Singularity

Slacker flow on the 06z for the far S and the SW, with higher temps resulting. Still making a lot of the cool breeze off the N. Sea elsewhere but I suspect this is being overdone at least a bit. Okay - that'll do for one morning... I've always been a hopeless addict when it comes to tracking and discussing very warm/hot spells in summer

So perhaps I've picked a good year to holiday in the Brecon Beacons then? Still half a month to go until that time though, and having such fine weather in the run-up does make one nervous considering what it takes to keep such conditions repeating for more than a fortnight in the UK. Seems like this summer has a better shout than many, though I have been admiring the westward extent of the heat plume early next week - over halfway toward the Azores and over sea temps already widely over 1*C above the LTA. Could be some reinforcement of the SST anomaly pattern that already promotes such intense and extensive heat plumes... a positive feedback that could spell trouble for Europe this season. I hate to say it but it feels like 2017 is well placed to challenge 2003 in many respects. Hopefully Europeans have made adaptations since then that can reduce the health impacts.

I'd say UKMO is a nice halfway house at +144 in that it has GFS' better alignment of lows and highs for persisting the settled conditions going forward, but ECM's less vigorous circulation around the high which would mean less inland extent of a cooler surface flow moderated by the N. Sea - this stronger flow being what leads to GFS predicting 22-23*C maximums for quite a few with 15*C 850s on Friday; although the isobars are aligned to bring a flow from the SE, the surface flow is more toward the E as a result of frictional effects with the sea and then land. The most widespread heat in summer occurs when a ridge becomes fairly weak in terms of SLP but with this being more to do with high temperatures (warmer air is less dense so less pressure from it at the surface) than the subsidence from aloft weakening - and that latter component can further intensify the heat via adiabatic warming (dry air warms as it sinks because the pressure rises as it does so and if you compress gases, there is more energy per unit space and so higher temps... oops I'm going a bit scientific lecture on you all!). In this light the ECM run is almost that 'pressure cooker' scenario, but it remains more aggressive with the Atlantic lows so doesn't quite get there - as I've said before this may be MJO-related, although forcing form that should be pretty weak and day 10 shows this with the upstream pattern looking ready to push a new ridge across the UK from the Azores days 11-14.

Late June may be hanging in the balance a bit as far as predominantly fine weather is concerned. Phase 1 MJO as favoured by GEFS and UKMO promotes such conditions with the potential for some high temperatures at times too, while phase 2 as favoured by ECM (with GEM borderline 1/2) encourages a more changeable regime albeit with the lows potentially interacting with ridges close to the E/NE such as to produce plume events. Interestingly such events become more likely if the MJO then continues on to phase 3. GFS, UKMO and ECM have all remained steadfast with their respective predictions over the past few days so trends are not available to aid when trying to figure out which way things will actually go. At least one aspect that does look to have an unusually high probability is that of predominantly above-normal temperatures - but by how much is anyone's guess!

Well how about that; both ECM and GEM have more or less reverted to what they were respectively showing 24 hours ago! ECM still with the MJO phase 2 factoring in later but it has remained outside of 8 days range - the day of change being put back - which is encouraging if a repeating ridge scenario is to continue. Anyway, odds on for at least three very warm to locally quite hot days in the south, perhaps even more than that if ECM or GEM pan out - possible blip Tue before a push back north; details beyond the weekend unclear as one would expect at this range.

UKMO is a classic thundery breakdown after the heat peaks on Mon. The deepening low Tue would likely move close enough on Wed to produce a westerly/south-westerly flow with showers for ay least northern parts, but with a new ridge from the Azorew looking to turn things back around pretty soon (based on typical summer patterns - so not a given, but good chances if we end up as UKMO shows for Tue... A big if, though). GFS is much more settled, pleasantly warm in the west and far S but cool breezes off the N Sea trouble eastern parts (albeit inlqnd extent of this and degree of impact probs overdone by GFS)

The ECM is fun for some heat early next week but looks to become an unstable mess before long and later heads down a route likely influenced by its keeness on a bit of phase 2 MJO activity which is not helpful. So funnily enough we now have GFS looking much better for stable and pleasant conditions going forward. GEM is close behind having flipped to the extreme with respect to Mon-Tue such that it has the most influential Scandi through. UKMO remains steady from the 12z and perhaps still on course for the low drifting north while close to the west of the UK. Or it may just linger to the S/SW. Best outcome of all when thinking ahead beyond early next week could be GFS 00z with a bit more adjustment east of the ridge position for Mon-Tue.

