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  1. Singularity

    [Global] Teleconnections: A Technical Discussion

    Nice one Tams From today's model trends it appears GFS has been playing catch-up on the following: ...and it may still be doing so with respect to the regional stratospheric impacts N and NE of the UK, depending on whether ECM/EPS are right to keep producing that interaction. Given the known bias to overdo the thermal wind (jet stream) response to temp gradients, I can see how even slight shortfalls in the Canadian vortex retrogression (and sharpening up) lead to a vigorous positive feedback of progressiveness as the cold air interacts more with the N. Atlantic and the jet angle steers the resulting systems more E than N. With a weaker jet stream, even intense surface LPs move more N than E and amplify instead of flatten the downstream (N. Atlantic) ridge. Tomorrow looks to be another really interesting day or model watching, one way or another. Better odds on a positive way this time .
  2. Singularity

    [Global] Teleconnections: A Technical Discussion

    I've been trying to understand what the likes of GFS, FV3 and GEM are up to with the Canadian lobe in the troposphere... in stark contrast to ECM and to a lesser extent UKMO which both follow anticipated trends with time very nicely (well, ECM maybe a bit fast?), they're somehow managing to keep it very dominant with not much in the way of Arctic highs to disrupt it. While I know they're inferior for stratosphere-troposphere impact modelling, I didn't think it was as bad as it currently appears to be - but with this in mind I wonder why they intensify the Canadian lobe so much - are they simply overcooking the response to deep cold being transported to that area by the temporary Asia-N. America cross-polar ridge alignment? The knock-on effect is to flatten the N. Atlantic pattern more so it's really making a mess of their modelling! Any thoughts on this much appreciated.
  3. Possible SMR (Sudden Model Response) to the downwelling with the EPS 12z suite. Tomorrow will either be distractedly exciting, or deliver another pendulum swing back toward a more gradual establishment of the mid-Atlantic-Scandinavia ridging and European trough combo, in which case I expect you'll be able to hear the toy throwing on the other site from here while those that see the wood for the trees roll their eyes for the umpteenth time this winter .
  4. Singularity

    [Global] Teleconnections: A Technical Discussion

    Hi @33andrain - true that they've got the diving trough across the eastern US, but it's not as sharp (i.e. narrow in west-east span of low heights) as it ought to be - though EPS is arguably still pretty close. The effect is more pronounced for NW Europe as you can see when comparing the three anomaly maps you've shared. Also looking for a stronger HLB signal emerging over the Arctic by the final days of the month; too many ensemble members not really going for this yet hence the mean +ve anomaly is a bit faint.
  5. Singularity

    [Global] Teleconnections: A Technical Discussion

    Modelling seems to have lost what solidarity it had on the Pacific-Atlantic pattern sharpening up 22nd+, hopefully this is just model shortfalls as opposed to actual ones being picked up on. Another cause of uncertainty is present for NW Europe, as there's little consistency with respect to how much the positive GPH anomalies just N and NE of the UK are able to work down from the lower stratosphere and, D8-D10, disrupt the incoming major trough associated with the polar vortex drain out of Canada.
  6. Singularity

    [Global] Teleconnections: A Technical Discussion

    IMO that's going to be a candidate for 'post of the year' 2019 @Isotherm . The where we've gone and where we're going one I mean, not the follow-ups, as great as they are . I've been watching the MJO projections like a hawk looking for the twitch out of the COD into phase 6 and eastward scuttling thereafter. So to speak! Could be a classic case of 'third time's the charm' when at last much is pointing in the right direction. I'm unsure about the MJO role for the U.S. though; looking at P7 composites both with and without a +ENSO background, I see a positive PDO pattern - not conducive to cold across the U.S. in general - but it sounds like you're anticipating that modification by a well-timed surge in AAM and interaction with the SSW forcing will push things toward more of a +PNA-like pattern across the Mid Atlantic and NE States? Meanwhile on this side of the Atlantic, the largest cause of uncertainty has become how far west or east the -ve NAO pattern sets up. Odds are it will start more east and then retrogress with time, but how far east it begins and how fast it retrogresses, well those are the million-dollar questions. There's an impressively strong signal for well below-normal heights over mainland Europe though, with signs that Arctic fair may continue to find its way down across the UK until quite a way through the retrogression process, due to the positioning of the vortex lobe across N. Asia. It's about as good as it gets over here for producing unusually large amounts of snow, provided there's not too much maritime air getting mixed in (except on high ground when this can just mean even larger falls of snow!).
  7. 2013 may be the closest historical reference we have in that it was a displacement-split hybrid, though this year's event looks notably stronger. Reversal troposphere landing zone narrowing in on some day in the range 19th-22nd Jan.
  8. The secondary warming is a very interesting phenomenon to see given the downward propagation already underway; as I understand it, the downwell mechanism from split events usually reduces the capacity of troposphere-stratosphere energy transfers to penetrate the polar vortex, but if a residual vortex is positioned in the right place it can enable some entrainment of stratospheric warming via its own miniature surf zone, which is what we're seeing projected for the N. Asian / Siberian vortex. This allows that warming to progress far enough to drive significant geopotential height rises above the polar regions. In this case, that should sustain or even further-widen the split of the vortex. The latter makes things very interesting for NW Europe but, I gather, those in the western and perhaps central U.S. should be hoping that the residual vortex over the W. Hemisphere doesn't head all the way across to the West U.S. region as that could increase the westerly flow off the Pacific and impede blocking formations west of the area affected by the negative NAO pattern that would likely be strongly in place across the N. Atlantic. I believe a stall of that vortex somewhere over the Mid-Atlantic states would be the optimal location for both sides of the pond to experience some noteworthy winter weather.
  9. It's really something watching in the GFS runs the tropically-forced troposphere-stratosphere wave breaks reinforce the anomalous stratospheric ridge in the lower and mid-stratosphere, causing the split to widen further in the 12-16 day range. Still a bit far off for reliability, but it makes a lot of sense for that to happen given MJO expectations. I expect EPS are lacking in this regard what with the surprisingly quick decay of the MJO that they are now projecting.
  10. Singularity

