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Paul

Model output discussion - winter proper underway

Paul

Please only post model discussion in this thread. 

For more general chat and banter, or moans and ramps loosely around the models, please head to the banter thread:
https://www.netweather.tv/forum/topic/86721-model-moans-ramps-and-banter/

For general weather chat including about the snow/cold chances around the country, please go to the regional threads:
https://www.netweather.tv/forum/forum/142-regional-discussions/

Thank you!

Message added by Paul

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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 !

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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. 

 

 

 

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Edited by Draig Goch

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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! 

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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.

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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

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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!

 

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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.

gensnh-21-1-240.png

gensnh-21-1-384.png

Edited by snowray

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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

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

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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...:)

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30 minutes ago, bluearmy said:

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

Some hope in the ECM clusters for that Blue:).

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Looks like we are going negative toward New year

ao.sprd2.gif

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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?

F541ABC6-6600-4D5E-AB0A-8CA6FAD37409.thumb.png.1413a1a4835f2c52535e7cb2b5f97d10.png

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

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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?

F541ABC6-6600-4D5E-AB0A-8CA6FAD37409.thumb.png.1413a1a4835f2c52535e7cb2b5f97d10.png

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

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31 minutes ago, Tamara said:

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

Fascinating as always. So would this be a fair summary - a good chance of the "hybrid" La Nina pattern disrupting the vortex, and a slightly lesser (though not insignificant) chance of a "traditional" La Nina bolstering the vortex?

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4 hours ago, booferking said:

There was a barrier erected on Greenland's coast line several years back so that would explain why we never see these heights smash through beyond the coastline i heard this in the grapevine the other day.:santa-emoji::drunk-emoji:

They got the idea after seeing just how effective our M4 is.

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MAKING SENSE OF THE VOLATILE MODEL OUTPUT

Although I will always look at any winter model output from a coldie’s perspective, I will try to provide much more balance in this post.  Apart from the usual issues governing how we react to and interpret any model output, when the possibility of a broad pattern change is on the horizon, we need to be particularly disciplined and patient.  This applies even more so to the vast majority of us here, when the suggested change is to a colder regime. These seem to be some of the issues:

a) Over the last couple of weeks our teleconnection specialists have quite consistently indicated that the background signals are pointing to a broad pattern change which is likely to favour generally colder conditions in Europe, including the UK. The likes of  @Tamara, @Glacier Point, @Catacol and @chionomaniac, have updated us at regular intervals to show us what we might expect. They have pointed out the possible downside risks but they have not mentioned anything to suggest a change of direction (at least up until 1030 this morning when I started writing this post!). ***EXTREMELY IMPORTANT UPDATE:  I was just finishing this post off and I see that Tamara has just provided another excellent "latest report" - we all need to take on board the "potential" for things to go wrong and should not allow ourselves to get over excited (or overly disappointed) at this stage. I will continue to look for cold solutions.***  Apart from "will it happen", a major issue concerns the timing of this pattern change. The window would seem to be from around Christmas time until early January (or perhaps a little later).

b) Assuming that we do eventually see this major change, in addition to the timing issues we do not know how long the transitional period will be (whether it will be a slow or fast evolution) and will it be a smooth change or a bumpy ride (with several advances and setbacks on the way).  From my experience, if we are to see a prolonged cold spell, these often take several weeks to evolve, although there are examples of a rapid change of type over just a few days (even here, I feel that there will still be plenty of clues in the run up to the cusp of that change).

c) Then we do not know how quickly and to what extent the models will pick up on these changes. Then some models are far too progressive and others might be well behind the curve. We know that all the models tend to struggle for a while when they start to latch on to a possible change and until there would seem to be more certainty of the eventual outcome, consecutive runs from the same model may show the change, then drop it and then pick up on it again later on. Even when one or more of the models pick up the pattern change signal more consistently, they then have to explore all the different routes to get from A to B. Given that this is a complex change that would go against the climatological of a strengthening PV and jet stream (usually at their strongest around the turn of the year), this presents additional issues for the models to overcome.  

