Singularity

There's still the same divergence between ECM and GFS tonight, with ECM firing the jet just south of the UK at times and bringing numerous rainfall events from Saturday through to Thursday next week, while GFS is keen on pulling the jet away to the north more, resulting in a changeable westerly flow with a mix of wetter and drier days - standard fare you might say. Still more runs needed!

Curious that GFS has suddenly started taking that low further southwest - two operational runs in a row with that outcome now. It takes until next Monday for things to break down from the south as the low moves slowly into the UK. Apart from some slow moving areas of heavy rain early next week, the run features a lot of dry weather until about 10 days from now. ECM is a very different story with low pressure arriving on Saturday and the jet stream firing up during the weekend to bring an onslaught of wind and rain events, though not at all severe in isolation (see examples below). I reckon there's three or perhaps four rain events in the period Saturday-Wednesday next week. Then things get a little more dramatic for 10 days from now, though we all know not to take this too seriously at such long range: GFS does also have an intense low tracking level with the UK, but the jet stream remains flatter so we don't see that 'scoop' of hot air being drawn up ahead of it. As you can probably tell based on which charts I have posted, I'm feeling inclined to go with ECM over GFS at this point in time, what with UKMO now in support and the tendency over the past few months for the jet to be stronger than we'd like to see (unless you enjoy wet, windy weather, that is!). I see GEM has also boarded the rain train as well this morning. It seems my concerns expressed about a week ago about a very wet period of weather may prove well founded - however, it seems to be scheduled to kick off about 5 days earlier than I had imagined back then. If it does follow such a timetable, then we'll need another pattern shift to avoid a soggy September overall - the likes of which GFS showed us on its 00z operational run this morning, though there are others ways of going about it. We still can't rule out the low staying away during the weekend though, and if that turns out to be the right way forward, the game will change somewhat, as the blocking high to our NE will be better able to resist the Atlantic jet stream as it changes up a gear or two.

I've been away all day, just had a chance to catch up with the models and it appears that they're pretty much clueless about what happens Friday onward beyond the broad theme of a high to our NE. Whether low pressure pushes in during the weekend or stays to our west remains unclear following what is notably different GFS 18z operational run, as is the behaviour of further areas of low pressure crossing the Atlantic during the following week. In fact the uncertainty for next week is about as high as it gets - just look at how much further south the lows travel on the ECM 12z (a troublesome looking outcome) when compared with the 00z (soon reverts to 'standard westerlies'). It all looks to be down to how different areas of low pressure interact - or avoid interaction. At least a day's more runs are needed before conclusions can be drawn with more than shaky levels of confidence. In the meantime, at least we seem to have put to bed that risk of rain affecting the western fringes of the UK midweek, though I'll admit UKMO is still a bit of a close shave.

I should include UKMO really - it's less progressive with that low on Friday, but it does look to be far enough north and west that it might engage with the jet stream during the weekend, resulting in a breakdown that is a day or two later than ECM but two or three days earlier than GFS. For what it's worth, GEM goes for the cut-off low to the southwest on its 12z run (and takes tropical storm Fred from the Azores to Iberia. The other models kill it off instead), while JMA has it drifting across the UK during the weekend, remaining a shallow feature as it travels far enough east to avoid engaging with the jet stream. Bringing all this together, something between the extremes of ECM and GFS is the safe bet, with the weather breaking down either Saturday or Sunday. With any luck we can push that back one more day - fingers crossed. Edit: come to think of it, there is a small chance that Tropical Storm Fred could cause us a bit of bother if it survives a trip to the Azores and is then drawn E or NE toward NW Europe and/or the UK. At the very least that would add a large amount of moisture into the mix, which could then be drawn north by the approaching Atlantic trough late this weekend or early next week. Unless of course the remnants head straight for us from the Azores (low probability but ECM's 12z evolution would allow for that I think).

