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  1. 43 likes
  2. 28 likes
    An unseasonally wet, cool and windy day amidst an underwhelming week of weather does not a summer make. Much as anticipated through the second half of Spring, the hand-over to Summer sees the atmosphere in better shape for sure than the usual suspect seasons of more recent years that went on to replicate todays rank offerings time after time. Best re-state that again for any who might be on doom-watch Tropical convection has tracked eastward through the Maritimes towards the West Pacific and the associated rise in atmospheric angular momentum tendency encouraged amplification of our downstream ridge ahead of the Atlantic trough in the closing period of May. The Global Wind Oscillation ( which is a representation of total global wind-flows as depicted through ebbs and flows in the jet-stream ribbon) has echoed this pattern with a decent amplitude Phase 4 orbit (to the very start of the month). This is a pre-cursor Nino phase (Nino phases are 5,6,7) and appropriately reflects a peak bandwidth of our neutral/slightly +ve GLAMM ocean>atmospheric circulation coupling The result, for many, a very pleasant 10 day spell of summer-like weather which rounded off a warm and very dry Spring as a whole. However, the MJO signal is abruptly aborting on its eastwards trek and losing signal back towards the Western Hemisphere. The atmospheric response is immediately to scrub the westerly winds added to the atmosphere through the eastwards moving tropical convection (and which had triggered the downstream rossby waves that amplified our Western European ridge). At the same time, after a flip from the seasonal final warming of the stratosphere had seen low heights percolate through the stratosphere right down to the tropospheric level during much of May, there has been some (temporary) low level tropospheric warming developing again, related to seasonal changes between the arctic and mid latitudes (especially in view of the unstable arctic sea ice) The nose of small orange shading (weakly positive height anomaly) depicts this on the bottom of the plot as we start June This has been mirrored by enough of a higher latitude blocking signal to depress the jet stream southwards, engage a steep temperature gradient to fuel secondary lows, and also squeeze out the mid latitude Euro ridge far enough away from us to, largely, shunt the hot and humid tropical continental plume elements of the warm air advection ahead of these depressions into mainland Europe. The SE corner maybe edging the periphery of the higher plume content of the WAA created by the last low, in the on-going chain, this weekend - and which looks to sharpen ahead of its approach in the Atlantic more than its predecessors. As atmospheric angular momentum tendency snaps back with the loss of the upstream eastward moving tropical forcing signal to the weak and indeterminate state back in the Western Hemisphere, then the consequent easterly winds added from the tropics as a result of this depress frictional torque (leading to negative tendency also in mountain torque). This exchange from the tropics (MJO) to the extra tropics ( including mountain torque) is what determines the changes in AAM tendency and jet stream wind-flow which change the weather patterns across the hemisphere. In terms of translating the Global Synoptic Dynamical Modelling (GSDM) to simple NWP synoptic pattern, this process decelerates the jet stream from upstream in the Pacific and across the US - and the sequence of lows is halted as pressure rises across from the Azores and mid Atlantic in the vacuum created by the abrupt deceleration of the jet. The models are now advertising this change quite clearly heading into next week but handling it differently in some cases. I think that the GEFS, prone as it is to West Hemisphere/Indian Ocean tropical forcing bias (and weaker than ECM in terms of modelling the extra tropics) has been susceptible in the last day or so to overdo the signal for amplified Atlantic height rises (as well as arctic heights). Taking into account the fact that the stratosphere/troposphere profile (above) continues to show a cool anomaly quite far down, and that background GLAMM is buoyant, this precludes and rather contra- intuitively questions a low angular momentum response that suggests building an amplified Atlantic ridge to our west and retaining the departing trough into Scandinavia straddling back towards the UK resulting in a cool possibly showery NW'erly. On that basis the current ECM and GEM 10 day ensemble means are good value for the background signals with the Azores ridge stretching eastwards and the default trough overspreading back into the Atlantic - effectively re-setting the default trough/ridge pattern (not Atlantic ridge/UK/Scandinavian trough). Updated GEFS suite still a more amplified Atlantic ridge and stubborn stronger Scandinavian trough, but starting to re-adjust the departing weekend trough away quicker to the NE and the incoming ridge closer to the UK Probably pleasantly warm with low humidity - the orientation and position of High very likely not far enough east for any plume scenarios These are the graphical representation of the latest ECM ensembles for London - representative enough to support the idea of some pleasant average summer warmth through the mid month period Looking further ahead, subject to return of the tropical cycle eastwards once more, that sets up the prospect of another heating trend occurring through late June, as the ridge by this time edges back to the east to re-engage the trough as recently. Therefore more heat and humidity possible as time goes on - more especially late June and into July So reasonable prospect of some fine pleasantly warm weather to banish this weeks dismal offerings to the perspective of a temporary if unwelcome memory - though the trough may return close to north western parts at times. Latest ECM 4 weekly shows continuity from previous updates and reasonably reflects steady improvements for second half of the month and especially late month and into July .
