mitigated, relatively supressed and shorter lived - despite the late break-up (certainly later than last year c/o Feb SSW 2018). QBO Calculated at NOAA/ESRL PSD 30mb zonal wind at the equator, zonal average For info https://www.esrl.noaa.gov/psd/data/climateindices/list/ 2018: -19.02 -19.37 -19.77 -21.41 -24.23 -28.45 -29.10 -20.41 -9.91 -2.79 3.36 + 8.05 2019: +9.02 +9.25 +11.82 (Jan, Feb and March figures) Mitigation of HLB sustaining too long also probably aided by a weak El Nino forcing which acts to help the ITCZ further north in late Spring heading into early summer sooner than under low angular momentum La Nina conditions. If we take a look at where globally averaged angular momentum is at what is looking like the bottom of the "lull" in the tropical>extra tropical wind-flow cycle, then there is scope for quite a pre-summer rally to boost prospects for warm spells in this run-up period. Still a little above average at this time, having lost the momentum peak of late winter Forthcoming prospects? As tropical forcing progresses eastwards through the tropics and westerly wind inertia builds in response, this increases +ve frictional torque tendency at the inception point where these westerlies add momentum to the atmosphere - starting the process of angular momentum tendency rising once more. Notice the red anomalies (westerly winds) progressing towards the Western Pacific as the easterly inertia (blue shading) ahead of the tropical wave is scrubbed out with time Another way of looking at the wind anomaly progression across the tropics is through the VP200 convectional anomaly chart - the convectional suppression (yellow and orange shadings) presently over the Pacific gradually being eroded by the advancing -ve convection anomalies heading from the Eastern Indian Ocean through the Maritimes and towards the West Pacific (equal to MJO Phases 3,4,5-6 on deterministic model MJO plots) These eastward progressing westerlies added to the atmosphere circulation from the tropics register a response from the Global Wind Oscillation (a phase depiction of wind-flow pattern additions and subtractions) and result in orbit from falling angular momentum Phase 8 to rising angular momentum Phase 4. This likely is a prelude to the GWO fully engaging the El Nino attractor phases 5,6 and 7 once more in the further outlook as the Nino standing wave in the Pacific is re-engaged during May and hence why in my opinion NWP is starting to advertise a ridge response once more rather than sustaining the trough On this basis, assuming active tropical >extra tropical forcing sustaining angular momentum tendency through the greater part of May c/o weak El Nino circulation and aligned with w/QBO, increasingly inhibiting Atlantic and Greenland blocking heading towards the important seasonal wavelength setting as Spring turns towards Summer, then whilst such a pattern will inevitably sustain backwards and then forwards once more- its not unreasonable to hypothesise further re-setting of the Atlantic trough and downstream W/European ridge and re-cycling of increasingly warm patterns from an ever warming continent as the days keep growing longer. In the shorter medium days 5 to 10 period, its a case of seeing how the models resolve the ridge placement now that the ejected trough is backed west into the Atlantic. This will determine how much cooler air advection comes south before the suggested higher heights close to Greenland fade in the longer term and hopefully set up a mid latitude ridge as day 10 ensemble means are trying to converge on. To copy paste the last line of the quoted post however : "A case though of keep watching to check this evolution stays constant and seeing how NWP responds"
  10. 18 points
    Hello Mike - this cross section of the layers of the atmosphere clearly illustrates the downwelling process of that final warming - quite the contrast to the +AO dominated close to winter and first half of Spring. I think that puts a perspective on this Spring and its mixed character. Aside from the anomalously very cool start to May which is concordant with the switch to -AO c/o the dynamic nature of the final warming, the CET means for March and April are fully contemporaneous with that earlier generally +AO profile - both months comfortably above average. So the capricious surface conditions of the season have rather masked the fact that this Spring as a whole (so far) has not been quite as poor as some might try to make out. Also the highly anomalous warmth of the second half of Spring 2018 is a distracting and distorting comparison perspective - even in this warming world and increasing occurrences of noteworthy temperature anomalies breaking frequent records, consecutive late Spring and Summer seasons of such homogenous warmth still represent an upper benchmark. This is the UK after all and not a sub tropical climate as much as it is not a cold continental one in winter. Expectations and preference ideals are too often asymmetric with geographical latitudinal realities Looking ahead, and striving to build on previous analysis - some further thoughts to add extra substance. There are signs a more coherent +ve PDO pattern might try to set up with come modest relative cooling in the West Pacific - and by comparison, warmth consolidating in the eastern Pacific. This accords with El Nino standing wave signature being assisted by the eastward propagation of convectively coupled kelvin wave (CCKW) MJO envelope. As