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Singularity

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  1. Spotted this from MV showing the EPS version of the 850 hPa zonal wind anomalies plot. Comparing with the GEFS one, we can see the latter's typical positive trade wind strength bias that forms part of the negative AAM bias we see in the mid- to longer-range (though less obviously these days what with the AAM plots for that model having glitched out). What EPS instead shows is the low amplitude Nino standing wave that promising UK summer fortunes are built upon, albeit perhaps not as coherent as is most desirable. No hiding the fact that the WWB has been seriously stunted in duration, but it still looks to have done just about enough to shift the atmospheric wave guide. I'm nodding at any longer-term modelling that has the Arctic blocking becoming increasingly 'Sceuro' based with subtropical ridging first interacting with it and then taking over as the predominant mode. CFSv2 has been doing this on many of its recent runs for final third of May through much or all of June, sometimes July too but other times with a dramatic collapse - which I figure are most likely to be runs where no further CCKWs or MJO cycles manage to occur this side of mid-July.
  2. The culprit here is the models suddenly latching onto a strong CCKW/MJO wave emerging in the Indian Ocean in a location that destructively interferes with the Nino base state. Sadly, the modelling of these waves has been particularly poor in the past year, for reasons unknown. It's making it near impossible to avoid occasional hiccups such as with the pattern evolution this coming Wednesday through into the following week. The eastward propagation should replace destructive with constructive interference by mid-May, with AAM recovering and the GWO resuming positive orbits, so an improving prospect during the first half of the month, especially as the effects from the final warming subside as well. The unfortunate coinciding of that FW with the CCKW/MJO awakening has served to further dramatise the collapse of fortunes starting Wednesday. This sort of variation is why the GSDM is a broad analysis and guidance tool rather than one to use for detailed forecasting. For that we need to rely on the NWP and (to some extent...) long-range models and, crucially, applying experienced judgement to them (for which the GSDM is usually very handy). Edit - a requested addition from Tamara: "We are better relying on the GSDM analysis than NWP interpretation of wind-flows as represented by the GSDM. Whole suites are prone to inaccurate reading of these signals and so any convincing apparent consensus for a solution can easily be consensus for the wrong solution." "That has already happened in the last week alone and these days I am just as cautious with ECM handling of the tropics and extra tropics as the GFS. The ECM has shown a lot of fallibility not just last winter, but through this Spring as well". Back to me again: We can see evidence of this from CFSv2 currently; it's initialised AAM is a bit too positive.
  3. Hi Matt, some good observations there and well constructed . True what you say regarding the AAM changes and increased westerly flow across the N Atlantic next week - but now, the falling phase is starting to look too brief for the Atlantic trough to push right across to the UK longitudes (thankfully, I’d you prefer it warm) before AAM cycles back around and the ridge builds back in. With the Pacific El Niño event underway, even though it’s weak, its reasonable to assume further positive AAM cycles going forward. The main uncertainty is the time spent in each phase, as the case for next week has shown. Got to rush off now - I’ll see if I can find time to expand on this later.
