Model Output Discussion - Staying cold into the new year

[danm]

1 minute ago, bluearmy said:

Day 10

Yes and no ..... there is only one model from top to bottom.  So it’s modelling the reversal and then goes on to model the remainder of the run.  That’s the no part. The yes part relates to the fact that models don’t deal with reversals too well as they don’t happen v often so as the run progresses, it’s likely to be even less reliable than usual. (Which isn’t great anyway) 

But the reversal hasn’t actually happened yet as far as I’m aware? Wouldn’t we expect further changes in the model output on how this impacts the trop once the reversal has occurred? 

[bluearmy]

6 minutes ago, Kentspur said:

Is that last image a long fetched Siberian flow from the NE? Beast?

The model does show a push of low temps west between days 12 and 30 which make it as far as scandi and e Europe 

 

2 minutes ago, danm said:

But the reversal hasn’t actually happened yet as far as I’m aware? Wouldn’t we expect further changes in the model output on how this impacts the trop once the reversal has occurred? 

we used to see an obvious change in the output once the starting data included the reversed flow but this was in a time when many models didn’t actually go as high as 1 hpa and had few modelling  layers in the upper strat.  The upgraded models we have now all go to the top of the strat and once the warming has actually begun up top (which it has now) then we should expect the model to do a good job. The actual reversal at 1 hpa is due to kick in tomorrow so if we see a discernible change in the output on Saturdays 00z runs then we’ll know why!  

[Cavehill Snow]

37 minutes ago, bluearmy said:

As shown above, too many clusters to get worked up over ...... just need patience until the output settles down .....we have a broad evolution but the envelope way too wide 

the extended period continues to show a relaxation of the cold but I’m way off being convinced that the onset of a reversal is a time for putting much analysis into output two weeks away .......

Quick question from a novice - is the icelandic shortwave @ECM216 nailed on to drop down, regardless of how far it goes n/s & e/w? Also, is it possible for the shortwave to drop favourably for us so that the eastern flow from Russia through Scandi can link up with Greenland heights? Tia

[chionomaniac]

19 minutes ago, Weathizard said:

Doesn’t downwelling start a while before the actual SSW event? There’s a few very good long posts on some other threads about it.

I think the point most are making is, ensemble suites are fickle at the best of times, let alone when we have such an unusual NH pattern and stratospheric warming occurring.
 

It does. But this year is so so different. We have the mid strat being put under so much pressure from both top and bottom. Lots of uncertainty in the trop output until how a subsequent possible split follows the displacement. 

[chionomaniac]

1 minute ago, Cavehill Snow said:

Quick question from a novice - is the icelandic shortwave @ECM216 nailed on to drop down, regardless of how far it goes n/s & e/w? Also, is it possible for the shortwave to drop favourably for us so that the eastern flow from Russia through Scandi can link up with Greenland heights? Tia

Anything at +216 isn’t nailed to occur anyway so trends and ensembles are the key here.

[sheikhy]

Icon changes and moves towards ukmo at 72 hours with that kink steve mentioned!!

[SMU]

ICON rolling & the macro analysis shows more of a kink to the flow in Europe - like the UKMO

Also lower heights over UK....

18z first-

[danm]

12 minutes ago, bluearmy said:

The model does show a push of low temps west between days 12 and 30 which make it as far as scandi and e Europe 

 

we used to see an obvious change in the output once the starting data included the reversed flow but this was in a time when many models didn’t actually go as high as 1 hpa and had few modelling  layers in the upper strat.  The upgraded models we have now all go to the top of the strat and once the warming has actually begun up top (which it has now) then we should expect the model to do a good job. The actual reversal at 1 hpa is due to kick in tomorrow so if we see a discernible change in the output on Saturdays 00z runs then we’ll know why!  

Thank you!

[SMU]

1 minute ago, sheikhy said:

Icon changes and moves towards ukmo at 72 hours with that kink steve mentioned!!

you dont need me anymore

[bluearmy]

5 minutes ago, chionomaniac said:

Anything at +216 isn’t nailed to occur anyway so trends and ensembles are the key here.

