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Shuttler

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  1. I don't see much downwelling of lower heights from the Upper Strat in the past 3 months or so. Compared to earlier this year for example, as is fairly evident I think from the time series plot. Just trying to understand what causing the perpetual positive GpH in the lower Strat and Trop (and Arctic blocking) since Sept.
  2. Hi. Can the more learned on this forum possibly explain why the Trop and lower Strat has been so de-coupled from the Upper Strat since Sept ? And set to continue for much of Dec by the looks of latest Ens and weekly fcasts (ECM46). I expect phases of this but it seems unusual to see such longevity in the winter half of the year. I'm trying to understand what may be driving the perpetual Arctic blocking and -AO signature in the absence of any sig downwelling from the upper Strat. Are we looking at a greater influence from the reduced Arctic sea ice or SAI this season, perhaps ? I do wonder if a split SSW (as I'm expecting this Jan) would break the Strat-Trop de-coupling we're currently seeing, though of course this is likely to induce further Arctic blocking for the second half of the winter. Any suggestions appreciated - with the ultimate aim of improving seasonal guidance !
  3. Sorry, didn't mean to post this here - please delete topic
  4. Hi. Can the more learned on this forum possibly explain why the Trop and lower Strat has been so de-coupled from the Upper Strat since Sept ? And set to continue for much of Dec by the looks of latest Ens and weekly fcasts (ECM46). I expect phases of this but it seems unusual to see such longevity in the winter half of the year. I'm trying to understand what may be driving the perpetual Arctic blocking and -AO signature in the absence of any sig downwelling from the upper Strat. Are we looking at a greater influence from the reduced Arctic sea ice or SAI this season, perhaps ? I do wonder if a split SSW (as I'm expecting this Jan) would break the Strat-Trop de-coupling we're currently seeing, though of course this is likely to induce further Arctic blocking for the second half of the winter. Any suggestions appreciated - with the ultimate aim of improving seasonal guidance !
  5. Shuttler