d) The “window” and “timing” of this change presents a big problem for us model watchers.  Many (but not all of us) would like to see a cold and snowy period over the Christmas holidays. Although a generally milder period is predicted for next week and the run up to Christmas, this does completely exclude the chance of one or two further cold shots prior to the broader changes later on. If (and it’s a big if) we can all take the emotion out of this, I feel that most of us would be happy to see a mild Christmas in exchange for a prolonged cold spell during January.

e) The biggest “timing” problem is that the main changes are indicated for deep FI or even slightly beyond that time. Today’s GFS output for T+384 only takes us to December 31st. If the major changes are to occur towards the end of the window (in early January) then the distant output still doesn’t yet cover that period. We can get an idea from the usually rather less reliable extended output like the EC, Met Office and NetWeather monthly updates but remember that they too have to decide how to factor in and interpret how these particular background signals might play out and unfold for Europe and the UK.  In fact their long range forecasts are generally based upon even more distant FI model output plus some guidance from experienced professional forecasters.

f) We know that model output much beyond D7 usually becomes much more volatile. What I have said in several similar posts recently, is that we can look for some consistency in the more distant output to see if it does seem to be picking up any signals that suggest a broader pattern change and then we can examine how each run evolves to get to that final outcome. The main stumbling block is that most models’ output ends by D10 or even before then for UKMO (D6 or D7 for the west Atlantic charts) and NAVGEM (D7/8).

g) We have seen the usual run to run volatility and quite apart from nailing down any longer term pattern changes, there is still considerable uncertainty and inconsistency for the middle period and the run up to and including the Christmas holiday. @Team Jo amongst others quite rightly reminded us yesterday not to get too hung up on one particular model run as there will be significant changes for better or worse for many days yet. I agree with that general advice but we can analyse particular runs to see what type of evolution might get us nearer to the pattern change that most of us are hoping for. For example, I did a shorter post (by my standards) yesterday (on page 41) going through the GFS 12z run. I described how the run appeared to be taking a route towards an eventual easterly. This was one of their most comprehensive runs showing the colder regime outcome. The next GFS run, the 18z departed from this outcome (resulting in the usual dismay!). The purpose of my analysis was not to over excite everyone (and I apologise if I appeared rather too bullish) but to demonstrate what might be achievable and what signs to look out for in a route to cold. For the sake of saving my reputation on this thread, I shall probably avoid falling into the same trap of over analysing a single model’s output and stick to my more balanced approach of cross-model analyses in between my main reports.

h) Even if we do manage to get to that much colder regime, there are various ways that the final set-up can end up and a vast number of routes to get there – that’s one of the most exciting aspects of model watching.  I have noted some disagreement between some of our regular posters about whether a northerly or easterly pattern will become establish (with heights either building to our north-west or north-east). If we are to see a prolonged cold spell, history tells us that many of them feature both patterns and can alternate between the two (usually predominantly easterly or polar continental but with occasional Arctic incursions such as in December 2010). Long northerly spells are extremely rare and even the most stable looking of set-ups can often be quickly overrun and pushed away by a change in the jet stream. A pattern from predominantly an easterly quarter can last for days or even weeks on end once established.  The background signals favour an eventual build of heights to our north-east. It would be quite possible to get there with an initial build of heights to our north-west, say towards Greenland and then the HP linking up with HP further east (Scandinavia and/or Russia/Siberia) with the pattern veering from the north to north-east or east. This happened in December 1962 and with a number of other long cold spells since that epic winter.

Right with all that in mind, I am going to have another look at the most recent output. I will cover the long-term output in this post with GFS and GEFS charts. I will prepare another fuller cross-model comparison for the D10 period so that ECM and GEM can be brought into analysis in my next post (either this evening or tomorrow morning). It may be that those models are not favouring the cold regime change at the moment.

