Model output discussion - winter proper underway

[Man With Beard]

ECM ensemble clusters this morning - after Christmas, the same theme that we've seen for a week or so - deep troughing close to the UK leading to the risk of storms. Around New Year, troughing eases off and we see hints of rising heights to the north, but - aside one cluster with 4 members in - nothing to get excited about from a coldies perspective. (Apart from those high up on northern hills, which could get blasted with snow next week).

  

Edit: Do you know what - just to be fair, those stormy charts at T300 are not completely without hope of snow - for example on clusters 1, 2, 4 and 5, it is possible that as one deep low moves through, at this time of year there might be just enough cold on the back edge for a temporary snow event, particularly if there is a bit of a clearance before the next low comes in and the front moves through after dark. Long shot but seen it happen in the 80s and 90s.

Edited December 18, 2017 by Man With Beard

[Daniel*]

30 minutes ago, Paul_1978 said:

Well well, surely there has got to be snow in this chart from the 06z T+222?

A lobe of polar vortex pays a visit heavily modified thought but nice to see. I’m sure there would be GFS 06z is the best run I’ve seen in a while..

[Singularity]

Too early to draw conclusions for sure, but the trend toward the Pacific cross-polar ridge has so far today been pretty major. Perhaps a case of gradually starting to smell the coffee... can only wait and see! Serves to make the later stages of next week nice and mysterious .

[Man With Beard]

Looking at the op runs NH profile at T192 - if this did actually happen, you can see how this might push cold from the Arctic in our direction shortly after - if the N Atlantic vortex eases - or if another unexpected round of amplification comes from the N Atlantic:

  

[carinthian]

2 hours ago, carinthian said:

Make what you want from the latest NAVGEM run. Christmas Savoury or Just a dream ? Anyway this chart gives some hope with signs of the zonal jet pushing further SE  on each run. Wonder if UKMO thoughts are moving this way for Christmas Day ?

 C

Looks like GFS is also picking up the trend for lowering of the jet with each run today, similar to NAVGEM output earlier with big pressure rises over N America also starting to show. Will trend continue for the later run ?  I think yes. The ECM latest run is far to extreme with its widespread Sub Tropical air mass into Europe by day 10.

C

[BLAST FROM THE PAST]

Indeed we should look west.  Boxing Day storm is something else!  Lots to be played out yet.  Going to be an interesting build up to Xmas.....a freeze no....but everything else is in the mix.

 

BFTP

[northwestsnow]

36 minutes ago, snowflakey said:

Looks like a very healthy Greenland High developing on that chart. 

Its a lovely chart and sooooooo close to something really beautiful- as ever the energy spilling out of the vortex segment over canada destroys the chance of a cut off greeny high..

Still, its an improvement on 00z we need this momentum to build...

[northwestsnow]

6z GEFS are improving again- they still scream zonal but hints that there will be short periods of PM zonal...

[carinthian]

7 minutes ago, carinthian said:

Looks like GFS is also picking up the trend for lowering of the jet with each run today, similar to NAVGEM output earlier with big pressure rises over N America also starting to show. Will trend continue for the later run ?  I think yes. The ECM latest run is far to extreme with its widespread Sub Tropical air mass into Europe by day 10.

C

The two charts for Christmas Day from the latest GFS run do really now start to show the trend to colder returning with 528 dam covering a fair bit of the north of Britain and precipitation of snow possible for Scotland , Northern England and North Wales, especially higher parts but not necessary restricted to height. Second chart continues to show a digging southwards of the jet. Lets hope this trend continues.

C

[northwestsnow]

Yes i'm pondering if christmas day holds interest still.....GFS6Z suggests it does and the updated BBC outlook 

' we could either see wet, windy and mild conditions for Christmas day, or alternatively a colder spell with some wintry showers in the north. '

So, the pro's are leaving the door ajar for a white christmas in the north- EC is a resounding no with any lying snow limited to the extreme NW of Scotland...

Edited December 18, 2017 by northwestsnow

[ACCOUNT DELETED]

GEFS & GEM shows the big amount of uncertainty by Boxing Day, although as expected really being over a week away.

[karlos1983]

4 minutes ago, northwestsnow said:

Yes i'm pondering if christmas day holds interest still.....GFS6Z suggests it does and the updated BBC outlook 

' we could either see wet, windy and mild conditions for Christmas day, or alternatively a colder spell with some wintry showers in the north. '

So, the pro's are leaving the door ajar for a white christmas in the north- EC is a resounding no with any lying snow limited to the extreme NW of Scotland...