such, it accords with MJO Phase 8 imprint and downstream rossby wave train amplification of the wavelength Furthermore, this contradicts the identity of Springs heading into summer like 2007,2010, 2011 and 2012 where a -ve PDO was part of either an imminent La Nina (2007 and 2010) or a long established La Nina (2011) or an even more established Nina struggling to transition to ENSO neutral (2012) If we take the globally averaged angular momentum budget, the characteristic low angular momentum state (as manifested by -ve PDO tendency) is clearly choreographed during the Springs of both 2011 and 2012 Quite different to 2019 A w/QBO prevailed as is the case this year in 2011 - however the Pacific feedback was very different and clearly much more La Nina-like than this year - and the characteristic mid Atlantic ridge and downstream UK trough increasingly played a hand as summer was arriving and seasonal wavelengths changed. Furthermore, the QBO phase does not accord with the very easterly state in Spring/Summer 2012 where some other background parameters were closer to this year than 2011. The strong e/QBO overrode any attempts made by the atmosphere to try to become less La Nina-esque during early summer 2012 and sustained blocking at the "wrong" latitude instead.. Calculated at NOAA/ESRL PSD 30mb zonal wind at the equator, zonal average For info https://www.esrl.noaa.gov/psd/data/climateindices/list/ 2012 -16.07 -15.25 -16.74 -17.62 -22.04 -25.89 -27.82 -27.93 -26.60 -24.51 -18.95 -10.02 2013 -6.07 -1.23 2.85 8.39 12.64 13.38 14.27 14.66 13.12 11.69 12.45 12.55 2014 13.13 12.68 11.72 7.15 -2.81 -13.98 -19.29 -21.64 -23.24 -23.86 -23.65 -25.38 2015 -26.70 -28.62 -28.15 -24.38 -12.33 2.18 7.45 10.97 12.07 13.38 12.79 11.39 2016 9.34 6.77 3.16 0.64 2.37 3.86 6.25 10.07 10.48 12.83 14.16 15.09 2017 14.92 14.78 14.35 13.88 8.01 -3.18 -10.48 -14.42 -15.28 -16.79 -17.20 -18.12 2018 -19.02 -19.37 -19.77 -21.41 -24.23 -28.45 -29.10 -20.41 -9.91 -2.79 3.36 8.05 2019 9.02 9.25 11.82 13.36 - (April update) Strengthening westerly phase evident. A +ve (westerly) QBO, in tandem with an El Nino forcing on the atmosphere is a more "hostile environment" for any final warming feedback to prevail than occurred in 2012 and failed as a result of too much La Nina -ve PDO forcing in 2011. Summer 2006 is that excellent w/QBO and El Nino combination example, previously referenced, where HLB in May gave away to anomalous warm mid latitude blocking early in June. In respect of the CCKW as a noteworthy event, it will be interesting to see seasonal model updates in terms of ENSO SST predictions as benchmark for how Nino might prevail. -May is often a key month here.. Should El Nino rally once more, with the standing wave engaged in the Pacific and the atmosphere reflect a coupled feedback loop with the extra tropical GWO starting to repeat orbits returned back to the Nino attractor phases, then portents are good for summer. Different to last year in respect of the likelihood of no persistent ridge for weeks on end and the Atlantic trough and downstream ridge breaking down and re-setting and allowing thundery breakdowns, and then cooler changeable interludes leading to re-set of the default warm pattern. That is not a forecast - but its quite typically traditional weak summer El Nino. There is little danger of the southern stream getting too strong as it did in the start of the "super Nino" of summer of 2015 - its more a case of avoiding increased trade winds breaking down the Nino-like trough/ridge pattern and creating a more persistent downstream trough instead. Especially because this years final warming has had a "dynamic" element to it, with considerable poleward heat flux drawn into the final warming and further amplifying the downwelling -ve zonal winds to the troposphere/stratosphere boundary. This might serve to give it that little extra resistance to the natural effects of seasonal wavelength changes and advancement of the ferrel cell in the tropics as assisted by the favourable effects of wQBO usually creating an elevated tropopause due to westerly shear in the lower stratosphere. But there are signs as previously discussed the odds are stacking against such resistance and whilst, as we know, the seasonal models like UKMET et al are not bullet proof - such general analysis as attempted here does provide some logical resonance and credence to such predictions of a warm summer pattern Time as always will tell - but much more will continue, as ever, to be gained from comparing progress of ensemble NWP suites in reading all these signals than wasting time trying to draw too many observations and conclusions from the smorgasbord of unicorns offered by intra day multi faceted operational output.at long distances All the computer models have their inbuilt biases, but the GFS continues to often display a -ve tendency (low angular momentum) response to its interpretation of tropical signal imprint on the synoptic pattern - particularly as the MJO completes its cycle and returns to the Western Hemisphere onwards to the Indian Ocean. Such timing as due later this month and where differences of modelling are already apparent with the ECM .So some further erratic output and disagreement could crop up as the coming week progresses in terms of the extended period. Good reasons therefore to particularly not overreact to operational data and also be cautious with ensemble suites and compare their progress over 2/3 days rather than 1-1..
