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Derecho I've lost faith in using the MJO passage through the phases as precursor to changes in weather patterns towards cold or mild. Following 'warm phases' of 3-4 in early Jan we saw a 2-week cold spell, we've seen the MJO recently pass through 6 and now loitering and weakening through 7, but very little amplification in the upper flow at mid-to-high latitudes to show for it in the models. What high lat blocking that has been showing and will likely continue to be shown down to changes in the strat, i.e. downwelling of weakening winds. And I don't get this obsession with using AAM as tool on its own, it seems that when ever it rises all falls we are told to look out for changes but it seems, like when the MJO moves through the historically 'colder' and 'milder' phases, many other drivers are at play, some not so obvious, drowning it out much influence from it over the N Atlantic sector / Europe. Though the biggest interference in what we would expect in lag to certain MJO phases being climate change. The state of the stratosphere is one driver, when it couples with the troposphere, still one to keep an eye on though. Be glad not hear about the MJO for several months, until the next cold season. I've given up talking about how it may influence patterns, as it makes me feel fraudulent!

B87 Strong trades around the dateline (easterlies) typically strengthen the mid-lattitude jet in response (stronger westerlies) and suppress AAM. It's why a lot of people tend to think that La Nina produces less favourable summers for the UK.

From what @Tamara said in some archive model thread forums may 2007 actually had a positive AO but when we came into the summer AAM collapsed dramatically. It was the same year where we had el niño to la niña transition, we had an east QBO in tandem with negative zonal winds blowing across the troposphere aligning with the weak sea ice and subsequently produced the poor summer it did. For may 2006 there was a lot of northern blocking but also a lot of robust wave activity so when we turned the calendar month to June it generated high AAM and a generally great summer up until August with the heat at its peak in July.

summer blizzard in 2006 I think there was a lot of northern blocking in May, but did the robust wave activity on a repeated basis along with rising AAM ensure we had a very hot two months ahead?