The real culprit behind the ECM 12z weekend washout is a weak low to the southwest failing to become cut-off from the jet stream between Thursday and Friday. This means that instead of the Scandi High being able to extend a ridge west such as we see in the GFS 12z operational run, that low is able to take advantage of a fairly strong jet stream and develop into a nasty feature capable of delivering a wet and wild weekend: It's a very wet looking run from that point forward, as a shortwave low swings around the main one on Sunday to deliver another spell of rain, and then a string of disturbances along a moisture-laden frontal boundary pile in two days later. GFS takes four days longer to bring the breakdown, and it manages to produce some fascinating charts from the 10th day onward. This for Tuesday 15th would see an unstable environment combining with an unusually warm, moist airmass to bring some potentially severe weather across the UK from the south: After which, the low pressure system hangs about just west of the UK, with a strong high over Greenland adding to the unusual setup: This setup is ideal for building exceptional heat across Europe (yet again this year!) and the run finishes by starting to draw it north toward the UK. The way the low is orientated, it's a shame the run stops there, as there's the potential for the 20*C 850hPa isotherm to reach the UK one or two days later, which would be exceptional, perhaps even unprecedented: Obviously I've chosen to display these charts purely for your entertainment - at such long range and with ECM disagreeing at just five days range, there's little reason to expect these charts to become reality. As much as I enjoy severe weather, that's probably for the best, as the amount of rain that could deliver would be most unwelcome having had more than twice the usual August rainfall here in the south last month. That's even with a two week dry spell in between!

Looking at BFTV's analysis on page 2, the September composite reflects a jet well south of normal, yet the October one reflects a jet stream tending to track to the northwest of the UK. Very interesting to see such a huge change, though it's just about possible that an arm of the jet sinks way down toward Africa in the October chart. For November, the composite suggests a lot of storm activity near the UK, and the southward extent looks to be a little further than usual. We also see a Scandi High signal, which is a logical accompaniment to a jet tracking south of the usual. Shades of November 2009, which was the wettest single month I've recorded in the past two decades. The following winter was interesting to say the least, but of course we only had a relatively weak, central-based El Nino that year.

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=3100 A very good post by Dr. Jeff Masters covering the Arctic sea ice melt season so far, including the nasty storm at the end of August, and looking ahead to the rest of this month. This quote from Steven Cavallo (a University of Oklahoma meteorologist who specialises in polar weather) caught my eye: “There are a lot of TPVs around, meaning the potential for surface cyclone formation is high, so I think the forecast sensitivity is very high right now and there could still be some significant ice loss.†It's then mentioned that there's a lot of uncertainty regarding storm formation in the next week or so, and how this could be related to unpredictable tropical cyclone impacts as the systems recurve and engage with the polar jet stream. This is followed by some discussion of the sea ice 'health' and another quote catches my eye, this one from Polar climate specialist Jennifer Francis (of Rutgers University): “Much of the ice that's left is either slushy, severely broken up, or covered in melt pondsâ€. There is then an interesting discussion of the potential for the El Nino 'mild winter for northern USA and Canada' signal across North America to be combated by a reverse signal driven by the high ice loss on the Pacific side of the Arctic. Could the Arctic forcing possibly override the tropical forcing?

A fairly typical delay in the pushing aside of the Scandi High appears to have occurred, with the breakdown now penciled in for Friday. Let's just see if it holds there or not... We do then look to be at risk of a trough stalling out overhead with some active areas of low pressure rolling in, after which GFS and ECM are keen to raise heights to our NW. If that happens, it will be important in terms of rainfall amounts whether a ridge builds in the mid-Atlantic or the jet simply fires away underneath a Greenland High, bringing lows our way from unusually far south. Needless to say, that would bring the potential for some large rainfall totals - but the mid-Atlantic ridge scenario offers something a lot drier, so it seems our prospects later this month remain very much up in the air. Having found evidence from past years to suggest that the jet stream probably does have the potential to both be drawn south and get a boost from the current North Atlantic SST setup (see page 5 of the 'Summer 2015 overviews and opinions' thread in the weather discussion area of the forum), I get the sense that the more high pressure we can hold onto this month, the better. For what it's worth, CFSv2 and JMA are going for unsettled westerlies dominating in October, followed by a very unsettled November. On the other hand, the Met Office ensembles prefer to keep high pressure over Europe closer to hand, and the Beijing Climate Centre's model brings that high pressure into play quite substantially. So all is not lost - not that these projections are to be taken all that seriously anyway!

