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Singularity last won the day on September 14 2018

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About Singularity

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    MSc Meteorology

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    New Forest (Western)
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    Meteorology - Science and Observations | Cycling - On and Off Road | Walking or Hiking | Electronic Music Creation
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    The Extremes! Passionate Hater of Drizzle.

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  1. Good summary as usual @Catacol It's a strange time really; there's a lot of agreement among those using tropical and stratospheric drivers on where we really should be heading overall during the coming fortnight (wedge highs emerging next week and then evolving toward a block in the Greenland-Iceland vicinity), but model confidence has rarely been lower. Possibly this is a result of the simultaneous occurrence of a stratospheric influence that's not usually modelled very well, a tropical influence that they tend to take a while to get to grips with, and a split jet situation over N. America which also tends to cause them problems. A triple-whammy of uncertainty amplifiers! So... if you want to stay stable of mind, best to expect no particular outcome to appear in the models with each new set of runs until we see at least 4 in a row follow roughly the same lines. For what it's worth here's the ultimate feasible outcome for cold conditions: 1st stage sees regional stratospheric influence works alongside the Euro trough to move some really deep cold over to the UK from the E via NE (like the ECM 12z of today, but cleaner E flow across the UK). 2nd sees the door open for the blocking high to retrogress to our near-NW while the stratospheric downwell raises heights Greenland-Bering, with further deep cold journeying our way fast enough to cut off the milder air that otherwise circulates around to us in the style of the ECM 12z of yesterday. Probability of that? I'd guess about 5%... but I expect that even just halfway toward it would still be memorable for at least some of us!
  2. So the regional stratospheric imprint N and NNE of the UK makes a sudden comeback in the GFS and UKMO output. This has become one of the most dramatic run-ups to a cold spell that I've ever witnessed! I did wonder what it could lead to from the east, as the 12z JMA of yesterday produced this outcome despite the trough off N. America not behaving very helpfully as it departed the landmass: Apologies in advance to anyone initially thinking this is a 12z run from today and then being let down upon closer inspection . GFS 12z's not far away from it though, really. Sadly, lower-res of that run has quickly taken on a pretty daft appearance from the hemispheric view but it's easy to imagine how things would go with the expected additional amplitude to the N. Atlantic pattern. This being something we've a good chance of seeing in the mid-range anyway so not worth taking anything beyond +120 that seriously (as much as you might want to with that easterly!).
  3. Anyone else of the impression that we have the stratospheric anomalies downwelling but in such a diffuse manner that it's trop-led forcing that determines where the landing position of substantial +ve GPH anomalies is within a range spanning from NW to NNE of the UK? The ECM runs of yesterday had a powerful trop-led 'opening of the door' just NW of the UK, offering one of the fastest possible routes to a cut-off HLB capable of sustaining for a long time. The 00z ECM and GFS of today have ditched that in favour of the trop being less helpful, leaving the strat to do most of the work, which takes longer and establishes the main height rises N or NNE of the UK. Ensemble guidance appears to be split between this and something akin to the ECM runs of yesterday. Let's see if the 00z ECM and GFS were just wobbling with respect to the trop-led ridge build in the mid-Atlantic. If so, it was a particularly big one!
  4. Well that was hilarious watching GFS use every dirty trick in the book to stop the widespread HLB delivering us cold beyond the middle of next week! Largely set in motion by it failing to separate areas of low heights (common GFS shortfall) plus the usual poleward bias. If trends continue HLB-wise, especially N and NE of the UK, such a long-lived ‘trolling’ outcome will soon be invalidated (I’m not ruling out temporary LP position / alignment frustrations as those are unfortunately quite common).
  5. Yes this is fascinating now. It's developed an extra LP just SW of Greenland to stop the UK-Scandi ridge heading NW as I envisioned could happen (typical, ha!) but there's three ridges amplifying poleward at once as of D10 due to the Pacific ridge building faster than the 00z ECM had it doing. Results speak for themselves. At last we see another GFS run that finds the vortex split. Only took it three days longer than ECM this time .
  6. Okay, for fun, I will air this possibility for how it could go from here if the usual model bias can be overcome: The dig of the trough down west of the Azores continues, pumping up heights just NW of the UK to work alongside those just N of the UK and advance toward Greenland as the Canadian vortex lobe comes apart at the seams.
  7. Slight timing offset but GFS is not far away from the ECM 00z now... this at least lends further credence to that ECM run as the most probable sort of route forward. Just that area N and NE of the UK continuing to be handled very differently by GFS. To counter that, it'll need to seriously pump the mid-Atlantic ridge northward as per the 00z ECM... and find some sudden height rises N of the UK if it wants to match that run even more closely.