John Hammond's Blog update from a couple of days ago, sums it all up quite nicely for me. I do really like the last paragraph. If the pro's are struggling, us mere mortals of the model watching world don't really stand much chance do we lol 

https://weathertrending.com/2017/12/15/on-the-horizon-christmas-forecast-still-up-in-the-air/ 

"Yes, we will be looking to the west for bands of rain to arrive from the Atlantic. But as the jet stream begins to slow down and meander into a more contorted pattern once more, so the best forecasters will need eyes in the back of their heads too. Looking to the east, a reservoir of cold air continues to build…"

Edited December 18, 2017 by karlos1983

[Frosty.]

4 minutes ago, northwestsnow said:

Yes i'm pondering if christmas day holds interest still.....GFS6Z suggests it does and the updated BBC outlook 

' we could either see wet, windy and mild conditions for Christmas day, or alternatively a colder spell with some wintry showers in the north. '

So, the pro's are leaving the door ajar for a white christmas in the north- EC is a resounding no with any lying snow limited to the extreme NW of Scotland...

The charts for this week look as boring as hell, at least next week shows some interest for weather enthusiasts, hopefully at least some of us will see something wintry between Christmas and New year.

[northwestsnow]

24 minutes ago, Frosty. said:

The charts for this week look as boring as hell, at least next week shows some interest for weather enthusiasts, hopefully at least some of us will see something wintry between Christmas and New year.

Met office suggesting something akin to Gfs6z for christmas day with wintry showers across the north west esp over high ground.

I think there is a growing risk NWBritain could see snow on the big day..not necceserily lying snow but one to watch over the next few days.. they also expect high pressure to take over in January.

[Iceaxecrampon]

GFS 06z

10 Days off.

Snowmaggedon?

All in all looking "unsettled" in between 25th and 31st.

[Iceaxecrampon]

53 minutes ago, northwestsnow said:

Yes i'm pondering if christmas day holds interest still.....GFS6Z suggests it does and the updated BBC outlook 

' we could either see wet, windy and mild conditions for Christmas day, or alternatively a colder spell with some wintry showers in the north. '

So, the pro's are leaving the door ajar for a white christmas in the north- EC is a resounding no with any lying snow limited to the extreme NW of Scotland...

....that narrows things down a bit then.

[Methuselah]

We'd be better informed if we could pirouette like Torville & Dean; we could look in all directions at once!

[northwestsnow]

9 minutes ago, Iceaxecrampon said:

....that narrows things down a bit then.

Yes i think it does...it will be either PM air from the north west or TM air from the west/ South west..

No mention of anything from the east.. ( as we know).

[Derecho]

Hello

Haven’t posted in a while given the model output had been fairly repetitive. However the 06z offers a route to colder weather. An interesting run that could have a lot of potential with a few tweaks.

So the thing that has been notable with recent output is the development of a very strong area of high pressure around western Canada. Some recent output has seen some quite remarkable SLP values, with yesterdays 06z seeing SLP values of ~1070mb across NW Canada!

I don’t think the high will get that strong but it does look like being quite a powerful anticyclone.

We see its development quite early on after T+96. Here is the view at T+114:


Again situated over NW Canada with a cold plunge over Central and eastern North America looking likely. This may fire up the jet, though a split in the Polar Vortex is still possible if the Russian/Arctic high links up with it.

This is shown quite clearly at T144, so the North America high increases even further in its influence.

Interestingly the ECM and UKMO offer some support for this. This high starts to have a knock on effect around Greenland.

At T174 high pressure starts building around Greenland. Given the cold polar air isn’t shifted this becomes a very intense cold based high. The ECM and UKMO are not as bullish on Greenland height rises but in recent weeks I’ve noticed the GFS has done quite well with it. Transient northerlies have been a persistent theme of this winter so far. So the GFS may be onto something.



The development of this high helps split the polar vortex. It is now shunted away from the south of Greenland somewhat and is split to our North and over NE North America. This shunts low pressure systems further south.

Cold air starts building to the North but the Greenland high isn’t strong enough to keep the cold air moving south over the UK persistently.



Though this may change. It could be very easy for the warm air being pumped up into the arctic by the North American high to reach Greenland and therefore helping develop a more stable block. Also the GFS after T240 tends to flatten a pattern anyway.

In the end our potential to avoid a euroslug high would be increased if the link up between the arctic high and American high occur with ridging over Greenland.