  11. 18 points
    ECM T240 out now, and there is a reason I've been posting NH charts recently, would only normally do in winter, the very strong final warming of the stratosphere is important here, we need to see this wane, and is doing. ECM T240: No ridging into Greenland, and a ridge coming our way...start of summer...
  12. 17 points
    I've been watching like a hawk for any signs that the Atlantic trough will behave more Nino-like and resist becoming negatively tilted with the blocking high being able to build to the northwest of the UK as a result. The 12z GFS and to a lesser extent ECM runs have finally brought that and have also thrown in a shift north with greater link to the Canadian trough for good measure, but it's just one set, with no preceding trend. So I can only hope that they're onto something; I want to see signs that the Nino base state is establishing itself better while we wait for the final warming fallout to fully subside. If they are on the right track, then we do at least see a more eastern position to the Arctic blocking focus become the most probable compared to a Greenland-Canada one. This provides the opportunity for the far south to see some useful rain (which it's been missing out on lately) without having to contend with low temperatures; troughs to the south are better able to drive warm air across the UK from the eastern Med. That being said - I have a sneaking suspicion that the models are generally being a bit too 'clean' with the Arctic blocking, with the actual result keeping the main focus of the blocking high further from the pole. A tendency to overdo those Euro troughs at the 5+ day range may also play into that.
  13. 17 points
    Some longer term musings from me tonight. My position coming into spring (my 'prior' in Bayesian speak) was that summer would be decent and hot one, but less settled overall than last year (see previous posts I think around early April), with more thundery breakdowns. How are things looking now? On no account can it be argued that the latter half of Spring is similar to last year! I think some of that can be put down to the late and exceptionally strong final warming in the stratosphere, which has resulted in the kind of high latitude blocking that those of a cold persuasion crave in the winter, this year without result. But that should dissipate, and if it does where does it leave us? Long range model output over the last few months has favoured high pressure domination in the region of the UK, although as far as I can see with more variability as to precise location re the UK (see my post yesterday on latest CFS runs). Sea surface temperatures are interesting, the current ones conducive to N Europe high pressure: Compare mid April last year and mid June last year: Clearly in April SST subdued near the UK after the Beast From the East, by June that's all gone after the hot second half of Spring last year. We haven't had that this year, so we could end up in a similar place by mid June, close to UK, but we need to watch the heat from Azores to UK, very strong last year, a signal there this year but weaker at the moment. The cold water south of Greenland is present in all plots though - some continuity there. So there may be some similarities with model output, SSTs going into summer, also atmospheric angular momentum (AAM) generally above average looks likely (see recent post by @Tamara ). Todays models, here GFS, FV3, GEM and ECM on NH view at T240: Whilst the blocking is to the north, the models are not suggesting a rampant Greenland high. Remember last year, in May the driest warmest weather was in the NW, only translating to the heatwave further south in mid June. Different so far, but is the journey into summer 2019 about to join a similar track to 2018, but a month or a bit more down the line. Will be interesting to see!
  14. 17 points
    Hi Knocker, you’re always welcome to post in here! Try not let anyone get under your skin (or whatever it is that is causing problems). Best to ignore any posts you may not be happy with, including ignoring/reporting any members that are being a nuisance, or you can always chat to us! Some people maybe getting a little bit over excited by some of the charts this evening - which, in a way, is understandable as I guess some of us are eager for some hotter weather. Some of the charts are likely being over-hyped too. There’s no total guarantee that some of those charts, especially the ECMWF ones, will come off like that. Charts a week(ish) away can always be liable to changes. I suppose though, the general pattern seems to be establishing to see some build of pressure next week. While I don’t want to force you to use this thread, your posts are appreciated by a lot of people (your morning summaries, for example, are really handy) and you provide balance and level-headedness with your content. (That’s not to say everyone else on here are biased with their posts, but you definitely one of the members that provides value to the Model thread )
  15. 17 points
    Starting to get interesting I see - these adjustments in the Sunday ridge position put me in mind of how we've seen many advertised cold easterly incursions become adjusted east or southeast of us. The plume creeping closer to us for early-mid next week shows the mark of the exceptional WWB that Tamara included in her excellent roundup yesterday. Top-drawer WWBs drive top-drawer amplification of weather patterns. We've been fearing further cool winds from the ENE but it seems the Atlantic trough might just about have a positive enough tilt (well, non-negative is what matters here) that the surge of warm air is due north then east of north, which then invigorates the polar jet to the north of the UK: ...keeping the HP cell from heading to our NW or N and so setting up a prolonged plume event for the UK. Remains to be seen how much the surface flow orientation will favour us , mind! While the 850s look very impressive over SW UK especially, surface temps don't look that way. While GFS' maximum temp predictions are probably showing some of the usual low bias that we see during spring-early summer events involving very warm airmasses arriving via a brisk flow, it's likely not to be by as much as some may think, as the surface flow is still from east of the plume on Tue and still a bit east of the main thrust of it on Wed. Further on, it appears that the Nino-like theme of reloading plumes punctuated by thundery breakdowns is becoming the GFS favourite. I'm a little wary, though, of just how much it lowers heights across the Arctic all of a sudden. It'd be a lucky break for UK warmth (or heat) - seekers though!