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    Do they? Oh ok, right you are then. You could of course have quoted said "way of the pear" musings by way of illustration - but I accept that would conflict with the real purpose of the post and not match its implication. There isn't any further comment needed really.... So, lets look at such a recent pear-shaped extract from almost a week back. A good illustration of why these summary posts can be so useful - for continuity purposes update and review of progress ....as well of course also any departures from expectations.... They are easily found in anyone's profile... Notwithstanding the obvious indicated ascendancy of the trough into week 2 as expected (first full week of June aka next week) the broad-scale pattern is not any departure from that outlined in that previous post extract - and there remains plenty of inertia within an embedding seasonal default Atlantic trough and downstream ridge signature to re-amplify the Euro ridge and adjust the warm air advection profile back towards at least some of us With geographical re-assignment of the UK an unfortunate human impossibility option to change things, whatever the knowledge and standing of the weather NWP observer, this type of summer pattern always favours southern and eastern UK more than north western most parts of the UK. Still, much better to be starting the season with the default tipped towards a trough/ridge profile than a ridge/trough one. It is, after all, very hard to achieve warm air advection and any plume scenario whatsoever around the top of an Atlantic ridge into an upper cold pool trough... Whilst the more changeable and mobile outlook arrives from the coming weekend, but only after some further very pleasant and warm weather this coming week, its been notable already in the last couple of weeks, how often operational models have attempted to raise pressure over the pole and towards Greenland and force the jet south beyond the t144 period - but then adjust back to the Atlantic trough/downstream ridge profile. Plenty has already been said about this previously in terms of the default summer pattern Some will continue to angst over (seemingly) every face value operational suite no doubt as I understand completely that it suits the purpose. ECM 12z unfolds already. I am equally sure further outputs will suggest more horrid "write offs" of *insert period of choice* In the days ahead and when time permits I would continue to watch on tropical forcing upstream to start to adjust the pendulum back towards downstream amplification of the Euro ridge and renewed warmth from the continent. Irrespective of what it shows, in that regard it will be interesting to see the updated ECM weeklies from week 3 which suggested support for that on Friday. For anyone who resolutely sticks to the dark side though, week 3 takes us from about mid June. If a happy pill doesn't materialise, or the recommendations made here simply doesn't wash, then someone with a crystal ball who can make to measure/manage expectations to any personal wish list will definitely help. Or maybe the model moods threads is the more suitable place to mutter darkness of the models (or apparent soothsayers) instead.
  4. 26 likes
    Here's the one that didn't get away. Taken at Crawley, West Sussex.
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    There have been some strange observations made today, as too often occurs in this thread whatever the time of year, and largely based on the usual knee-jerk response to longer term suggested NWP. A favourite mantra of mine is it is the net collective signals (from the tropics and extra-tropics) that lead the models, not the models that lead the signals - the latter belief of which is how posts appear to be slanted by some on here. Its the net balance outcome of these signals at any given time (which is in constant natural flux) that determines the push and pull of the jet stream and which in turn determines the circumglobal positions of troughs and ridges. We cannot always trust the models to read these signals correctly, and often enough they slam on the brakes into reverse when they realise something else is going on. As posted the other day, a transitory signal from the tropics is adding a modest amount of easterly winds to a global atmospheric circulation that has a decent total amount of westerly inertia in it (relative to the restrictions of an ENSO neutral signal) That total 'westerlyness' of the atmosphere is registered in total atmospheric angular momentum which heading through the first week of June has been running close to +1SD set well against a similar longer term trend of neutral/weakly +ve AAM. . Clearly from that there is more westerly inertia in the atmosphere than easterly - and it is the westerly inertia that promotes warm downstream European ridges - regardless of whether these are always able to extend their influence over the whole of the UK except in the most classic summers for any extended time. The models (especially the GFS with its I/O tropical bias) will be, and have been shown to be already, prone for being too progressive with any attempts to scrub westerlies from the atmospheric circulation and hence break down heights over Europe at the expense of heights to the W and NW. In context, we are some way away from the position of another a summer such as 2011 which had emerged from a strong La Nina event and struggled (and failed) to shake off the shackles of this atmospheric imprint despite the