So now a classic three increasingly warm/hot days and a thunderstorm scenario for southern parts from the ECM 12z. GEM 12z very similar (unusually so really!). UKMO 12z looking like a slower breakdown - suddenly it's the model showing the most prolonged very warm/hot spell. GFS... improving with less retrogression than earlier runs. Examining the quick plume scenario, almost certainly the low deepens too much (almost all recent examples of plume-breakdown lows were overdone by ECM, often by 10 mb or more in terms of how low it goes at peak), but otherwise you have the classic lifting out N/NE with a new ridge coming in from the SW days 8-9. We then find that the Azores high has been shifted entirely west and leaves us at the mercy of an Atlantic low, but this is the La Nina-like behaviour that I'm wary of given Tamara's insights the other day - though I think it will be hard to completely avoid a more changeable westerly interlude given a bit of MJO activity now getting underway in the tropical Atlantic which ECM is keen to propagate east to the Indian Ocean by 3-4 days from now. Impacts for us by days 9-10 seems a bit too fast a response though!

Hmm okay, at least GFS is having second thoughts here - but only after bringing all that cool air down to produce mediocre temps down south and poor ones up north for Mon-Wed (but only Tue-Wed in far S). The plume looks angry. Poor old Iberia and of course ECM roasts the entirety of France as well.Could be a June to remember down there.

I believe we are seeing an ideal sequence of events for making apparent the difference in model bias; during the weekend it's the flatness and progressiveness* that sets GFS apart from ECM while UKMO has typically tended to be somewhere between those two in that respect, and beyond that time it's the low-GLAAM bias (via too much forcing from Indian Ocean convective activity) that causes GFS to retract the Azores High so far west. I don't think ECM and UKMO are entirely without some low GLAAM tendencies though; the way ECM opens up a gap for LP to dive into days 8-10 does show something akin to low-GLAAM pattern modification, although it could perhaps be within reach of typical variability around the base pattern of an Atlantic trough and Euro/UK ridge. Based on the above which has the big drop scheduled to start in 5 or 6 days time i.e. during the weekend, I expect GFS will continue to be very stubborn until if/when (most likely when, well hopefully!) it's forced to moderate that drop as a result of observed data leaning away from that sort of thing. We've already seen it reduce the progressiveness a bit for the weekend such that Sunday joins Saturday in being fine and very warm for most of England and Wales - the far north being the exception along with Scotland. * This is because the overall pattern is trying to shift east with time and so the slower the trough is, the further east it makes the turn into Scandinavia/eastern Europe.

Interesting, thanks for that info. Broadly close to what the French ARPEGE model shows but it has temps 1-2*C higher at peak in the SE region. I have noticed that the BBC often refers to temperatures on a par with that model. Unlike in late May, there will be very light winds for inland areas in this spell so temp errors should be more down to boundary layer modifications which is a known difficultly for models given parameterisation methods. I expect though that most of the error will be restricted to large urban areas and other hot spots brought about by terrain effects.

Thanks for your efforts I have dared to become more hopeful about the Arctic's prospects after some runs showing lower mean pressure over there in the 7-10 day range - but already this has started to feature some quite intense LP systems in the ECM runs and given the thin and unusually mobile ice for the time of year, I fear there could be responses to a LP regime more like what would usually be expected late July or early August i.e. more destructive than protective. This would be most likely with storms on the Atlantic side due to the shallow basin there. The Pacific side would have far less warm water upwelling do deal with but mechanical destruction plus movement of ice away from areas with the sea surface layer chilled by melt-water toward areas where solar input has seen little restraint could still make for bad results. Curiously enough the state of the tropics is currently akin to what would be typical of over a month from now so it's as if the entire N. Hemisphere is that far ahead of schedule. With climate change this, of course, may simply be the new 'typical' that we must get used to. So it is that the temperature lag becomes less of a mitigating effect on the strength of the sun's rays - June could become a very challenging month in the decades to come.

