Glacier Point

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  1. somewhat mischievously on my part.. comparison with what is currently being modelled and 'selected' years at the same stage for 10m zonal mean winds 60-65N..
  2. I know it sounds counter intuitive tcc, but there are good reasons for a weak vortex and more precisely a weak zonal wind flow during November to substantiate a tropospheric ridge in the mid Atlantic. Other drivers [ENSO state, Maritime Continent forcing] are aligned nicely to deliver this.
  3. Well this is getting interesting and a possible game changer. Why chop down a tree when you can squash a seedling ? Following the lead of the models of late last week, we have begun to tick down on a warming signal and significant weakening of zonal wind speeds in the middle and lower stratosphere. Both GEFS, GFS and EPS remain solid on developing this. The operational GFS getting close to a reversal.. And right down the middle of the GEFS mean, some members dropping into reversal.. The EC EPS is similar and would give a sizeable clustering around +5 to +8 m/s. That is one weak vortex. Already. Even if we were to assume worst case scenario, those two GFS members going up would still translate to a sizeable negative zonal wind anomaly. The mid tropospheric modelling continues to develop a deep upper lower dominating the North Pacific in the week 2 time frame. That is near perfect geoeffective positioning for upward wave (Wave 1) deflection into the vortex leading to a push of the vortex towards the North Atlantic. We are yet to see these being manifested in the strat modelling as they are a little way off, so a weak vortex looks set to become event weaker.
  4. That signal not just confined to the GFS op. GEFS and EC means all showing a similar signature. Not in itself a large warm anomaly, but of interest if you are following the logic that high geomagnetic activity equates to cooling of the upper layers and vortex intensification and swift transfer to a +NAO regime. We are travelling in the opposite direction to that right now. Still quite some time to go and we know how quickly cooling can develop. For what it's worth, EC and GEFS at extended range showing conditions ripe for Wave 1 development, possibly Wave 2 into early / mid November. A distinct lack of westerly zonal wind anomaly in the troposphere right now, all restricted to the Southern hemisphere.
  5. Messy - if nothing else on the basis of the messy and slightly incoherent composites for phase 6-7 of the GWO for January and how we relate those to the back end of January into February where these become more coherent.
  6. GFS starting to pick up the amplification coming out of the Western Pacific 23/24th January - where will the anomalous ridge manifest itself over NW Europe ? 12z going for Scandinavia. Not sure I'd agree with it there, and much will depend on modelling of the decline of the vortex over Greenland.
  7. So, verification for posting in as much I can do so given we are in the midst of model mayhem and projecting forward using NWP is not going to be convincing. The only things I can verify at this stage are: GWO passing through phases 5, 6 and then into 7 with a lagged atmospheric response up to 10 days. Well, Check. Atmospheric response for phases 5 and 6 and observed in this critical period: and the observed mid month so far.. Not bad. Timing was specified out to 10 days from the 9th/10th but still what I would regard as the margin for error, particularly as the posting was dated end December when none of this was sniffed at. Also note the slight west based -NAO observed that was well signalled, long in advance of any model solution. So mid month northerly, followed by lull as the pattern becomes more Atlantic driven as the NAO becomes more west based for a time. This is now, so reanalysis in a few days will be interesting, but I reckon I'm good for that. Turning to the final third January into early Feb, this does present some difficulties as monthly change overs are problematic - do we use composites for January or February ? Notwithstanding this, broad guidance on the assumption of a stalled GWO or even heading back to phase 5 is towards the mid Atlantic / southern Greenland anomalous ridge and northerly / northwesterly./ northeasterly vectors. Granted, current long range modelling is not there (but caution advised in relying on this, moreso at this juncture given synoptic variability), but trending there (06Z GEFS mean has a strong but flat mid Atlantic ridge). Here comes the usefulness of being able to understand why that might be and when that might change. I would suggest the current strengthening of the stratospheric vortex is destructively interfering with the tropospheric pattern by strengthening the vortex west of Greenland. This prevents the Atlantic ridge from extending northward into Greenland. When or more importantly how will this change ? With the GWO heading back to phase 5 around 23rd -28th January, we should expect some more amplification to be levered into the upstream flow. That gives us back end of January or more realistically early Feb, although you'll appreciate the margins for error and the final few days of January would not be beyond reasonably possible. That also coincides with the likely displacement of the stratospheric vortex away from Greenland. So bottom line here is that we continue to see signals for mid Atlantic ridge extension towards Greenland and -NAO conditions during late January into early February. That should be put alongside current model consensus which does not suggest this.