Behold! ... I know, it needs a lot of explanation doesn't it? Okay, so what I've done is take a look at past years in a bid to determine whether it's safe to believe that the cold anomalies in the N. Atlantic this year have encouraged the jet stream to locate unusually far south this summer, while also increasing the strength of the associated west-east flow (zonal wind). I thought about putting this in the climate change science forum, but I'd like non-members to be able to see it as well as members What you can see above is my fairly crude analysis of where the positive and negative SST anomaly regions are relative to the peak zonal wind anomalies. For all years, the black lines represent areas of anomalously high zonal wind, with particularly strong anomalies represented by two or three lines next to one another. This can be loosely interpreted to represent where the jet stream spent more time than usual. The years up to 1995 only show where SST anomalies were greater than 1*C (solid orange lines) or lower than -1*C (solid blue lines), while for 2000 onward I have included dotted lines to show relatively weak anomalies (0.5 to 1.0*C in orange, -0.5 to -1.0*C in blue). This difference is purely down to this being work in progress - I intend to analyse more years in the near future. What can be interpreted from the analysis output is that the peak zonal wind anomalies tend to occur between areas of SST anomalies near 1.0*C or greater and areas of SST anomalies near -1.0*C or lower that are located to the north of the aforementioned positive anomalies. Sometimes, the peak zonal anomaly lies within the negative SST anomaly region, but rarely does it occur within positive SST anomaly regions. There is also some suggestion that particularly extensive and/or strong SST anomalies add some extra kick to the zonal winds (therefore jet stream);1991, 1992, 1994 and 1995 all show this well, while 2003 at least hints at it. The mechanisms behind these relationships are open to debate, are are the implications should these findings continue to be supported by future analysis. I welcome your input on this matter, forum members Notice that the time series is missing a number of years. These are years where there is little clear relationship between the SST anomalies and zonal wind anomalies, which you can see in the next image: Of these, the lack of a clear relationship between the SST anomalies and peak zonal wind anomalies could be put down to the following: - 1996 and 1997 are lacking in anything more than weak anomalies (though looking at it now, 1997 could still qualify for the clear relationship group) - 1999 and 2001 have a very messy SST anomaly pattern - 1993 has largely negative anomalies, and 1998 largely positive. If you have reasons to disagree with my interpretation, please don't hesitate to put them across

Test post (haven't been able to get desired post to, erm, post). Okay... editing in the desired post content bit by bit: Great post by the legend that is GP, which is about as surprising as waking up in the same room as you went to sleep in! The 1972-73 event featured a winter across the North Atlantic that was broadly similar to those of 1983 and 1998, in that the NAO was markedly negative, and the UK saw an increasingly strong influence from high pressure after a relatively unsettled start. 1998 has the interesting presence of anomalously high 500mb heights over Greenland and into Scandinavia for the period Nov-Jan, which fades to neutral when looking at the Jan-Mar period. This suggests that blocking can't be ruled out for at least part of the winter even if we do follow a path similar to 1998. That said, the positioning is another matter as far as seeing some decent cold, snowy conditions. Something that's really been puzzling me lately is what took place during the winters falling within the 1957-58 and 1965-66 El Nino events; blocking was common to the west (and at times northwest) across the majority of both, and overall heights were anomalously low across Europe and the UK: Turns out it's the link to the plot generated using esrl.noaa.gov that is preventing successful posting. You'll just have to imagine it I'm afraid! So far, attempts to identify major differences in the spatial distribution of SSTs haven't revealed anything of note; for example the 56-57 event bears a lot of similarity to the 1982-83 event.