       GFS 6z for 0700 Dec 31st:          GEFS 6z for 0700 Dec 31st:                    Control                                                Mean

       gfsnh-0-384.png?6?6                                                                           gensnh-0-1-384.png             gensnh-21-1-384.png      

Although we still haven't quite got to the easterly, the GFS 6z produces another example of almost getting us there at the end of its run. It has a +PNA with a strong belt of HP passing right across the Pole and towards northern Russia and on south-westwards from there through Svalbard and down to the Norwegian Sea and into northern Scandinavia. The vortex is totally split and that is usually a wonderful sight for coldies! We can ignore the Greenland HP (at this stage) as it mostly represents the thick ice sheet and high plateau there and is not a true surface HP. Significantly there is another belt of HP ridging from western Russia through to southern Scandinavia. There is LP over north-west Russia and low heights over central Europe. The LP to our west looks dominant but I'm almost certain that it is not! I do not think it'll make any eastward progress and in any case its developing a nice negative tilt with south-easterly winds and some cold continental air looking set to drift into eastern districts (that would perhaps produce a brief battle zone snowfall but probably starting as rain - no point in getting into any detail this far out). The HPs to the north-east and north are likely to dominate developments going forward. If this was anywhere close to the actual pattern at the time, I feel that the easterly is only a couple of days off from there. CAUTION: just one run and similar to the earlier GFS 12z run but very different to the intervening 18z run - I expect similar lurching from one (cold) outcome to another (warmer solution) from the next few runs.  

The GEFS control chart (above) is also not that far from producing an easterly.  Again with a +PNA and HP into the Pole. The LP over us is sinking southwards and as it does that it'll introduce colder continental air and with the HP over north-west Russia already ridging into Scandinavia, it'll drag in the easterly behind it. The mean chart (the last one above) obviously averages out all the perturbations and can mask some of the more extreme solutions (whether warmer or colder) in the ensemble suite. You can still see that overall GFS is favouring the pattern change but it's unclear where it'll set up. There is a fairly positive PNA (which must mean that some runs have a more neutral PNA) and still HP across the Pole and linking with HP over Siberia and northern Russia (a strong signal) and weakish LP in the Atlantic (must mean a range from some much deeper LPs and some with HP there).

So, with that "uncertainty" I move on to the perturbations. The full GEFS panels are often posted on this thread but they always seem to come out as a block of very small charts and are difficult to view (or is that just me finding this problem?). Just for once I thought I’d post each chart individually for a closer examination. As useful as the ensemble comparison graphs are they can cover up some important detail which might lead one to a rather different conclusion:

GEFS 6z:         Perturbation 1                               Perturbation 2                                 Perturbation 3                                Perturbation 4

              gensnh-1-1-384.png        gensnh-2-1-384.png        gensnh-3-1-384.png       gensnh-4-1-384.png

                            

GEFS 6z:         Perturbation 5                               Perturbation 6                                  Perturbation 7                               Perturbation 8

              gensnh-5-1-384.png        gensnh-6-1-384.png        gensnh-7-1-384.png        gensnh-8-1-384.png 

 

GEFS 6z:         Perturbation 9                               Perturbation 10                                Perturbation 11                             Perturbation 12

              gensnh-9-1-384.png        gensnh-10-1-384.png         gensnh-11-1-384.png      gensnh-12-1-384.png

 

GEFS 6z:         Perturbation 13                             Perturbation 14                                Perturbation 15                             Perturbation 16

               gensnh-13-1-384.png        gensnh-14-1-384.png         gensnh-15-1-384.png       gensnh-16-1-384.png

 

GEFS 6z:         Perturbation 17                             Perturbation 18                                Perturbation 19                             Perturbation 20

               gensnh-17-1-384.png        gensnh-18-1-384.png          gensnh-19-1-384.png       gensnh-20-1-384.png

Phew, I'm not going to this again!  Not only is it very tricky, it's also difficult for me to read the charts and comment on them afterwards, especially with this new rule of a maximum edit time of only 5 minutes. So, from my earlier notes (I may have a few small inaccuracies in this part), I will say that perhaps it's easy to conclude that perturbations 2, 4, 5, 6, 7, 12, 15 & 17 offer warmer solutions and an ens graph might well show these as the equal largest group. Most of these, however, still have a mostly blocked Atlantic and only some of them have a stronger Atlantic flow. Perturbations 1, 3, 8, 9, 13, 18, 19 and 20 (the equal largest group) have pretty deep LP sitting either right over the UK or to our west but mostly with either Arctic or Polar Maritime air in its circulation. The remaining four, perturbations 10, 11, 14 and 16, have various forms of HP close to or over the UK.  The majority of the perturbations have colder than average conditions, several are much colder. A common theme through, is that most of them have a +PNA and HP somewhere in or across the Arctic. Even several of the warmest charts for the UK have intense HP in the Arctic. On most of these the vortex is at least under attack and in some it's broken. This generally is indicative of an upcoming pattern change. Some are far more progressive than others. Overall, plenty of uncertainty but totally absorbing model watching. 

