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Catacol

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  1. Another great post Tamara - and I personally like (from a ego perspective) that I have reached a stage where every paragraph you write makes sense to me. There was once a time when I'd get lost..... The chunk above I think is interesting. I don't think many of the enthusiastic amateurs who have tried to make sense of the current winter forecast feel the signals are broken. There is, without doubt, a core of people who are desperate to know "when will it snow" and get frustrated by their own lack of understanding....and like the Luddites then throw bricks at the machines. But taking those with a love of learning (and in winter a particular bias towards snow from many) I think the frustration is the fact that we know we cannot yet read these signals well enough to produce a forecast sufficiently accurate to make good micro forecasts. I'm not sure if that will ever come - we will always be dealing in probabilities....but the probabilities did seem weighted towards a more blocked pattern this season (and maybe there will be one last hurrah for the NW Europe brigade despite the downgrading long range forecasts from the UKMO) and the destructive forcings that have impacted on the SSW/Pacific combo were not spotted. Here in Europe we have the top performing global model in the ECM and its EC46 partner - and it bust the forecast quite badly. UKMO experts also got it wrong. The post match analysis will indeed be really worthwhile because we must try to know more in an effort to translate the GSDM into something that can provide some microscale accuracy. So - the signals were not "broken" - we just didn't translate them correctly. My skillset is in history, and historians argue constantly about the "correct" reading of evidence from past events. The evidence is there in front of us - but mapping it out accurately remains something beyond the wit of any computer or brain currently. Side question - was there a forecast anywhere that correctly matched state of the QBO with the downwell as has occurred and lack of MJO success in forcing the pattern? It would be interesting to know if anyone anywhere got those relationships close to what has occurred so far. As a snow hunter I'm hoping to see that Siberian retrogress as you mention - but I've lost confidence in constructive signals this season creating coherent impacts. I can see modelling toying with it - but that Canadian energy centre seems intent on disrupting any heights over Greenland or further east. Maybe we need to factor SSTs in more closely - I have rather begun to ignore atlantic SSTs and the temperature gradient with a cold east US, and that may prove to have been a fairly major error in the micro pattern post match analysis.
  2. That ties pretty much exactly with the thoughts of a UKMO expert who has taken to twitter and makes some pretty good thoughtful statements. In his view the strength of the SSW has so perturbed the trop that MJO impacts cannot be properly felt. Lack of that "stable" pattern. In this context the position of vortex shards I would assume has become all important, and unfortunately for the UK one section of the disrupted vortex has pretty much sat of Canada for most of the winter....preventing effective height rises around Greenland and consequent neutral to +NAO. For a while there was a signal suggesting it might retrogress back towards the pacific - but it didn't effectively enough. And without effective MJO support - no change. UK now left with a very average winter after such early promise. Ah well - live and learn. There is so much I want to learn about all this - and I know the learning is happening.....but trouble is - the more you grasp the more you realise there is still left to grasp!
  3. Big thanks - that's what I love about this thready - it's full of learning. This chunk above has given me a focus for the months ahead - I dont know enough about QBO impacts and I certainly dont know enough about relative temperatures of tropical and polar stratospheres (linked I guess to the BDC) and so my own sense of the winter has been off. And observationally the staccato nature of events that you intimate here ties in precisely. I have watched charts day after day show the AH try and ridge north only to be blocked by energy coming from Canada across the north atlantic, and the ridge never getting the sustained shove needed despite good looking momentum and torque cycles in a background Nino state. The MJO has also behaved erratically (though to be honest when doesnt it??) - and this ties in again. The speed of propagation through 6 - 7 - 8 earlier in January was particularly startling....... Whether NW Europe ends up with a taste of winter or not this year, I'll be back for the next season a bit wiser thanks to theories like this.
  4. That's intriguing. I wouldn't want to probe into your methodologies too far, but something readable about the harmony between trop and strat preventing -NAO would be gladly received if you have it. Reading on Solar I've got, Here's hoping that solidly negative February is just around the corner.....