Briefly on the SST anomaly debate - I have taken a skeptical approach to this over the past few months, but the idea has been cropping up on an increasing number of weather sites, and the logic behind it seems sound... at least for the summer and early autumn months. I suspect that in winter, the interplay between the cold Arctic airmasses and warmer airmasses at the low to mid latitudes tends to override the SST influence to a large degree. I've been looking back at the SST and zonal wind patterns of past summers in a bid to identify any relationships, and so far it appears that when there are large negative SST anomalies covering a wide area, the jet stream tends to favour a path that tracks either across or just south of that region. I need to analyse a lot more years to be sure though! On to this morning's model output, and there's more of an appetite for bringing some warmer air into play across much of the UK for at least a time next week. ECM does this particularly well (see below two images showing 7 days ahead). Despite how far ahead in time this is, the recent run-to-run model consistency with the overall pattern lends high confidence to the developments during the middle part of next week. GFS supports this version of events well, though the warmer air isn't drawn across the UK quite as effectively. Temperatures are in the high teens widely, with the low 20's in parts of the south for example. Further ahead in time, both ECM and GFS transfer high pressure to Scandinavia, in keeping with yesterday's runs. We also continue to see ECM favouring the progression of low pressure more to the SW of the UK with a chance of heading into Europe, but this looks less convincing this morning, with more of a risk that low pressure rides up the western flank of the Scandi high in a similar vein to recent GFS operational runs (see below image showing ECM 10 days ahead). With this in mind, I'm starting to see early signs that the second half of September could turn out to be very wet. This comes from the fact that the Atlantic westerlies typically pick up some strength as the month progresses, and that this ls likely to clash with that blocking high over Scandinavia in the near future. IF the blocking holds steady over Scandinavia, we could find ourselves facing situations like what the GFS 00z operational run produced for 17th September: What this shows is the warm sector of an Atlantic low - and its associated frontal systems - becoming slow moving over the UK, with secondary low pressure development then taking place along the cold front. This is a recipe for delivering prolonged heavy rainfall, and with such a blocked northern hemisphere pattern, we often have to endure a week or two of such events occurring every two or three days before the pattern relents. It's too early to get ourselves concerned though - the blocking high could well manage to hold up the Atlantic storms to the west of the UK, or perhaps it will simply be shoved aside with a standard sequence of lows barreling through from west to east (still wet, but not to the extreme). There is, though, a tendency for the stalling point to be in the vicinity of the UK when Scandi Highs are at large, because after all, we're located at the major boundary between the maritime Atlantic environment and the continental Eurasian environment. Britain is like a massive pier sticking out into the ocean!