  16. 16 points
    The May GloSea5 output has been published today, so here are a few charts for the June-August period. Bottom line first, here are the tertile probability charts for 2m temperature and precipitation: Strong signal for above average temperatures, and no real signal for precipitation. I think this is consistent with a largely settled summer, punctuated with thundery breakdowns. To the extremes then with the outer quintiles plots for 2m temperature and 500mb heights: The hottest category is much more likely than climatology and is an increased signal over last months output. The heights plot shows less than 5% chance of the lowest category, should be the last nail in the coffin for those who are predicting a 2007/2012 redux!
  17. 16 points
    Gorgeous end to ECM this evening!! Yes please!!
  18. 16 points
    Eagle eyes obviously present... Based on yesterdays assessment those day 10 means reflect good cross model continuity for re-set of Atlantic trough and downstream ridge and warmer air to approach from the south. Taking account of the caveats that could still alter this evolution for all the detailed reasoning also given yesterday and recently, it still pays to do some QC on NWP assessment in terms of latest suite consensus (at the very least) before reacting However, the next few weeks continue to advertise a significant westerly wind burst propagating east through the West Pacific to the dateline and providing a timely shot to keep an atmospheric Nino feedback going into early summer. We are not quite there yet, but Its worth keep repeating that this is increasing the chances of warm plume scenarios rather than cool and changeable North Atlantic flow around a mid Atlantic ridge and downstream trough response
  19. 16 points
    Outlook - Due to become colder by the end of the week but the weekend should be sunny for most with light winds. After that still a tad uncertain with the energy flows jockeying for position. The percentage play is for the Atlantic trough to win on points. The 300mb wind field at midday Monday illustrates this quite well The 500mb NH profile and the Atlantic surface analysis for midnight and the 0300 UTC UK chart A clear start to the day in the east and N. Ireland and this will remain the case pretty much during the day, albeit clouding over somewhat. But the cold front that is causing patchy rain in western regions at the moment will move slowly east with the patchy rain becoming increasingly showery. during the afternoon a trough will bring more showers to N. Ireland. The temp spread reflects all of this with the south east becoming quite pleasant The showers will peter out through the evening and overnight but will continue a while in northern Scotland and the south east of England. So generally a clear night with the odd fog patch by morning. But note the trough over Scandinavia is getting organised and the associated cold front is on the way south. Thursday will be a day of sunshine and heavy showers but the cold front is now tracking down Scotland so a belt of more persistent rain here and colder air in it's wake Over Thursday night and through Friday the cold front stalls across the country as the subtropical high amplifies in the west so essentially a cold day with frequent heavy showers, The cold front clears the south coast during Friday night as the ridge moves east resulting in Saturday being a sunny day with temps a tad below average after a frosty start, Not feeling that bad in the very light winds. But showers will still effect eastern coastal regions as troughs track down the North Sea in the northerly flow by Sunday we are getting to the tricky time, After a widespread frost a generally sunny day with temps still a tad below average but still possible showers in eastern regions. And another cold front is on it's way south and is just north of Scotland On Monday the gfs has the front tracking down the country some some rain and showers around with temps still a tad below average
  20. 16 points
  21. 15 points
    Funnel cloud captured over Peterborough this morning!
  22. 15 points
    Extract taken from post of last week to assess progress, at the end of a beautiful Easter weekend and when some of us are looking for clues when the next warm and settled spell may appear Had been looking for some further evidence to keep backing up the quoted suggestion and to prevent any slippery slope into a late Spring cool trough gaining further traction into a more extended period. Here it is: This velocity potential (VP) 200 anomaly cross-section represents an eastward moving convectively coupled kelvin wave (CCKW) modelled to cross the Pacific during the first half of May. This matters because it provides a further boost to westerly wind bursts across the Pacific (to follow the current ongoing increased easterly trade winds close to the dateline) ensuring that upwelling of sub surface warmth can prevent any continued decline in this weak El Nino - and re-set the rossby wave pattern downstream once again back to being pre-disposed to building ridges instead of programming a persisting trough In association with the CCKW, deterministic MJO modelling has started to pick up on increased eastward progressing amplitude activity which should support a recovery in angular momentum tendency to resurrect from the the current downturn as part of a next uptick in ridging to replace the trough Unsettled for a time, yes - however its conceivable that the models might over programme the duration of the trough, but in any case, there are at least signs that the suggested improvement has some reasonable support to ensure that further fine weather has a chance of returning following the upcoming unsettled, cooler and windier spell A case though of keep watching to check this evolution stays constant and seeing how NWP responds
  23. 14 points
    Meanwhile back at the ranch and high pressure is set to be influential over the next few days with plenty of sunshine and the temps creeping up in most areas. Eastern and southern coastal districts may not get the full benefit of this. The NH 500mb profile and the North Atlantic surface analysis for midnight Today will start sunny in most areas and once any patchy mist and frost has cleared this will be the case through the day and feeling quite pleasant in the light airs. Perhaps not so much in the north east and down the east coast. But there is the odd trough around in the east and showers will pop up here through the day which could be quite heavy with hail and thunder in the mix. The showers will dissipate through the evening and overnight resulting in a clear, calm, night with a fairly widespread frost. By Sunday the high cell has settled over the country, centred adjacent to Kings Lynn, so a sunny day and warming up a tad with the exception of the north east and the east coast. Monday another warm and pleasant day, with the usual caveat, albeit the troughs and energy flows are taking closer order Over Tuesday and Weds the energy flows continue to put the ridge under pressure and the high cell migrates to the north east but still a couple of relatively warm days, particularly in the north, but with the usual caveat.