It may not happen but its worth watching. Also some stormy weather on boxing day seems to be a recurring theme…

[Frosty.]

It looks like a period of action packed weather from xmas into the new year and some interest at times for coldies with the jet occasionally digging south introducing colder (polar) more wintry incursions mixed in with spells of milder, wet and very windy weather..it will make a nice change from the dull as dirty dish water weather this week with light winds, a lot of cloud and some thick fog in places..with the exception of today and tomorrow across central, southern and eastern england where some crisp fine sunny weather will occur where fog clears..from midweek it looks cloudier and milder with mist and hill fog across england and wales, becoming fresher and brighter across northern uk before dull weather extends north again later this week for a time.

Edited December 18, 2017 by Frosty.

[Tamara]

 

 Teleconnection drivers tealeaves that influence NWP are science based.  They don't only 'work' when its cold, and appear 'not to work' when cold is, apparently 'cancelled' They are intended to be used objectively to try and assist anticipating changes in NWP relating to ALL weather patterns of whatever type, and at any time of year.

So, with all that in mind, once again into the breach....

The Global Wind Oscillation is still bogged down in, but now heading into higher amplitude transitional Phase 8, reflective of easterly winds (La Nina-like) continuing to be added to global wind-flows and subsequent falling atmospheric angular momentum.

Decelerating (easterly) windflows upstream in mid latitudes is synoptically represented by the upcoming increasingly very amplified Pacific pattern - as manifested by the burgeoning Alaskan ridge

.

That EPO ridge... Has been much spoken of in these summaries in recent few weeks in anticipation of developments of this feature returning towards years end and being a possible foe in terms of downstream cyclogenesis - as well as the friend that it is often portrayed as on this thread in terms of it morphing into a cross polar feature to ultimately help back off the Canadian vortex and take out the sting of its downstream jet gradient.

NWP is fully focussed on this upstream phase now for Christmas week, but wise as ever to step back from the face value furore of the intra day models and consider both the longevity and the intensity of what is programmed and what may occur after.

Steer from tropical convection is very muddy, with added 'noise' from typhoon activity in the Pacific.   So the period of conclusion of the latest MJO wave in the Pacific and its conclusion and return to the start of the next cycle in the Indian Ocean is rather tricky and problematic in terms of the likely floor limit to angular momentum and how this impacts the Pacific ridge heading on further from Christmas week - and downstream implications of pattern in terms of re-amplified vs continued flat.

A shallow phase return to GWO Phase 4 heading into the New Year with little or no emphasis on Nina Phases 1,2 and 3 of the GWO should assist a careful steady ultimate dismantling of what looks like (at present) a heavy vortex load - and enough reason to resume a relatively relaxed look to building pressure, and then evolution to heights to the N and NE (which a GWO Phase 4 in tandem with January wavelength change would bring in terms of atmospheric angular momentum bouncing back and re-amplifying the downstream pattern)

However, a greater fall in AAM brings a traditional La Nina pattern close in attendance and lends initiative to the vortex - and implies that the Alaskan ridge is no friend upstream the other side of the pole, but instead more and more amounts of polar jet energy are fed downstream and with a persistence of a flat pattern and lack of profile to achieve enough of a NW/SE angle that assists trough disruption.

Both of these scenarios have been signposted repeatedly on several occasions (and still counting) from some way out if one is willing to read the tealeaves whole text

All the careful weighing up done, I still have an inkling that it could well be that the suggested evolution of the festive cyclonic phase will look rather different by the time the festivities themselves arrive. But then I admit its also far too easy to want to listen to John Hammond all day long...

[northwestsnow]

6 minutes ago, Tamara said:

 

 Teleconnection drivers tealeaves that influence NWP are science based.  They don't only 'work' when its cold, and appear 'not to work' when cold is, apparently 'cancelled' They are intended to be used objectively to try and assist anticipating changes in NWP relating to ALL weather patterns of whatever type, and at any time of year.

So, with all that in mind, once again into the breach....

The Global Wind Oscillation is still bogged down in, but now heading into higher amplitude transitional Phase 8, reflective of easterly winds (La Nina-like) continuing to be added to global wind-flows and subsequent falling atmospheric angular momentum.

Decelerating (easterly) windflows upstream in mid latitudes is synoptically represented by the upcoming increasingly very amplified Pacific pattern - as manifested by the burgeoning Alaskan ridge

.