ENSO base state moving away from La Nina during that summer. GLAAM continued to register up to -2SD throughout summer 2011 As a result of this, the summer that year saw tropical forcing concentrated throughout in the Indian Ocean, due to the La Nina footprint. The upshot of an Indian Ocean tropical forcing signal is to decelerate the Pacific jet and amplify the pattern further upstream from the Pacific with the result that the longwave pattern will accordingly adjust retrogressively. In this way the downstream sequence of ridges and troughs evolves into an Atlantic ridge and downstream trough in our sector of the NH. No surprise the summer of 2011 was AWOL of any warm air advection summer downstream ridges and the default was the Pacific and Atlantic ridge and Scandinavian and/or /UK trough. Plenty of illustrations from the archives of that summer, but these few are typical enough. Despite this weeks UK hiccup, the late Spring and early Summer period has already displayed far more inclination to pump up warm European based mid latitude ridges than was seen in the whole of that summer. IMBY perspective distorts this true perception. In the present, total relative atmospheric angular momentum is down, as a response to the I/O signal. It is this which the models are reading in terms of the medium term shifts. But relative AAM is the response to the fluid flux of tropical and extra tropical signals at any given time and not necessarily an indicator of future sustained trends. Hence why caution needs to be taken in terms of extrapolating suggested hemisphere shifts in NWP into any long term trend. In this way, any NWP suggestion of the appearance of a retrogressed Atlantic ridge (and potential downstream trough) has to be judged in perspective as a snapshot in time against the background state of this summer rather than any semi permanent sea change. That also means it has to be viewed within the parameters that the atmospheric circulation will allow in terms of ebb and flow of atmospheric angular momentum. The atmosphere can disconnect from the ocean ENSO default signal to a point as happened in 2011 in terms of the continuation of a defacto Nina signal, but boundaries always exist according to how much both westerlies and easterlies can be added to global wind-flows (the Jetstream) c/o tropical forcing into the extra tropics at any given time. This year, despite any trend towards a definitive El Nino seeming less likely in the foreseeable future that seemed possible not too long back (and which would help boost summer prospects more towards sustained heat) those boundaries are still set some way higher than they were in the likes of 2011. I would continue to view any deviation from the default signal of Atlantic trough and downstream European ridge as an interruption to the status quo rather than any sea change (if it happens at all). The GEFS is almost certainly exaggerating the allowable bandwidth to a low angular momentum state (c/o Indian Ocean forcing) and therefore its modelling (and any other modelling which suggests the same far flung 2011 style La Nina summer pattern) should be taken with a large truck-load of salt. The ridge may ebb and flow east and west, and this will effect how the trough interplays with it, but as stated in the previous post the other day, any sustained switch to a displaced Atlantic ridge and a cool trough is counter intuitive on the basis of evidence available. So no change in overall thinking of before and, for what little it is worth, on the basis of the perspective offered here, a decent enough summer pattern should prevail, in my opinion, even if it isn't the sustained Mediterranean classic many hope for - and will likely stay as a changeable mix of warm/very warm settled spells punctuated by trough/ridge re-loads which see the jet stream dip south briefly before further re-set. Such a pattern will always favour the south more than the north. Nothing IMBY in stating that - its just the way this type of pattern accords with position and latitude of geographical land-mass. Nothwithstanding varying north/south perceptions which are understandable to some degree, there is still far too much glass half empty in here, or disproportional face value judgement and extrapolation of NWP, as per usual. As illustrated, it could be a lot lot worse and there is set to be some days of very good summer weather to enjoy.
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    Alas, due to my absurd difficulties I've snapped three images from my video until I can get into line. First two are CGs (although I cannot fathom why the second pic, which was so close, only seems to have captured the bottom half of the bolt) while the third is in the midst of what I felt was a downburst.
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    But it does not get the point across, I have searched using Google and cannot find any reference to the word in meteorology so why use it? Simple words mean far more than clever phrases. I suggest this as an ex senior weather forecaster.
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    It looks like the low next week will remain out west so we should see some further pulses of warm to very warm temps - don't be surprised to see the upper 20s hit again in the south
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    Managed to get a few shots at Pevensey last night, although the rain hit and forced me under cover before the lightning came close enough to catch the spectacular crawlers that followed.