  24. 14 points
    It was a lovely sunny day here in Barra although cold in the North Easterly wind. Here are some photos I took today,
  25. 14 points
    Outlook - Today marks the transition to more unsettled spell of weather which will last the rest of the week before amplification of the subtropical high heralds the start of a more settled and 'warmer' spell. Precisely how the detail of this pans out depends to a large extent on the orientation and intensity of the surface high cell The NH 500mb profile and the Atlantic surface analysis for midnight Today will dawn cloudy in many areas with showery outbreaks in the area of the stationary occlusion and the trough to the south of it. These will pep up during the day, mainly over the north of England and Scotland, but later some may well bubble up over central England and Wales. The south and south west remaining dry and pretty sunny and thus quite a N/S temp contrast. But cloud and patchy rain from the waving occlusion, which is the forerunner of the deep low at 20W , will impact Cornwall by mid Afternoon. During this evening and overnight the bands of rain, heavy at times, associated with this occlusion and the follow up associated with the aforementioned low wil track north east bringing some very wet weather to central southern England and Wales. Still some showers in the far north where there may even be a patchy frost. By tomorrow the UK is totally under the umbrella of the complex area of low pressure so a wet and quite windy day in some areas, The bands of rain will continue to swing north but slowing down resulting in some reasonable totals in the north east of England Sunny intervals in the south behind all of this but thundery showers will evolve during the afternoon in the potentially unstable air, A cold day for most of the country but warmer air has ingressed the far south Over Wednesday night and through Thursday as the trough moves slowly NE the main center tracks across the UK into the North Sea and the trailing fronts and troughs embedded in the general circulation give another very unsettled day of heavy showers and longer periods of rain. By Friday the main trough has cleared away to the east with the UK in a very slack gradient but there are still a few showers around courtesy of the odd trough and convergence zone But the pattern change alluded to at the beginning is getting underway with the arrival of the upper trough in the western Atlantic Saturday a day of sunshine and the odd shower with temps still a shade below average but the pattern change continues apace with the trough now dominating the western Atlantic and promoting the amplification of the subtropical high just to the west of the UK
  26. 14 points
  27. 14 points
  28. 13 points
    I've not posted for a few days because I don't think there's much to be gained by analysing every run just at the moment, the picture re next week has been clear for a while - settled, sunny for some but not particularly warm. Thereafter somewhat uncertain and it will need a few more days of model runs to properly resolve that. But it's a good time for a look at the CFS for the next two months, as always it needs to viewed probabilistically over a number of runs. Here's the averaged Z500 anomaly for June for the last 8 runs: The clear signal is for higher than average heights close to the UK, but as per my last post re CFS the position varies significantly, so that would imply to me settled spells, of varying heat, and some thundery breakdowns thrown in. Let's have a look at July: Similar picture but perhaps with increased confidence of higher heights closer to the UK. Nowhere on analysis of this model, or indeed any other, suggests anything like 2007 or 2012, as some have suggested. There could be some significant rainfall, that's not ruled out, but it won't be a result of a cement mixer low camped over the UK for days on end, it will be from thundery downpours in my view. Finally, the May GloSea5 output is due in the next few days, will be interesting for sure, recall that March update had high probability of hottest outer quintile (50% ish) whereas April was more balanced (25% ish from memory) although the UKMO contingency planners forecast didn't really follow their own model with 45-50% of temperatures in the highest 20% from climatology. Will comment on it when it is published!
  29. 13 points
    The ext EPS mean anomaly has been reasonable consistent over the last couple of days and basically has just moved the weak atlantic trough a tad east as the amplification declines. This would not portend anything nasty creeping out of the woodwork and probably a period of dry and quite warm weather with temps a little above average. With the pattern indicated this evening Scotland does quite well in the temp stakes. Always a possibility of systems pushing in from the west. This evening's NOAA in the same ball park
  30. 13 points
    Awesome stuff folks... Place is buzzing a bit like winter time... Everyone pulling together like one big happy family.. I give you all a round of applause for your exciting and enthusiastic posts... Oh it will be interesting to see if anyweather has anything to say on the subject this evening....