Lets break this winter down into something a little more digestible in terms of the GSDM/teleconnections and some of the predictions that have been made based on them. I'll be mainly quoting my own posts through the winter but will add in some of Tamaras too if/where appropriate, compare that to the observed state of the AAM/MJO and the corresponding impacts on the weather patterns. I'll discuss the December & in particular the January cold spells too and try and diagnose where things went "off the rails" vs the expectations, particularly with the January cold spell. Any bold text within the quoted sections is something I've added to explain certain variables/add context to certain things that otherwise is not explained within the quoted text itself. Hopefully this post will provide some context on what was expected & why vs the outcomes. Perhaps those that claim it's a load of "rubbish" will gain some much needed context. Early December: The opening few days were cold across the UK with blocking extending up through the N Atlantic and into Greenland. Blocking broke down rather quickly. When did forecasts first start to pick out this colder spell of weather? (I wont be focussing on NWP modelling, mostly teleconnective) here's one of my posts from November 22nd: That post from November 22nd went onto discuss what comes after the surge in momentum and the MJO progression continued to cycle on; So.. the signal on November 22nd was for colder weather across the UK late November/early December but teleconnections, in this case the MJO & AAM were towards a return of the Atlantic. By the end of week 1 of December blocking had gone and Atlantic weather systems were across the UK. A prediction that proved right 2 weeks in advance using the teleconnections. I'd class this as a win. In that same post from November 22nd I went onto discuss the expected progression through December in terms of the background state flagging late December/early January as a potential time period where blocking/cold weather could manifest, an attempted prediction more than a month ahead. Did this prediction hold true? In terms of the AAM, yes. Through December we did indeed see a substantial rise in total AAM thanks to the MJO progressing through the Indian ocean and into the Maritimes. Unfortunately, as we know the MJO began to collapse as it passed through the Maritimes, this is something that happens fairly frequently during El Nino winters and particularly in the context of a strongly +ve IOD which, despite weakening, was in place during December. FIRST FAIL: The expectation of a colder late December was a fail, the MJO cycle did not progress as anticipated and due to collapsing this left little "oomph" to generate the blocking that was anticipated/mused upon. I wouldn't say this was a fail in teleconnections but a failure in forecast modelling, indeed models had been overly enthusiastic about a more amplified cycle (albeit GFS/ECM were less enthusiastic than the ridiculous output from the BOM model at the time) Here is the complete MJO cycle, the blue line represents Decembers progression & then subsequent collapse. This meant, late December was mild with little in the way of blocking, despite the AAM/GWO responding through December as expected thanks to the very same MJO progression. +Frictional Torque led to +Mountain torque adding westerly momentum into the atmosphere and driving total AAM upwards, as depicted here; MJO moves eastwards creating +FT, this, via rossby waves transfers northwards increasing +MT and we see the substantial total AAM rise following these two events. The collapse in MJO however led to this late December pattern; Interestingly, the +EAMT during December helped to trigger the minor SSW in late December. +EAMT increases heatflux into the stratosphere. So, prediction of the AAM proved correct but collapsing MJO failed in the late December expectation & indeed we missed the boat for early January, JUST! Indeed, contrary to the belief in this thread that "People who use the GSDM never explain when it fails", I did quite an in-depth post discussing why anticipated late December blocking had perhaps failed and indeed discussed my own personal failings in understanding, you can read that here; Early - Mid January Through early to-mid January we saw what was technically a 2 week cold spell, the first week was largely dominated by high pressure (with a brief less cold spell in the middle) with the 2nd week of the cold spell being much colder. Here are a few re-analysis charts to show what happened; This cold spell was the subject of much debate on teleconnections at the time which had seemingly favoured a continuation of cold beyond the 20th (when the breakdown ultimately came) with expectations very much being that wedges of high pressure could continue to deflect the jet stream southwards & keep the cold in place, despite the waning of high latitude blocking, naturally, this didn't come to pass and instead we saw a quick return to mild & indeed stormy weather with 2/3 (I forgot) named storm systems. My post on Christmas Eve below, highlighting some excitement re: potential for cold patterns through January. Now, some IMPORTANT CONTEXT: This was around the time a SSW was unfolding, originally modelling had predicted it to be a major SSW (technical reversal) but modelling backed away from this idea. My post on the 27th December highlighted this; Ironically on the same day (27th December) I had urged caution re: a SSW disrupting what at the time teleconnectively was a favourable tropospheric pattern for cold weather patterns. So.. these two posts 11 days before the first day of the January cold spell (beginning on the 8th January). Tropospheric & teleconnective drivers pointed towards blocking but I was cautious re: the SSW potentially making things unfavourable instead. So, yet another example of teleconnections leading the way in terms of broadscale predictions. In actual fact, during early January the mod thread was awash with comments about sinking highs and the likelihood of cold collapsing, those of us subscribing to and applying the GSDM knew this wasn't going to happen, here are a couple of posts from the 3rd January where I tried to reassure that this wasn't what was expected. And; Indeed, as the re-analysis charts above show, we did NOT see a sinking high & we saw retrogression week 2 of the cold spell. Another win for teleconnections vs modelling. Now, lets fast forward a little bit. We know how the cold spell evolved & the thinking that was being put forward at the time. I.E talks of 1979 and 1947, teleconnectively this was being advertised & indeed we saw some absolutely stunning modelling output in the extended at the time,remember that SSW I just talked about? That's about to bring us resoundingly back into reality. The impact of this SSW could not have been forecasted beyond a week & unfortunately, the late December SSW came back to haunt us. Here's a post I made on January 9th. Just for context, here's what actually happened on the 16th & 17th: The low missed southern England by just a couple of miles and our friend the southern Euro high was further north than previous modelling had anticipated. The conversation within outputs between the 10th - 15th was largely focussed around the tracking of that low pressure system. Zooming back out to teleconnections though and the previously mentioned SSW, when precisely did the wheels fall off? Remember, the cold spell came to an abrupt end on the 20th January, on the 9th things were ticking along nicely. On January 12th, @Tamara posted this; And my subsequent response; Expectation on the 12th January, 8 days before the cold spell ended was for residual heights to remain around Iceland/N of the UK, it was clear the main blocking would weaken and indeed less cold air was being advertised but as Tamara explained, a southerly tracking jet was still a possibility underneath wedges. By the 13th, it was largely game over for a continuation of cold, here's what I posted; I theorised at the time that the recent warming in December had perhaps reshuffled things out of favour with blocking & indeed subsequent analysis (especially when factoring in what would be a technical SSW on January 16th) would show this to be the case. The warming shifted the Canadian PV eastwards into the Atlantic sector which caused the entire pattern to flatten and pulled the jet northwards, any hopes of residual highs to the north were gone. This is NOT something teleconnective forecasting can predict, this is not something that was foreseen at long lead times but was actually a very short term change which changed the entire outlook going forward and we all know what happened beyond the 20th. On the 18th, I posted this. I stand by that. Hopefully I have shown in this (admittedly very long post) that teleconnective forecasting has done well throughout this winter and has signposted the broader changes within northern hemisphere patterns. What is hasn't done is tell you that it will snow in your location on a specific day, or promised snow to anyone. Rubbish the science as you wish, but it has proved a valuable tool throughout this winter, short term changes within the configuration of the polar field cannot be predicted at longer ranges but can have a big impact on the weather/broader patterns regardless of teleconnective forcing, this, as stated, cannot be predicted or incorporated particularly well within the GSDM. Once February is over I will do another post analysing what happened teleconnectively through this month, expectations for a cold February were high during January, evidently that hasn't come to pass.