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    As summer proper comes into view, I know the model output comes in for greater attention given the trend of the last few summers (starting with 2007) for the weather at the start of June to be a precursor to the remainder of the season. How are we looking at the moment ? My seasonal assessments to clients have been very critical of the chances of an El Nino event evolving, and it looks like that will be the case. Upper ocean heat content just hasn't been supportive of a warm ENSO event developing. So that's a non-factor. What then of what has been much more significant as a sub-seasonal and inter-seasonal driver since last autumn, what we might term Indian Maritime Tropical Forcing (or a persistence of coupled ocean-atmospheric windlfow patterns denoted by thunderstorm activity around Indonesia and New Guinea) ? Of late the sea temperature anomalies leading this have weakened and rainfall patterns shifted in the spring. This was more to do with the lagged effect of a sharp breakdown of the stratospheric polar vortex. Although sea temperatures across the Tropical Indian and Pacific Oceans remain only weakly conducive, this driver looks to get a bit of a boost from the passage of a MJO wave in the next two weeks. Strangely, the MJO was suppressed in this region during the winter, and its renewed strength might indicate that this lo level tropical forcing is no longer as sustained. Either way, MJO phases 4, 5 and 6 and tropical forcing in this region during tend to support ridge development over northern and western Europe in response to troughing in the Atlantic. My eyes are really drawn to two factors which I think will be key players (or more indicative of other forcing and the atmospheric responses). The sea temperature anomaly profile of the North Atlantic is near perfectly aligned for troughing and downstream ridge development over Europe. Anomalously warm pools off the Eastern US coast and to the west of Africa and Iberia have developed over the last few months whilst cold pools all the way through the central part of the North Atlantic have developed and been reinforced by weather patterns in the last month (again related to stratospheric breakdown). That is a warm signal for much of Europe. Repeating cut off lows off the Eastern US, and possible enhancement later in the season by tropical systems should persist that cold pool and lock down the warm-cold-warm spatial arrangement of sea temperatures. The other key development has been in the polar atmosphere. This isn't necessarily a driver per se (although it was in terms of the breakdown of the polar stratospheric vortex in April), but it serves as a useful tool in understanding how the atmosphere is responding to global drivers. The breakdown in the polar vortex in April serves as useful starting point. Sharp downwelling of negative zonal winds (positive height anomalies) were observed, and this basically imprinted the atmosphere with a blocking (-AO) signal, which manifested itself throughout the circulation, even over the Tropics). The anomalous warmth over the Arctic will have served to constructively interfere with this signal, culminating in those destructive night frosts recorded during May. However, since the breakdown of the stratospheric vortex, the upper part of the polar atmosphere has cooled and heights have fallen quite substantially in the upper part of the atmosphere. There are two years which illustrate why the coming few weeks will be keenly monitored. During 1995 and 2007, two completely different summers (dry and warm versus blocked and wet), the evolution leading up to and during the breakdown of the polar vortex was very similar. However, what followed in the stratosphere and upper part of the troposphere were completely different. During 1995, a cooler stratosphere and lower heights extended their influence much lower into the atmosphere and the resultant weak polar easterly flow was characterised by much less blocking. Contrast that with 2007. The extension of low heights was much less, with blocking (positive height anomalies or red shading) much more robust in the lower part of the atmosphere. Looking at the profile to date, the extension of low heights is impressive and suggests something more akin to 1995 is the case (although there is still some time for similarities with 2007 to rear their head). It is the speed of the atmospheric response to the breakdown of the stratospheric polar vortex that is most telling for me. So we have a weak polar easterly (less risk of influential blocking over the Arctic) signal allied to a trough signal in the North Atlantic. Those two suggest a higher pressure tendency for Western Europe and summer where the continental ridge is allowed to develop as the season progresses. So in essence, the June through August signal is more weighted towards above average temperatures and below average rainfall for much of Western Europe.
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    Yes indeed, temperatures in the mid and high twenties are a tad underwhelming aren't they - especially when a UK settled warm/hot spell is restricted to a mere week and perhaps a day or two longer A relocation to the tropics solves disappointment in such a way as its possible to bask at a less tepid and sustained 30c + all year around Speaking of the tropics, the opening week or so of June sees easterly trade winds strengthen http://www.bom.gov.au/climate/enso/#tabs=Trade-winds This the result of a convection signal furthest away from us in the Indian Ocean, which will act to dampen atmospheric angular momentum tendency The upshot of this is that rossby wave alignment will re-configure from upstream with emphasis likely to switch from the continent (notwithstanding the on-going uncertainty of timing of eventual breakdown of current increasingly very warm/hot spell) towards the Atlantic with some interplay between the Azores ridge and the Atlantic trough. This implies a somewhat flatter pattern over UK and NW Europe and temperatures closer to normal to a little above at times the further south and east one heads. No wash-out by any means and still some usable summer weather to be had. However, once the tropical signal migrates eastwards and atmospheric angular momentum tendency re-boots , the pattern will re-amplify in our mid latitude sector and more widespread settled summer service should be resumed with the prominent Euro ridge returning and the trough banished away well to the NW. Its then most likely a case of something of a replay of what we have with heat returning north from southern Europe. Enjoy the lovely weather
  13. 18 likes
    Just enjoy the weekend, it looks an absolute beauty across the southern half of the uk and Monday looks hot too..too often we look too far ahead when there is great weather right in front of us!