    [Global] Teleconnections: A Technical Discussion

    Brilliant work by Tom and Zac (as usual!). There's some humorous/tragic irony (depending on what forecasts you had at stake!) to be found in the way that Dec, in particular the festive portion of the month, has been effectively sacrificed in exchange for improved prospects for Jan. The sustained MJO amplitude through 4-5 has indeed been surprising (for a Nino background) and it's trashed my predictions of a markedly colder final third to the month here in the UK, though it has at least become more settled and cooler. While I've been expecting Jan to be the main cold month since mid-Nov, there was uncertainty over how much it would deliver in absolute terms and I wondered if it would really amount to much HLB-wise. The way things are actually panning out is almost as good as could have been hoped, SSW notwithstanding (if that downwells fully, it'll be optimal!). Hints in the 12z ECM of yesterday of the reversal making its way down to the lower stratosphere, albeit a bit tenuous with near-neutral rather than negative anomalies on D10. Not heard anything on the 00z of today; been out and about. Trying to avoid being as involved as usual in matters - got to cool my brain off sometime - but the unusual events taking place are making that kind of tricky!
  11. Always worth bearing in mind that these are still just model projections for the downwelling, and compared to what they can do otherwise, they're not very good at it. Even ECM/EPS has its limitations in that respect, and I'm talking about as soon as 5 day's range. Admittedly I'm basing this on past experience rather than published scientific material, but it's served me well in recent years. I also believe, as several others do on here, that the tropical contribution isn't yet being resolved at its true magnitude; the troposphere may well be more 'welcoming' to negative zonal wind anomalies than the models currently assume.
  12. Singularity

    [Global] Teleconnections: A Technical Discussion

    Sensational round-up there Tams These atmospheric swings are practically violent in nature. It's no wonder that the models are struggling so much; they're predisposed against rapid fluctuations as usually that's part of modelling error; it's actively constrained. Not only that but over the past decade I've gained a strong impression that even with slower-paced developments such as the MJO propagation, they tend to give the current atmospheric state too much staying power in the face of changing tropical or stratospheric forcing. For the final days of Dec onward we've got both happening at once. I look forward to the time that the models really catch on. EPS already look to be in the right ballpark but there's a good chance their consensus will have some adjusting forward in time to do with respect to cold-conducive weather patterns, as the MJO amplitude across the Pacific adjusts upward; currently they fit a scenario of slow P6 traversal (favours for example strong UK-based ridges trying to extend NW and having increasing amounts of success as the MJO closes in on P7) dominating the pattern out to about a week into the month, then the lagged component of the SSW impacts either taking over or joining forces with the MJO moving through P7 (i.e. there's a mix of those two scenarios in the ensemble range; some are strong in P7 but others decay the MJO away). James
  13. Singularity

    [Global] Teleconnections: A Technical Discussion

    First 10-14 days MJO-driven with some quick response negative AO adjustments (more poleward ridging than usual) provided we get a split on the ECM timescale not GFS (which is about a week slower to get there, or doesn't manage to at all, depending on which run you look at), then remainder of Jan mostly SSW-driven. The quick response as part of split events seems highly disagreed upon on 33ar. For what it's worth, I've long believed it to be a fundamental feature of split events that sets them apart from displacements (alongside the more prolonged lagged effects).
  14. Must be all those Xmas dinners; that's a lot of oven heat at once escaping into the atmosphere . GFS & GEFS still wobbling about, though I'm getting conflicting analysis from different sources. I can see that even when it has the split, it's not getting the two vortexes as far apart as other guidance, so this is probably why some are more negative about it than others; good separation is needed for them to truly be divided from one another with the anomalous ridge able to muscle in between and bring about impressive tropospheric responses.
  15. There's a reason why my virtual bin content is 90% GFS charts . Let's see if it can manage to propagate the response down into the troposphere for early Jan. I believe that major split events always (or at least, almost always... some disagreement occurs when comparing various reanalysis data) bring a quick (within +1 week of peak reversal) response mainly focused on the AO region but modifying any trop-driven poleward ridges in interesting ways, followed by a temporary relaxation, before lagged response kicks in by +2 weeks from peak reversal. So I'm really looking out for tropospheric developments in the model charts covering the first 7-10 days of Jan (allowing for wiggle room on peak reversal timing).