  31. 13 points
    Extraordinary charts from all models for the time of year spewing out now, GFS the latest at T192: Uncertainty is reducing, warm spell becoming the form horse, other horses are falling at the first fence...
  32. 13 points
    So to the 12s and this high pressure scenario drawing up heat from the south is gaining traction big time. ICON 12z at T180: +16s into the SW. Big flip to warm? It's what we have been expecting...
  33. 13 points
    Over the next 36 hours it will be wet and very windy over the southern half of the UK. But it will be quickly followed by a far more quiescent period which can be simplistically illustrated by three snapshots of the 500mb profile within the five day period. Meanwhile the Atlantic surface analysis at midnight As can be seen Storm Hannah is at 25W and is tracking east to be over Ireland by 1800, As a preliminary event the occlusion associated with another system is already bringing showery rain to the south west and this will track north east during the day to be over southern Scotland by 1800. And by that time rain from the frontal system associated with Hannah will be effecting N. Ireland, west Wales and the south west of England. Temps for a change better along the eastern region of England As the low tracks across the Irish Sea and the north of England during the night the band of showery rain will move north east, followed by showers, but a region of more persistent rain will effect north Wales and the north west by dawn, associated with the bent back occlusion.But the key feature here is the wind which will pick up rapidly with severe gales along south western and southern coastal regions, particularly the west coast of Wales. Hannah will track into the North Sea during Saturday but the band of rain associated with the occlusion will continue to effect northern, central and eastern regions of England during the day. It will also still be quite windy in south west and southern regions with blustery showers. Quite a cold day as well With Hannah out of the way a very fleeting transient ridge builds on Sunday but some patchy rain will effect western regions as a warm front associated with low in the central Atlantic nudges in A warmer day all round Over Monday and Tuesday the pattern changes illustrated at the beginning are taking place with the UK in a very slack gradient resulting in a couple of days of sunny intervals and broken cloud but some rain may infiltrate the west from trailing fronts. And a much warmer couple of days
  34. 12 points
    The Cfs looks a lot better in Fi!!beasterly for christmas
  35. 12 points
    Major over analysis of the GFS going on at the moment.... 8 runs a day, far to many, every run bringing something a tad different! Even with Northern blocking we can get some very respectable temperatures in the sun... Its not the doom and gloom some are making it out to be. If we was at the back end of June now, and HLB was still evident, I may be a touch concerned, but even then the final half of summer could end up a treat! Calm yourselves... No dramas!!!
  36. 12 points
    It's looking a really good week next week away from the east coast, just a bit chilly early and late. I'm going to predict a high of 24C somewhere in the west Am I permitted a slightly off topic comment just for once - I just don't where else to post it - Are people watching "Hurricane Man" on Dave Channel? Amazing show, shot by people chasing the eye walls of last year's big hurricanes. A must watch for weather fans.
  37. 12 points
  38. 12 points
    FV3 at T192: The heat looks a direct hit on this one too. Cross model agreement imminent I think, actually we can probably call a massive warm up now, whether it will be a significant spell for the time of year, that remains to be firmed up.
  39. 12 points
    How hot can it get...in May? Drivers take care...tacky tarmac alert:
  40. 12 points
    The 19C isotherm touching Cornwall by next Tuesday on GFS 12z..
  41. 12 points
    Outlook - The current calmer and quite chilly weather will give way to more unsettled conditions next week as Atlantic troughs become more influential. But it will take a while for the cold air to mix out and temps remain below average , or thereabouts, for a while, albeit with regional variations. The NH 500mb profile and the Atlantic surface analysis for midnight and the 0300 UTC UK chart The fresh wind down the eastern regions has eased overnight and so with the clear skies a widespread frost to start the day. But once this quickly dissipates a sunny day for most and not unpleasant in the light airs. The odd shower may bubble up in central areas of England. But to the north an occlusion is tracking south, accompanied by a band of showery rain, with snow on the mountains, and will effect Scotland by late afternoon. The band of cloud and showery rain will continue to move south through this evening and overnight followed by wintry showers but a clear night once again elsewhere and another widespread frost Monday is a bit of a mixed bag with the occlusion straddling the country so cloudy with showers in the vicinity and showers more of the wintry variety further north in the colder air behind the front. Generally a day with temps again below average. The weakening occlusion is still straddled across the country on Tuesday so another day of sunny intervals and showers but changes are afoot, The TPV is still over Scandinavia but the associated trough has taken on a negative tilt which facilitates movement of the Atlantic trough east. The complex surface low moves across southern England and France on Wednesday bringing with it some heavy rain and strong winds in many areas and a very varied temp distribution with warmer air creeping into the south for a time. By Thursday the upper trough dominates Europe, including the UK, and with a few surface features doted about, including a low of 989mb in the North sea, another day of sunshine and showers, perhaps thundery with hail in the mix, And these may well coalesce to give a more persistent spell of heavy rain in the north. Another cold day with temps below average. But it's worth noting here the intense upper trough around Newfoundland which has an important role to play shortly.
