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Mike Poole

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Mike Poole last won the day on February 15

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  1. WYorksWeather Interesting SST anomalies there. I would say there is some work to do to get into a good position for summer from there. I am expecting an abrupt change to warm/hot weather to manifest itself at some point, but I would not expect it before the last third of April. The reason I say this is due to the SSW, with a signficant reversal of winds in the stratosphere providing some continuing influence as the effect continues to downwell - the renewed westerlies predicted above at 10hPa will act to force this and we probably have to wait it out before the more benign spring patterns can take effect. By that time the sun will be much stronger, and, as I say, an abrupt change is possible - at which point the SST pattern should start to change as well. So spring very much a slow burner this year, which is in contrast to the years when the strat vortex merely peters out into the final warming without a late SSW, and spring patterns can take hold much earlier.
  2. I think a UK high as per GFS 12z around the 8-9 day mark is one plausible evolution, but it is as part of a transition towards blocking further north later as the effects of the SSW start to have some impact, so if it happens I don’t think it will herald the start of a proper settled spell unfortunately. And there are other plausible evolutions that don’t have the high pressure go through the UK anyway.
  3. It is a fair question. The evolution up to and after a SSW seems to be predictable on a much longer timeframe than other things affecting our weather in the winter. And when that includes snow for us at some point during that evolution, everyone is interested to discuss it! But in recent years, BFTE18 excepted, there have been interesting evolutions in the stratosphere but they have done nothing to halt the run of diabolically poor winters. This year, the strat has been absolutely fascinating, and quite different to many recent years, and yet it has done nothing to help promote any decent cold spell here. It is far too soon to say whether this has just been down to bad luck, or whether the bar to clear to provide the forcing necessary to get blocking in the right place is now getting so high with climate change that SSWs are going the way of favourable MJO phases - i.e. just don’t seem to deliver any more. Time will tell… summer blizzard I agree. It looks to me like there is perhaps more of a signal for some high latitude blocking in the 10-15 day range on the models in the last day or two, but it looks a bit anaemic - so the SSW probably will have an effect, but nowhere near enough now to turn the clock back to winter (for those who hanker after that!) but also, as you suggest, will still probably manage to hinder the progress of decent spring weather that most now want. Ho hum!
  4. ECM clusters not offering much insight out to day 10, just one cluster from T120-T240. But in the extended we have this from the 12z: Cluster 1 looks fairly standard +NAO, i.e. wet. But the others look moe interesting, cluster 2 has a weak block just north of the UK. Cluster 3 goes for the cross polar ridge, as per the GFS 12z. Cluster 4 develops a strong block just south of Greenland.
  5. Nick F Interesting. I really can’t see the 1/250 year event! It has been a very odd year in the strat, but both the first and second SSWs were by the barest of margins. There is not enough time elapsed since the second one, for the third one to count as a separate event as I understand it (needs 20+ days westerly winds in between) - but there is no denying that the latest one is by far the most significant reversal - and it may have some effect later into spring - but I can’t see it being anything spectacular.
  6. GFS 12z is interesting in the second half of the run, from T192: First, a welcome period with high pressure in charge over the UK, which would be long overdue and pleasant. Right at the end, the NH pattern looks very much as though the SSW is having an effect, and splits the vortex. GFS has been playing around with stronger blocking scenarios towards the end of the month, so one to watch as we count down to Easter.
  7. TwisterGirl81 There are about 6 SSWs every 10 years. Whether that is considered rare or not probably depends on the point of view - but my post was about the training dataset for AI models, and for most of that training dataset there won’t be a SSW happening.
  8. My bet is the AI models won’t catch on to any post-SSW patterns quickly. Given that SSWs are rare, it is unlikely that the AI models will suss the evolutions with an SSW in play from the current pressure patterns over the evolutions without, from the training dataset that they are based on. No sign on the latest AIFS run, of the kind of pattern that GFS has been playing with in deep FI, T360:
  9. I’ve been wondering for a couple of days now whether we are starting to see the effects of the strat reversal now in the extended clusters: I think if we do, the likely area for blocking appears to be Greenland, as shown in clusters 2 and 4, maybe also 3 by day 15. One to watch, if this does happen it will be against the backdrop of the flabbier pressure patterns of spring rather than winter, and of course very late for any cold, but if the right pattern evolved, an interesting Easter weekend is still very much a possibility.
  10. Well looking at the zonal winds, I’m don’t think the required 20 days has elapsed since the winds went back positive at 10hPa 60N after the last ‘SSW’, (19th Feb looking at this chart). So the upcoming evolution should be recorded as the aftermath of that SSW, not a new one. Which seems wrong, but I believe those are the rules.
  11. Rain All Night I think it probably will return positive before a final warming in April. A period of reverse winds rarely lasts longer than a month, and so there’s still time left to return positive before the vortex peters out for the summer.
  12. ECM clusters this morning T192-T240: Cluster 1 hangs on to a continental flow to the UK to T240, the others essentially a return to westerlies. The key thing seems to be the low out in the Atlantic at this time, if it is kept further west and shallower as cluster 1, then the block is stronger and the Atlantic held at bay. The zonal wind reversal in the strat has now happened, and the peak reversal about -14m/s expected in about 4 days - it will be interesting to see whether there are changes in the week 2 modelling as this goes through. If it is having an immediate effect, I would expect to see the block showing more resilience in runs to come. If its effect is still some time down the line, that probably wont happen.
  13. ECM clusters T192-T240, there are just two options this evening: Interestingly, the rain fest of the GFS is in neither of them, so that model seems to have gone off on one this evening. Cluster 1 (contains the op, 32 members) stronger block, maintains the flow off the continent until T240. Cluster 2 (19 members) brings in a southwesterly flow courtesy of the low in the Atlantic. My impression is there’s still quite a bit of uncertainty but it seems to me like gradually, the runs with strong Atlantic influence are reducing or getting pushed back - slightly - it isn’t a strong signal.
  14. Quite a difference as far as the UK is concerned by T168: The first low goes under according to GEM and UKMO, the next low, UKMO it’s a case of ‘to be decided’, the GEM starts to inflate it, the GFS is well on the way to a wet and mild thereafter. So UKMO this afternoon with the better block and cold option, with chance to add.
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