That EPO ridge... Has been much spoken of in these summaries in recent few weeks in anticipation of developments of this feature returning towards years end and being a possible foe in terms of downstream cyclogenesis - as well as the friend that it is often portrayed as on this thread in terms of it morphing into a cross polar feature to ultimately help back off the Canadian vortex and take out the sting of its downstream jet gradient.

NWP is fully focussed on this upstream phase now for Christmas week, but wise as ever to step back from the face value furore of the intra day models and consider both the longevity and the intensity of what is programmed and what may occur after.

Steer from tropical convection is very muddy, with added 'noise' from typhoon activity in the Pacific.   So the period of conclusion of the latest MJO wave in the Pacific and its conclusion and return to the start of the next cycle in the Indian Ocean is rather tricky and problematic in terms of the likely floor limit to angular momentum and how this impacts the Pacific ridge heading on further from Christmas week - and downstream implications of pattern in terms of re-amplified vs continued flat.

A shallow phase return to GWO Phase 4 heading into the New Year with little or no emphasis on Nina Phases 1,2 and 3 of the GWO should assist a careful steady ultimate dismantling of what looks like (at present) a heavy vortex load - and enough reason to resume a relatively relaxed look to building pressure, and then evolution to heights to the N and NE (which a GWO Phase 4 in tandem with January wavelength change would bring in terms of atmospheric angular momentum bouncing back and re-amplifying the downstream pattern)

However, a greater fall in AAM brings a traditional La Nina pattern close in attendance and lends initiative to the vortex - and implies that the Alaskan ridge is no friend upstream the other side of the pole, but instead more and more amounts of polar jet energy are fed downstream and with a persistence of a flat pattern and lack of profile to achieve enough of a NW/SE angle that assists trough disruption.

Both of these scenarios have been signposted repeatedly on several occasions (and still counting) from some way out if one is willing to read the tealeaves whole text

All the careful weighing up done, I still have an inkling that it could well be that the suggested evolution of the festive cyclonic phase will look rather different by the time the festivities themselves arrive. But then I admit its also far too easy to want to listen to John Hammond all day long...

Thanks T

All to play for post new year- interestingly Exteter still leaning towards a cold high near or the the north of the UK as we move through january- the pessimist in me always leans on the poor return for us here in the UK but 30years of hurt (to coin a football song) probably play a big role in that (OK 30 years of hurt with the odd moment of elation ).

I guess all we can do and wait for events way of shore to determine how January will play out..

[feb1991blizzard]

I get the point about the CFS being not the greatest model and obviously deep into a 6th month run then it should theoretically be as useful as a chocolate fireguard, however, this latest run has a colder April than March, Feb or Jan, you just know that is plausible!!

[karlos1983]

19 minutes ago, northwestsnow said:

Thanks T

All to play for post new year- interestingly Exteter still leaning towards a cold high near or the the north of the UK as we move through january- the pessimist in me always leans on the poor return for us here in the UK but 30years of hurt (to coin a football song) probably play a big role in that (OK 30 years of hurt with the odd moment of elation ).

I guess all we can do and wait for events way of shore to determine how January will play out..

And yet I sometimes wonder why the likes of @Tamara go to the efforts of writing such in-depth and informative posts, as one model run can lead to "zonal train for days/weeks to come" type posts, when we have had full warning of this current period of modelling and our possible routes as we head toward the new year.

I appreciate that not everyone will share the views, but so far.......so good imo.

Thanks Tamara, I always enjoy reading your posts!

Edited December 18, 2017 by karlos1983

[Guest]

IT'S TIME TO THINK OUTSIDE OF THE BOX

We know that all the models have their own biases and vulnerabilities and when there are considerable uncertainties regarding a "possible" broad scale pattern change, all the models tend to struggle factoring in any changes and the timing of these. The strong preference is to revert to climatology which at this time of year is when we usually see a very strong and highly organised PV with the jet stream at around its most powerful and often pushing right across the UK. This can lead to a train of LPs crossing the Atlantic with some stormy conditions or at least unsettled and windy weather - mostly pretty mild but with the chance of brief Polar Maritime shots which can produce short-lived colder snaps with perhaps some temporary wintry precipitation and if a ridge in between systems can produce the odd overnight frost. Even when we see some pretty blocked patterns in late November or early December, these can be blasted away very quickly. Whilst it's easy to believe that these pretty typical early to mid-winter conditions will usually hold sway, we know that this is not always the case. It's not just the models that tend to revert to climatology, it's most of us too! Whether we are newbies, amateurs with a whole spectrum of experience or even professionals with all the modern sophisticated tools at their disposal, our mind set is almost conditioned to expect the "norm" ! Now, I realise that I'm being flippant and I have no intention of being disrespectful to anyone, especially those with considerably more expertise than myself but please bear with me.