  42. 12 points
    The NH 500mb profile and the Atlantic surface analysis for midnight and the 0400 UTC UK chart The cold front and more concentrated rain has now cleared the south coast and as can be seen the cold air is established over all of the country, particularly Scotland. Still some showery activity in the south west but that should soon clear leaving a bright but sunny day for all, albeit quite cold. The exception to this will be the far north and eastern coastal regions where there will be frequent wintry showers, with hail and thunder in the mix, in the strong northerly wind. And here it will feel decidedly chilly and quite unpleasant. Showers will die out through the evening and overnight with just a few lingering around coastal areas and with the wind abating quite a widespread frost by morning With high pressure moving in Sunday will be a day of light airs and plenty of sunshine and just the odd shower, so although the temp still below average not unpleasant. But by the afternoon an occlusion sinking south has brought a belt of showery rain into northern Scotland with a freshening wind. The weakening occlusion will continue to sink south overnight and through Monday so some showery rain in the north but largely sunny south of the front. Temps still below average but still very light winds Tuesday a day of showers and sunny interval with the weak front stalled across the country but changes are afoot with the TPV over Scandinavia but with the associated trough now negatively tilted the door is ajar for troughs to make headway from the west And by Wednesday this has duly happened as a low moves across the country bringing a day of rain, heavy at times, and gales to coastal areas. Scotland will perhaps escape the worst of this
  43. 12 points
    Some hail showers this afternoon and some great cloudscapes in a fresh N wind. Its currently snowing just now at 3.5c
  44. 12 points
    First, agree really informative and interesting post from @Tamara. Secondly, yes I still believe it is going to be a nice summer, but we have to get through some less summary weather first. There's big upheaval going on in the stratosphere with regards to the final warming. During April, the zonal mean zonal wind in the stratosphere has gone from +2 standard deviations from average to -2 standard deviations. I think it is difficult to link cause and effect with the weather with any degree of certainty, but I think this rather dramatic warming is influencing the weather currently predicted in the models - which certainly isn't what I was predicting for this time around mid-April. But this influence should be fairly short lived. You can see the cross polar ridge dissipate on the GFS 12z out to T192: But this shenanigans in the troposphere and stratosphere will time out, while other drivers supporting a hotter than average summer remain, such as sea surface temperatures, yes in the Pacific, but more importantly perhaps in the Atlantic sector: This pattern has been consistently referred to in the UKMO 3 month forecast. So, heat seekers, wait this current period out, I'm optimistic summer will show its face mid May!
  45. 12 points
    Looking at the anomaly charts and a change from just a few days ago with all 3 now show troughing as the main 500 mb feature over and around the UK, the EC-GFS in particular have it from a cold source, so little signal for much warmth 6-14 days from now, and probably mainly unsettled or changeable. https://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html
  46. 12 points
    The shorter term is the easier bit to update on. Alas, the seasonal warming across the Arctic looks to make the pivotal difference to the amplification wavelength and latitude of the ridging and put the UK just enough on its "wrong" side with a much cooler start to the B/H weekend than seemed possible.. Such fine lines here.... Hopefully a recovery of temperatures as the polar flow gets cut off and feeling much more seasonal to round off the long weekend Thereafter much hinges on how sustained the westerly wind bursts across the Pacific are c/o the tropical cycle propagating eastwards during the first 10 days of May and discussed in thorough detail in the full post from which the above quotes are extracted from.. That post dealt with the upside to the possibilities. This one equally deliberately looks at what can, and might, go wrong. Wrong at least for those of us hoping for warmth. Seasonal models are most unreliable with atmosphere and ocean trends during the Spring but start to gain greater reliability once more heading towards May. These forecasts are generally becoming less supportive of El Nino than they have been, with indications it will not last far into summer. What is important here is not so much the base state per se, but the travel of direction of the relationship the atmosphere adopts to it and takes the lead. A downward spiral of Pacific SST's implies westerly wind bursts scrubbed out at the expense of strengthened trade winds and consequentially - an associated falling angular momentum trend with the amplification wavelength dictated well upstream in the Pacific rather than our closer downstream European sector The MJO looks due to return to the Western Hemisphere later in May at the end of its cycle, and much will depend on how successfully the tropical wave will imprint the standing wave in the Pacific as it passes through the region and provide maximum upside to angular momentum before it starts to fall back again as it completes. Any shortfall in this, lends itself to a collapse of AAM tendency at the most pivotal time as seasonal wavelengths attune to summer changeover. Cautionary caveat attached to any CFS forecast and associated model biases, but based on the programmed evolution of the forthcoming tropical cycle, this prediction has good enough credibility and is fully consistent with the daily updating trends. In any shortfall scenario (should it verify) the baseline for global momentum would fall below that of the low point just arrived at in April which in itself followed the descent from the late winter "peak" of this weak El Nino. Such a situation lends itself to a quite different scenario outlined in the above post with the Atlantic trough and Western Europe/Scandinavian ridge scenario reversing to an Atlantic ridge and downstream trough. Therefore cool, changeable and showery rather than any warm/very warm plume scenarios. Clearly its far too soon to know exactly how this is going to play out - so no need for any undue suspicions just yet. Its too close to call and warm scenario A could yet still prevail. However, May as often is the case, looks set to be a crossroads month for the high season that follows it. So its worth in my opinion looking at possible things to look out for in the modelling in the coming few weeks, and the scenarios and different pathways that might start evolving as we get nearer and nearer to the start of summer proper.
