Glacier Point

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Glacier Point last won the day on November 24 2016

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  1. Not sure the upstream teleconnections are as favourable as being advertised by RMM MJO plots. 200hPa velocity potential is much further east than would be considered for phase 8, and threatening an Indian Ocean evolution: That's more phase 1 territory which is no where near as favourable for high latitude blocking. Factor in the displacement of the upper vortex towards Siberia and you get a signal for Euro ridging as per NWP extended means. Very similar to the mid / late November episode. That's not to dismiss the text book spike in tendency in angular momentum that has occurred on the back of the evolution of the tropical wave through the Pacific, but my take on that would be for more of a hit to the stratospheric vortex at the end of the month and more robust blocking signal to the NE / N at this time, and into early March, although for the lowland snow chasers that's too late I appreciate.
  2. Nice addendum there Nick. The key from this will be how fast we move the MJO as a proxy for angular momentum back across the Indian Ocean. The faster the better if you're looking for a swifter return of any easterly type pattern. The potential northerly advertised by week 2 GS and EC ops, just a case of wait and see on that one as its not fitting any GWO / tropical influence and must entirely by largely atmosphere driven- which is notoriously difficult to get a handle on.
  3. Quite like the GFS op 06z as a road map for how the next 3 weeks might evolve. We have a strong push of equatorial easterly winds extending across the West Pacific and Indian Oceans, with developing convection in the West Indian Ocean. This is consistent with a developing U200 wind picked up by Mike Ventrices' product: MJO forecasts also consistent with a phase 1 - 2 projection. I think that the eastward propagation is also a reasonable assumption (having my seasonal reasons for it to do so which I can't go too much into). So a stage 1-2-3-4 evolution likely. In terms of how this transposes to the Global Wind Oscillation, we need to consider that relative angular momentum budgets remain close to climatology, so high amplitude phase 2 is not likely (this would be high amplitude if angular momentum were well below normal (i.e, strong Nina). A drop in angular momentum resulting from -ve torques very consistent with a big phase 8-1 projection in the GWO. Analogues broadly consistent with longwave pattern week 1, particularly weakness in heights across sub-tropical North Atlantic - but need to adjust for ongoing low heights to our North. So support for this idea that the trough to our south will lift poleward and westward over time and merge with the trough dropping from the north. Thereafter, low amplitude phase 2 to 3 transition likely as tendency in momentum begins to rise. Composite analogue consistent with the idea of Euro trough evolving to some kind of ridge over NW Europe in response to a dominant upper trough in the Atlantic. Quite how that plays out with any dropping of the main lobe of the pv into western Siberian Coast open to doubt, but fwiw, gfs seems logical. After that, rising angular momentum with the MJO transitioning through the Indian Ocean into the Maritime Continent signals another bout of hemispheric amplification as the GWO enters phase 4. With a low frequency signal for Atlantic troughing and NW European ridge, I wouldn't be surprised to see us back we we start now. Ridge developing over Scandinavia / UK and pushing westwards. With the polar stratosphere exhibiting some unusual behaviour, these composites may need to treated with a degree of caution on exact placement of ridges and troughs, but the broad scale ideas should be there abouts. One aspect I'm really not sold on at all is the idea of +ve heights remaining for very long over the East Canadian sector for very long. So weatherwise that should translate to a blocky type pattern with shallow ridges and troughs and essentially feeling raw for week 1 into week 2 with temps below average across much of Europe. Risk of above average temps returning to western Europe week 2 into 3 but that will be dictated by any push of colder air southwards during week 2 and a rather messy mix could arise with surface cold persisting. Concern would be if the MJO stalled in phase 3 resulting in a more meridional pattern with the UK on the warm side of any Atlantic trough. Into week 3, more amplification developing should see us regain an easterly feed. So back around to where we began...
  4. There is a view, one which I would endorse, that the RMM Indices are not capturing fully MJO activity. For example, right now, upper and mid tropospheric winds are flowing all the way across the West and Central Pacific all the way to the East African Coast. Likely significantly enhanced convergence and convective activity around West Indian Ocean (MJO Phase 1).
