Met4Cast

This up-coming SSW does appear to be strongly linked to the MJO & associated +MT events, particularly the East Asian Mountain Torque. A paper from, Balwin & Dunkerton 1992 titled "Stratospheric variability has important implications for surface climate" seems to suggest greater forecast accuracy of SSW events following MJO orbits through phases 6/7. We've been in a slow meandering phase 7 for a little while now but the previous eastwards progression into the Pacific triggered a (albeit quite weak) +FT event, the slow phase 6/7 has helped to amplify MT quite significantly & more prolonged than the initial +FT would have led you to believe. This strong & sustained +EAMT has allowed for continued heatflux to deflect upwards into the stratosphere, unsurprisingly originating from the Himalayas (and to some extent N American mountain ranges) as per the first strat observe chart attached below. What comes next in terms of predicting future weather is quite difficult. AAM anomalies continue to flux equatorward so despite a likely SSW & continued forcing from the MJO on the face of it suggesting high latitude blocking I'm still not convinced there'll be enough "oomph" to transition from an Atlantic ridge to a Greenland ridge. I'm of the opinion that the late February cold weather will be more transient in nature, snow risks across N hills, perhaps along the N boundary of low pressure systems but by and large nothing out of the ordinary or exceptional, southern England once again probably struggling but determining the cold/mild boundary at this range is virtually impossible. Deep Scandi trough > Semi amplified Atlantic ridge seems the best bet currently. Colder than of late certainly, but widespread snowfall? Low likelihood from me currently.

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.

feb1991blizzard Indeed, does make me wonder how much impact this SSW will have, current EP flux forecasts (GFS) suggest mostly EQ-Flux but these are based on the GFS det so change as frequently as that does. I really wish we had more data available in this area by other models.

feb1991blizzard Yes much better. As stated in previous posts I think late Feb/early March holds the best potential. Slow moving MJO phase 7 through late Feb > early March suggests Atlantic ridging retrogressing to Greenland & eventually a west based -NAO (GFS dets currently hinting at this broader evolution in the above timeframe) In terms of the AAM we still have a lack of poleward fluxing but with a major SSW & split there is a window of opportunity for blocking beginning to appear within the context of a very unstable polar profile. Not convinced on anything *prolonged* given the above but certainly potential for a cold spell at the end of the month. Blocking however might struggle to become sustained in the right places for long periods.

North-Easterly Blast Worth noting that the May SST link with the following winter was largely debunked & is no longer used by the Met Office as an NAO predictor! With that though you could see the thinking, i.e SST’s do have impact on the NAO to some extent. Is the opposite true? Do cold Septembers correlate to cold winters?

Haven’t they? The recent +EAMT & more broadly strongly +ve MT event is one of the reasons we will be seeing a major SSW next week. Rossby wave packets generated in part due to momentum being deposited directly into the Pacific jet & causing the jet to extend eastwards have allowed for significant heat flux into the stratosphere to finally deliver the knock out punch. Indeed, Tamara mentioned this likelihood a couple of weeks ago and now we’re seeing it play out. The strongly +MT was signalled quite a while ago as the MJO progressed through the Maritimes & into the Pacific generating strong +FT, MT always follows FT. In terms of the MJO not impacting as expected, the above is an example of an anticipated consequence of the MJO, the reason we’re not currently seeing blocking despite favourable MJO is because the MJO cannot & should not be used in isolation. Here’s something I posted back on January 22nd: So actually, this has been rather well sign posted for a couple of weeks now & those of us that subscribe & try to apply the GSDM framework have spoken about this likelihood a few times.

It’s not “clear cut” that a warm September = a mild winter either looking at the data shared in here by others. I think there’s some conformational bias going on here, in a warming world each individual month is more likely to be mild & as such, a mild September may well be followed by a mild winter because mild winters are far more likely these days. It doesn’t mean there’s a link and the evidence isn’t strong enough to show that there is. What are the mechanisms? Why does a warm September = mild winter? What drives that? What are the feedback loops that cause it? You have to demonstrate & show a positive feedback loop which influences weather patterns, otherwise it’s not helpful, useful or demonstrable. Edit: Just read the rest of the thread, I see @Mike Poolemade the same point re: climate change.

Indeed, no surprise to me that modelling hasn't continued with the build of heights northwards yesterdays UKMO/ECM signalled. I do think the GFS is being too progressive with the Atlantic still though & suspect we'll end up closer to a UK high, this mornings ECM probably a good fit. I think any amplification could come towards the end of the month/into early May but unlikely to see anything of interest re: proper cold/snow before then. It has been a very odd winter, the MetO have done rather poorly with the long-term forecasts. The SSW remains the wildcard & partly the reason there's some hope towards the end of Feb, ensembles certainly show a cooling trend albeit mostly from a Scandi trough again rather than any substantial blocking patterns. Very odd year.

Maybe the SSW will bring an early spring instead.. Horrific!

