Model output discussion - winter proper underway

[feb1991blizzard]

2 minutes ago, northwestsnow said:

6Z just looks very very wet - no easterly that i can see...

Trend there - split PV, it would happen down the line - all the GFS is at that range is one ensemble member, look through the GEFS suite when it comes out and see how many have that massive split of the PV.

@swfc its been showing reasonably consistently now albeit with differing levels of greatness wrt UK potential snow setups.

[Singularity]

The progression we're seeing the models explore (somewhat inefficiently perhaps, but getting there) is one in which the Canadian vortex has a window in which to venture towards Europe via Greenland, but then comes under attack from upstream changes with the Pacific ridge heading back poleward and initiating a buckling of the jet pattern that should encourage the vortex lobe to come apart a bit, with some getting pulled back into N. America while the rest either heads into Europe (as either a large organised trough as 00z ECM tries for or a smaller one following trough disruption as per the 00z) or digs south in the middle-N. Atlantic. 

The former resembles our predominant pattern of Nov-Dec so far, but tweaked to allow for more the way of Scandinavian height rises as a follow-up to the trough dropping in. The latter is a different path, more like we had to go through in Nov 2009 - and laden with the risk of some mild, wet weather while we wait for ridging to make its way sufficiently north from Europe to turn the tables in favour of cold. This manner of evolution has a habit of drying out just as it turns cold enough for snow, though.

GFS 06z is very much the latter scenario. 

 

This setup is also easy to tilt unfavourably with a bit of climatological bias and/or over-deepening of troughs, which I believe explains some of the less than inspiring ensemble behaviour of late. 

It is for reasons like this that the festive period has a valid stormy weather risk, but given the (at least) equally plausible alternative scenario of a trough setting up over Europe again, I'm not inclined to expect a windy washout route at this stage. 

GFS still managed to get quite close in the end on a hemispheric scale - a nice interpretation of the Pacific-Scandi relationship, shame about that dartboard low!

[Daniel*]

Just now, tight isobar said:

As i suggested-previous post-.. not wriiten off yet-12z- 

But if you fail to see a backtrack via gfs then i just dont know??

Given that after 240 things get interesting ...but when dint they of late via gfs model..

Lets see where we are @tea time!!??

I don’t see a backtrack as such still interested in amplification in D7 now even the ECM clusters are solidly behind it that is a GFS win here immaterial to final outcome.

GFS 06z ends on an interesting note again height rises to N/NE. Reasons to be optimistic IMO.

[N/A]

GFS 6z, can't upload any charts atm but really liking that high pressure sat over or close to southern UK throughout next week, some decent prolonged dry, mild perhaps even sunny weather at times for the run up to Christmas. It's not until Boxing Day, it could turn wet and very windy albeit very mild in the west but of course that's a long way off. 

Edited December 15, 2017 by Dafydd Tomos

[bluearmy]

3 minutes ago, Daniel* said:

I don’t see a backtrack as such still interested in amplification in D7 now even the ECM clusters are solidly behind it that is a GFS win here immaterial to final outcome.

GFS 06z ends on an interesting note again height rises to N/NE. Reasons to be optimistic IMO.

The amplification at day 7 is not a sustainable one 

The 06z op is not that far removed from the 00z in evolution with the jet headed for Iberia and building height rises to our ne over time 

bit of patience required as might not happen first bite at the cherry as singularity has referenced  above 

[ICE COLD]

Just a question from me . The last cold / snowy snap that we just had last weekend didn't the pattern keep backing up west as we got closer to the cold spell . Just thinking it may do the same this time around the 23rd + 24th . Or am I wrong ? ?

[phil nw.]

1 hour ago, TEITS said:

I find the difference between GFS & other models fasinating. Yet again we see the GFS Op run supported by the GEFS control.

For the sake of everyones sanity it is best to assume the GFS is wrong and that Xmas is likely to be mild. However I certainly wouldn't be willing to bet on this just yet!

Beyond Xmas and I shall repeat myself by saying a return to a colder pattern is much more likely to come from N/NW than the NE/E.

Yes any cold is more likely from the nw as i posted yesterday- looking at eps/gefs again this morning pretty much confirms this.

Overall it does promise a pretty mobile outlook with the Canadian trough extending well into the Atlantic as we approach the holiday period. Apart from the upstream ridge,the Atlantic jet looks comparatively flat however  with cold air close by to the north it wouldn't take much buckling of the jet to bring it south behind passing frontal systems.

 

Edited December 15, 2017 by phil nw.