With little going on in the shorter term, developments a whole week ahead are drawing my interest. What we have here is agreement between GFS (top) and ECM (bottom) for high pressure to be situated over Scandinavia with an easterly flow affecting at least part of the UK (most likely the southern half), this pulling in fairly cool air from the northeast. This could actually work out quite nicely for most or all of us, as the airmass looks to be low in moisture content (so few clouds), winds look fairly light (so not too much trouble on eastern coasts given that the North Sea SSTs are near their annual peak), and temperatures could reach the high teens widely based on the GFS operational output. We just need to hope that where that cooler air meets the warmer air over Europe, there isn't any development of low pressure, as that would be a major spanner in the works as far as fine weather is concerned - for the south in particular. Looking further ahead, we see what is arguably a very typical divergence of the two models with respect to that Scandi High; the GFS operational run fires the jet stream through the UK on a NW-SE trajectory, but also maintains enough of a flow going north again to prevent what would otherwise be low pressure 'undercutting' the Scandi High and heading into Europe. Instead, the Atlantic low appears to ride up the western flank of the Scandi High for a time, after which a half-hearted undercut simply opens the door for the jet to power through the UK west to east through much of the 10-16 day period (a very 'flat' pattern - see the first of the two charts below). For a 'classic undercut', we have to turn to ECM, which makes no attempt to take low pressure up the western flank of the Scandi High, instead taking the low toward NW Europe with interesting prospects going forward from day 10 (see the second of the charts below). Now here's the thing - with a near normal SST situation in the North Atlantic, I would tend to favour the undercutting low scenario, but summer this year has shown on many occasions how the anomalously cold region of SSTs in the North Atlantic can promote a stronger jet stream that powers through the UK instead of being held back or at least diverted by blocking areas of high pressure. On the other hand, the latitude at which SSTs drop off fastest as you go north is located quite a way south of the usual position this year, which may increase the odds of the jet powering into Europe and leaving the Scandi High in place. I think it could be quite telling which way it goes at this early stage in the season - a tendency for the jet to dive into Europe can be a neat characteristic to take into the latter stages of November

Each and every model run differs with the details, but I've noticed a trend toward Monday seeing a lot of atmospheric moisture being rained out across the south. It could end up being a thoroughly wet day there, but only if the heat and moisture pushes far enough north Sunday evening and overnight. The Sunday threat has been very hit and miss - about as much as I can ever recall seeing at such short range. In fact, there's the potential for a band of precipitation - showery or persistent - to develop across part of the south tomorrow afternoon, but no two model runs agree on this. Even nowcasting may struggle to pin it down. Like Harry, I spotted the potential many days ago, as the clash between hot European air and cool Atlantic air looked ripe for downpours, but the lack of a distinct area of low pressure to drive developments led to a lot of forecasts lacking in precipitation across Southern England up until about 48 hours ago. Only since then have areas of enhanced instability started to become apparent. Such is the nature of thermal ('heat') lows, which are largely a result of rising motion. In theory, the thermal low should be capable of developing into a baroclinic low with distinct frontal boundaries as the hot and cool airmasses collide, but the pace and location this is seemingly anyone's guess at this point in time.

Erika appears to have a problem with multiple circulations at the moment, all attempting to exploit the decent outflow and intensify. This can't actually happen as the centres interfere with one another. Unfortunately, this messy situation may actually result in Erika hitting Hispanola head-on, which would likely bring devastating rains as the huge moisture field collides with the high mountains over the central part of the island. Yet we don't want to see the cyclone get very organised and move N of Hispanola, as that gives rise to the 'Bahamas Bomb' scenario. Really, there's no real way to 'win' with this cyclone. The official NHC track is one of the least troublesome scenarios yet still threatens a lot of severe conditions, as the cyclone grazes Hispanola without strengthening and then just about manages to organise and reach hurricane status over the Bahamas, after which it moves very, very close to Florida: Fair to say the rains with this scenario could be a major issue for Florida. The one possible silver lining is the major reduction or total removal of drought conditions in Puerto Rico over the next 24 hours. Heavily countered by the flash flooding risks though!

We can see good upper level outflow for Erika (the high cloud streaks are typical of that), including two distinct outflow channels (from NE into the Atlantic and from SW across the Caribbean). This raises the potential for strong low level convergence to take place, which means the system has an opportunity to lower the surface pressures and intensify the wind field. If this happens during the next 24 hours, it will defy the recent NHC projections, which have showed no increase in intensity during that time due to fairly strong wind shear and some relatively dry air getting in on the act. The trouble is, the storm's large size, with very expansive convection, appears to have modified the surrounding environment enough to shield the core of the system from these detrimental features at least for the time being. Impressively, this has occurred during the evening hours, when tropical cyclone convection is typically at its weakest (due to the reduced sea/air temperature contrast I think). A stronger than expected storm may track more NW than projected by the NHC, which raises the risk of it avoiding much interference from the high terrain of Hispanola for example, which would be bad news for the Bahamas, as conditions look to be very favourable for rapid intensification of a well structured storm in that region. The storm needs to be as disoraganised as possible if a hurricane is to be avoided. The storm may then take one of a wide range of paths - anything from crossing southern Florida to turning north and tracking up along the East U.S. Coast looks possible. There's even an increasingly favoured scenario in which the storm gets trapped beneath a ridge of high pressure while east of the U.S., wandering about for a few days or perhaps performing a 'left turn' and moving NW into the U.S. landmass, in the style of Hurricane Sandy from 2012. You heard it here first...! Seriously though, that's just one of countless possibilities so please don't take that as anything more than speculation