  4. A very insightful and at times somewhat shocking video. What hits me hardest (edging out the part about what happens after the latent heat of fusion stops being required) is the sea ice thickness plot for 8th March shown at 8:58. Compared with last year's already record low mid-March thickness, the ice away from the Canadian coasts is another 0.5 to 2.0 m thinner this year - placing a lot of it in the sub-2 m thickness category which typically fails to survive even a modest melting season. Last year with the widely 1.5 to 3.0 m thick ice, I was thinking it could be a bad one if the weather's either very warm and clear or very stormy - in the end it was neither so we lucked out. This year, I believe it'll take an unusually cloudy and calm summer to save the sub-2 m ice. Not a common combination for obvious reasons. So it seems to me that there's a high probability of going below the 2012 minimum this year - but one can't be too presumptuous given all the complex feedback mechanisms in place so I'll reserve any firm judgements until we've seen what the next few months bring. If and when we see a 'blue ocean' event with 1 mn or less square km of sea ice at minimum, we'll enter a period of fascinating but, sadly, most likely very disruptive climatic responses. Even where we're at currently, I'm seeing evidence that the Hadley Cell has strengthened with a greater incidence of unusually strong and persistent ridges at the mid-latitudes in recent years. Such as the Ridiculously Resilient Ridge that brought extreme drought to California, and the multiple runs of 2-3 weeks of HP-dominated weather across the UK during the past year or so (including the one that culminated in the record-high Feb temps for large swathes of the UK & Europe), of which there appears to be yet another in the works (starting on Monday; duration not yet certain but the trend is longer and longer!). Seasons featuring a Blue Ocean event may see the Hadley Cell strengthen even further, bringing even more resilient ridges to the mid-latitudes. There could (I must stress the speculation here; this is all based on theoretical modelling) even be a persistent poleward shift of the subtropical high pressure belt, which would shift the climate zones north with it; e.g. Mediterranean turns more like desert, and temperate (such as the UK) turns more like Mediterranean. I'm not sure how long this would take though; could be within one decade or some half a dozen. I know that in the late 90s there was a lot of buzz in the UK over climate change bringing a trend toward Mediterranean-style summers by the late 21st Century but I feel that the rates of change (due to overlooked feedbacks) were being seriously underestimated back then.
  5. Getting close to the true melting season now (after s false start a week ago), and the time to review the state of affairs with a eye to what vulnerabilities are greater or less compared to recent years. I need to allocate some time to look in detail but my initial impressions are a stronger ice situation on the Atlantic side but mostly in areas that should melt out regardless, and weaker ice on the Asian and Pacific sides - even compared to 2018 for the latter which is really saying something; there was some crazy opening of waters last week before some recovery but with the ice of course being very thin and fragile now. Given the weak Asian side ice, it’s concerning to see snow cover extent running some 1 SD below normal and with modelling suggesting little in the way of cold spells to try and turn things around within the next few weeks. Could be an exceptionally or even record early spring warmup for quite a lot of the high altitudes of Asia unless the modelling is wide of the mark.
  6. Here in the UK and also across a large part of Europe, something truly extraordinary seems to be going on now and until further notice. Seeing that magnitude of 850 hPa temperature anomaly twice in the space of a week and three times in the space of 11 days is just staggering. The 500 mb height anomalies are also very impressive, especially later next week. All assuming the 12z ECM (with the 12z GFS similar but the 06z having been more so) that forms the basis for these charts is along the right lines - but the signal is proving very strong in the modelling now that the chance of some cross-polar ridging has largely been dropped (yet again this winter). Looking for the causes of this, well it's going to be an unusual combination and I have a theory that firstly, the propagating anomalies from the strong MJO passage across the tropical Pacific are being distorted by the negative AAM anomaly at 30*N (a Nina-like feature; as discussed by Tom in recent days) that as far as I'm aware continues to resist change even in the face of an extremely strong WWB across the Central Pacific (perhaps due to the anomalies from that being focused S of the equator as Snowy Hibbo proposed), and secondly, the lack of a strong lower stratospheric vortex (it's near the LTA which is a good deal lower than it is for Dec & Jan) is providing little in the way of zonal push on the blocking high, meaning that Atlantic troughs only serve to pump it up further via warm air advection aloft. If it wasn't for the continued Nina-like interference, I expect the high-latitudes would be permitting the height rises needed to set up a powerful retrograding HLB from Scandinavia to Greenland, as is typical following MJO propagation through phases 7 & 8 with a Nino background (though given the weakness of the Nino we'd probably have seen the blocking head too far west for the UK (from a cold perspective) pretty soon - like what happened to start March last year, but probably less dramatic!). One factor I'm unsure of the role of is the QBO; does a westerly QBO at 40 mb and above have a direct ability to keep the AO more positive? I don't expect so based on what I currently know (it impacts the stratosphere's interactions with the troposphere, not the troposphere's interactions with itself) - but I could be missing some crucial information. I'm planning to read into this good and proper if and when I can make the time, but if anyone can provide a short answer to this particular question, that'd be greatly appreciated .