 

Edited by Guest
Correct typos and check charts

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Maybe the meds will go back in the cupboard after the 12z..

Much more favourable synoptics already.

A slower evo-perhaps but again early positive signs...

Let check the suites out-evolve!!!

Try taking the eye off canadian lobe..

And set-for pacific/russian exactions....

gfsnh-0-84.png

Edited by tight isobar

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1 minute ago, tight isobar said:

Maybe the meds will go back in the cupboard after the 12z..

Much more favourable synoptics already.

A slower evo-perhaps but again early positive signs...

Let check the suites out-evolve!!!

gfsnh-0-84.png

I’m baffled and this isn’t the first time. :wink: What on Earth are you seeing? I see no difference. 

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On 10/12/2017 at 22:19, gottolovethisweather said:

For anybody wondering, we humans and current computer modelling techniques do NOT allow us to know anything for certain, as denoted by what has just happened over the past 24 hours with the snowfall. Not an attack on you, per se but your highlighted sentence above should perhaps replace the word "knows" so that it states "supposes" or "forecasted" i.e. guesswork. Yes, it is the best advice we have on offer currently and all of us will interpret things differently as do all the various weather models and their individual members runs. I would suggest others follow who or what model they want to but never take anything for granted. My prediction is the milder zonal blip will be brief in duration and to be fair, we can't even predict what will happen tomorrow yet with any great certainty either. The bigger stratospheric effects are often lost on me so I'll take on board others views there but I will never take any forecasts post D4 with high confidence levels, more especially so at this time of year.

 

Night all, enjoy the snow where you have it and do take care out there during that morning commute. :hi:

1

Some fantastic input in here again today, thanks, guys n gals.

The 12zs are rolling and tonight's ECM will provide those first clues for the big day. Well, it's been nearly a week since I posted and the fears of a mild zonal onslaught (often a default UK winter pattern in recent years) has barely come to fruition for any part of the UK. The first double-digit maximums are forecast on 20th December, the first time Newbury has seen such temperatures for many weeks.

Now upon stepping back from the inter and intra-runs of the various model outputs for several days, my feeling is that only the far NW and perhaps western parts will see much Atlantic frontal influence in the run-up to Christmas. As for IMBY, I'm happy to bank the frosty, sometimes cloudy but dry HP dominated setup. As at least getting about, rarely being soaked to the skin and a general dryness is a far more pleasant winter weather type than predominant southwesterly driven moisture-laden onslaught. I think this HP dominance will gradually push Northwards and perhaps, allow a return of the NW-SE diving shortwave scenarios in time for the Christmas break. A Boxing Day wintry breakdown from the NW possibly? Could well be the case, so watch this space! :friends:

Edited by gottolovethisweather

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10 minutes ago, Daniel* said:

I’m baffled and this isn’t the first time. :wink: What on Earth are you seeing? I see no difference. 

Atlantic ridge slightly stronger at 138 hrs tbh.but not a lot!!!!

Edited by swfc

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10 minutes ago, Daniel* said:

I’m baffled and this isn’t the first time. :wink: What on Earth are you seeing? I see no difference. 

Watch as  the run opens up @around 192 for phasing.

And the devolpment of backing of heights into greenland.   In snapshot.

Should be benificial..although minimal!!

But we need these micro exacting placements within early frame.

Screenshot_2017-12-15-16-07-37.png

Screenshot_2017-12-15-16-06-58.png

Edited by tight isobar

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3 minutes ago, swfc said:

Atlantic ridge slightly stronger at 138 hrs tbh

It’s not being slightly pedantic the run looks a bit flatter however only up to T150.

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