Although we have seen two instances of troughs dropping from that area into nw Europe in December. Another one is surely the form horse .....the ens support the evolution but how far south and at which longitude is the issue now imo. 

[sheikhy]

4 minutes ago, Steve Murr said:

you dont need me anymore

Steve just look at the difference of the flow at 102 hours compared to the 12z!!!

[The Beast From The East]

4 minutes ago, Steve Murr said:

you dont need me anymore

Oh yes we do

[BARRY]

4 minutes ago, Steve Murr said:

you dont need me anymore

oh yes we do still waiting for that Boom 

[chionomaniac]

Just now, bluearmy said:

Although we have seen two instances of troughs dropping from that area into nw Europe in December. Another one is surely the form horse .....the ens support the evolution but how far south and at which longitude is the issue now imo. 

I agree, but at that timeframe the form house has to have negotiated two rounds of fences and still has another jump before finishing off in the home straight lol. 

[Allseasons-Si]

Oooooh!,....the..

...are playing havoc with the models

look at the heights gaining south of Greenland.

18z v's 12z

 

[Battleground Snow]

4 minutes ago, sheikhy said:

Steve just look at the difference of the flow at 102 hours compared to the 12z!!!

Hey 2 posts about icon before I could get there ! I think the 12z had a malfunction, 18z much better with the heights further north and better alignment like the other models. Shame it only goes to 120

Edited December 31, 2020 by Battleground Snow

[sheikhy]

1 minute ago, Battleground Snow said:

Hey 2 posts about icon before I could get there ! I think the 12z had a malfunction, 18z much better with the heights further north and better alignment like the other models. Shame it only goes to 120

Waiting for that kinky chart of yours from the gfs 66 hour chart in a while!!dont let me down

[stodge]

Evening all

First, a Happy New Year to everyone on the thread and across NW especially the long-suffering Mods with whom, as you can see, I am shamelessly trying to curry favour.

Cold and still here in lowland East London with a maximum of 2c and a number of locations in the south-east had an ice day.

Last evening, there was a lot of uncertainty in the output especially from T+144 to T+240 so let's see if any of this has been resolved.

12Z GEM: T+120 tonight takes us to next Tuesday. Between a slack area of LP over Northern Italy and a ridge of HP from the Atlantic across northern Scotland to Scandinavia, an E''ly airflow covers much of the British Isles. As we are told these days, uppers mean nothing and we should be looking at dew points. Despite that, 850s are -4 to -8 generally. From there, a new LP develops to the north of Iceland and starts to move SSE toward the British isles as the HP splits with one lobe setting into the Atlantic. The new LP looks to be phasing with the residual trough over the Ukraine. Shortwaves over France but the Atlantic LP extends a ridge while the Atlantic LP is near the Canaries. Perhaps some slightly less cold air moving in from the north-west. Moving on and the LP moves south over western parts of Britain and Ireland and then more SE to be in the Channel by T+240. An E'ly flow re-asserts across northern parts as heights build back over Iceland and Greenland. Uppers remain -4 to -8 with some colder air still lurking in the North Sea to move across northern parts. I'm sure I'll be told it's all cold rain - I don't believe it (as Mr Meldrew would say).

12Z GFS OP - well, a cold or very cold evolution from GEM to start the evening. At T+120 no surprises from GFS OP. Uppers of -8 generally. From there, as you would expect, some differences emerge. The LP develops to the north and tracks south though well to the west of the British Isles. It phases with the continental trough which moves back over the south of England and across Ireland. The airmass over the British Isles remains cold at -4 to -8 850s with a SE'ly developing over northern Britain by T+180. Heights remain to the north west and north east. From there, the LP first shifts to the south of the British Isles and then moves ENE forming, by T+240, a complex trough over Central and Northern Europe. Heights in the Atlantic but a new LP forming to the west of Iceland. 850s remain at -4 to -8 at this time. After T+240, the LP over Iceland goes nowhere and the trough begins to fill and new heights build over Scandinavia extending a ridge SW across the British Isles which would suggest a drier evolution. The Atlantic airmass is trying to push in at T+312 but the Scandinavian block is holding firm and keeping the cold air over the British Isles. Further into FI, the HP moves SW to be over the British Isles as a deep LP and a cold lobe of air sink into eastern Scandinavia. There's a hint of ridging back toward Greenland by T+384. It's milder in the south but cold air is still over the north-east with some frigid air over Scandinavia.