  8. Comparison with ECM 00z on the right shows that GFS is now getting close with that vigorous low off Canada (it's tighter and deeper than the 06z) so should show more amplification across the N. Atlantic than the 06z had, but remains very different just N and NE of the UK with LP being taken east with no resistance. This may be to do with the regional stratospheric influence above that region (+ve height forcing).
  9. ECM fits theoretical expectations by far the most of the 00z det. runs and EPS of the ens runs. GFS & GEFS have had a positive NAM/AO bias for several weeks now. FV3 mostly not but with a few lapses for reasons I can only imagine. So... ECM 00z may be a bit fast to build the blocking highs but aside from that it’s the most believable solution based on everything we know at this time (yes, the usual caveats apply!).
  10. It's actually closer than I initially thought on the ECM 12z; a rain-snow mix across the far-south on Weds and that's with hardly any precipitation (suspiciously so!); heavier and more prolonged showers would likely have shown as snow as happens to be the case across Devon away from the immediate coasts. Shows what we're in the game for should we go down the vigorous deep cold trough route. FV3 12z has raised an alternative of note though; if the low from the subtropics moves more N instead of NE then the route forward markedly and something even colder and snowier results (except for the windchill which would be stronger in the deep cold trough scenario). Something to watch out for in the ensembles.
  11. Indeed. With such low heights the 850 guide is not as helpful and I was surprised to see rain for the far central south and southeast in the raw data. Model must have drawn in a shallow milder layer off the sea... but these are usually under-modified as they head inland. Odds are the low will be weaker with less wrap-in trouble anyway (based on historical precedent). A pretty vigorous system is certainly possible though due to the very unstable nature of the deeply cold airmass crossing the mild ocean SSTs.
  12. The apparent regional strat-trop forcing of higher heights just N and NE of the UK by the start of next week has all but vanished now with just a hint of it from UKMO... seems it, ECM and GEM all imprinted it too fast. I did say a couple of days ago that the speed of it was surprising to me! Could be that the lower-stratospheric ridge will actually set in a day or two later and aid in driving the imported cold trough right down into Europe and set up a bitter easterly. GFS 12z suspiciously lacking in that aspect. Better effort with the N. America - N. Atlantic pattern though; just a bit more sharpening of the troughs and ridges needed.
  13. I see two main causes of uncertainty; the strength of Pacific MJO influence sharpening the upstream pattern starting around about D10, and the interaction of the Canadian vortex 'drain' with regional +ve GPH forcing from the stratosphere and a surge in AAM, both of which encourage height rises just N and NE of the UK. It's most intriguing how all but GFS had a brief fling with a much stronger regional stratospheric impact yesterday. Seems they saw less resistance to it from the Atlantic sector - perhaps a bigger AAM surge than they've been going with so far today. Question is whether that regional stratospheric influence is being underestimated and if so, is the difference to reality going to be large enough that the major trough from Canada gets disrupted after all, even if it's vigorous and the N. Atlantic pattern offers little assistance? ECM D10 suggests it could be, but GFS remains keen on a diving low rather than a disrupt-slide outcome. Of course, given the known AAM bias, the N. Atlantic might help us out more after all... hence two main causes of uncertainty. Confidence in the modelling is unusually low until further notice!
  14. My main take from the ECM 12z is that it's very encouraging because it has the surface cold in particular fighting back against the Atlantic troughs even after those receive a bit of a boost from a circumstantial tightening of the thermal gradient (to which models tend to overreact anyway...). When less than ideal routes still land at the same general outcome, you know the signal has a strong basis. On a side note, the models have added some MJO amplitude in their projections today but it's hard to see so much taking place with the SSW downwell in progress. Lagged effects from the P4-P5 activity would encourage a flatter pattern for NW Europe in the 12-16 day period. While the modest amplitude MJO forcing could pretty easily be overcome by the SSW downwell and high AAM state - just look how hard GFS still finds it to get rid of the Euro trough pattern - I'd rather keep the road smoother, so to speak, so hopefully the models are overdoing the MJO amplitude (though a bit of P6 activity would be alright for slider lows, and P7 for widespread HLB... suppression only really wanted in P4-P5).
  15. I think GFS tries for a feasible outcome if the MJO stays quiet, in which we have Canadian-Siberian vortex lobe exchanges taking place while west-Scandinavian blocking keeps us under a cold continental feed, but the usual bias (zonal flow too strong, not enough recurve of the jet under the block) led to it looking much less appealing than it could have done. If, instead, the MJO manages a bit of activity over the C. Pacific then a ridge to our NW becomes more probable. Odds are, we'll have a much better position in a week's time than GFS has us down for anyway, so I've little concern with it this evening. Same goes for D8+ of GEM though it's hardly a poor outcome with the new trough diving sharply into Europe on D10 and another easterly on the way; it's just that it would be preferable to keep our existing cold pool going.