Is that based on the BBC? I saw them mention 27*C yesterday. Even that would be most amusing though in terms of GFS being miles out just like it was in late May - but perhaps even more so this time around!

Given the situation with forcing from the Indian Ocean being allowed too much impact on GLAAM, it's not surprising to see ECM shifting toward GEM (the new king of trend spotting?!) this morning with GFS also making a good move in that direction. Longer-term we see GEM and ECM building ridges across to the north of the heat plume which is one way to prolong the heat but always with the risk of a thundery low pushing up from the south. Typically enough we see GFS enthusiastically bringing a low through having not managed to get the plume across much of the UK in the first place. From past cases we know this is always a significant possibility, but I have seen a similar number of cases go the other way as well . GFS does actually make some attempt to restore a mid-Atlantic trough + Euro ridge combination early into lower-res, before the GLAAM bias forces westward retraction of the ridge. That this has been delayed is notable. The GEFS started to show a split between retracted and not retracted ridges yesterday evening and that has progressed further this morning. Interesting times ahead if you like 'proper summer weather', and it also seems to me that the NetWeather team should consider updating the GEM viewer to include output beyond +144 hours .

ECM is as quick with the low into Scandi as UKMO, but thankfully further east. The UKMO run is a shocker and probably related to the model considering the MJO becoming active in the tropical Atlantic in a big way just as GEFS has been predicting for a number of days now. ECM and GEM continue to vote against this. Generally I can see the broad idea being a low passing by to the NE of the UK by a certain, impossible to be sure of distance Sat/Sun and then the ridge building back in from the west; UKMO could still go that way but with more LP influence during its closest approach, but the details are up in the air right now - a total nightmare if you're having to try and produce anything more than very broad-scale temperature guidance at this range! Hah... dark humour from ECM as it's day 10 chart depicts some unpleasant deja vu with an unusually deep low becoming slow-moving S. of Iceland Not as windy as this weekend has been but... wait, why am I considering details with a chart this far out in time?

GFS and GEM agree upon a fine weekend for the southern half of the UK while the northern half is troubled by areas of cloud and even a few showers in the case of GFS. Then we yet again see GFS show the impact of its extreme tanking GLAAM projections as the ridge gets pulled west by Monday with a rather cool northerly by Tuesday. I'm not even going to post the charts as they don't seem worth the effort. GEM on the other hand... well, this is arguably just as implausible but I would say that's in terms of the details rather than the broad pattern; odds are a broad 'heat low' won't drift up along such an ideal path from the plume that's extended hundreds of miles west of Iberia by the end of the weekend (an unusual sight but GFS shows this too; the ridge across the UK is orientated just right for that to occur). BUT that doesn't make the charts not worth posting because this version of events is seriously entertaining to look at ; C'mon ECM... you must be tempted to have a go at illustrating a sensational plume event? Given how the 00z ECM went by comparison, it seems it really comes down to how far west the troughs drop down across C./E. Europe, as when this is as far east as GEM shows, the ridge follows suit, and then the door is opened for a low to develop on the western plume periphery which for once is not aligned with anywhere in the UK. Who's betting we end up seeing the pattern adjust so far east that the classic 'only just with quick breakdown' plume events takes place after all?

Many thanks for that Tamara. It explains in great detail what I have only had time to apply in the form of suggestions that the longer-term GFS/GEFS is likely too far west with the ridge. Meanwhile ECM and the EC ens appear to be much less prone to this sort of misjudgment - less prone, but not immune. Given the above, I am very interested in the fact that ECM is not all that different on day 7 to GEM, and only goes away from the hot weather scenario as a result of further amplifying the pattern such that the ridge extends north rather than locking into place. The day 9-10 GEM charts deserve to be posted out of admiration of what's just about possible if all manner of things fall into place; It requires the right balance of LP areas making it across to the east of the UK and staying west of the UK, such that the ridge does not venture away from us. These I am posting for the sheer fun of it . I daresay GEM is on course for a maximum near 34*C somewhere in the SE on Tuesday 20th. Not that where ECM goes is without its merits; Western areas would fare nicely out of that, eastern areas less so - though the anomalous warmth that have been widespread in the North Sea so far this month would help to mitigate the ability of low cloud to advance inland. With the blocking to the NE standing in stark contrast to GFS' blocking to the west, the difference in model bias could hardly be better illustrated. Now as much as I'd like to, I can't go ignoring the UKMO 12z, unfortunately; This is extremely progressive but it occurs as a result of there being no new trough moving in to interact with the pre-existing one in the mid-Atlantic on day 5. All other models have this feature developing so UKMO really stands out with the lack of such an outcome. Even so. it serves as a reminder that even at 5 days range major changes remain possible. In fact it's 4 days at the moment given that GFS still has the shallow Iberian low moving much closer to our shores than the other models do. More runs needed!