  5. Perhaps David - and this is the signal that has been seen coming all winter. Furtado still confident of a -NAO signature....and MJO, GLAAM and impacts of vortex disruption have all looked aligned at some stage to bring a block into being over the North Atlantic that will act as a trigger for the start of winter... ..BUT we are still looking at an EPS ensemble forecast that refuses to turn the NAO away from a positive state and is now building heights down into SE Europe as the trough fades and pressure also rises over the UK. Not reading the script at all. Frustration would be an understatement if cold is what you want to see in winter and the UK is where you live. I know this thread is not a cold hunting one, so important not to skew it into one....but for me - as the clock ticks and the pattern continues to play hard ball - the lessons that may be learned from a winter that has refused to create the expected long wave pattern over the north atlantic will be huge, And to ask a question here I've asked elsewhere - why has a -NAO signature become so rare in recent years?
  6. Thanks Armando. I can visualise the process now. Some follow up - given the impacts you describe of a WWB caused by MJO convection, is a lagged easterly response therefore an inevitability? I note from the Hovmoller plot that the WWB in late December was paralleled at the time by a trade surge....and yet the big burst of early January didn't get an instant response - lagged by 2 weeks? I guess I'm asking to what extent we can predict destructive interference to the base state and to what extent it is an individual process unique to each burst. Torque cycles, frictional to mountain then to increased GLAAM have a cyclical relationship that ebbs and flows with a sense of predictability. Is there any such pattern to a destructive response to a WWB?
  7. Hello Tom I'm a few days behind - but that was a great read a page back. One of those moments where, as an ongoing enthusiastic learner, I know I've advanced a bit further down the road to understanding. I've picked out the bit above that made me stop and stare the longest....and I'm still trying to get my head around this. The propensity for upper divergence - no problem. But I'm struggling on the disruption to typical Nino forcing through increased trades. Can you walk me through that like i'm an idiot? Lowering of tropical momentum as a mechanism for upsetting expected Nino actions and depositing positive forcing on high latitude regions I can conceptualise fine too.....but how does convective generation create increased trades in this scenario? And what does it look like on the plots? Is this a disruptive impact that we can hope to predict in advance, or is it a case of one of those oft-described "disconnects" that, to me, feel like moments where the science doesn't work and expectations fall flat....so we just call it disconnected. Edge of knowledge envelope most definitely reached - but want to grow that envelope. An answer to my question here might go a long way to providing a solution to the ongoing conundrum of a winter that, so far, hasn't quite panned out as expected - certainly not in terms of timescales anyway.
  8. Genuine musing as posters in another place get increasingly frenzied at the lack of -NAO and the resilience of a troughing pattern coming east out of Canada that is either preventing the formation of Greenland blocking or benefitting from the failure of the blocking signal to translate into any action. Mid atlantic ridge just sitting tight as it has approximately for a long time now. A lot of evidence continues to point to a -AO on the back of the SSW downwell and a high amp pattern that should see pressure rise somewhere in the greeny to scandy corridor.....but I'm just beginning to wonder if the constant pushing back of the beginning of this pattern is telling us something we should be listening to. i'm out of my knowledge base in explaining it as so far this winter every moment of expected amplification after November has ended up with a limp product, and while Europe now slips under the influence of a trough that is setting up a long way south, implying strong amplification, the accompanying ridge just doesn't want to bounce. Any thoughts here would be useful. I popped out a few twitter messages yesterday to some of the main US weather gurus and got a reply from one saying effectively all good - no change... - NAO on the way. But assertion isn't argument and the silence is beginning to become deafening in some quarters as to just what is making a -NAO signature so very difficult to achieve in the recent past. Without digging out the stats the number of -NAO months in recent months has been extremely small. Anyone got thoughts?
