Singularity

GFS 06z then 12z for: Friday 25th; Saturday 26th; Sunday 27th; With GFS now finally picking up on that shallow surface low west of Iberia Thu-Fri, the end-of-week temps have taken a notable step upward across the south-eastern third of the UK, particularly for Sunday. If we could combine that with a SW-NE alignment of a flat jet, that'd be great for settling things down more widely and for longer. It is of interest that both UKMO (middle) and GEM (right) keep on going for this version of events, in the face of the GFS (left) idea of having a lingering shallow low by Scotland keeping the jet aligned more NW-SE; ECM was quite well aligned with UKMO and GEM on it's last 12z run, but the 00z was very similar to the GFS 12z I've just analysed so who knows what ECM will get up to this evening...! Both UKMO and GEM are in fact stunners for day 6: It's going to hurt if it turns out they're leading us up the garden path! What is it with GEM and plumes...? It did better than the other models with the June and early July plume events but has had a fair few misses since then.

Depending on cloud amounts, I daresay the SE corner could chase down the hottest final weeks of August on record from this ECM 12z run. While it's true that both UKMO and GEM offer good support for the weekend ridge that kicks things off, GEM is keen to remind us how easily they can displace away from us again should the Atlantic jet not take on such a simplistic SW-NE orientation through/near to Iceland as the ECM 12z shows. Got to give ECM a round of applause for effort though .

The way it has moved in recent months has been suggestive of ocean currents (in particular regions of upwelling and downwelling) finally shifting in a manner conducive to eroding the cold pool from the west. This is not surprising given that historically such a phenomenon has not been observed to cycle through more than three winters running. That being said, it was exceptionally strong at peak so an unusually long-lasting effect on sub-surface waters can't be ruled out. I wonder if anyone has a vertical cross-section of SST anomalies for that region to hand? TIA

Seems to me the impact of Gert has been enhanced by the relative position of the trough that it merges with to one at higher latitude. While we do see the advected warm airmass aloft leading to a ridge build ahead of it which GFS has been increasing with each new run (bringing it ever closer to the 00z ECM run), there's also a compact trough crossing Greenland which serves to shift the main path of the jet stream away from the trough containing Gert's remnants and so cause it to become cut-off from the main westerly flow. If we look at yesterday's 12z GFS with the faster ex-Gert-trough combined system, we see how it escaped this influence from the Greenland trough, with the ridge-building instead simply expanding the Azores High N/NE in a classic fashion. Returning now - today's 12z GFS even sees the warm airmass wrapping around the low close to us encourage a northward arc of the jet around Iceland. The 00z ECM was very similar in this regard and by way of response developed a surface high to the NE of the UK that helped to keep the cut-off low stalled out west of the UK. The 12z GFS has turned out similar to that ECM 00z, but without quite managing to fully shut down the west-east motion of the cut-off low. Typical of the model really. Then we see the next Atlantic trough disrupting against the block - again similar to that ECM run - and as such we find ourselves continuing to live out a warm but often unstable way of life. This change of 'mode' could be enough to bring the mean August temps close to the long-term average for many parts - but this may be accompanied by some seriously large monthly rainfall totals given how wet it's already been in many places (even here in the far S. it's headed above average following thundery downpours today, having been right on it - literally 100% of the norm - up to yesterday).

Well UKMO is certainly the ugly duckling with respect to the start of next week. Given all but ECM paint a very dreary (but not all that wet down south) picture for what once looked to be a fine Sunday, it'd be sad to lose out on anything warm next week too, so here's hoping the consensus to stall the low out west - and the strong trend GFS has displayed in this direction having been as progressive as UKMO this morning - will count for something. With any luck we could even score a shot of hot weather although odds are it'd be restricted to the SE'rn third or even quarter unless the stalled-out position of the low can trend even further west. There are hints that the pattern will be changed for the longer-run rather than just briefly, but not necessarily in a manner that favours plenty of dry weather should the Atlantic jet keep on buckling as the ECM 12z depicts. It's one of those occasions were we could do with a nice straight section of jet extending east from the area of low heights in the vicinity of Greenland. That being the one thing UKMO plays nice with this evening. GFS would have been on par with that if it hadn't gone and made so much of low heights over Europe - that being something to keep an eye on too given what happened Wednesday of last week.