I think that any comparisons with 2007 thus far are likely to be coincidental (and not really true in weather type). In 2007 the Nino collapsed after January and SST's were already negative by April. In Feb-April the low -AAM suggested by the collapsing SST's (strong trades and possible atmospheric coupling) actually does tend to produce a somewhat anticyclonic response (for reasons beyond me). Our Nino is still hanging on with a WWB progressing over the next week or two likely to mean that our first collapse attempt won't occur until at least May (although sub-surface SST's are -5).

Summer8906 the subtle differences with this year to that year were we were coming into a weaker solar cycle than what we are having now. The advantage of spring 2007 was most of the days if not all of them had a positive AO until when AAM dropped dramatically come june. Think I read that from a post Tamara made in an archive model thread.

You're talking about the MJO & AAM as if they are two separate things, but they're not. AAM is simply a measurement of how much westerly momentum is in the atmosphere, the MJO influences this via frictional & mountain torques, i.e driving positive MT increases westerly momentum. More westerly momemum tends to = a more perturbed jet stream and thus, a higher likelihood of high latitude blocking but it's equally important to see which direction those anomalies are travelling. The MJO is taken in isolation too much in this forum & more generally, it's just 1 variable of the global windflow budget so it's no real surprise that looking at the MJO, checking the composite & expecting the atmosphere to respond and look like the composite isn't really working, the whole point is to view the MJO as part of the windflow budget, the MJO is incorporated into the GWO. The AAM, or GSDM isn't supposed to be used to determine regional specific weather but to help diagnose global weather patterns, it's essentially the best tool we have for medium-extended range forecasting. GSDM (which incorporates processes like the MJO) > Global NWP modelling > High res modelling The GSDM provides context to NWP modelling in the same way NWP modelling provides context to more localised high resolution modelling. You're right, the MJO is currently in a phase which if you view in isolation and look at the composites, does favour high latitude blocking, but that's not the entire story. AAM is positive at the moment indicating a good link between the +ve ENSO state & the atmosphere, however as discussed here in recent days fluxing of positive (and negative) anomalies are and have been equatorward rather than poleward, this serves to inflate the Iberian/S Euro high, whereas poleward fluxing (see early Jan) helps to amplify high pressure into the Arctic regions. The current state of AAM fluxing helps explain the current patterns we've been seeing despite, on the face of it, a favourable MJO. I do wonder if the very warm SErn Atlantic waters has perhaps helped to extend the Hadley cell this winter and thus inflate the Iberian high regardless of other forcings such as the AAM, it seems very much to have been the default, base state through much of this winter despite seemingly (and often) favourable teleconnective forcing. Climate change is without doubt changing the dynamics. I don't think we should just ditch the MJO, GSDM etc just because it hasn't performed with pre-determined outcomes. If anything, this winter has been a fantastic learning point on this, but it is important not to take them in isolation or out of context.

summer blizzard you expecting this summer to be like 1973, 1995 and 2016? You could put 2007 in there but 2007 had an east QBO which I believe was the skurge with that particular summer and AAM dropped significantly when it came down to June onwards. Also the Rihanna featuring Jay z record with umbrella was a major curse with summer 2007, at least it was a season to look at with good humour albeit not so good for homeowners who got flooded out literally and there was a record number in insurance claims that year too.

Those CFS forecasts are completely useless, I can't say I ever look at them beyond mild curiosity, I certainly don't factor what they show into my predictions within the GSDM space. The (almost) real time plots produced by David Gold are more useful in determining the broader direction of travel, there's typically a 14-20 lag between initiation & pattern changes so it's often more useful to see what's happening *now* vs what might happen in the future re: AAM. For example, we have seen and are continuing to see subtle equatorward fluxing of both +ve and -ve AAM anomalies, this generally favours stronger Iberian/S European heights and indeed that's what we're seeing represented quite well within broader NWP modelling, despite on the face of it a favourable MJO for blocking and despite the fact we remain in a high GWO orbit. This is the reverse of what we saw through December with anomalies instead fluxing poleward reaching the realisation with the blocking early-mid January. Worth noting though that the polar field is very important to factor in as well, the stratosphere can dominate or disrupt expected patterns at relatively short notice that no amount of applying the GSDM or various other teleconnections can help with, the mid-late January period was a good example of this, that SSW reshuffled the trop pattern and sent energy from the Canadian vortex eastwards across the Atlantic sector, instead of the blocking that had been expected we saw the pattern flatten & a stormier, milder period of weather ensue, as Tamara said "expect the unexpected". Indeed the opposite was true for the December cold spell, broadly the GSDM was not in favour of blocking but the jet stream hitting road blocks as it crossed the Atlantic allowed for blocking to amplify, so, it’s not perfect by any sense of the imagination but it can and absolutely does provide context to NWP modelling and give a much broader picture of what’s driving our weather. More often than not, the direction of travel re: AAM tendency is more important than the aggregated total AAM in the atmosphere. But, perhaps this isn't the right thread for this kind of discussion re: future forecasts and is better left in the Mod thread, just wanted to perhaps add some context for those reading the thread and wish to learn. This isn't some "elitist cult" and I'd be more than happy to help anyone wishing to learn more about this, just as @Tamara has often very kindly and patiently helped me, though admittedly I'm still very much a novice.