  8. Updated upper level velocity potential update (GFS) is interesting.. Continued migration east of the -ve anomaly towards the Maritime Continent during week 2 but note also split emerging between North and South Hemispheres with the Northern Hemisphere element well into the Western Pacific. That suggests tendency in angular momentum will show an increase during week 2. No dramatic fall off in angular momentum. Also, GEFS and EC EPS consistent on dropping an upper level trough through the Western Pacific (i.e. downslope of the Asian Massif) 23-24th Jan, with upslope ridges and troughs - good precursor pattern for generating westerly inertia into the Asian Jet. Net result, GWO will continue to orbit high amplitude phases 6-7 and, with the renewed injection of westerlies coming, shade phase 5 as well.. Stress again, these composites are for February, and Jan composites not so keen on ridges in these locations but still suggestive of Scandinavian troughing (bet messy otherwise). So the close we get to Feb, the more I would expect the ridge to our west and north-west and trough to the east to bear out. Strat allowing..
  9. Op GFS has just shifted in a massive 600m in its 500 hPa geopotential height over Kara Sea at day 7 between 06z and 12z runs. It also now has the North Atlantic a seething pool of meridional flow where once there was a unified deep upper low.... Atlantic hurricanes in January, this is just bonkers.
  10. GFS has too much bias towards the MJO in phases 8 and 1 which invariably transposes too much negative pressure on angular momentum. Re Strat - not sure we'll get a proper warming, more another perturbed vortex albeit a pretty significant one.
  11. CPC analogues rolled forward days 10-12 confirm the idea that we are heading towards an Atlantic ridge / Scandinavian trough solution in the last week Jan into early part of Feb... which might be useful as the models seem to be losing all coherence as we approach the business end of the winter. Relative angular momentum has peaked in the last few days and, as tendency in relative angular momentum (the rate of acceleration or deceleration) cannot be maintained forever, some negative tendency is expected in the next 10 days. Total and relative angular momentum will however remain high as a large surplus of westerly inertia remains in the atmospheric system, demonstrative of a fully coupled atmospheric - ocean circulation. That places the GWO in a quasi stationary phase 6-7 orbit for the next 10 days. Composites are a bit messy but broadly align to Scandinavia trough a deep low in the Western Atlantic. This is complicated as we are approaching a monthly change, and February's composites hold some value. But generally Atlantic attack from the south-west and re-asserted Scandinavian trough as the theme. The GFS and EC monthly and EPS MJO signals suggest the MJO to become coherent in the Indian Ocean and towards the Maritime Continent during weeks 2-3. It should be remembered that there will remain a low frequency signal for convective anomalies in the Central and Eastern Pacific as well, so the MJO projection onto the system will be altered and angular momentum will remain high. MJO composites alone of limited value and it should be stressed again that the MJO signal needs to be transposed onto the GWO. The main point to draw from this signal is that angular momentum will begin to rise again during week 3 (early Feb). This gives a stable GWO phase 7-6-5-6 type look to the pattern for the next 2-4 week period, with phase 6 being a strong attractor within the base state. Composite is very consistent and now familiar as we turn towards the back end of Jan into Feb...Scandinavian trough, anomalous ridge centred just south of Greenland. Those looking for early spring warmth in the first part of Feb may be disappointed. As wind vectors, I would be thinking NW, N and NE, allowing for a bit of westerly flow days 7-10.
  12. Andrej - are you able to plot previous GEFS means on top of your zonal winds graph so we can keep a check on how the individual GEFS runs are progressing this ? Thanks
  13. I would go along with Cohen's view on a temporary bounce in the AO as a precursor to the early stages of warming being programmed now widely across NWP. Think of at as a Tsunami. The seas get withdrawn prior to the wave breaking onshore as the tropopause is depressed over the Arctic and lifted around the edge of the polar region. That bounce may actually be from -6SD to -2SD, enough though to send the GFS into a tailspin. Today's EPS and GEM ensembles dropping strong hints of mid latitude highs being in position from day 10 onwards, and lowering of pressure over the Arctic. How long will they stay there though, that's the key question ?
  14. @Noballslikesnowballs tropical forcing centred in the central part of the Equatorial Pacific. Check the period forecast off that analogue.....
  15. Not sure the GFS is handling this North American trough, or indeed the blocking over the Arctic too well at all. 06z and 18z runs seem to be particularly volatile on this with large inter run variation.