Anyone who reads my posts will know that I'm a "coldie" and always looking for signs of changes to colder patterns but "most" of the time I do try to provide some balance to what I say as well as assessing the evidence. Most (but by no means all) of the members who visit the model thread are seeking cold set-ups and particularly those that deliver some snow events. That's why following the typical model output can quickly take one from agony to ecstasy and back again but let's take all the "emotion" out of this for now. 

From everything that I have studied and posts that I have read (on this and the strat threads) I can see that we have a highly unusual set up. Our teleconnection specialists who focus on the background signals that drive the model output and the longer range forecasts have highlighted a "possible" broad pattern change to a colder regime but with uncertain timing and how long the transition and evolution might take (perhaps around the turn of the year or into early January). They have frequently updated us and pointed out the downside risks. This is the battle between the re-amplification processes and a strengthening and more organised PV and more powerful jet stream. Even if the latter materialises and manages to flatten the pattern, all might not be lost. If there are still underlying amplification signals (I won't go into the relative impacts of the weak east Pacific based La Nina conditions, an eQBO, angular momentum changes, low solar activity, high Asian snow cover or near record low Arctic sea ice build up and abnormally high sea surface temperature there etc as I only have a limited understanding of the relative impacts of these processes) the PV can easily weaken again and/or take up a more favourable position/shape (from a UK colder pattern perspective) and the jet stream might weaken and/or buckle/meander and/or split and/or take a much more southerly route. I have pointed out in several recent posts how quickly patterns can change from an ugly looking PV and powerful jet to something very different, sometimes in just a matter of a few days. I demonstrated this with several analogues from past cold spells which I will not repeat here.  Most of you will remember last winter which had a very blocked and sometimes rather cold set up. We had a vast amount of MLB and very little HLB. Just like now (in fact far more unanimously) the models were predicting a breakdown to a very stormy and zonal flow from around the third week in December 2016. Almost all of us became resigned to a prolonged period of our "climatological norm" weather patterns. The exceptions were our teleconnection specialists who pointed out to a quick return to a blocked pattern. In fact @Tamara kept telling us that we would see almost entirely MLB and she was spot on (despite what some of the doubters have said in hindsight). Of course, MLB patterns rarely deliver more than the briefest of cold spells and that might be why quite a few members dismissed those predictions.

Now Tamara and others will always tell us that the signals and conditions can change and they always point out the downside risks and update us regularly on how things are likely to unfold. Our strat specialists (many of them are also but not exclusively teleconnection specialists) have also been explaining and demonstrating how unusual the patterns are up there. It's way above my pay grade (which is zero as far as professional meteorology is concerned!) to explain this in detail or accurately but in simple terms we have not been seeing (at least until recently) the usual stratosphere/troposphere connections for this time of year. It seems uncertain of how quickly this might change. There has been a lot of talk and hype about the prospect of a Sudden Stratospheric Warming (SSW - time for the mods to put far more of these commonly used abbreviations into automatic cursor slide-over full words for newbies to understand) event sooner or later this winter. I know just about enough of the basics to be aware about the reliance on.SSW events. We rarely see full on SSWs and many of them occur more naturally as the final winter warming events as we move into the Spring season. A strong mid-winter SSW will produce at lot of HLB patterns and displace much of the Arctic cold towards the mid latitudes. The UK will only sometimes be in the favourable position of this HLB. In fact SSWs can change the patterns and interfere with an existing colder regime. Let's say we manage to develop our cold regime setting in by early January, with (perhaps) a few northerlies but (probably) mostly easterlies (see my "northerlies vs easterlies debate" post from several days ago), then we get an SSW later in January. This could just as easily shift the cold pattern further east or west (with us in less cold or mild conditions) as it could prolong or enhance the existing cold. What we see more often are one or more short periods of moderate strat warming - in fact this happens to a lesser or greater extent in many of our winters. This can assist in producing a colder period, especially when it's in conjunction with an amplified MJO in it's 7, 8 and 1 phases which favour HLB. The other thing about SSWs, is that we do NOT have to rely on them to deliver winter cold spells. Far more winter cold weather has been produced with little or no assistance from strat. warming. The epic winter of 1962-63 did NOT see a full on SSW but did see several brief periods of modest strat warmings. I'm not saying whether or not we'll see an SSW this winter, just that we certainly do not "need" to rely or hang our hopes on one. 