  9. Really good and interesting post Tamara - enjoyed it very much. I've cut and pasted some bits by way of some follow up discussion - I'd value your thoughts... 1. Timing. Agree 100% that timing has been an issue this season so far - with signals in place and being pushed back. And not for the first time to be honest - in previous years we have seen timings pushed back and processes slowed. The only exception I can think of immediately would be the very swift end to the "Beast" of March this year where extraordinary processes led to such a swift retrogression of the block that warm air undercut our late winter UK cold much faster than anyone, including the Met, predicted. Ignoring that example as an example of really unusual conditions is there any thought as to why timescales tend to run longer than expected, and why NWP is often too progressive with signal reading? Is this just a bias we need to absorb, or are there physical processes within GSDM modelling that arise frequently to jam the spanner into the wheel? I'm happy to accept bias if that is all it is....but wondered if you have any insight into the physical processes going on. 2. Paras 2 and 6. I also see a disconnect in terms of sub tropical mid latitude ridges - but am also very aware of higher than expected GLAAM readings for the season as a whole so far - and have posted about this before. Given what you neatly describe as a "pre-amplified pattern" what is your reading of the impact of this pre-amplification....and do you think it has any impact on the apparent mid lat disconnect we are seeing? Has pre loading of the atmospheric AAM served to boost the Hadley Cell by impacting significantly just north of 30N? I cant quite conceptualise the overall impact of this pre amplification - and being a visual learner of less than average scientific knowledge but quite sharp visual/conceptual understanding I need to get a handle on a process before I can interpret it! 3. NOAA have posted that the MJO slowed down as it interacted with rossby wave activity - relates to para 3. I'm struggling here. I thought that MJO activity initiated much of rossby activity in the first place....but their pdf post recently suggests they are mutually exclusive and this activity has interfered with the forecast. From where does rossby activity originate if not from MJO passage - and why would it slow progress down? Just more model bias?? 4. Parallels with 2013 are really interesting. Funnily enough I was just running this site linked to me by Singularity that shows the 2013 split...and thinking that it looks much like the one we have coming. Very similar around Jan 9 http://birner.atmos.colostate.edu/SSW-animations/anim-PV/2012-2013_530K/loop.html - and the same wQBO label too for that year. Sebastiaan over on Netweather has noted that the majority of split vortex events in wQBO years tend not to downwell. In 2013, however, we got the downwell. Or....was it actually more of a tropospheric "sandwich" - with upwelling impacts caused by the 5 - 8 GWO orbit impacting on the trop which was simultaneously being harangued from above...and ultimately is the success of any downwelling SSW all about timing between strat and pacific? Which puts us back, once again to timing. My current bugbear. My own thoughts for this season have panned out not too bad - but timing is a problem. I notice you also referenced my little pet issue of "seasonal wavelengths" - a topic I've asked several people about on more than one occasion and never had a concise and punchy answer as to what these wavelength transitions/processes are and why. If you have guidance there I'd be glad of it. Keep up the great work - very thought provoking.
  10. It's only 12th December and there is a way to go on this one yet. I don't have all the archive data - how many times (if ever?) has a wave 1 warming attack done enough to shatter the vortex? The flux charts posted by Amy Butler tonight certainly suggest a high level of heat about to strike at this already weakening vortex....but is a wave 2 setup a necessary precursor to destruction? Maybe early January. I've seen that suggested by Chio...
  11. Big question for me is whether we can get a second bout of wave 2 impact. A split is certainly better for overall winter synoptics than a displacement - and current extended modelling isn't picking up further wave 2 potential. Will the Siberian one sided punch be enough to take this weakened vortex down? Or do we end up with a very stretched and distressed vortex over the atlantic, but still intact? Big difference in tropospheric impacts down the line....
  12. Sorry for the slow reply Matt - was hoping we'd get some updated files from GSDM to show what I think is about to happen vv 30N and 60N - but in essence: yes.... when there is a jet surge at 30N AAN has to balance itself out and there is a consequent fall in AAM up towards 60N. If you look right across that chart you posted the oranges are almost always balanced by greens and purples to the north - that balancing of the AAM budget. Right now we are seeing the jet extend and when we get our next GSDM update I'm pretty sure we will see an ongoing increase in MT at 30N. This will almost certainly be matched with a decrease at 60N. The increased resilience of the Scandy High in the next few days maybe more than just hocus pocus and natural "resistance" of the block - the atlantic is gradually having the rug pulled from under it...