Three models, three markedly different rates of progression with respect to the low containing the remnants of Hurricane Gert. Not often you see UKMO and ECM so far apart at 5 days range. Once, the fastest outcome looked the best with a ridge building in behind, but GFS has been tending toward holding that ridge back to the west anyway so it's lost its charm there. The slowest outcome - i.e. ECM - does at least offer a potentially very warm Monday followed by a thundery breakdown on Tuesday that would likely prove entertaining for a fair few on here. That the low remains slow-moving in our vicinity afterward... well we're getting used to that as the atmosphere just keeps on resisting any break away from a La Nina-like tendency; the GEFS mean for the Pacific 850 hPa winds has reduced the extent and magnitude of positive zonal wind anomalies i.e. weaker than average trade winds for the week ahead and that's not helping with trying to get a ridge to take hold in a position NE of the Azores rather than over or NW of there. It's been fascinating in a horrific sort of way to see these trades just keep on coming back strong. We had such a lengthy Nino-like atmospheric state lingering on after the oceanic El Nino event of 2015-16 and it does seem as if the atmosphere is determined to balance things out even if the ocean refuses to fully embrace a La Nina condition (anomalies remain inconsistent spatially, with more of those positive-negative 'waves' in the anomaly patterns). With the broader atmosphere still managing to be impressively warm in the absence of a Nino oceanic setup, perhaps we should not have been so taken aback to see these strong trades... speculative I know, but it's as good as I can come up with for now

GFS 18z actually puts forward a trend toward earlier and stronger ridging of HP across from the Azores... it's been quite some time since that manner of trend was last seen more than very briefly. The broader scale idea here is the Thu-Fri trough disrupting with the resulting shallow secondary low sliding over to SE Europe and providing support for the big blocking high that will have been over E. Europe for some time up to that point in time to finally make a move west and give the Azores High a helping hand. Its pretty much the best way to break out of the La Niña-like pattern without relying on major upstream changes in forcing, but it requires a lot to fall into place in a nice orderly fashion. Then again, so did today's Premier League results

So at day 8 we have agreement on a setup reminiscent of a few 'almost' weekends in the past month or so; kind of warm but likely limited at least away from the SE corner by lots of cloud around. Question is can we for once build HP further across the UK from there? GFS and GEM say 'yeah sure', but ECM 'kind of but not really'. Hmm. The C. Pac trades are having another resurgence this weekend but it's not as strong as was originally predicted by the models and there are signs of some more sustained reduction emerging for next week, particularly around the Dateline and a little east of there; You can see how our earlier chance of getting a good break from the La Nina-like LP dominated pattern was thwarted before it had really got going (the blob of yellows around the Dateline 7-10th Aug) and as a result we've only got a couple of 'ridge-ish' days before the next assault by Atlantic storms. We can only hope this next chance doesn't get cut down as well else we'll most likely see GFS moving toward something more like what ECM has this evening. Given the cooing of the C. Pacific tropical waters by the recent strong trades it will take some active atmospheric forcing away from it to prevent a quick return to the La Nina-like atmospheric state. The autumn prospects are in the balance what with this uncertain ENSO tendency (is this just variability that longer-term will be around the neutral line, or the beginning of a proper La Nina spell?). So are the winter ones to some extent but it's far too early to think about that!

That the location of anomalously strong trades is shifting, and with some anomalously weak trades developing either side, implies a shift in the longwave pattern (a key component of which Carinthian highlighted over the US earlier) so we have a shot at escaping the current lingering trough setup at least for a time. The pace of this being what the models are struggling to resolve. It seems up until yesterday morning they were a bit too fast, then yesterday evening they turned too slow, and now we have a fairly realistic looking compromise with the ridge having to fight for its place a bit Thu-Sat before finally gaining proper access to at least southern UK by Sun/Mon.