[Daniel*]

12 minutes ago, bluearmy said:

The amplification at day 7 is not a sustainable one 

The 06z op is not that far removed from the 00z in evolution with the jet headed for Iberia and building height rises to our ne over time 

bit of patience required as might not happen first bite at the cherry as singularity has referenced  above 

Well regardless this may change. I only see one example of a somewhat sustainable ridge amongst 00z GEFS. Perb 13 hopefully thirteen is not unlucky in this case.  

Edited December 15, 2017 by Daniel*

[Faronstream]

GFS 06Z looks pretty good with HP influences over scandi around christmas and towards new year, frosts and dry weather for many parts of europé expect England, we have seen far worse than this

[Daniel*]

Ghastly evocative to Winter 2013/2014 no thanks! 

 

[bluearmy]

I can’t take 3 monthly means as worth anything re detail

a single month is difficult enough to draw any conclusions from but 90 days!!

we could have two weeks of wintry nirvana second half jan with that pattern shown on the tweet for the remainder of the period and we wouldn’t see it. 

We also wouldn’t see repeating wedges of heights which could lead to sliders on that chart -  you can make a prediction that the three months is likely to return an above average temp profile but that’s about all !

I don’t see a euro high btw !

[ACCOUNT DELETED]

GEFS 6z for Porthcawl (nr Swansea) shows milder weather returning, especially in the upper air temperatures and a quick rise in pressure from now, quite a strong high pressure too approaching 1040mb with 12-13C possible by Tuesday before turning a bit cooler, as expected precipitation looks fairly low (although there are a few 'spikes') until Christmas on this run, so a very different feel after the cold weather we've had so far this month. 

 

 

 

Edited December 15, 2017 by Draig Goch

[NorthernRab]

11 minutes ago, Daniel* said:

Ghastly evocative to Winter 2013/2014 no thanks! 

 

Difficulty with 3 month mean charts over Jan-March, as mentioned by @bluearmy above, is that they could contain 5 weeks of blocking in Jan / early Feb of various intensity followed by 8 weeks zonality or vice versa.

In short, not particularly helpful! 

[Daniel*]

2 minutes ago, NorthernRab said:

Difficulty with 3 month mean charts over Jan-March, as mentioned by @bluearmy above, is that they could contain 5 weeks of blocking in Jan / early Feb of various intensity followed by 8 weeks zonality or vice versa.

In short, not particularly helpful! 

True, but definitely a deeply unsettled winter it depicts especially for the NW. All three also suggests the jet stream will be more S than climatological norm, so we may get on the cold side of some quite inclement wintry weather. Best thing as blue says no strong signal for a Euro high dominated winter which often is the spanner in the works.

[bluearmy]

Looking through the ec clusters and the theme of the gfs 00z and 06z ops is not without reasonable support. 

I would certainly be looking at this general evolution becoming more evident as we head through week 2

[northwestsnow]

3 minutes ago, bluearmy said:

Looking through the ec clusters and the theme of the gfs 00z and 06z ops is not without reasonable support. 

I would certainly be looking at this general evolution becoming more evident as we head through week 2

Yes on balance i agree blue- think patience is going to be required for any meaningful cold- my issue is once a zonal set up gets going (in recent years esp), it becomes a huge task to shift it!

 

[snowray]

10 minutes ago, northwestsnow said:

Yes on balance i agree blue- think patience is going to be required for any meaningful cold- my issue is once a zonal set up gets going (in recent years esp), it becomes a huge task to shift it!

 

Indeed, it becomes almost impossible to shift and if thats the theme going into January well that this is a worrying trend that we have seen a lot in recent winters.

Edited December 15, 2017 by snowray

[markw2680]

11 minutes ago, northwestsnow said:

Yes on balance i agree blue- think patience is going to be required for any meaningful cold- my issue is once a zonal set up gets going (in recent years esp), it becomes a huge task to shift it!

 

Quite right about zonal but this isn’t like normal winters for us, so far anyway so I don’t think any zonal will be as stubborn to shift as normal. We shall see

[bluearmy]

a zonal flow into Iberia will be just fine  .......................

[northwestsnow]

1 minute ago, bluearmy said:

a zonal flow into Iberia will be just fine  .......................

Haha yes blue it certainly would!!

Watching brief for me for a few days- hope things move in a positive direction for the coldies over the subsequent NWP outputs...

Fingers crossed...:)

[phil nw.]

30 minutes ago, bluearmy said:

a zonal flow into Iberia will be just fine  .......................

Some hope in the ECM clusters for that Blue.