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    Let me be clear: What Britain needs now is a strong and stable area of high pressure; 29-31C in the south and 22-26C in the north will do fine, IMO.
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    Just a genuine question 'deconstruction' why? Heights declining or falling 'trough deconstruction' where on earth do some of you get these expressions from Highs/ridges decline troughs fill, or perhaps warm out? sorry back to the unsettled theme from most models.
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    Attack of the jellyfish! Could be a nice sunset tonight
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    NMM hi-res has sizzling heat along the M4 corridor from an IMBY perspective, should top 90F both days, with the chance of a rogue severe thunderstorm along the corridor if the high potential energy can be realised (nice convergence zone from London across to Bristol might well provide the forcing required)
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    Alright, so now I've managed to sort the pictures out properly (was posting from my phone earlier!) please find the full set from this afternoons 3.30pm storm over Bexley... So I knew something was going to happen on the way home when I could see the shape and size of this thing, it looked proper Usa style. I stopped on some backstreets I know with the most unobscured view I could get (difficult in the suburbs I know). Panoramic shot... Decided to quickly head home but just had to stop on the main road I was on and take a picture of the storm as it was looking meaner by the second This was the view to the north... Pulled up. Wait whats that to the north east?... Cheeky scud? Then turned to my south and saw scud condensing out on thin air and saw it was startng to rotate. I've seen enough storm chasing videos to know what that meant and quickly got into position as the scud tightend into a rope and a beautiful, but short lived (20-30 seconds at the most) multi vortex funnel cloud formed right infront of me... After I got in the thunder and lighting started and lated a good 30 mins. Very loud. Seems to have headed off to Essex now. I thought today was going to be a total bust but I'm very happy to be proved wrong. Hope others have just as much luck, These storms are wild.
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    Put together some of the better lightning strikes my dash cam caught last night. Must have been dozens I witnessed, but dash cam didn't get them all. This was down by Brighton and then Eastbourne.
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    GIF time! I made this animation of the airmass composite:
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    This is the view to the south just off the coast.
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    Had quite a nice night, had plenty of lightning and thunder but as usual it being night time, the quality of capturing lightning is hard and usually terrible quality, but I saved 3 lightning strikes and in the process of uploading my 20min video of the MCS as it was happening
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    A few from me One before the storm (pic 3), one after (2), and the distant anvil (1) was from a particularly severe looking storm (on radar at least) near Ripon.
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    Some really depressingly negative posts by some on here this evening....take a look at the radar, numerous heavy showers breaking out over the Peak District spreading up and into east Yorkshire.....lots of signs of mid-level instability for southern UK with plenty of Ac Cas, & Ac Cas with virga. The heavy showers up north are in conjunction with a trough moving in from the Irish Sea providing the forcing, and these showers have the potential to develop into quite strong thunderstorms over the next few hours.......further south over central/southern/south west England, we're seeing plenty of mid-level instability as noted above and a waving trough sitting out to the west of the mainland has the potential to destabilise as it moves east overnight, in which case, elevated thunderstorms with plenty of lightning is possible
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    I work (in a uniform) and it's not pleasant in this weather. But I'd happily have 3 months of this every year in summer, it's not 'selfish'. Nearly everyone is happier in this weather, especially when it occurs on a weekend, as they can enjoy the outdoors/their garden/the beach etc without wearing 20 layers and freezing or getting blasted by winds or soaked, like the other 9 months of the year.
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    As much as the trend from the ECM, GFS and UKMO models has slowed the weekend low and kept it further northwest, GEM remains distanced from them with a much quicker weakening of the Atlantic low with the plume hanging on across much of the far-S right through until late Monday. A slower ridge arrival next week is the price paid, but it's still on a par with ECM even though in that case it's due to how that model keeps the jet so flat across the Atlantic until Thursday with a very shallow disturbance finding its way across to interfere with proceedings. Anyway - I'd be amazed if GEM was victorious at such short range, but I am inclined to see some further slowing down of the warm air removal as a probable trend in the other models, in which case GFS and UKMO may also slow the ridge arrival next week but frankly I'd be very happy if it arrived by mid-month and then tended to stick around or keep on reloading for the following 10 weeks or so... is that too much to ask for?