Based on the 12z UKMO and JMA runs, there does appear to be at least a small chance that the jet stream cuts off the high heights over Greenland, keeping us in more of a westerly flow or even anticyclonic by early next week (though JMA does about-face a day later): Funnily enough I can recall seeing similar issues in late January last year, when the models were struggling to resolve whether we'd have energetic storms powering across to us beneath a cut-off blocking high or not. Thankfully the lows don't look as vigorous under that arrangement this time around! Assessing the currently favoured outcome, there's an impressively long northerly (or close to northerly) fetch on the ECM and GFS 12z operational runs, bringing air south from high in the Arctic. The high topples before the cold air can really start piling in (is it winter already?!), but we still get some impressively low 850hPa temperatures out of it. The idea of the high gradually drifting over us during the following days is nice to see, hopefully not a red herring. There looks to be a low risk of a major trough dropping down close enough to our east to prolong the chilly northerly, which would certainly have the gas and electric companies rubbing their hands together in anticipation! (I sincerely hope this smiley is exaggerating)

A lot of variation within that, though... (Link to Generate For Yourself) (Link to Generate for Yourself) For these I've chosen the polar opposites from the strongest El Nino events since 1950 to emphasise my point. To relate this to the thread topic, what CFS sees ought to be dependant on some other factor(s) alongside the existence of El Nino, though I'm not at all sure what those are. I've checked out SST anomalies covering the PDO region and seen no real patterns there, for example. In fact, looking at the wider SST pattern, the only notable difference between the 6 months prior to the -ve NAO group (1958, 1968 and 2010) compared to the other is that the -ve NAO group follow the development of negative SST anomalies in the Central Pacific, roughly in line with California (example here). That's as far as I dare go in this MOD thread, my apologies to the mods for the short venture into long range prospects

It will be interesting to see whether the pressure rise for the west in 8-10 days time is undone by low pressure development SW or S of the UK that lifts north, as we have seen a number of times this summer. I can see how this could be a consequence of an enhanced thermal gradient between what again looks to be a combination of an unusually hot NW Europe and anomalously cool mid-Atlantic. In the meantime, tomorrow has the potential to deliver some high rainfall totals across Southern England, as a small area of low pressure, carrying some decent moisture amounts (but far from exceptional) interacts with cooler air to the NW. The high-res models offer a range of paths for the system and its rains, some only clipping The Southeast while others take precipitation as far northwest as Bristol. Good luck if you're forecasting for any outdoor activities!

Whoops... I really need to get some more links together so that I can review the data before making posts, rather than relying on what's clearly insufficient memory Great post by the way Last winter, the atmosphere spent a lot of time in a more La Nina like state, which I think may have been down to residual positive SST anomalies in the western Pacific. I'm surprised that the Pacific pattern was so close to the Modoki composite to be honest. I wonder, what is the outcome from that correlation and regression method you showed a snapshot of when working with only strong Modoki events, or weak ones? Same goes for east Pacific events. If someone knows a means of undertaking such analysis, I'd greatly appreciate your advice What with the emerging hints of a 'tripole' in the Atlantic SSTs this year such as we had in 2010, I'm starting to explore the potential for a cold Nov/Dec combination, just out of interest/hope (yes, I have a 'give me a cold winter' mode waiting for the slightest excuse to activate... ). Obviously this particular train of thought is not to be followed up in this thread, but the time will come before long I imagine!