The other thing that I have observed is that many posters deny seeing even the remotest chance of an easterly. Even if we get lucky and the building blocks for a colder regime fall into place, it's likely to take a while for an easterly to evolve (again, I covered this about a week ago). So, let's say the pattern changes (which I believe are far better indicated than some seem to realise - see below) to colder conditions take place around the turn of the year or during the first week of January, an easterly might not appear until a few days later (we could go straight into a Scandi HP but equally we could go from a brief northerly which veers to east). In fact the latter might be better for early cold prospects as the northerly would help to build a cold pool in Europe and then we can tap into it with our easterly. If we get a faster easterly evolution, then we may have wait a while for the deeper cold air to arrive. That's why we need to be very cautious initially of looking at a normally very reliable early indicator, the ensembles for "De Bilt". I see that yesterday's 0z set showed pressure rising towards the the end of the run (which still ends rather too soon to provide any firmer indication, quite apart from it running into the normally more unreliable period). The comment was that it didn't show any real downturn in temperatures (850s or surface values). So, although the higher pressure might be over central Europe with De Bilt and us on the warmer (or less cold) side or could equally be the early stages of an easterly evolution with the more significant colder air still several days further away.

I am also surprised that so many on here seem to feel that the models have not been indicating any changes to a colder regime or even moving away from that altogether. This takes me back to what I said in my opening paragraphs and have "banged on" about in many of my recent posts. I have been focusing on two things: firstly the longer term to see the range of outcomes suggested by the models and specifically the number of ensemble members suggesting a pattern change to a cold(er) regime and secondly, any much earlier indications of these possible changes. The operational output has gyrated between warmer and colder evolutions from run to run. Given that the ensembles have shown two main groups (with varying degrees of support) for either solution the swings in the op and control runs is hardly surprising. Rather than moving away from favouring the colder evolution, I strongly feel that the reverse has generally applied in recent days! In fact, the previous ten GEFS longer term ensembles were pretty consistent with only yesterday's 0z (now 5 runs ago) temporarily dropping the cold signal (I commented yesterday on this unusual swing for almost all the ens. from mixed warm/cold groups to almost entirely warm and immediately  back to warm/cold on the next run). I started writing this report before the 6z runs rolled out. I was happy enough with the 0z runs with most of the models seemingly picking up on colder signals but the 6z runs have moved further towards this scenario. This is not to say that they'll swing back later but it definitely holds out greater hope for coldies. In fact, I see that there has been an increasing trend/support towards some colder (far from very cold) incursions in the shorter term. Even this week's return to mild weather is being watered down with HP much closer to us and at least some frosts (and fog) in the offing. Then the uncertainties really get going with some models showing milder and wetter weather for the Christmas holiday period but other showing much more Polar Maritime air in the mix with the chance of some marginal wintry conditions. I know that this will start to excite those (including me) who would like to see a white Christmas but I'm not counting on it at this stage. What is really encouraging me is the medium term (around D6-8) period with much stronger "earliest" signs of a possible move towards the cold(er) regime for January.. So I'll close with one of my cross-model analyses for this period using each model's most recent output:

                    UKMO 0z T+144                                    ECM 0z T+168                                       GFS 6z T+180                                    GEM 0z T+180

                        

 

                   NAVGEM 6z T+180                                JMA 12z T+180                            GEFS 6z T+180-  Control                       GEFS 6z T+180 - Mean       

                        

Even UKMO at T+144 (the furthest it goes out to on the Northern Hemisphere view) is starting to show signs of disrupting the PV as do "all" the other models to a lesser or greater extent in this period around a week or so away from now! The most consistent feature is the very strong push of the Pacific/Alaska ridge deep into the Arctic. Several models take this even further. Then deeper into FI we only have GFS and the ensembles to view. I am cheery picking just one for now which is the earliest time frame yet for a completely split PV:

       GEFS 6z T+264 Perturbation 19  

          

I will not show any more eye candy charts for the longer term now but there are plenty more of them there and we may see even more of these in future output "if" the models continue to home in on the pattern change signals. Finally, I have just read Tamara's excellent and encouraging update (whilst editing my post). Please read this very carefully and several times. She, as usual, points out the downside risks. I'll probably be back tomorrow - just can't stay away right now! 

Edited December 18, 2017 by Guest
Correct typos and check charts