12Z Parallel: another cold evolution from GFS but with that reversion to milder we've seen for the last few days albeit still at the far reaches of FI. Let's see what Parallel has to offer this evening - well, at T+120 no surprises. Uppers -4 to -8. The T+120 indicates instabilities to the north of Iceland and by T+180 a new trough has formed which is moving SE towards the North Sea. Heights remain to the west and a NW'ly airflow covers much of the British Isles. There's cold air to the east and moving down from the north and north west. The evolution to T=240 gets more complex - the trough effectively splits with one section moving quickly south into Europe and forming a new major LP in the Mediterranean which keeps an East or North-East flow across southern and eastern Britain. Part of the energy remains to the north west and forms a new LP to the west of Iceland but between them a small ridge of HP stretching from the Azores through central and northern Britain to Scandinavia keeps most settled and dry. Less cold is moving into Ireland but it remains cold or very cold over most of the British Isles. The milder air moves in from the west but with heights building across Scandinavia a battle ground develops and Atlantic LP disrupt against the cold block and shift SE across southern Britain into Europe. By T+312 the uppers are telling the story with -12 850s off the east coast and positive uppers over Ireland. As often happens with these battlegrounds, neither side wins - by T+384 there is a strong anticyclone over Scandinavia and a SE'ly flow over the British Isles with the Atlantic pressure systems driven back west. The 850s are turning much colder with -12 850s crossing into eastern Britain and -16 to -20 uppers in the flow over Europe so this could be dry and frigid air.

12Z ECM - I have to say the Parallel looks a real winter treat for some even if there's a temporary milder incursion. On then to ECM - the T+120 is as you would expect -the profile of the heights marginally different but -8 uppers widely across the British Isles. As with other models, new LP develop to the north of Iceland and start to move south but this phases early with the European trough and remains to the north and east so the airflow over the British Isles is a NW'ly but the uppers remain -8 so still cold. From there, the LP moves south r south west and phases with the Atlantic trough - with heights now rising to the south, the wind flow shifts round to a milder W'ly direction and I wonder if we're seeing a west-based negative NAO set up developing. Milder air coming into the south but still cold to the north.

Looking elsewhere, the 12Z Control is mostly cold throughout with milder air encroaching at the very end of FI in quite an unsettled synoptic pattern.

As for the 10 HPA charts, 12Z Control instigates an initial split at T+78 and while the PV regains some cohesion, it is split apart by a new warming in FI and by T+384 is in fragments. It's a similar evolution on the Parallel which begins the split at T+60 while the OP is much the same.

Conclusion: with the notable exception of ECM (which could be an outlier), another very strong evening's output for cold fans. The Parallel offers a huge promise of some really frigid air for mid month if we can get the Scandinavian HP in place (always a better bet for longer term cold than a Greenland HP). There's a lot of uncertainty into FI as you would expect - the extent to which that is being driven by events in the strat I don't know but the split now looks on at 10 HPA and I leave those with greater expertise than me to determine the speed of downwelling and the impact. The west-based negative NAO remains a concern but the overall picture remains cold and we're seeing from GFS the possibility that might develop similar to other recent fast downwellings in terms of allowing frigid air to transfer west from Siberia towards Europe. The times they remain interesting.

[Allseasons-Si]

The 18z ICON finishes in line with the other models at 120.

[Uncertainty]

Well what a year it’s been... Horrendous for the most part, but early 2021 brings with it possibilities for snow lovers that have been wholly absent in recent years. 
 

