hope members dont mind, here is a post from tamara on NW for those who don't go there or not have read this yet,
The pattern as has evolved over recent days is a very good illustration of where, on a northern hemispheric level, things have actually accorded quite well with expectations (i.e Atlantic amplification and Euro trough) Then, also in follow up, the broad-scale suggestion of that ridge strengthening towards a blocked pattern with a further retrogression signal starting to come into view. It is the upcoming period and that longer range amplification signal that provides the next headache
I think it is on this basis that the use of longer range tools such as the AAM/GWO circulation and stratospheric modelling to try to predict opportunities for colder spells (and any other type of weather pattern obviously) has its true worth and value. The worth in learning about these tools is invaluable imo because, as I have discovered especially this winter, it is possible to spot some distance out when the next opportunities for a cold pattern might arise (as well of course what the problems might be in achieving those opportunities, or trying to decide whether any desired colder pattern might arise at all)
We have seen this winter just how enigmatic the signals have been - we have only had at our disposal an atmospheric circulatory signal that has provided periodic Pacific > Atlantic pattern retrogressions and attendant amplification signals heading from upstream> downstream. It has not been driven by an anticipated Siberian -AO signal for northern blocking to evolve
The regularity of the cyclical nature of the atmospheric pattern has in truth made anticipating the way ahead relatively easy- even though it has not been the best of news. The GWO orbits this winter have featured -AAM phasing between 1,2,3 and 3,2,1 in the first half of the winter - but have progressed to a higher amplitude phasing (Phases 4/5 to 8/1) in the second half on the winter so far that have increased the same amplification signal of the first half of the winter and has also enabled the stratospheric profile to change through increased torques and MT's which has shaken up vertical wave activity and assisted us with a displaced vortex
However, this is a perfect example of where the atmospheric circulatory pattern has progressed to achieving macro scale improvements to a frustrating and enigmatic winter pattern, but, these are still only improvements within the limitations that the dominant background pattern allows - and these better opportunities still cannot ever guarantee the precise 'will it snow' close details that so many of us crave on this forum.
The UK, is a micro dot, in that broad-scale hemispheric context, and as we know especially when we are restricted by a pattern that is not predisposed to HLB in the heart of the winter, then it is going to be even harder to come close to fulfilling the potential wintry parameters that such a broad-scale pattern offers.
This illustrates exactly why my own posting leaves the closer examination of possibilities to others to comment on - and we all hope very much that these are in our favour.
So, as to the way ahead?
That GWO orbit continues with repeated rinse and recycle signal. The MJO phase cycle teleconnects to underpin the anticyclonic Feb spell - and the constant retrogression signal remains (we see the ECM picking up on this).
The uncertainty for me is what is likely to happen to the vortex, in terms of movement and re-organisation. We are losing the displaced signal, but we have further wave activity to consider and the GWO orbit tells us this. Phase 4/5 (which is the here and now) signals a second imminent +EAMT and this should assist to try and re-shuffle vortex energy back towards our side of the pole after the upcoming transfer across the pole to Greenland.
An example here of timing being the essence. Timing of an amplification signal with vortex energy transport across the pole is very hard to gauge - and it is here that the fate of the latitude of our current amplified Atlantic ridge has rested. Wave activity over Asia courtesy of EAMT is set to be followed by further vertical wave activity the other side of the pole as the GWO orbits through phases 8/1 and into the next Pacific retrogression signal... that the ECM is picking up on already.
So, in summary, we get some assistance (repeat circuit of late Jan) from another +EAMT for vortex movement to our side of the pole (GWO 4/5) and then we get a subsequent -MT for upstream Atlantic amplification (Phases 8/1/2). Sounds familiar.
http://www.atmos.alb...wo/gfsgwo_1.png
Mention has been given before of eventual translation of this amplification pattern to an HLB scenario. This, with an underlying weak El Nino to hand (which traditionally favours the second half of winter for cold spells) has been perfectly plausible based on some reasonable expectation that the inner core of this (swear filter) vortex would burn. However, thus far it has managed as a relatively weak and unstable feature to escape such a torching.
The changing wave lengths will make a difference there is no doubt - the question is will this provide the optimum synoptics in the Spring, if they arrive at all, rather than the last part of February? Its still too early to answer that question, and there is time yet for sure - but for now eyes anyway on this next retrogression signal. There is another plunge of cold air on its way to supplement what exists to our north and east.
How much within the limitations of this cyclical quasi upstream>downstream amplification recycling can we squeeze out, without Europe to our east and south being the total beneficiaries once more?
Originally Posted by: sizzle