[winterof79]

Looks like we are going negative toward New year

[Tamara]

Posted this extract below from a post made the last week of November. Against the background of encouraging a-typical Nina signals that have evolved during the subsequent period and been discussed in detail in a variety of subsequent posts, the echoes of this earlier thinking revolving around the North Pacific ridge and the quite different potential downstream solution possibilities that stem from it, have always stayed just below the surface - and as suspected, still cannot be dismissed 

In terms of the stratospheric feedbacks though, the question mark in my mind is the extended hints of the Pacific pattern starting to show the first signs that La Nina is going to tighten its control from upstream with the building of the Alaskan ridge. On that basis a highly anticipated two week stratospheric forecast is just that, and on the basis of potential upstream changes that ultimately spell return of the jet, it cannot be wholly assumed it will automatically favour this side of the pole as the Pacific pattern starts to take control.

So I don't personally agree with some of the views being expressed that this is a "good thing" for downstream prospects in terms of sustaining a cold weather pattern beyond the early to (possibly?) mid December period. Its a typical La Nina development that often happens as wavelength cycles occur with the change of month and season and has the effect of increasing Canadian cold and re-booting the energy into the downstream polar jet. Such inications are minority model solutions at the moment that show increased upstream flow in FI, but I think its not a case that they are automatically wrong, simply maybe on the progressive side

Note the reference yet again to seasonal wavelength changes in terms of the tug o' war between the various competing drivers.

This, to repeat yet again as in all other posts, is something of a make or break factor in terms of whether the atmosphere continues to go along the Pacific "destructive" Nina tropical forcing path (hence the evolution to a poleward Pacific ridge, westwards shift in the polar vortex to the NW, and ascendant heights to the NE) or the more traditional La Nina Pacific ridge (which pressurises the downstream vortex leading to increased polar jet flow upstream, and increased temperature gradient, and flatter faster northern arm jet flow over a de-amplified Atlantic ridge)

There is even a hybrid version of the two that is conceivable - implying some Atlantic trough disruption, heights attempting to rise to the NE, but with angular momentum still not sufficiently elevated relative to La Nina to allow the North Pacific ridge to become enough of a poleward cross polar -AO feature to reduce the influence of the Canadian vortex bleeding too much energy into the Atlantic to back the cold west. I believe a few of the recent winters since the cold period up to 2012/13 have illustrated the latter two less favourable (for cold weather wishers) themes and which have been a bane to the majority of the seasonal audience of this thread.

I think the equatorward propagation of the stratosphere>troposphere wave coupling leading to +NAO that is currently discussed in the relevant thread is part of the more traditional Rossby wave propagation that occurs when atmospheric angular momentum is in a cyclical downward phase (which, as totally expected, it now currently is) and effectively, at least temporarily, cancels out any troposphere>stratosphere +AAM poleward rossby wave propagation that has previously been imprinted by tropical convection>extra tropical processes - and conversely attempts to amplify the tropospheric pattern

In simple language it explains the mixed competing NWP messages that have been suggesting quite different things evolving - and means :

The difference between a La Nina Pacific ridge pattern hybrided by an opposing (almost El Nino like) tropical convection pattern which triggers poleward propagating rossby waves to amplify the tropospheric pattern and further perturb the polar vortex at higher latitude through +MT events

and,

The much more traditional La Nina rossby wave train which bolsters sub tropical ridges in both the Pacific and Atlantic, increases polar jet flow and an associated downside +NAO signature

The question remains, is the current complex competing stratosphere and troposphere processes just a smokescreen hoop to jump through before the east based La Nina Pacific tropical part comes into play once more and leads to the much discussed and anticipated return of -AO, emergence of Scandinavian heights, and cold backing south and westwards - or is there going to be another final stumble again to the traditional La Nina flatter +AO/NAO pattern?

No-one, including the wisdom of the Met Office, equivocally knows the answer to this - but I think for now at least that percentages still favour the momentum of the Nina east based tropical pattern disconnect and therefore no reason, at this time, to allow too many longer term conclusions to be drawn beyond the current stratospheric>tropospheric dance and lull in the AAM cycle which is leading to the upcoming +NAO phase

That said, I think based on the continued intense focus on this thread of NWP suite ups and downs, it does no harm though at all to keep track of a few grounding realities on the way

 

 

[karlos1983]

I see tropical storm Kai-tak has formed near the Philippines and is due to track west over the Philippines and in to the South China Sea. Could this be a potential spanner in the works?

we would prefer to see these moving out into the Pacific?

[georgiedre]

7 minutes ago, karlos1983 said:

I see tropical storm Kai-tak has formed near the Philippines and is due to track west over the Philippines and in to the South China Sea. Could this be a potential spanner in the works?

we would prefer to see these moving out into the Pacific?

I remember from before that they need to go into the north Pacific to affect our weather