This was not looking the case in mid November, at that point in time the ‘factors’ that guide seasonal forecasters and lowly musers such as myself were ominous, we had

- Strong La Nina Forecasts

- Weird but mostly west QBO

- Some evidence the above 2 factors could weaken the MJO signal especially towards the western Pacific 

- Strengthening Stratospheric PV with v low polar cap heights 

- No Urals blocking to speak of

- Unfavourable  N Atlantic / N Pacific SSTs

- An unspeakably horrendous met office 3 month contingency planner for cold in November that gave a colder than average DJF CET <5% 

Add this to the generally flat westerly seasonal mode output generated in late November and based on the above factors...

In short, it was bleak.

And yet...

We are now at the point when we can confidently reason that those Seasonal forecasts were broadly wrong, perhaps fundamentally so. The weakening of the SPV, precipitated by the dominance of the Urals high in late November / December has exposed these forecasts as fantasy. 
 

With the fuse lit by record breaking pressure differentials from Mongolia to Kamacha the reversal of the zonal winds is now assured. This now looks like a long-lasting event, and present forecasts from the GEFS/EPS have for some time been indicating a second warming later in January that would surely toast and split last year’s nemesis into oblivion for the best part of the winter 

 

That is a serious reversal. Let’s be clear about that, not a quick dip into negative territory before a quick VI and game over for February. The longer lasting the better to ensure long lasting tropospheric effects and present evidence suggests that is likely.

The present cold spell we find ourselves in is causally connected to this weakening, as we would not be afforded the moribund Atlantic jet were have now were we in the canonical VI period we usually endure in this period. However, the full effects of the warming are still to be determined, but my educated guess is the SLP anomaly for JFM will not look like this, heights to the south, low to the NW:

On the contrary, for the NA sector it might even be reversed! The latest EC46 thinks so...Here’s week 4 which is fairly representative...

Hmm - Heights to the NW, lows to the south!

Maybe the seasonals got their colours wrong. Better luck next time

Now before we get to excited, the above is not a forecast for a very cold and snowy UK for the next 2 months, indeed, the extended range of the big three (11-15 days from now) have for many days been indicating an Iberian high and swerly string out between that and the Northern blocking.

This would be unfortunate but it may only be temporary before the full effects of the start warming leak down to the troposphere and fully reverse the flow. Regardless, the anomaly chart for the same date is still not reconcilable with the seasonal means

Mu point is, it really looks like a bust for the seasonals this winter and a huge boon for the human intuition and gut instinct that questioned them.

Happy new year and take care everyone. This forum is what it is because of all of you, the one liners and moans, the ramps and the out of the prams. The detailed analysis and the professional input. I’m sure, like me, it’s helped keep lots of people sane during a very trying and desperately sad year.

Roll on 2020.

[keithlucky]

51 minutes ago, danm said:

But the reversal hasn’t actually happened yet as far as I’m aware? Wouldn’t we expect further changes in the model output on how this impacts the trop once the reversal has occurred? 

The reversal is under way by the end of of next week the models will settle down,By the 12th January a total split and a total demise the strat votex, exciting times ahead.!

Edited December 31, 2020 by keithlucky

[moorlander]

First off wishing all a happy, illness free and peacefull new year.

None of us have a crystal ball nore a time machine to hand so take what ever this winter has to offer in the form of it was better than last year by a country mile and enjoy the up's any many downs of model watching. 

I still have high hopes of a memorable winter ahead.

Roy

[Allseasons-Si]

I had to bring out  @Mark wheeler's pet the mighty NAVGEM...

it make less fuss of that trough coming down from the north so it should disrupt favorably if that where the outcome come tomorrow.

18z gfs rolling out now for the final time in 2020

and i would like to wish everyone here in this thread and across the board at NW a Happy New Year,..a toast

                                                                                             

                                                                                                     

Edited December 31, 2020 by Allseasons-si

[NorthYorksWeather]

Anyone know if there is an 18z GFS this evening? A night off maybe?

[ICE COLD]

No 18z rolling yet ? That will top off this horrible year