  47. 12 points
  48. 12 points
    3 months away..... but since we're in fantasy island heres Christmas Eve on the CFS monster 9 monther, cant wait
  49. 12 points
    The NH 500mb profile and the Atlantic surface analysis for midnight There is currently a negatively tilted upper trough running from the southern tip of Greenland with a low center to the south west of the UK. Under the umbrella of this there is a complex mix of fronts and low centers and one such occlusion will bring another batch of heavy rain into south east just about now.This will track north west in the general circulation through the day reaching central Scotland by 1800. In the wake of this heavy showers will pop up over Wales and England, with perhaps hail and thunder in the mix. Still reasonably warm away from the rain and where the sun pops out, mainly in the south of England and, for a change ,northern Scotland The rain will be slow to clear Scotland tonight and heavy showers may persist it the south west but elsewhere should be clear with the odd fog patch, But by dawn more persistent rain will arrive in the south west courtesy of another occlusion moving in from the west. Through Friday the heavy showers transfer to the east as the band of rain tracks north west with the occlusion and generally a much cooler day albeit with some warmer spots such as the south east of England and northern Scotland. But by early evening more rain and strengthening winds will effect the south west as an intense little low west of southern Ireland gets closer.. Over Friday night and through Saturday the low will track east across Wales and central England bringing heavy rain and strong winds, which could well be gales force in western and southern regions. Needless to say quite a cool day The low will be well clear by Sunday so a much better day but cloud and patchy rain will creep into western regions courtesy of another frontal system associated with a low south of Iceland This rain will still be effecting western regions early on Monday but should clear to leave a day with with the odd showers but plenty of sunny intervals and a much warmer than the weekend.
  50. 12 points
    Day 2 Convective Outlook VALID 06:00 UTC Wed 24 Apr 2019 - 05:59 UTC Thu 25 Apr 2019 ISSUED 20:26 UTC Tue 23 Apr 2019 ISSUED BY: Dan Plume of relatively high ThetaW will advect northwards from France and across England and Wales during Tuesday night and Wednesday morning, as an upper low over the Atlantic west of Biscay extends a trough northwards towards Britain. The net result is increasing elevated instability by Wednesday morning as upper forcing arrives on the forward side of the aforementioned trough, aided further by potentially strong surface heating by midday and during the afternoon hours (dewpoints 12-14C). ... AHEAD OF THE COLD FRONT ... At the start of the forecast period, showery outbreaks of rain will likely be affecting parts of Ireland, south Wales and S / SW England associated with the surface cold front. North of this front, elevated convection is expected to develop during the morning hours across the Midlands and East Anglia, which may become increasingly surface-based provided there are sufficient cloud breaks for surface heating. As a result, there is an increasing risk of scattered thunderstorms developing with time, particularly by the afternoon and early evening in a zone from the north/east Midlands northwestwards across northern England, north Wales and perhaps even the Isle of Man. An approaching jet streak from the SE will increase speed shear and favour some organisation of thunderstorms by late afternoon and early evening across N / NW England, which combined with up to 1,000 J/kg CAPE is likely to lead to fairly frequent lightning and hail up to 1.5cm in diameter from the most intense cells. Some localised surface water flooding may be possible, especially where storms occur over large urban areas. The areas at greatest risk of organised thunderstorms are the N + NW Midlands, NW England up to south Cumbria. Lightning activity is expected to weaken by the time thunderstorm clusters approach the far north of England and southern Scotland as instability wanes. ... BEHIND THE COLD FRONT ... After a temporary lull in activity, the next shortwave will swing northwards from France during the evening and night hours. As a result, instability will increase across the English Channel and then into southern Britain, though not of the same magnitude as the activity across central Britain during Wednesday afternoon / evening. Scattered showers are likely which may produce a few sporadic lightning strikes, though probably not frequent or widespread enough to warrant a SLGT. Decaying thunderstorms from northern France may pass close to SE England on Wednesday evening also. http://www.convectiveweather.co.uk/forecast.php?date=2019-04-24
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