It's certainly not an exclusive club and I'm sure if you reach out to David Gold he would be happy to provide the username & password to the site where the charts are hosted. Unfortunately when Ed Berry passed away (the founder/main researcher of the GSDM) NOAA shut down the AAM pages where all the charts were publicly hosted. There used to be a forum on 33andrain specifically about teleconnections with a hell of a lot of research from both pro mets and people like Tamara, Blessed Weather etc trying to understand and build up a library of scientific papers but unfortunately the forum shut down without any real warning and so all that work was unfortunately lost. Besides that one site there's very little information or data available now, there's this CFS based AAM maproom but it's not very good. AAM/GWO Mapwall ATLAS.NIU.EDU Weatherbell also offer AAM/GSDM charts within their top tier subscription, though you're looking at >£100 per month so not particularly accessible or justifiable just to access some charts. There is still a lot to learn about the GSDM of course, it's certainly not perfect as this winter has perhaps shown but perhaps this winter isn't a good example of it's use, it's been a bit of a strange one in terms of the MJO, the stratosphere and just our luck here in the UK really. Despite a south shifted jet for much of winter, despite -NAO and -AO we just haven't been able to get things in the right places for the UK despite what looks to be an almost record breaking cold winter across N Europe. There's not much else I can add that @MattH didn't cover in his post in response to what you said.

Met4Cast i am aware of how AAM and mountain torques are linked to the MJO. But I'm not convinced that the fluxes poleward or equatorward can specifically be linked to anomolous pressure tendencies in a particular locale, such as 'inflating Iberian / S Europe high pressure cells. What literature did you get that from? I would have thought Atlantic SSTs, TPV extending south from Greenland premoting WAA and expansion of Hadley cell north in winter would be the main drivers. Does comes across to me like GDSM forecasting is an exclusive club who's members have secret access to AAM charts. Where do the rest of us find them? The joy of this thread is everyone has access to a huge range of NWP charts now, much more than 2004 when I joined Netweather, so we can discuss, debate and challenge each other and those with less understanding can ask questions of the more knowledgeable. But with the GDSM posts by a few on here who have the special access generally go unchallenged and so readers just take your word for it. I'm not saying I don't appreciate the time you guys put in to explaining how you interpret the AAM charts and come to your conclusions. But most of us don't know how these charts change with each update so can't discuss them and perhaps challenge why a previous forecast suggested x may happen but in the end the weather had other ideas. When I started learning meteorology in depth in the early 00s no meteoroloy books or journals I remember refered to GDSM. But I have read some of the papers Blessed Weather has kindly put on Netweather. But still yet to be convinced it is any better than other tools for longer range forecasting. Browsing wx forums in the USA, notably Americanwx, there is seldom reference of AAM by ProMets, only really on here gets a mention. Yet to be convinced myself, but you never know, I may be swayed more one day.

B87 so many people are remembering 2007 as the dregs of a summer, when in actual fact the first half of June wasn't that bad, it had average sunshine throughout the summer and August was actually pretty nice albeit on the cool side. I think may of 2007 actually had a positive AO, but when we got into the summer AAM tanked, one of the reason behind our very unsettled summer, other reasons were the flip from niño to niña, the east QBO was partially responsible in tandem with negative zonal winds blowing in the troposphere aligning with the weak sea ice . You contrast that to may 2006 when there was a lot of northern blocking, but that swiftly changed when the calendar changed to June and the jet stream migrated further north giving us a very hot June and July combined. Also the west QBO and niño like atmospheric waves gave us the hot summer of 2006. It was a great season up until August really.