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    Thanks for the detailed round-up @Tamara , I keep losing track of the GWO/GLAAM developments as - ironically - I spend so much time working on other areas of research and development . So while on the face of it the model trend this evening resembles a backing-down from having shown too much of an MJO phase 6 response, this is really more of an overdone IO forcing by GEFS (in particular) that happens to bear close resemblance. The usual horrendously large negative GLAAM bias beyond about a week's range. At least knowing of that I was expecting an improvement in that model's output anyway . So now we have two models (UKMO and ECM) moving the weekend low very slowly through to Sun with the SE tasting the fringes of a continental plume - at the risk of some destabilisation impacts perhaps, depending on the interplay with the base of the trough (i.e. with associated upper convergence and divergence regions). GFS remains more progressive but has trended slower over the past four runs. As if for a laugh we then have ECM flirting with a Scandi trough more than the other two, but this looks to be driven not by a GFS-like overcooking of IO forcing but instead a more meridional jet ahead of the large-scale deceleration. This could just be the model showing it's amplification bias - though the range is a bit short for it to be a major factor. For 8 days from now, the evening runs feature one very pleasant outcome, one rather cool but drying up and trending warmer afterward as the ridge drifts east, and one with an impressive blocking high sat right overhead (thanks to split jet setup as explained by CreweCold earlier). Not bad going at all Interesting that it appears GEM may well have some of the negative GLAAM bias that GFS does, though it's also known to over-amplify so the true balance of play is somewhat mysterious.
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    To quote ESTOFEX for today..."Convection is unlikely to get going full speed until later this afternoon, early evening, at approximately 6pm" still another 3 hours of solar-heating left, plenty of high temps, high humidity & DPs, with clear slots. I'm certainly not giving up on today until at least midnight comes.
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    Yet another tricky potential thunderstorm breakdown coming up, so I thought I would put a few thoughts down about the different aspects I am looking at. The first scenario I am looking at is the possibilities tomorrow afternoon with a warm sector trough moving across the UK. Scenario 1. During tomorrow light low level winds will begin to swing round to come from a more maritime direction bringing in a little extra moisture. Above this is still the elevated mixed layer with a marked CAP or warm nose at around 800hpa to 850hpa. This CAP appears to be slightly weaker the further north in the UK you go. Forecast models don't appear to particularly agree about whether this CAP will go and far to often we have seen models predict storms based on knee deep high dew points. We have also seen high instability produce not even a speckle of rain because triggering is not in place or the CAP is stronger than forecast. The extra ingredient I am watching closely is the potential for a little wind convergence (maybe around Oxford) which may trigger a pulse storm. Hodographs are curved marked in the south of England but less so further North so supercell development initially is very questionable. With inflow being curved into the south of any pulse storm then there is potential for a pulse storm to develop a rear downdraft and slowly develop tornado potential. It is not clear cut and parameters are likely to change so the forecast at the minute would have to be classed as a very slight risk. Warm sector troughs in the UK are however one of the scenarios which can produce moderately severe storms in the UK. Best guess is that the east and north east would be favored for storms at the moment. Scenario 2 I looking at the cold front and low pressure system moving across the UK in the early hours of Thursday. We have marked vortcity advection, potential for very high cloud tops, but the timing is such that surface temperatures are low. I am thinking there might be a small window of opportunity where the front becomes rooted in the boundary layer sometime between 6am and 10am. So again this would be a very slight risk mainly in the East and North East due to timing. Summary Looks like both a forecasters delight and nightmare. Delight because they get to examine and explore charts and detail they would not normally do. Nightmare because the potential for getting it wrong is very high. My best guess is that for scenario 1 the high level cloud showing up in the warm sector on satellite images may put a damper on things. For scenario 2 then the vorticity driving this scenario looks concentrated further south on satellite images than I would have expected. When in doubt I tend to look at jet stream forecasts and upper level divergence and this looks fairly strong for the early hours of Thursday. I expect a lot more detail to come out as models re-align with actuals and at this point I cannot make an accurate assessment. I don't suppose this was much help, but might point to things to watch.