Continuing to focus on next weekend, what with the Bournemouth Airshow taking place as well as the Beaulieu Super Car Showdown. It has been strange seeing GFS consistently output solutions which have the jet stream diving further south, more of a divide of low heights between the Atlantic and Europe and a stronger Scandi High than the other models have been coming up with. By this I mean that GFS has always seemed the most reluctant to go that way in times past -but you know what, I can't recall much of a Scandi High and dividing low heights situation since the model was upgraded in late January (or was it February?) this year, so perhaps that did a number on its old foibles - or has it caused the model to be overly keen now? Up to this morning, I was beginning to suspect that was the case, what with ECM having gone off the idea again despite giving it good consideration the previous evening. Yet now we have UKMO dropping a major hint that we could see the cut-off low develop after all, though the t+144 chart doesn't suggest such an effective 'undercut' of the Scandi High as GFS has managed this evening. What a run that GFS 12z operational is - with the stage set by t+144 (see above), temperatures climb into the high 20's quite widely for England and Wales next weekend, and then some spots climbing up to 30*C or so to start next week. Madness? Fantasy? Or a realistic way forward? Well guess what, ECM's gone and flipped again. The cut-off low develops a day later, but it's very much there for all to see by Sunday, and ends up moving too close for comfort by Monday (unless it was to deliver in terms of thunderstorms): It's worth taking note that the later development of the low means warm air doesn't push back NW against the cooler Atlantic air until Monday. It could be warm in the SE corner through the weekend (maybe 25*C if the skies are clear enough) but otherwise a nearer average situation I reckon, and on the cool side for the NW. The good thing is, UKMO now has the Atlantic trough as far west as GFS for Friday, disagreeing with the ECM 12z operational, which raises the likelihood that the NW will instead escape the Atlantic flow next weekend, along with the chances of seeing that warm air hold on through the weekend for a wider portion of the UK - or even push further NW if we go the way of GFS. There's still too many days to go before the weekend can be called one way or the other, but I'm feeling more hopeful after this evening's 12z operational runs I'll leave you with this - ECM agreeing with GFS in showing the Scandi High pushing further west by the middle of next week rather than getting shoved away east. Complete with the usual over-dramatised storm system in the Atlantic :

A fascinating read from Neven. July '15 truly was extraordinary when considered in terms of the dominance of high pressure and anomalously high temperatures combined. Interesting what Neven speaks of near the end - the odds of a July like we had this year increasing in a warming world. Makes sense when the warm air heads poleward - pressure falls more slowly in warm air, so the scope for unusually strong and persistent areas of high pressure is increased (or so I understand it, correct me if I'm wrong).

The spatial distribution of Pacific heat anomalies is likely an important factor, though intensity does play a part. I've heard it said that East Pacific events (the classic type) tend to promote unusually strong highs over Europe later in the winter... which ties in with recent CFSv2 modelling (http://www.cpc.ncep.noaa.gov/products/people/wwang/cfsv2fcst/htmls/glbz700e3Mon.html). In 2010 an 'El Nino Modoki' (more central-Pacific based) was followed by a very negative NAO in December. I've seen that attributed to the El Nino, but also to SSTs in the North Atlantic (a tripole setup - warm subtropics, cold west of Europe and warm once you're as far north as Iceland. Similar to the current pattern in fact!). Which was more important? I can't really say to be honest We could do with some decent wave breaking events into the stratosphere, as with so much extra warmth in the atmosphere, those would have the potential to bring about SSW events later in the winter. Yes - I was lurking on the forums during those warming events in Dec-Jan this year that very nearly went the whole hog but in the end proved insufficient to overcome what I seem to recall was fairly poor positioning