Thanks for that encouraging information BA, one day I will pay for access to the extended EC ens again - probably ready for it to dangle many carrots next winter

With a very different QBO profile there should be notable differences to last winter even if ENSO is in a similar state, but there should in fact be less of a lingering La Nina tendency in the atmospheric circulations so that'll make for two notable differences. Being further away from the solar maximum should also help. Whether it will work out nicely for our little slice of the N. Hemisphere, well that's a matter beyond effective resolution at such long range.

The retraction west of the ridge is really bugging me - it's not part of the script for the month when going by historical precedent. It ties in with the big drop in GLAAM being advertised by GEFS and it seems this must be present to some extent in the ECM guidance now as well. Looking at global convective coverage, I can see what looks to be a tropical cyclone near to the Bay of Bengal - perhaps this is a factor in the models depicting a La Nina-like pattern shift. Question is then how legitimate the level of response is. I expect GFS/GEFS to be over-the-top as usual so those runs showing a mean Scandi trough edging west toward us to produce a lot of trashy weather aren't causing me concern at this stage... but it could well be that we see a 'gentle northerly' type regime as per the ECM 00z days 9-10 which would result in mean temps quite a bit lower than the majority of long-range guidance was suggesting back at the end of May (mostly due to cool nights). I'm not sure though; we've been here before with the models depicting an undesirable pattern shift only for a Euro ridge to find its way into the equation after all, so at the moment I am inclined not to take the output all that seriously beyond a few day's range. After all there's that shallow low from Europe to be resolved, which as usual GFS is keen to lift out swiftly NE while the other models would rather let it stew over the continent with little direct impact on us. Why can't it just be a simple outcome for a change?

More like ECM makes less of the ridge, not nothing - but it is indeed a more unstable run with a likelihood of thunderstorms across the SE in particular Sun-Mon. Signs of a new ridge from the west on day 10 although it would probably not be soon or strong enough to save the northwest from seeing a bit of rain off the Atlantic for a time. I'd say this is a more 2006-style approach as opposed to 1995-style. Looks sufficient for 30*C to be breached in the SE Sat and/or Sun given day-on-day heat build. It's an interesting but relatively low probability outcome given the close alignment of the other three. I don't ever dare to fully cast aside the ECM though.

Just when you think it's sorted... it's really not! ECM's turn to toy with shallow loe development over Iberia... similar to the UKMO 00z but not looking to break down quite so soon past day 6. How will the renewed push of HP from the SW ahead of the Atlantic trough interact with the shallow heat low? Imagine if the low got trapped in place - I've seen ECM try that one before so you never know! @Captain Shortwave ah juuust beat me to it Regarding GEFS longer-term, I'm hoping it will prove correct to adjust the mean ridge position eastward to account for GLAAM bias. If not, a fresh spell but mostly dry in the west at least will have to do I suppose. Edit: I knew it, ECM loves to try this sort of thing! One day it will actually come to pass