  7. What's this, the GEM being wheeled out...?! Ha - for a change, it shows something useful beyond a few day's range. We see the ridge make an advance northwest as a strong ridge joins forces from the Pacific, and over this way, it becomes a matter of waiting for the Euro heights to subside southward with the jet cutting across somewhere in the vicinity of the UK to meet the deep trough retrograding toward N. Europe. For the U.S. the main interest lies in what happens shortly after that, as the blocking high in theory sets up over Greenland and then retrogrades gradually further west with time. The usual nor'easter potential arises with this during 1st half of March. The ECM 00z was only a little more sharpening of the Atlantic trough away from reaching this point by D10. Meanwhile, GFS continues to be GFS and to an extent I struggle to reason with. For example, at just 5 day's range its 12z has the European high centred nearly 1000 miles south of the 12z UKMO, 12z GEM and 00z ECM runs. Curiously, it's treatment of this has barely changed despite the RRM projections for the MJO having undergone a sudden massive adjustment to fall in line with ECM/EPS. The observed MJO is very odd today though; almost identical to yesterday's. What's up with that? I can only imagine! p.s. Interesting points @Snowy Hibboregarding the positioning of the WWB - I look forward to reading your thoughts when you do share them. My existing understanding is that a WWB across the dateline is as good as it gets for producing +FTs where they can significantly affect the broader-scale patterns via weakening the subtropical highs etc, but which side of the equator the WWB is mostly on hasn't come into my analysis before .
  8. @MattHugo, There was evidence in favour of the E to W transitional QBO stage supporting SSWs occurring, but not necessarily propagating all the way downward. I believe for that we needed a predominantly wave-2 driven vortex split event, instead of the mainly wave-1 driven displacement-then-split event that we saw. Reason being that the former drives a much faster response that would likely have outpaced the descending W QBO and established major easterly flow anomalies in the troposphere. The much slower 'drip-down' nature of the event we've seen instead has allowed the W QBO to become a blockade that's kept most of the negative zonal wind anomalies in the stratosphere. I have a feeling that the manifestation for a time of a very unusual three-way vortex split right after the reversal initiation may further have impeded the downwelling by distributing the negative zonal anomalies more widely, essentially making them more diffuse. At the time of the SSW, part of the response was a cooling of the upper troposphere above the tropics, enhancing convection even where the base state doesn't support it. Alongside the negative zonal anomalies, the SSW-driven positive temperature anomalies have also been held in the lower stratosphere, keeping the upper tropical troposphere cooler than usual and allowing the convection to continue to behave in ways that don't tie in with the Nino base state (interference with the patterns the Nino base state otherwise drive being the scrambling of the tropical-extratropical processes that Tamara refers to). Climate change may have taken this even further than it would otherwise have gone via increased overall oceanic heat content, but that's a matter of debate - to me the stratospheric mishaps seem more important for this particular winter's turnout. I think we can see a good example of the interference this coming week; the neutral ENSO MJO composites (top row) fit the ECM 00z much more than the Nino ones, despite AAM and GWO observations indicating that it would usually fit more to the positive ENSO composites; GFS fits mostly the neutral P6 composite before seemingly jumping straight to something akin to the P8 neutral composite (see below, left) with little P7 response - probably due to how it stalls the MJO in P7 for a while; continued eastward propagation is needed to bring about the typical response to activity within a given phase of the RMM plots. The negative NAO-related UK cold potential for late this month and into March depends on how well we can break free of the Nina-like interference and so bring about an MJO P8 response more typical of the Nino base state. So more toward the right-hand composite than the left-hand one. Note how I'm saying 'more toward' here; the composites should never be taken too literally (ideally we'd have different ones for each possible combination of MJO phase, GWO phase and AAM tendency, but there simply aren't enough historical years of obs data to do this meaningfully!). As you can see - the temperature regime across the UK will be extremely sensitive to how much the interference gives way.