The lack of data available is something that is irksome, more data is always a good thing but the AAM remains limited both non-public & public. I don’t know why NOAA shut down the page but I presume funding was a big part of the decision & a lack of someone to take over and continue the research. EDIT: It seems copyright was a big part of the reason when Ed Berry retired from NOAA, see Tamara’s post below The Met Office however do use the AAM internally, mostly for the contingency forecasts but do occasionally use it for the extended forecasts that appear on the front page of the Met site, the GSDM is obviously very complicated so i’m not surprised they don’t mention it, they probably prefer to simplify it & discuss the MJO for example instead, something relatively easy to explain vs frictional & mountain torques and even then, it’s only in recent years the Met have begun to talk about drivers such as the MJO, they never used to. In terms of evidence, there is plenty of scientific papers on the subject if you google it, including papers from Met Office scientists. https://www.psl.noaa.gov/map/clim/wb2007_ams.pdf And this from Met Office scientist Adam Scaife Long-range predictability of extratropical climate and the length of day IDP.NATURE.COM Ensemble forecasts from a dynamical model suggest that fluctuations in atmospheric angular momentum and the length of day can be predicted over a year in advance, thereby... Mountain Torques and Northern Hemisphere Low-Frequency Variability. Part I: Hemispheric Aspects JOURNALS.AMETSOC.ORG Abstract The NCEP–NCAR reanalysis dataset for 1958–97 is used to analyze intraseasonal variations in mountain torques and the large-scale atmospheric circulation patterns... There are many, many papers written about the topic & as I mentioned previously a huge extensive list of them was on the 33andrain forum but that was sadly lost. There was a thread on this forum dedicated to AAM/GSDM but it wasn’t particularly popular unfortunately, but here are a couple of threads that might be useful for those wanting to try and gain a better understanding. Indeed, Glacier Point relied heavily on the GSDM for the often very accurate Netweather seasonal forecasts, it’s a shame he no longer does them.

I see the ill-considered posts are doing the rounds once again on here, quite remarkable and, as usual, one of the key reasons this thread persistently becomes unappealing to many as the years come and go, myself included, but I oddly keep returning. It would be a superb platform if it weren't for a set few who wish to dismiss aspects of meteorology just because they don't properly understand them or wish to dismiss them for unfounded reasons, more of an opinion. Let's start with the AAM - If the number of posts over the years from Tamara et al haven't highlighted the importance and usefulness of the GSDM and the AAM, then I don't know what more can be done, so for those who feel that way, then, yeah, move on, but to take a quick look at the forum and see some of the comments is just pathetic. In addition to the AAM - The charts that a set few posts are from a source that is run by the IBM Chief Met in the USA, David Gold. Nearly a year ago now the login for these was leaked and, as a result, his server was overloaded and it went down, for months. Those that use these and despite what some have recently said, even in the USA, where they are used, individuals were heavily disappointed they were down. Therefore, anyone after access to these needs to get in touch with him directly, as another burst of logins would cause further problems once again. There is no 'secret club' or anything like that, just a ridiculous statement, there is a reason, it's not a widely known source and I certainly won't be sharing login details when told not to. I've been using and studying the GSDM for the best part of 4 or 5 years now and within that time the amount of examples where it has helped to pre-empt NWP and also help to reinforce it are numerous. This area of meteorology has crept into forecasting more and without providing details is a foundation for some of my long-range forecasts for work and clients, especially in the energy sector. Meteorology and weather forecasting is a fluid process, things change, adapt and have to be modified. When an outcome doesn't happen as some expected then it is the comments, previously, that make an appearance, but shouldn't. As Tamara has stated many a time it isn't A+B=C and that includes the teleconnections and the GSDM, but it is how it is used and adapted that is key. I can't add much more, to be honest. We all have our opinions, but despite months and years of some trying to educate and discuss the likes of the GSDM to then swiftly knock it all back, including teleconnections too is ridiculous and I apologise for the off-topic post, but this needed to be said. Regards, Matt.

AAM/GWO forecasts are a bit thin on the ground,but found these for anyone interested. https://atlas.niu.edu/forecast/aam/cfsv2_aam_fcst_current.png https://atlas.niu.edu/forecast/aam/GWO_members_current.png Both from this page: https://atlas.niu.edu/gwo/

Tamara That doesn't doesn't give the excuse to be condescending for those that question the GDSM tool. How can it be verified that AAM is implied in more likely being responsible in creating certain patterns and not other drivers? Which begs the question how can you and others be so confident? Again, it feels like closed doors to those to question the tool's validity for fear of being shot down because they don't have the hours of learning the subject and all the GDSM updates to hand to draw on to be able to question a prediction. I don't doubt that GDSM has It's place, but many of your posts seem mostly centred on the evolution of AAM to make predictions and not talking about other drivers and persuading the reader to disregard model guidance. Then when patterns do not evolve how you suggest, there is no admittance by you why it didn't play out how you predicted.