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    The ecm mean is a lot better than the 0z,at 240 hrs we have the best ridge of high pressure at 1020 than the rest of the world at our latitude,bring it on
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    My, really busy in here this morning! I suspect the charts are not showing heat and storms, is that why? For sure the 3 anomaly charts, see below, are not, it looks a rather unsettled spell for a week or two. Unless of course the charts decide otherwise, seems a bit unlikely to me for at least a week anyway. At least I don't now have to water the garden every day. Every cloud has a silver lining as the saying goes. http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html slight signal for ridging over Europe on the GFS http://www.cpc.noaa.gov/products/predictions/610day/500mb.php
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    Storm & Convective Forecast Issued 2017-05-26 10:34:00 Valid: 26/05/2017 06z to 27/05/2017 06z CONVECTIVE/STORM 2 DAY OUTLOOK - 26TH-27TH MAY 2017 Synopsis An upper-level trough to the west of the UK is forecast to only slowly advance east toward the British Isles over the next few days as it encounters a slowly weakening upper ridge extending north over mainland Europe. At the surface, a cold front will advance from the west across western EIRE tonight before continuing east across England and Wales during Saturday, tending to fracture as an area of low pressure develops across EIRE before tracking NE across Scotland. An increasingly moist and unstable airmass will be in place ahead of the cold front across the British Isles, contributing to moderate to strong instability which will be mostly capped until forcing for ascent from a short-wave trough arrives across the far west tonight and across all parts on Saturday into early Sunday. Elevated thunderstorms are possible across western EIRE this afternoon/evening, then the rest of EIRE, SW England and Wales early hours of Saturday. Then on Saturday, there is a broader risk of thunderstorms developing over parts of the UK, ahead of cold front advancing E and NE, with a MARGINAL or SLIGHT risk of severe weather associated with these storms. DAY 1 OUTLOOK – VALID UNTIL 06Z SATURDAY 27/05 … EIRE, WALES, SW ENGLAND … A plume of higher theta-e and steep lapse rates, associated with an Elevated Mixed Layer (EML) originating over NW Africa, will advect north across western British Isles this evening an overnight. This warm moist conveyor with steep lapse rates is forecast to destabilise later from the south with approach of shortwave trough ejecting NE, currently west of Iberia triggering storms off NW Spain and western Portugal. Elevated thunderstorms are possible across western parts of EIRE this afternoon and into the evening, before developing more widely across EIRE overnight, perhaps upscale into a MCS, then thunderstorms perhaps developing/arriving across SW England in the early hours of Saturday morning, before spreading north across parts of Wales too by breakfast time. There is a risk from these storms of heavy rainfall leading to flash-flooding, hail, gusty winds and also frequent cloud-to-ground lightning. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ DAY 2 OUTLOOK – VALID 06z SATURDAY 27/05 – 06z SUNDAY 28/05 … EIRE, N IRELAND, IRISH SEA, SCOTLAND … A Mesoscale Convective System or storm clusters maybe ongoing across parts of EIRE/N. Ireland and Irish Sea fringes of Wales and NW England on Saturday morning along slow-moving frontal boundary augmented by developing area of low pressure. This area of heavy rain and embedded t-storms is forecast to drift NE across Scotland into the afternoon, with other storms breaking out further SE away from this MCS, any storms bringing a risk of 20-30mm of rain in an hour less with heavy bursts and also a risk of hail, gusty winds and lightning. … ENGLAND and WALES … Warm moist conveyor / theta-e plume aloft will continue to spread N and NE across the England and Wales on Saturday morning ahead of cold front advancing from the west. Low-level moisture will increase too, perhaps dew point reaching 19-20C towards SE UK – which will yield impressively large CAPE values of 1000-1500 j/kg over this area by lunchtime. Heavy showers or thunderstorms are likely to be ongoing across SW England and Wales in the morning, these then spreading or developing in an arc that will shift north and east across England and Wales during the morning and into the early afternoon – as upper shortwave and attendant surface cold front advances NE. 40-50 knts SWly flow aloft and backed S to SEly flow at the surface in the unstable air ahead of cold front will yield 20-30 knts of deep layer shear which will be sufficient to sustain strong updrafts capable of large hail up to 1 inch in diameter, given large CAPE values indicated. Storm-relative helicity charts indicate the potential for a tornado too with any more discrete storms, though more linear mode of storm organisation modelled suggest this would be a very isolated/brief risk. Otherwise, storms may produce rainfall totals of 20-30mm or more locally – leading to a risk of flash-flooding and hazardous driving conditions, also a risk of isolated strong wind gusts and frequent cloud-to-ground lightning. A SLIGHT risk area for all severe hazards is shown on the forecast map across central, northern and eastern England - where CAPE and forcing will be strongest. Issued by: Nick Finnis
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    It doesn't get much better than this, like high summer today..lovely.