I make that 4 days with tight pressure gradients on the Pacific side of the Arctic and 2 days very tight, with something resembling a certain infamous cyclone at least in terms of pressure gradients next Thursday. This is all just one run from one model of course, but it does fit in with recent multi-model trends and tendencies. Rough times ahead in which we'll see to what extent thin and fractured ice turns the balance of power in favour of a relatively warm (at depth) ocean versus an atmosphere that looks to chill out nicely, albeit not without some warm, moist airmasses poking in from time to time; We'll have to keep an eye on the roasting western U.S. given it's potential to feed exceptionally warm air into the circulation of these deep lows being advertised.

Copying over from the MOD thread in case it gets removed: The Arctic situation is actually very interesting, if a bit alarming at the mo, with more than half of an already second-lowest extent of ice on record in a very thin and heavily fragmented state, with a fairly week storm having just managed to wipe out an unusually large swathe of ice in Beaufort while a stronger storm looks to hit much of the remaining Pacific ice starting in 2-3 days time. Some serious wedges of relatively warm and moist air wrapping into these storms too. A quick atmospheric cooldown is desperately needed to combat the oceanic mixing/wave action feedbacks (but I'm not so far seeing much sign of anything sustained of that nature).

This logic has its merits but less so when the jet stream becomes more meridional which looks to occur over Western Europe just about enough later next week to turn the flow over the U.K. more to the south with temps increasing accordingly across at least southern parts. This being despite a continued tendency for some changeability to the weather. The Arctic situation is actually very interesting, if a bit alarming at the mo, with more than half of an already second-lowest extent of ice on record in a very thin and heavily fragmented state, with a fairly week storm having just managed to wipe out an unusually large swathe of ice in Beaufort while a stronger storm looks to hit much of the remaining Pacific ice starting in 2-3 days time. Some serious wedges of relatively warm and moist air wrapping into these storms too. A quick cooldown is desperately needed to combat the oceanic mixing/wave action feedbacks. This is of course for another thread but the above can be considered a counterbalancing tidbit in this area of the forum that's viewable by non-members I will cease my OT activities without further ado.

To me the ECM for example depicts a (slightly) decelerating upper flow into a ridge anomaly located in a region where climatology already tends to have a ridge. Any positive height anomalies overlapping the U.K. are a good sign at this time of year although when a shallow as currently shown this should be interpreted to mean 'more often dry and warm than cool and wet' as opposed to a total abolishment of the latter form of weather. Greatest proportion dry and warm being in the south with such position of anomalies - mostly dry here but with room for a brief small low to zip through as per the ECM 00z.

We'll have to keep an eye on the impressive area of hot air that'll be concentrated over SE Europe by Monday, as the ridging tendency increases across and then a little east of the UK; the hot airmass should tend to drift west over the following days and then north which means even if we only see a brief plume in the middle stages of August, it could be a potent one. GFS has found a way to prevent this progression in the form of that shallow low on Monday interacting with the plume while that's still over SE Europe, deepening very much and driving the plume away from us instead of toward. One may find this overdone given the lack of GEFS support as MWB has pointed out - and in any case GEM has shown us how such low-plume interaction needn't result in such a deep low anyway, with the plume only having its northern reaches blasted away. So yeah - I'm willing to raise the bar of hope a little this evening with respect to seeing some temperature anomalies at least some way on the positive side of the LTA in mid-August