Tamara It's all very well and admirable learning about and explaining GDSM and how works in the bigger picture of the global atmosphere. Many of us, including me, appreciate this alternative and unconventional way of forecasting. But it was the aggressiveness of the response from MattH when I dared questioned it's validity which was quite a shock to me and others. Because the subject is very technical to understand and explain it immediately puts a barrier to most questioning its validity because they aren't confident to put up a counter argument with lack of data access. If the GDSM is such a great tool, how come it's no longer available from NOAA. Or anywhere else. Met Office don't mention it publicly but do with all other drivers including MJO. There's no substantial evidence or papers that the theory is water tight and certainly with confidence can anyone attribute to AAM influencing weather patterns over N Atlantic. We can't question those who make these predictions using GDSM because we don't have to hand archive charts, verification stats and any access to such data. The thing that irks me is that predictions are made in MOD based on these GDSM / AAM plots but with little reference to other drivers, linked or not and we're told to ignore the model guidance. But, then there's never any follow up when these predictions don't come off as pescribed.

Following on from the recent strong WWB event in the Pacific we've seen a fairly strong +MT event and this led to a large spike in AAM tendency and a return to more neutral values in the overall AAM as expected. Going forward, a brief lull in westerlies around the date line but they do look to return during early November perhaps helping to push the AAM into more positive (and thus El Nino) territory. A positive AAM broadly means more westerly inertia within the atmosphere, a more enerergized jet stream and therefore a more amplified one (increased chances of blocks). I'm happy with how things are progressing on this front. In terms of the stratosphere, a rather substantial increase in u-wind strength is forecasted into November with some runs bringing us into record breaking strong territory for the time of year, I do wonder how much influence the extra water vapour from the stratosphere is at play here, or whether this is more broadly just "noise". The old saying "the bigger they are, the harder they fall" springs to mind. A strong vortex is more likely to deflect "attacks" from the troposphere so an SSW might be a little more tricky, however; given the above AAM progression, El Nino and eQBO combination I do wonder if we'll see repeating tropospheric patterns putting pressure on the vortex before finally delivering a final blow. A bit of a wild card this one though & not overly predictable at longer lead times. Studies do show however that an SSW within the context of a strong vortex is more likely to result in cold air outbreaks. Still watching to see if we see a more coherent MJO signal emerging, the post from @MattHa few days ago touched on this and seemed optimistic that we would do, so here's hoping!

Yeah, it's an interesting one and the wait goes on for a more obvious link. There is still evidence for a more coherent MJO passage and associated WWB over the next 7 to 14 days, which may start to tip the balance in favour of a more +ve AAM trend, but this is still not likely to be anything like what happened back in May which contributed to the +ve AAM pattern then. It is also interesting to look at the AAM plot from the last year and, as usual, they tell the story, atmospherically well. We can see the significant propagation of the -ve E'ly AAM anomalies through April and particularly May to the higher latitudes, as the tropics and sub-tropics were dominated by W'ly momentum. Since then we've had nothing and, again tells the story of the summer well. Clearly, the collapse of the AAM in late June/early July was a key event for the summer which was a curveball for us all... As we can see as well since late July the overall AAM trend has been -ve, even though, as you mention, oceanically, we are now in an El Nino state, it's all very troubling for the outlook period. With the IOD peaking through the late year I'm less concerned about this than the other year when it just snowballed everything, while the overall combination of El Nino and an eQBO should bring some results, at a minimum aiding the increased probability of a mid-winter SSW. The one caveat and uncertainty that troubles me is the influence of the high H20 content within the stratosphere from last year's Hunga Tonga volcano. I think there are or now are some papers out on this, produced this summer, but not had time to dig these out. But from what I know the science behind it a much increased H20 content within the stratosphere should/could help to cool the stratosphere more significantly and effectively, thus increasing the chances of a more robust vortex, but, then if that were to come to fruition could lead to a more spectacular vortex demise if an SSW were to occur. As ever, plenty of jigsaw pieces to look at and try and put together, but the pleasing aspect this year, unlike some years which makes an outlook even more difficult, is that, overall, we have both teleconnection and seasonal model support in terms of a general +ve NAO start and then a much-increased risk of -ve NAO winter, in time and, for me, that is still the form horse. Any early cold, potentially short-term driven by the MJO, depending on timing, while the main thrust of colder synoptics likely to follow into the New Year, but, as ever, time will tell. Overall, however, despite all the usual offsets/unknowns that can come with AGW, I believe we will move into a winter that has one of the highest probabilities of bringing colder synoptics for a good number of years, driven, primarily by the eQBO and Nino combination, while the SSW risk should be higher than usual too. Cheers, Matt.