  5. Day 10 onwards looks more of interest for a ppn point of view (although the depth of surface cold right across Europe is of real note). With the longer range guidance firming up on a longwave pattern setting a +ve height anomaly over Baffin and NE Canada, and the Euro trough remaining in situ or drifting slowly west, chances are that a ppn signal will attempt to approach from the south-west. Getting a dry enough and cold enough reservoir will be critical. As a side note, not too sold on the model solutions for the NAO west solution to be so dominant and sustained as suggested. We had a similar episode in December which didn't verify anywhere near as strong and long.
  6. Well this is going to be an interesting standoff. ops jumping around, but we have cmc, gefs and eps means all showing very coherent and cold solutions day 10 onwards, +ve height anomaly centred Iceland, becoming more Greenland over time as the North Pacific ridge retrogressive and pulls the core vortex with it. Cmc until now has been unconvincing on this. It's worth noting that evolutions to cold patterns have not been straightforward, witness last November. Also problematic is the strong emphasis on the southern arm of the jet and rather diffuse northern arm (as has been the case all winter). Still not totally convinced by the Greenland bit, and would favour Scandinavia as the destination for ridge development. Interesting times, particularly coming against the wQBO / solar backdrop.
  7. Point taken, although; a sustained period of well belows with a mean vector from the north-east alternating with north; just enough residual pv centred west and south-west of Greenland to feed the block; and, during our coldest period of the year, would be viewed by many of the population outside of this forum as falling within the all evils.
  8. Another eps going for a progressive undercut and block development to the north in the extended range, sustained cold from day 8. Very cold European outlook. Pandora's box about to be opened.. just need to nail the drag back of the core of the pv across the sw USA.
  9. Well that's 3 from 4 last eps means to show a broadly similar pattern for Europe with +ve height anomalies stretching from Greenland to Svalbard and Euro trough with low heights across the central part of the North Atlantic. Broadly in line with considered signals for gwo and mjo forcing. That pattern with a pool of cold air already in place, and just the slightest suspicion a period of enhanced amplification may be coming onto the extended range (mid to late Jan) via uptick in angular momentum tendency (beyond what models are advertising)
  10. Indeed Nick. With a strong signal for -ve U wind anomaly developing through the Equatorial Pacifc in the next few days, it's not so hard to see where this is coming from. That's centred on 120w which gives a strong projection to a MJO phase 8/1, regardless of what the wheeler Hendon plots show right now. GFS also suggesting a net easterly U wind anomaly through 20N and 30N across the Eastern Hemisphere at the end of the month giving a classical Nina look the atmosphere. That should engender a low AAM base state, weak amplitude GWO phase 2, which favours ridging to the North-east Atlantic. Interestingly should also set up a strong +ve frictional torque, and precursor to amplification later on in the month. With the configuration of SSTAs in the west Pacific and Indian Ocean still favouring convective anomalies over the Maritime Continent, would expect to see downstream wave breaking favour a low frequency patter of themain lobe of the polar vortex displaced slightly west and south of Greenland which suggests we might need to correct that ridge position further east over time. So whatever transpires wrt ridging to our NW and north over the day 7-10 timeframe (and reload over the northerly really well advertised in eps tonight, as essentially it has been the case for several days now), my eyes drawn to the north-east in the extended. Back that up with a cold, often anti cyclonic period in the medium term, you start to build a case for a below / well below monthly outlook. < Alistair - perfect timing!
  11. Well, with the GWO in likely low amplitude phase 2, we do have some agreement on what the extended gefs / eps are leaning right now [positive height anomalies to NW and below average temp signal]. The neutralisation that took place in angular momentum during December places us now exposed to short term spikes in tendency in relative angular momentum [amplification across the North Pacific ridge]. We also have the scope to begin to assume what ever was swamping the long lead signals in December has / is beginning to relent. Those longer lead trends did suggest building ridge tendency to our NE in time, so the longer term game for first three weeks of January will be significantly influenced by what ever cold poling develops over western Russia. I've gone on record earlier this season suggesting there would be a disconnect between upper stratospheric conditions and lower strat / trop conditions. Right now with a strong upper pv, and the model output in front of us......