I often find the NAEFS to be quite a good guide for the broader evolution of the pattern, it's the GEFS and GEM ensembles combined. This currently suggests steady as we are out until the 19th with the pesky Iberian heights making themselves known. Towards the end of the month, and perhaps more broadly it signals a trough returning to Scandinavia, perhaps introducing colder air as a result but still not exactly blocked. Perhaps something similar to the recent colder spell, i.e Scandi trough led rather than blocking led. In any case - It's currently difficult to make an argument for widespread cold/snowfall, if anything that remains a very low probability looking at NWP modelling. It becomes perhaps even lower when factoring in the teleconnections, despite an up-coming major SSW. Lets hope for some changes in the coming week.

Derecho Just to go back to this, here are the SST's during early January 2010 compared with the current SST's. both El Nino years and both had anomalous warmth in the SE Atlantic, one major difference however is the strength of the tripole, much colder waters stretched across the central Atlantic in 2010 vs this years, I suspect this perhaps helps to explain why we saw a cold winter in 2010 vs this year. Not to say the anomalous warmth is the entire reason for this winters broadly mild weather, but certainly an argument could be made that the warmth helped to inflate the Iberian high this year. MJO was also broadly more favourable through February in particular.

Yes, because following the whims of individual det runs through this winter has been a complete success.. I can't say I care much for what the det runs show if I'm honest, they could show the next BFTE and feet of snow across the whole of the UK but if it's beyond day 3 it may as well not exist.

There’s currently no real sign of anything colder reaching the UK in the next 2 weeks. I think we can *probably* write those off. There is the potential for something colder late Feb/early March on the basis of a downwelling SSW, extended ensembles do show a switch to colder weather albeit not very confidently at present. In terms of background forcing, the MJO remains favourable however the AAM does not, two different forcing coming out of the tropics/sub tropics makes forecasting more uncertain & nailing broadscale patterns difficult, especially when you factor in an increasingly unstable polar field (SSW).

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.

Just skimmed through the first few pages, this thread is a fantastic resource for those wishing to learn more about the teleconnections/drivers of our weather, including the GSDM, AAM/GWO/torques etc. “Guest” is “Bring Back 1962-1963”, not David Gold but a different David. Wonder why his username isn’t showing? Regardless, @Nick F& anyone else who wishes to delve into things more, this is a good starting point.

Tamara has, in fairness, on several occasions this winter discussed what went “wrong” in terms of the pattern changing vs expectation, as have I, Catacol & various others in the Model Output Thread.

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.

Earthshine I plan to go back through my own posts this winter & do a more in depth write up on what I said about the AAM/MJO & compare to what actually happened & then compare that with the weather outcomes when I get a bit of time. I’ll likely wait until winter is actually over though.

Derecho It might be worth looking at the MJO from that year & comparing it with this year, i’ll see if I can find the AAM from 2010 too, be interesting to compare the different variables & try to “diagnose” it, so to speak! I have to go to work now though so no time to do that today!

Weather-history Indeed, i’m not saying it’s quite that linear but we had more variables for a cold winter vs against this year and we still came out in the top 10. But then again the UK is a tiny island, difficult to upscale that. Obviously it’s more complicated than A+B=C as this winter (and the winters you mentioned) show! In terms of solar activity - I think the link there is rather tenuous, it may help in some aspects but I don’t think it’s a driver of global weather patterns, at least not one that can dominate other earth based forcing!

jules216 -QBO does more than just increase SSW probabilities, it generally helps to promote a weaker sPV overall, which we have seen throughout this entire winter. But that’s just 1 variable, there were plenty of other variables favouring increased likelihood of blocking going into this winter, declining IOD should have helped the MJO gain more traction, that didn’t happen. What we did see is the anticipated rise in AAM/GWO to link the Nino base state with the atmosphere. We did see periods of fairly deep -NAO and -AO which was again, anticipated going into this winter. We did see a south shifted jet stream, most of the drivers talked about going into winter did “come off” and have the effects that were expected, from a UK point of view though it didn’t produce & i’m sure there’ll be lengthy discussions on why. For northern Europe it absolutely did produce, Scandinavia for example has been absolutely bitter as have many other Nordic countries.

northwestsnow The fact this winter is likely to come out in the top 10 mildest winters is pretty telling. -QBO, El Niño, two, soon to be three SSW’s, weak strat throughout, declining IOD, on paper this winter should have been absolutely bitter. In reality? Not even close.

We hear this every single year. “next year will be better”, it was said last year about this year. It was said the year before last about last year. Analogues categorically do not work anymore, last winter was a great example of analogues utterly failing. The climate is shifting too quickly for them to work, the baseline has changed, comparing winter to years gone past may have worked (somewhat) in the past but i’m firmly of the opinion that it doesn’t anymore, our climate isn’t the same as it was 20 years ago, let alone 50-100 years ago.

MJB I was speaking with James Peacock on Twitter and he thinks that the anomalous warmth in the SE Atlantic has propped up/strengthened Iberian heights this winter, given the link between climate change & an expanded Hadley cell it does make me wonder if this winter was a “real time” example of the type of winters we can expect in the future. Getting decent cold spells into the UK is becoming increasingly difficult.

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.