Given the pace of the model thread jumping in here to add some output, almost too much to look at right now given NWP output, Strat Output, MJO in play and AAM turning the corner. First off picked the 30hPa level given the top of the envelope projections shown in Merra for a couple of variables driven by the strong W1 warming. Lovely view of the progression of the warming and the impacts on the vortex as it distends and is split. Also viewable as animation here , graphics not as great - but does highlight another pulse of warming out at D10. Then the 100hPa look which is probably the most exciting one currently in terms of echoes to NWP and what is driving chaos and variability. Vortices splitting at just 72 hrs and the energy shearing from the Canadian lobe spirals south - whipping across the Atlantic. The Canadian lobe pulling back, whilst the Siberian lobe progams the Northerly regime. Interesting to analyse these views as the exchange of energy between the daughter vortices provides neat insight into what may translate into NWP. It is a delicate balance of separation from the split in terms of how the vortices interact. Friday update saw only brief separation and energy transfer from the parent Siberian vortice back to Canada - reinvigorating the aforementioned filament and placing further pressure on the ridge attempt into Greenland, so much so in fact - it looked to be heading to a Scandi solution before getting stuck halfway house in the 'no mans land' which leaves us looking at less than appealing from a cold perspective output. This break is far from resolved yet and given it is happening within next 72 hrs, twists and turns to come. In relation to the MJO - beginning to look more coherent and composites show the direction of travel imprinting, it is never a=b for these so use as guidance, last updated in 2014 so nearly a decade of data not in them. A vortex already heavily assaulted this winter, technical SSW or not - it feels as good as one currently, with more duress ahead. Wondering if January is just an appetizer for February as AAM rebounds.. Finally a look at the development of the blocking regimes from Xmas Eve to date from EC as we progress from nowhere to the stuff we all like to see from a cold ( and dry) perspective in Winter.

Blessed Weather Great post! I had actually been planning to create a post on this at some point in the coming days so good timing too. I think your conclusion on it being a strong reflection is probably correct, there were several things going on which likely led to the results we saw. It's quite difficult to "untangle" it all with limited vertical direction of travel on the charts, but I'll try & explain what I think happened using this strat observe chart. 1: Minor warming occurred in early January and as highlighted in your post, Amy Butler & Simon Lee both talking about this leading to the -NAM state & Greenland high, I think this is probably right but we also saw AAM anomalies propagating poleward with support from the MJO meandering in phase 3, this minor warming likely added some extra juice to what was already becoming a favourable tropospheric led pattern for Greenland blocking/HLB. 2: This -NAM then worked upwards into the stratosphere at a time we saw yet another SSW (whether this caused it or merely helped it? I'm not sure), I suspect this -NAM is the reason for the technical reversal we saw with this secondary strat event, the upwards propagation of -NAM however probably served to "cancel out" any downwelling from the major SSW in mid-Jan which then ultimately led to a breakdown in blocking and return to +ve zonal winds in the troposphere, as shown on the strat chart above due to the Canadian vortex shifting eastwards into the Atlantic sector. Quite a complicated entanglement of different forces/drivers coming together, one that would absolutely not have been possible to predict at longer ranges and something that seemingly caught even the experts out, let alone us mere mortals! From what I've read since, these reflection events are rather rare. So.. typical UK winter luck at play?

CryoraptorA303 Good a analysis. Pattern matching isn't perfect at all but IMO it's more useful than the mumbo jumbo of the MJO etc, and yes I have read the papers. Put it this way, pattern matching clearly pointed to a very mild February, I said as much in late January but the new so called signals pointed to extensive northern blocking and a cold month, even the MetO were taken in. It was never going to happen! December and January were very similar to other strong El Nino winters so the outcome for February was inevitable, add to that the fact that mild December's and January's are nearly always followed by a mild February, 1983 is a rare exception. The fact that other 'signals' got it so badly wrong goes to prove how unreliable they are as a forecasting tool, yet we still hear evangelist going on about MJO phases, AAM and the dreaded mountain torque, give it a rest guys or at least explain why it went so wrong while good old fashion pattern matching had February spot on. I respect people who research new areas in meteorology but some humility would be welcome. Andy