  12. Both GEFS and EPS going for a substantive +ve height anomaly developing in two phases at the day 5/6 and day 12-15 mark centred over Western Russia / Eastern Europe, the latter quite significant at this range. That's meat and drink to the precursor Wave 2 pattern. Should begin to see model outputs beginning to deliver splits in the lower to mid stratosphere during the 1st week January.
  13. 500 hPa height anomaly for the NH for the first 12 days of the month not really reflecting the likely outcome for the month's end and certainly not the expectation from earlier on. The core tropical forcing signature is moving back to where one would expect given sub seasonal drivers - centred to the Western Pacific. Contrary to what be expected looking at some model outputs, zonal wind anomalies remain modest and towards the weak category across much of the mid to high latitudes all the way up to 30hPa. The presence of a sub-tropical jet flow very evident looking at sectional plots. And yet, a pattern forecast that refuses to reflect these and other sub seasonal drivers. Why ? These are all likely related, but I suspect that three things are relevant here. 1. Drop in angular momentum with southward momentum transport across 30N - GEFS projection of a -1.5SD reduction look as if they'll verify. 2. West QBO phase which is on steroids, December's index value will trump all other Decembers by a mile. 3. Arctic sea ice registering at nearly 1.5m sq k below the climatological norm. I think that latter might be the most persuasive given this is the factor which defines this year in difference to others given similar forcing. Does the Arctic have to bottle up cold in order to restore some kind of equilibrium to surface temperatures there ? Looking ahead, I get the model consensus to develop a substantive Euro / Scandinavian ridge. That tallies with what I expect to be a dominant subseasonal player orchestrated by the arrangement of SSTAs across the Western Pacific. The inference for January being a withdrawn Bermuda ridge and trough angled NW-SE across the eastern part of the North Atlantic. This composite probably needs a tweak or two to reflect increase heights over Scandinavia, but the broad gist looks about right. With a large corrective drop in angular momentum and assuming no substantive upward corrections (can't rule that out), GWO likely to be low amplitude phase 2 for the remainder of December into week 2 January. Composites for these on a monthly basis: >> Again, not counter to the Euro / Scandinavian ridge, if anything whiff of the ridge extending westwards but I'd caution interpretation of surface temps on that basis. Note the suggestion there of continued polar vortex lobe west of Greenland, sufficiently far west to allow for the Scandinavian/ Euro ridge to breathe. That composite for December probably being swamped by factors outlined above, so direct interpretation not advised, but an attempt to build a second ridge in the North Atlantic merging with the ridge to the east of that would be something to look for, albeit in a likely suppressed form. One other thing to look for, and perhaps of greatest interest, will be pattern projected for at least the next 10-15 days. +ve height anomalies over Eastern Europe / Western Russia will be geo-effective for Wave 2 increase in the low to mid stratosphere, taking effect early January. GFS typically beginning to reflect this a little prematurely but I would expect to see splits developing in the trop vortex within the 1st week of January. The combination of cold air potentially entering the fray far stage right and +ve height anomalies over Scandinavia ? One for those of a nervous disposition to look away. Can we lower heights sufficiently to our south over Iberia to advect this cold pool westwards ? In the meantime, dry and relatively mild conditions look the form horse until perhaps some interest in the modelling last week of the month. Edit: just noticed. Compare GEFS plot above with composites for tropical forcing centred over the West Pacific / Maritimes - good reflection across the North Pacific, North Atlantic and Scandinavia. Seems to be capturing much of the NH forecast pattern end December.
  14. To add an extra layer of difficulty for NWP... Another shift in tropical forcing. Latest (12z) run data shows a marked westward shift in some of the tropical forcing fractions to the Horn of Africa. Convective anomalies also in the Western Pacific. That's MJO phases 6-7-8 if you like that sort of simplicity. It may take up to 24hrs for models to fully assimilate this. This time time round, this shift should not destructively interfere with the expected base pattern 20th December (ish) on, indeed, a degree of constructive interference ?. Ergo, +ve height anomalies to the north and north-west of UK more favoured.
  15. Well you're very kind - but run the op gfs 70hPa sequnce and you'll understand what might be going here. This is classic stuff when the troop vortex rapidly intensifies without the mid and lower strat cooperating. the block forming in our locale next 5 days is showing signs of being a true block. No model run has been able to break it down, except from over the top via the northerly, or through discontinuous retrogression.