Check out that strong jet diving almost straight south in 6 days time. It's no wonder that the model develops low pressure in the vicinity of Iberia over the following few days. The position is ideal for bringing very warm air to the UK from the heart of the Mediterranean, which takes some 5 days to reach a peak - at which point temps are hitting 30*C or so across parts of the SE. I particularly like the weekend charts, given that I'll be attending an airshow on Saturday and a car show on Sunday: High 20's across the S and SE The important question is whether this run too good to be true? Well... sharp dives south of the jet as we see in 6 days time do tend to at least attempt to produce cut-off lows, usually level with central or southern Europe, but for the low to remain in such a state for as long as the 12z has it, there needs to be a quick change in the jet stream to a west-east track, so that the upper level winds associated with the low become disconnected. The GFS op has a strong surge of westerlies associated with an active low tracking to Iceland, which does the job nicely: The 06z GFS operational run was remarkably similar, just a day slower with the Icelandic low. This raises confidence in the cut-off low coming into fruition, though not so much the import of warm air, as it was less pronounced on that run compared to the 12z GFS operational. However, glancing at the GEFS, I can only find 3 or 4 perturbations that have a cut-off low in the right sort of place for warm, settled conditions, which is rather alarming... or is it? There are other scenarios that seem at least reasonable or in some cases better, depending on where you stand on late summer heat; 5 or 6 have warm air advection ahead of a large Atlantic trough, similar to this morning's ECM 00z operational, so warm but perhaps increasingly unstable through next weekend (some maintain the ridge throughout). A couple have the cut-off low in place, but some way west of Europe, with a large Euro High bringing very warm to hot conditions. The remainder have the low very close to the west, unsettled but still on the warms side. It's striking that not one run manages to power the low right the way through the UK and only two have the UK fully at the system's mercy by the start of the following week. High pressure is keen to put up a fight, and all this coming after a fine, dry week for the south in particular - and for once the north isn't getting entirely left out ECM's rolling out as I type, and as of T+168 (for next Friday) it still has the jet stream heading more SE than S, which by Saturday leaves us with a large Atlantic low to the NW and a weak ridge across southern parts of the UK. It's a shame, given that the 00z was more in line with the GFS 12z. ECM even dares to raise heights dramatically over Greenland, a scenario for which I see little support elsewhere. Yet we don't see much cross-model support for GFS either, with GEM and UKMO sticking with the jet diving south, but choosing to have the Atlantic trough move with it rather than spawning a cut-off low. I can see a cut-off low on the JMA run, but it ventures into Southern England by the weekend, producing a warm but showery outcome. To summarise, GFS unfortunately represents the most optimistic outcome for next weekend, with JMA, GEM (and probably UKMO) offering warm but unsettled solutions, and ECM going with a fairly benign setup for most of us (but unsettled in the NW). What I've done here tonight is taken you through the model output exactly as I have viewed it tonight - a 'live' analysis, you might say! I'm left cautiously optimistic about next weekend, but pleased to have such a fine looking run of days leading up to it, even if I won't be able to make the most of those... the fine evenings will be much appreciated, while the daylight still lasts!

Good points Geordiesnow, hopefully the cold nature of the high will help mitigate the ice losses, shame about the warm air imports though - we are seeing more amplification of the global patterns, and I suspect that if a powerful recurving typhoon in the Pacific comes along in 8-10 days time as per current model output, we could see some funky looking weather patterns for a time late August and into September. A couple of rapidly deepening lows near Siberia on the ECM 00z op run - the second leading to unusually strong winds from there to Svalbard and a little way into the N. Atlantic. Just one possible outcome of course.

The model output for the NH isn't looking so good for ice retention from about a week's time, with the cloudy, snowy conditions clearing out in favour of increasingly strong areas of high pressure. Not that the favourable conditions have been very successful anyway... the sea is clearly king this August.