    Model Output Discussion 18z 28/07/13

    Latest 00z Ensemble Mean output for days11-15 (23-27 Aug) confirms the likelihood of High pressure dominance, and as we stand centred close to the UK & NW Europe. Breaking it down into individual days for each model suggests this will run throughout the period, indeed the transition point to this pattern seems to commence around the 20th. There is also a consensus on above average temps through this period, though anomalies (both 850 and sfc) are not great, around +1 to +2C overall. So, yes we seems to be heading into a drier, lighter wind and very pleasant possibly sunny phase for the latter third of Aug, but at this stage not a major heatwave.
  6. Hi, I am wondering if the current supremely negative AO (including the outlook for the next 2 weeks+), HLB and the relative mid-latitude cold (including much of Europe), is a continued hangover from the SSW we had in early Jan, and the resultant displacement/split of the PV ? It looks to me like to Strat PV has returned to a nearer normal state, and with downwelling this may have brought us a greater incidence of +AO by now. Or, is the negative pattern more of a response to MJO Phase 7 or 8 ? Just trying to understand the possible driver of this pattern. Thx
  7. I'm sure you'll be pleased to hear: the ECM Ens 240-360h is not as bullish as the weekend models, which were returning a re-intensifying PV polewards. The latest run has back-tracked to a large extent, and now maintains a split vortex (in the mid-upper strat) with centres of action in the vicinity of Canada, as well as close to Siberia, and polar ridging from both the Pacific and Atlantic sides, albeit weaker than currently. There also appears to be further warming from the Canadian sector into the polar region, totally oposite to previous. The GFS Ens output at this timescale does something very similar, with both vortex centres in a similar position and also in a very weakened state. This adds weight to the expectation of no rapid return to 'normality' in the near future, and as picked up by last nights ECM 32dayer, which maintains the negative pattern and Greenland blocking through to first week of Feb, and relative cold/spells of snow for UK and much of central/northern Europe throughout.
  8. I only see the Ens mean for a couple of levels, namely 10 and 50mb. I'm pretty sure full subscribers to the ECM output can get to see each individual Ens member, as well as Ensemble clusters. It would be fantastic to see this, including the control run and Ensemble spread, as I see for the tropospheric output. Now, regarding the accuracy: the Ens forecast from 15days ago nailed the current situation extremely well i.e. splitting vortex with centres over Canada and Siberia. And also got the SSW timing spot on. Will be interesting to see which of the GFS or ECM will be closer to eventuality in 15 or so days time. I've done very little verification of the ECM Ens at these timescales, so can't vouch for reliability against the GFS Finally, a strange and probably very obvious question, but can someone tell me what 'FI' is short for. I've got a rough idea, but can't put the words to the acronym !? Got to get this off my chest.....!
  9. The ECM Ens for 240-360h declines the cross-polar ridging, allowing the more intense PV over Canada to gradually edge back towards the pole, though by 360h (21st) it's not quite pole-centric. This would seem more likely going into the last week of the month. The split part of the PV over Siberia gradually loses its identity. Polar temperatures at say 10mb are back below seasonal norm in this period, with no evidence of any further upper strat warmings. Just want to add my congrats to all involved in this superb, informative thread....
  10. I only see data for a couple of fixed levels from the ECM Ens, namely 10 and 50mb. I can't answer your query, but have quizzed my sources and will come back if/when I have an answer. For information, the ECM Ens at the 10 and 50mb levels between 240 and 360h maintains a split PV in pretty much the same locations as the op at T240 i.e. Hudson Bay and Siberia, with no great re-location in this time frame. We therefore see the Polar High extending through from the Aleutians to Greenland/Iceland throughout.
  11. This doesn't tie in with the GFS Ens mean at this point, which maintains a displaced vortex N.Russia, and closer to expectations. Also, the warming moving through the China/siberian sector is too aggressive. You can never rule this scenario out, but seems unlikely at present.
  12. Sorry, meant since 00z Wed 19th............!
  13. Has been a consistent pattern for the last 3 ECM Ensemble runs, since 00z Tue 19th. Bear in mind it's developing towards the end of the run, so can't really check before that. I suspect there is a marked drop off in accuracy and consistency of the GFS strat forecasts, be good to see some verification if anyone has a useful link. ECM Ensemble mean less prone to swings between runs as you'd expect, but of course a more muted output at this timescale.
  14. To repeat, no splitting of the PV on the ECM Ens 240-360h, but maintains it's position (at 10hPa) close to Novaya Zemyla throughout. There is a pulse of warming over Siberia in the Upper Strat by Christmas Day as we all know, but it seems a second and more enhanced pulse of warming develops over Siberia in this period and moves to the pole by 360h. It looks to me as if this could be the killer blow, coming in shortly after (and thereby tying in with a possible SSW around 10th, as has been suggested). Still time to change, though ! Incidentally, the GFS Ensemble mean out to T384 does nothing of the sort, maintaining a strong but still displaced PV in a similar area, and no warming close to the pole - 10hPa temp anomalies of -12 to -18C in/around the pole at T384. This contradicts some of the Hires output. This begs the question - how reliable is some of the GFS HiRes output at this timescale, I've never really verified it. Should we be making greater use of Ensemble mean beyond say T240 ? Certainly if the experience of using the tropospheric output is anything to go by - though I doubt Strat forecast can be as volatile as this !
  15. The ECM Ens mean for 240-360h has a very stretched PV (at 10hPa) from northern Scandi to northern Siberia, before re-intensifying into a more focussed vortex over central Siberia. In this period the upper strat warming (evident at 10-30hPa) over Siberia remains there, rather than propogating to the pole as per the Hi-Res GFS, and actually weakens slightly in situ in terms of anomalies. In fact over the Pole itself temperatures in the Upper Strat are stable or even cool slightly, with no major warming evident here. Meanwhile, the canadian warming mainly evident at 50-100hPa intensifies in this period, with marked height rises becoming focussed on northern Canada.
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