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    The question these days is not whether it will turn notably unsettled, but for how long. That the GLAAM state is already trying to move away from the La Nina-like state - right in the face of what GEFS was projecting - suggests it shouldn't be for too long but we'll see. The 18z GFS yesterday looked like a nice straightforward response to this change after a typical lag time, but the 00z this morning has delayed it again and the 00z ECM presents a lengthy road to recovery as of day 10, though it is one of the more extreme possible outcomes with the longwave pattern given the amount of amplification it produces so some caution has to be applied there. Difficult times ahead and goes to show that an ENSO-neutral background has little power to prevent the atmospheric state wandering away from it from time to time. Judging by what many longer-range models are predicting for July as a whole (strong NE'ward extensions of the Azores High by a week or two in) it seems a wander back toward neutral or even slightly El Nino-like may be expected to feature. Hopefully our patience will not be tested too much.
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    An almost textbook supercell shape to this one north of Berwick-upon-Tweed...
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    I have just nearly poo'd my pants lol,this just overhead to my NW and as it moved away and a tower/towers going up to my south,sorry for the tele lines
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    In my years of model watching, I have never ever seen UK CAPE and LI values showing this at 24 hrs out I know these parameters mean little in isolation but my word, if something does initiate it'll have untold amounts of energy to draw from
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    I was just having a look at some of my IP camera's footage, and found this:
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    I did the same, went from Camber - Dungeness - Dymchurch. A whole bunch of cg's out to sea before any rain arrived and once the torrential rain started there was non stop strobe lightning, absolutely crazy!
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    Bit the bullet and travelled further south. Currently holedup at Northampton services eating a southern fried chicken flatbread (don't get those in the north ). Depending on how things evolve I can stay here and search out a vantage point or if it's a bit further south east I'm heading to Barton Hills nature reserve near Luton instead. Things better kick off! The prospect of videoing night-time elevated thunderstorms was too good to turn down
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    As has been stated previously, storms tonight are not rooted to the boundary layer but rather an elevated plume and so any cloud, rain or cold sea temperatures are going to have no effect on them. It also won't feel that humid until after the intial mess has moved through as this is the warm front on the northern edge of the humid plume. Having said that it does feel humid here with dewpoints of 13c. The question is where any storms are likely to be and just how widespread. This afternoon the estofex forecast read like this: "Thunderstorms weaken offshore over the English Channel with cooler LL air while crossing a sharp E-W aligned CAPE gradient. CI will be more isolated in nature, although upscale growing convection can't be ruled out with one or two clusters affecting the English Channel until sunset." This is what we are seeing, with a weakening of thunderstorm activity as planned. For tonight Estofex has: "Confidence in more widespread CI increases during the night with the development of a diffuse/weak LL vortex over the W-English Channel in response to the approaching upper trough. This vortex pushes a wavy front east and a cluster of organized thunderstorms is forecast to evolve over NW-France and/or SW-UK. Forecast soundings reveal more elevated convection with MUCAPE of 1 kJ/kg and 20 m/s DLS. Also, 0-3 km shear increases to 15-20 m/s over far S-UK. Expect thunderstorms to grow upscale into a cluster of storms while crossing S-UK from WSW to ENE. Large hail will be the main risk. However, given amount of 0-3 km shear and persistent influx of moist/warm air from the S, a severe wind gust theat with a rapidly eastbound moving bowing line is possible. Weak mid-level height falls and the quasi-stationary nature of the evolving LL vortex over the W-English Channel lower the chance for a forced line of convection but indicate more of an internally organized (cold pool driven) event. Hence, the final outcome of that event depends on mesoscale impacts and nowcasting of the front's placement during the night and remains somewhat uncertain right now." In other words the confidence grows that there will be elevated thunderstorms overnight over the Channel and push ENE and they will likely form into an MCS. The uncertainty is where they will form and this means it is not certain yet who will get them. Where they do occur it looks interesting
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    Wouldn't worry too much 10 days ago ECM showed colder air filtering down from the north Reality the warmest day of the year so far in the UK with high pressure over the UK
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    You should always keep in mind that 'being realistic' is a no go area in this thread, particularly in winter, if it is contrary to the wishful thinking of the cabal. There is also a good case for consigning 'upgrade' and 'downgrade' to the swear filter as they are both subjective and one persons upgrade is another's downgrade. Think of the space that would free up in winter.
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