Just spent half an hour reading through this entire thread, it has got a bit feisty in here! Overall a very disappointing winter, away from perhaps northern Scotland. It's a shame as this winter held out a lot of promise, but failed to deliver. My perspective on the use of medium range forecasting tools - everything that falls into the teleconnections bucket (GSDM forecasting, analysing MJO cycles, global wind flow budgets, AAM etc) - is that they are useful, and we should continue to progress our knowledge of how these factors can influence broad scale synoptic weather patterns, that could then influence our own weather. However, we also shouldn't make firm predictions of UK weather based off of them. They give us a first step to understanding whether the atmosphere is pre-disposed to supporting a blocked, cold, snowy set up or not, but nothing more. It can't be used to say 3/4 weeks out that the UK will or will not experience a particular type of weather, simply that the likelihood of it occurring may or may not increase. Surely though, that is all longer range forecasting is supposed to do? Provide a probabilistic view on what may happen. At the end of the day, so much needs to fall into place for our little island on the eastern edge of a large ocean, influenced by warm ocean currents, with a prevailing wind that originates from the sub tropics that there is little point getting emotionally invested in model output beyond about 96 hours or teleconnection data several weeks away. Absolutely view them, understand the drivers, try and make predictions, but there are far too many people here who literally hang off every single suite of models, attempting to count down from day 10 to day 14, hoping nirvana charts will deliver. We all hope they verify, and there is nothing wrong with looking at or discussing them, but I do think a few people get so engrossed in them that when they often fail to verify they literally spiral into a cycle of doom. Why put yourself through it? I have learned over 20 plus years of model watching not to get invested until a cold spell is modelled to within 4 to 5 days at the absolute maximum, and even shorter than that when it comes to snowfall. With all of the advances in weather forecasting, the technology we have available, and other tools that are giving us a much greater understanding of atmospheric drivers, the same is still true for our small part of the world - forecasting a particular type of weather is fraught with difficulty beyond 5 days.

This thread is very necessary! And, quite fitting, in a weird way, to have the post-mortem while this excuse for a winter is still alive! Before giving my thoughts on winter, I just wanted to make a comment on the GSDM - I don’t usually, because I don’t want to get caught in the crossfire between those who are passionate believers and very defensive when challenged, and those who use it as an easy target for criticism when it doesn’t snow. I don’t have access to the GSDM charts myself, but I do factor into my thoughts the excellent posts on here from those that do. I have read some papers on it, and @Tamara kindly provided me some useful help on aspects of it a few years ago - it seems sound and very useful, and given it is founded on the principle of conservation of angular momentum, it makes sense to me as a physicist. I don’t think it is infallible though, forecasts seem to be predicated on the assumption that AAM will rise/fall in a predictable way, and I also have a question mark (in winter) about how intuitions derived from the GSDM fit with things occurring in the vertical dimension i.e. the stratosphere, which I think has been relevant this winter. It also doesn’t inform on local UK-scale issues which can be so important. The backdrop to this winter was world weather patterns out of past precedence with extraordinary sea surface temperatures. My view in the run up to winter, was that any attempt to make predictions based on analogues was therefore pointless, and I put more weight in the seasonal models - because they simply simulate the laws of physics, without knowledge of past patterns, I figured they would be the best guide. They weren’t! At best, they could be said to have predicted a weak vortex, which there definitely was, but on pressure patterns relevant to the UK, they have not performed well. We have had a very weak strat vortex ever since the Canadian warming (first one for 30 odd years). The trop has been leading the dance most of winter, and the strat vortex has been behaving really quite oddly. I thought that surely with that in our favour we must be in with a shout of a decent winter. Wrong! But why? It seems to me that there are two primary possible reasons: Climate change has done something to global weather patterns that have made it next to impossible to get the kind of synoptic patterns which in the past would have delivered cold to the UK - the dreaded ‘Iberian high’ being a symptom (but not cause) of this. We were just very unlucky this year. Even unfettered by the strat vortex, the trop vortex just never got itself into a favourable position. I still think with a different roll of the dice we could have ended up with something memorable. One of the reasons I don’t (yet) believe reason 1, that decent UK winter patterns have become next to impossible, is because they have showed up in the models this year, not just the odd run, but substantial clusters of ensemble runs - we have just not managed to count them down into the reliable. They would not show up if they were no longer physically possible, for whatever reason, due to climate change. So, I put most of it down to bad luck. Which brings me to my final learning point which is disregarding the model output. It is OK to bin an individual run if the output gets so contorted you know (from looking at charts that have actually verified) that a run is garbage. But, I think we have been a little quick to dismiss larger swathes of model output on the assumption that ‘the models are misreading the progression of the MJO’, ‘the models always underestimate Iberian heights’, ‘the ECM is prone to over-amplification’, or ‘the GFS is off on one and will come into line’ etc. I hold my hand up - I’ve done this - and found later that the disgraced model was on to something after all. All in all, a very disappointing winter, but while we have had no meaningful snow (locally, again, 4 years on the trot now), it has been a (morbidly) fascinating learning experience.