  9. Really important to bear in mind that the GSDM guides us with respect to the probability of certain patterns manifesting, which means no guarantees should there be unusual developments such as the MJO (which is one of many contributors to the GSDM) not behaving like historical guidance indicates it should. Numerous times this season, the GWO analysis has revealed us to be in a position from which a typical Nino-like MJO behaviour would serve as the launchpad for significant high-latitude blocking development, only for there to instead be Nina-like MJO behaviour, and to an extent that I believe to be unprecedented for the background state otherwise being observed. I dread the thought, but this may be a symptom of climate change; a distorting of the climate responses to certain forcing setups. We need a number more years of evidence before drawing more definite conclusions, though. As if those multiple instances of MJO disobedience weren't enough, the one time that it did behave more Nino-like, the downward 'flushing' of zonal winds as a result of the major SSW initiation served to blockade the Arctic latitudes against the strong poleward ridging. I honestly consider that to be the most unfortunate (for those who predicted and/or sought after major cold weather outbreaks) destructive interference of broad-scale weather pattern drivers that I've ever observed. Right now, we're seeing evidence that the MJO will finally be able to behave in a more Nino-like fashion, at a time when the GWO analysis puts us in a decent position to build some HLB if it does, but the models are being extremely difficult with their MJO projections; Here we see GEFS stubbornly continuing to predict that the MJO will go through another stuttering period before moving into P8 around 20th Feb. It's been shifting the stall back in time for a few days now as the observation data has instead revealed eastward propagation, so I'm sceptical that this new stuttering interlude will unfold. ECM/EPS sees no stuttering interlude so seems more credible in that respect, but I'm not sure I buy there being so much loss of amplitude in P8; there are some unusually low SSTs off the S. American coast at the moment but they only have a narrow span so I'd be surprised to see such a strong restraining effect on the tropical convection. I'm hoping to see something close to the ECM/EPS eastward propagation, with at lowest a halfway house between that model and GEFS for the amplitude. That'd be better for HLB development across the NAO region than what either of the model means currently project so we'll likely see a significant negative correction to the NAO if it comes to pass... anyone feeling lucky?
  10. This coming melting season will be of particular interest to me as unless something highly abnormal occurs in the early spring, the Arctic will head into the peak solar months with a lot less of the anomalous heat and more importantly moisture release from the oceans that has served as a negative feedback on Arctic sea ice extent and area loss by enabling more low pressure and cloud formation (while volume has still fared very poorly due to mechanical effects from increased storminess). Essentially, I’m wondering if this season will ‘do a 2012’ and so, via storminess taking until significantly later in the season to get going and so allowing much more solar-induced melt momentum (mainly via melt pools), drop to near or beyond the record low Sep minimum despite starting higher than the recent ‘norm’. In such an outcome we’d certainly see the importance of volume over extent. It could be simultaneously fascinating and horrifying... hopefully this scenario will not come to pass and the negative feedbacks will turn out to be more a result of increased mid-lat to Arctic heat and moisture transport - though arguably this would still be a bad discovery as that still means a lot of extra energy to reduce sea ice volume by mechanical action and any substantial rain events that occur.
  11. Funnily enough, the MJO projections from GEFS resemble those that preceded (having served as the trigger for) the major split SSW of last year. We're in a post-SSW residual 'dripping down anomalies' state this year so the powerful wave energy won't have a path to take into the mid-upper stratosphere this time - instead we're looking to the tropospheric response, with the possibility of some assistance to the HLB from those residual negative zonal wind anomalies descending from the stratosphere. I can see an optimal outcome for HLB where the timing of the MJO aligns fully with a drip-down of negative zonal wind anomalies across the AO region and enables an unusually large anticyclone to establish spanning most of the Arctic basin and extending down toward the mid-latitudes of the N. Atlantic and N. America in particular. That's the best-case if you like the idea of widespread exceptionally cold, snowy conditions during late winter and early spring. I reckon we're in with a shout of seeing that develop, but I wouldn't yet bet on it during what's so far been a winter of repeated timing mishaps! A more typical HLB sequence with the centre of anticyclonic action retrogressing from NE Europe to E Canada seems more probable. How fast it does that, is anyone's guess! 00z and 06z GFS runs pretty much managed to explore each end of the plausible range.