https://www.wunderground.com/cat6/arctic-sea-ice-primed-phenomenal-melt-season Some excerpts from an excellent article on the situation at hand: "...the ice is so depleted that even a melt season from here on that’s average by recent standards could leave the ice at a record-low extent" "Colder-than-usual weather at high latitudes helped keep the ice extent from shrinking in May as much as it typically does." - a slight misfire here as the colder weather was mostly on the Atlantic side in conjunction with the mean winds driving ice toward Barents-Kara and so holding up extent as BFTV has just explained nicely "Since the ice’s horizontal extent isn’t quite at a record low, this implies that the average thickness is exceptionally small right now" "The fear among Arctic observers is that early-summer conditions could take advantage of that thin ice and produce a dramatically accelerated melt at some point in the next few weeks, perhaps leading to a “cliff” (a striking drop...)" There is then an overview of the Beaufort High, it's recent intensification trend, and how that both encourages clear skies (24-hour solar input at this time of year) and can potentially set up the Arctic Dipole Anomaly(ADA) pattern that draws warm air in across the Pacific side while pushing the Atlantic side sea ice out toward the ocean where it meets its end. So it's similar to the May pattern this year, but with the high pressure shifted west from Canada to Beaufort. The favourism for an emerging ADA pattern in recent model guidance is then highlighted. It seems we are entering a critical period over the coming fortnight in which some jaw-dropping reductions in extent may occur - but as always, nothing is a given when it comes to model projections for the Arctic more than 5 or so days ahead. There is also mention of the likely role of oceanic heat flow through the Chukchi Sea into the Bering Strait in such extreme preconditioning. This is something I agree with as it seems a logical tie-in for the fact that the Pacific side is so well-advanced in places compared to historical years for early June. There is then a summary of results from a model called CESM-MPAS which strangely enough predicts a melt-supportive ridging pattern in June-July and some troublesome storminess in August, yet keeps the minimum extent above that of 2012, at around 4 million sq. km. I wonder if it generates clouds within the ridges aided by the increased availability of moisture due to more open waters in the early summer? I have been wondering a similar thing about CFSv2, which relentlessly predicts sea ice extent somehow becoming above-average by August - though it would have to be happening to extreme levels to produce such a projection for the extent numbers. To conclude, the Arctic is very vulnerable, but there is still the chance of a great escape, well at least from setting a new minimum. On the other hand, I'd not be surprised to find it looking more like the middle of most recent Augusts by as soon as early July. The spectrum of possibilities is broad to say the least!

We have good agreement now on the flatter outcome for mid-next week (pending the delayed ECM 12z), but this is in fact a case of 'lose a little, win a little' because the flatter jet encourages a strong north-eastward ridging of the Azores High by the weekend while also propelling a lot of warm air in our direction to accompany it. At that point the surface conditions will depend heavily on the position and shape of the high pressure. The GFS 12z opts for a very round area of HP that becomes just off the coast of N. Ireland by Sunday, with warm air aloft but a relatively cool surface flow off the N. Sea affecting many eastern parts - though I believe the impact is overdone by the model, and temps should be higher than the mostly low-20s being shown for western parts. The GEM 12z on the other hand has the high stretched right across from the SW as it maintains more of a classic extension of the subtropical ridge across the UK, and with uppers above 10*C for all but a tiny patch over the Solent, it looks capable of producing temps widely in the mid-20s, perhaps high 20s in the usual hot-spots. Going forward, GFS is still trying for a shift in the HP to sit west of the UK but with less enthusiasm than before, while GEM keeps abroad trough to the NW with the extended ridge nicely maintained (quite the flip from the 00z which developed blocking to the W and NW). Hopefully the ECM 12z will be more toward GEM 12z, just as the 00z was

Reviewing the model trends, the pincer movement of unusually warm air remains on course to occur across the next few days. It seems to have been drawn out a little in terms of duration. Then comes the surge of warmth from eastern Asia, and while this thankfully looks less direct than was the case a few days ago, it still introduces quite a bit of anomalously warm air and potentially above-zero surface temps to the Pacific side of the Arctic. After this we see in the 9-10 day range some hints that the Atlantic side may see a torching via blocking in the vicinity of the UK and western Scandinavia. The GFS 18z was similar to this but the 00z this morning has instead produced blocking right across the Canadian side and so attacks the Pacific side from Alaska while keeping the Atlantic side chilly; - but this is against recent model trends and ensemble signals and may well be a result of the model seeing a massive drop in GLAAM that seems unlikely to transpire to such an extreme extent (we're not in a La Nina). Or it could just be a random fluctuation - the 06z will be telling in this regard.