An interesting alternative route continues to be advertised by UKMO and with GEM now very similar as opposed to halfway between it and GFS as was the case yesterday. It would seem to produce a decent day on Monday with near-average temps before either a col (UKMO) or slack easterly (GEM) brings the threat of slow-moving showers but with light winds allowing it to feel very pleasant in sunny spells. Shame there's not likely to be any very warm (let alone hot) air ready to drift across; the slack weekend westerlies have by early Monday pushed maritime air as far as Germany for example. There are however issues going forward with this hold-up of the low, as it can then quite easily spend a number of days hanging about not far east of us, interfering with the attempts by the Azores High to ridge across us; While it's true that GEM is likely getting a bit carried away with the strength of the Atlantic westerly flow on this run, there is a case here for the swift eastward progression of the Mon-Wed low offered by ECM to be the better outcome as far as the longer-term prospects are concerned. With westerly momentum looking to wax and wane in a periodic fashion over the coming 6-14 days, we just need a bit of luck for a westerly push to displace the Azores High over us, and then a weak westerly interlude to coincide with a trough by the Azores with the high remaining displaced toward us. If only it could play out that simply!

Well, UKMO has come up with something more interesting for Sun-Mon in the form of a much weaker low than GFS has been consistently predicting (I know it's the 06z GFS still for some reason but the 12z hasn't changed things much). Warmer, particularly in terms of the feel of things, but with slow-moving showers meaning a few spots could see more rain than in the GFS version of events - while others see less, of course. GEM is still uploading when it comes to the above format but essentially it's halfway between GFS and UKMO on day 5 but then lowers pressure to the SE resulting in a well defined area of low pressure close to our SE that then lifts gradually N, restricting the ability of the Azores High to build in. So not a great effort from that model in the end. Questions remain over to what extent the AH may pay as a visit starting day 8 or 9. GLAAM is orbiting positive for the first time in quite a while which suggests a better chance of a settled spell - best since early this month in fact - but the C Pac trades continue to pulse stronger from time to time, and there is a strong signal for the MJO to kick off in the Indian Ocean or Indonesia, with the location making a big difference; GFS favours the former which drags GLAAM downward and increases the odds of a changeable W to NW flow returning before long, but other models are more toward the latter with eastward MJO propagation potentially helping us to hang on to ridges for at least a few days at a time. August certainly has a 'climbing the ladder' feeling in terms of reaching higher standards of weather - with gravity representing that sense that it's harder to get where we want than to fall where we don't.

A thoroughly uninteresting 16.7*C is my hopeful estimate for this month. This may however hide some more interesting details

Really this has become a very tricky season to anticipate. On the one hand there are the conventional metrics which paint not too bad a picture relative to the past decade (but still very poor compared to before then), but in the other we have those using visual imagery and finding that areas of ice represented as 50% or so concentration are in fact a sort of slush seemingly (much) less than half a metre thick that could 'flash' out in the space of a day or two without much notice. One mid-strength or more storm could achieve that. I have my concerns that an ice pack consisting of countless very small fragments of ice with at least as many small spots of open water between may not be measured correctly even by the area metric given limitations of resolution. Do we currently have a close mesh of slushy ice posing as a nice solid central area of compact sea ice? In these often cloudy, windy times it's hard to build a clear enough picture to say for sure. This conundrum is leading on the ASI forum to a persistent cycle of post times between 'things look really bad from visual' and 'ah but the area and compactness metrics suggest we should finish quite a way above 2012 and perhaps even some way above 2016.' I have to say though, I've read these 'not so bad' posts now and then for at least a month now... and extent has confined to keep pace with 2012 and 2016. Hence my concerns expressed above.

That's a very interesting proposition - it sounds to me like it relates to the amount of energy absorbed over time by ozone for example which will be anomalously low when solar activity has also been such relative to the position in the cycle? Given the effect on winter prospects, I like this theory very much .