  12. Masterful post from Tamara there - if that doesn't hit the nail on the head regarding what the GSDM is and isn't to be used for, then I don't know what can! Considering that prominent divide in the EPS - I expect this has some relation to the wide spread of MJO solutions ranging from a total stall and decline (FT flips back negative, model responds by adding mid-lat westerlies which tilt the trough positive... probably with a fast bias as tropical-extratropical transfer is assumed to be more efficient than is the reality) to continued propagation with some amplitude (+FTs continue, polar jet has insufficient momentum to head E or NE without disruption, trough tilts negatively). Meanwhile GEFS are 100% keen on propagation, albeit with some interference that looks like a possible Rossby Wave passage (?). This temporary stall possibly being why GFS has started to produce some suddenly upticks in mid-lat zonal flow in the 10-16 day period? I'm encouraged - with respect to potential westward blocking advance from NE of the UK during days 5-15 of Feb - by the increase in eastward propagating EPS members today, while I'm sceptical of GEFS which behaved similarly in the last cycle only for the observed MJO to propagate rapidly eastward across P7 at modest amplitude.
  13. Some weird and wonderful scenarios appearing in the modelling as they come to terms with the strat. downwell interacting with an improving, but not yet certain tropical picture. ECM's being persistently difficult with the N. Atlantic sector though; every trough crossing is kept broader and better-structured than the other modelling indicates. I miss the days when it used to jump at every opportunity to disrupt them and send lows sliding away .
  14. Brilliant insight Tom (@Isotherm), I'd not really thought about the divergence independently of the MJO cycle in that manner. You sound very confident that it will subside and I can see why given the model guidance at hand. This raises the obvious question - how come the models aren't showing much of a negative NAO response despite seeing the subsidence of the upper divergence? Perhaps it's a parameterization issue (yep, I actually used a z there!) preventing the required propagation processes from unfolding properly? Prospects become very interesting for NW Europe once suppression of the subtropical high is factored in... some chance of a cut-off high to our NW while blocking out east also tries to get in on the act? Possibly I'm getting ahead of myself there but with all the troubles of late I feel like thinking a bit more positively for a change!
  15. In light of Tam's insightful discussion of the Nino disconnect, perhaps there are some encouraging signs here for a relaxation of that during the final days of the month; the MJO progress east has trended faster and further, and the MJO-unfriendly trade wind burst has been weakened and even brought to an apparent end on Jan 28th. The disconnect has proved very troublesome for longer-range guidance, because it's not a steady phenomenon and as such it's not possible to assume a certain amount of adjustment to what the dynamical and statistical tools are indicating should take place. This being why the talk of 'potential' has been even more strenuous than usual; we know very well what could happen if the disconnect cuts us a break, but can't reliably anticipate whether it will or not and hence whether things will work out fine or go awry with respect to bringing the weather patterns that the majority on the weather forums seek. I've learned quite a bit from how things have panned out so far this winter. Biggest of all is the nature of 'diffuse' stratospheric downwelling following a predominantly wave-1 forced split; that unlike the faster, more aggressive variant forced by a true wave-2 split, it doesn't just smash down the door and come roaring in, instead knocking politely and requesting that the tropospheric occupants be kind enough to let it in. The NWP models are struggling to pin down if and when the opening of the door will take place, which I believe is why the zonal mean for the lowest layers of the atmosphere keeps fluctuating wildly between runs. There's also the added complication of regional downwelling, which is kind of like the reversal-induced anomalies reaching an arm in through the window... or something like that! It's a shame that I've had professional guidance at stake this winter, as it's offset the fascinating scientific aspect with a mounting sense of frustration and being so unable to provide confident guidance and seeing even the most cautious of outlooks struggle to look good because in the end, you have to come down on one side of the fence, as few will appreciate just sitting on top of it and saying 'sorry, too much conflict of signals, we'll just have to wait and see!'
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