  13. JMA MJO composites here.... easy to use. http://ds.data.jma.go.jp/tcc/tcc/products/clisys/mjo/composite.html
  14. Hehe - that's as close to a winter ramp style post as I've seen from you Tamara... Eyes firmly fixed on mountain torque to start - looks to me like the forthcoming spike in AAM driven my MT could be quite steep judging by forecast pressure anomalies over Rockies/Himalayas. GSDM from there fairly predictable as you point out. The tricky bit is knowing how the vortex shake down is going to look. Much harder at the moment to get a handle on this into January. On its knees it may be - but whether it splits or not will be important as to specific weather patterns to follow.
  15. We will wait and see whether the high declines significantly - I suspect NWP might be a bit over progressive, but given that we wont see the impact of the next frictonal/mountain torque cycle hit until after the 15th (probably more like the 18th I reckon) then a waning of some kind was always likely. Progression of the MJO back through the IO is going to be important, particularly if the magnitude of that signal is as significant as some data is suggesting. It will provide the extra oomph on top of a NH pattern still predisposed to potential blocking thanks to the ongoing impact of GLAAM to maintain high lat blocking longer term. Superimposed on top of the long term impacts of the SH/AL combination and the end of December into January looks very interesting. The rate of decline in relative AAM has certainly been steep in recent days. To be honest though it probably had to be. AAM had reached such significantly high levels that they could not be sustained - and like an elastic band stretched hard the ping back has been strong. Relative momentum between earth and atmosphere constantly tries to equalise, and when momentum at 30N falls away sharply it has the impact of increasing momentum via poleward momentum transport at 55/60N. So - we see some extra energy in the atlantic now precisely because the drop back at 30N has been so steep. At least that is my understanding of one of the complex mechanisms at work here. Likewise - when torque is fully reengaged according to fairly predictable cycles we will see a rise in momentum at 30N and consequently less of an atmospheric signal across the north atlantic for a trough aimed straight at the UK. The atmosphere will once again be predisposed to a more meridional look and blocking returning. See also MJO signal reemerging on top. And if that torque includes an east asian element which looks likely, then the extension of the pacific jet serves to force eddies both equatorward and poleward as it passes through, also helping to reinforce that meridional effect and possibly introduce a signal for retrogression (never read that....but it is my interpretation.) So - to conclude. And this is purely my own take on it, and not grounded in extensive knowledge of atmospheric physics because I am not a physicist. GLAAM was high and under lowering pacific wave and lowering torques has pinged back, noticeably at 30N. This has injected energy at 55/60N while torques remain low and the next pacific wave reforms. So - the Scandy High will come under pressure, though it may hang around long enough to benefit from the next torque cycle that has already begun in terms of frictionals, and will soon see mountain elements emerge. Cue extension of pacific jet forcing with accompanying eddies, and cue also a fall in momentum at 55/60 which will promote less of a westerly pattern. So - sometime around 18-20 Dec a blocking signal strengthens once again. Reemergence of the next pacific wave will reenergise the nature of that pattern and further reinforce blocks in place. Impacts of any vortex disintegration then to sit on top of this in the New Year - but that is too far ahead to get my small brain around. Where might blocking sit? This is my own area of greatest frustration, because I struggle to conceptualise the process. Others are wrapped in data and composites - I need to visualise a process to understand it. I have asked questions about the impact of various patterns on the exact position of the wave pattern and never received an answer that has made my puzzlement go away. I have read of "seasonal wavelengths" - but again never had a clear answer to what that means. So - my best guess would be a reemergence of a Scandy high with a signal for retrogression if we get the jet extension - but none of this is grounded in any certainty because I cannot get a clear visual model in my head. It could quite easily by a mid atlantic high on that basis, or maybe a UK high. But my gut, and best sense of where the pattern will sit when torques reengage, says Scandy once again. I am an enthusiastic amateur and not a qualified Met like you - so please take my analysis as both potentially imperfect and certainly not intended to be anything close to patronising!!
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