Models are depicting the MJO essentially hitting a wall in the form of those C-Pac trade winds which now have increasing ensemble support to simply shrug off that approach (I know it doesn't truly work like that but I'm going for dramatic effect here). In fact, why not go the whole hog; Ladies and gentlemen, welcome to hell on Earth for summer holidaymakers. Okay, now for the disclaimer; Unless the models are handling this incorrectly - as in any or all of the MJO, the interaction with trades or the manner in which the pattern responds over here (it tends to change a bit in August compared to June-July). These are pretty dark times with just a few chinks of light such as 'Tuesday might be pleasant enough' and 'still a chance of warmth in the SE on Wednesday' but surely some day things will recover. Probably in September knowing our luck . When looking back at what went wrong, the name of the head villain is 'standing La Nina-like atmospheric wave'. Not as catchy as most but an accurate description of the culprit.

Well this is of some interest; GFS is the most progressive by some margin for days 5-6. Still room for a very warm day in the SE on Thursday if ECM knows the way. GEM is so slow that the flow hasn't yet brought as much of the very warm uppers north - the rounded shape of the low doesn't help of course. Any signs of the low becoming a bit more stretched out as per the ECM 12z are worth raising an eyebrow over as that increases the potential to get a wedge of very warm air in across the S and SE. Ideally that low needs to become very slow moving while further west than the current consensus but there hasn't been much sign of a trend in that direction.

Good spot @summer blizzard, tense times for Caribbean-N. American residents/tourists given a lot of other parameters supporting a high frequency and potential intensity of cyclones this season, and who's betting it'll make a hash of an otherwise improving picture in our little slice of the hemisphere

1983-84 saw a mild December followed by tasty January for snow in the north but frustrating elsewhere, due to predominantly polar maritime airmasses, after which February was distinctly uninteresting - well as far as I can gather from various reports. Good thing the QBO isn't the only factor that matters . The winter was not long past a solar maximum for example - but then again, we're not yet on the right side of the minimum for any significantly different forcing to be expected (based on current literature, anyway). Overall there is still a lack of particularly strong signals regarding the overall 2017-18 winter prospects but it is only July after all . Best I can say is that the QBO shouldn't be an obstacle like it was during the last one!

That sharpening of the trough (increased southward extension with little change in west-east span of trough) is the best straw we've had to clutch in quite a while GFS is the most enthusiastic of the operational runs this morning so once again we're looking at a less generous ECM run and willing it to play nice for a change . Good to see some shift in the respective ensemble suites for the two models though. GLAAM is on another upward trend - exceeding that depicted by recent modelling from GEFS, and despite an apparent stall in the MJO propagation yesterday the models became more keen on further progress east toward the C-Pacific where an associated westerly wind burst should be able to weaken (or with any luck cancel out) those anomalously strong easterly trades. Maybe there is some chance that short-term underestimation of GLAAM could nudge things far enough in favour of subtropical ridge extension through Europe to encourage the sharper, stalling trough scenario for mid-next week, but the greater impetus toward an improving picture still looks most likely to set in nearer next weekend (by the start of it, with a bit of luck). Again with the usual caveats regarding those pesky trade winds.

Well, the main component responsible for our descent into some kind of hell is has weakened and looks less coherent over the next week or so - but it seems there is too much lagged response still feeding through to put the brakes on that next low making its way across the N. Atlantic early next week. I say seems because there's inevitably at least some chance the models are overdoing the longevity and/or strength of response. If that low does make it across it will represent an extraordinary sequence even under La Nina-like forcing. Helped into reality by the unusual N. Atlantic SST patterns and perhaps a dose of low Arctic sea ice forcing too which seems to encourage some extra southward deviation of the jet stream even when it's fairly strong - although that last link is still debatable due to a lack of observed cases (less than a decade of years sea ice extent on a par with what we have now - but among the closest are 2007, 2011 and 2012... which all had another thing in common! The other two are 2010 and 2016 which weren't so bad but the latter still had its issues as I'm sure we can remember - just not in the same half of the summer). Given the predicted easing of C. Pacific trades and the MJO making some eastward progress from the Indian Ocean, our chances of breaking free from this pattern do look much better by some 4-8 days into August - but this depends on those trades not revamping against the model expectations which I do have to wonder about given the tendency of the past month or so.