Model output discussion - Christmas approaches

[Mark Parsons]

1 hour ago, Paul_1978 said:

The charts are dated 25th and 26th December. Has anyone been expecting anything of note before then? I’ve not seen anyone expecting any particularly cold or snowy on or before 24th Dec. 

South West weather presenter David Braine this morning was showing a sleet symbol for Thursday next week and he said things could get quite interesting by the end of next week...........

[Ali1977]

6 minutes ago, tight isobar said:

Stil separation- but the mean and members arguably trending colder with more members.. some absolute crackers in there too

What is still noticeable is the precip spikes 23/24th, so these will be the sliders/snow events coming in from the SW. all still to play for!!! 

[snowking]

On 17/12/2021 at 11:20, bluearmy said:

Thing is kris, does the dense cold air have long enough to establish over scandi to deflect the jet se?  I’d say perhaps not - and the griceland heights will play a bigger part ….their lessening over the past 36 hours responsible for current modelling trend to bring the lw trough in at too high a latitude and phasing with the scandi trough too far north ….

of course still time for those heights to be modelled stronger 

Yeah that's a good point and we have to be mindful that the ECM in particular has been prone to exaggerating heights near Greenland in the mid term for quite a few years now (to the point that when it gets one right, it's normally just stopped clock syndrome). Then again, certainly when thinking back to Jan/Mar 2013 we also saw underestimation of the resilience of the Griceland wedge in the medium term across most models, so all in all, clear as mud

[Met4Cast]

1 minute ago, snowking said:

Yeah that's a good point and we have to be mindful that the ECM in particular has been prone to exaggerating heights near Greenland in the mid term for quite a few years now (to the point that when it gets one right, it's normally just stopped clock syndrome). Then again, certainly when thinking back to Jan/Mar 2013 we also saw underestimation of the resilience of the Griceland wedge in the medium term across most models, so all in all, clear as mud

Apparently this problem was fixed in the most recent update

[snowking]

On 17/12/2021 at 11:43, Met4Cast said:

Apparently this problem was fixed in the most recent update

Interesting Dan. Hopefully a good test of that coming up then!

[northwestsnow]

I think Blue makes a very good point .

The evolution does not have cross model consensus just yet and a few hundred miles makes a huge difference...

Only then can we be reasonably confident .

That may come this evening ,we are talking 120 - 144 now which is also I suspect ,in FAX chart  territory and it is always good to know what the pros are thinking ...

I'm at analysing every slide  on meteociel at this point!!

Surely it's not just me !!

[winterof79]

37 minutes ago, Bradley in Kent said:

Deep down I think we know which set of the two is more likely to happen. In winter I'll say the top 3 mildest options are way more likely than top (or bottom) 3 coldest options then flip that round for summer. 

As many have mentioned, the next few days will be very up and down both model forecast and emotion what with the strings of Christmas attached! Best to take small piggy steps and not worry too much about what happens at day 5 which seems to be the cross roads or where those two ensembles sets diverge. Lets cross that bridge when we come to it.

(also thanks for posting and highlighting, that ensemble chart really sums up where we are!)

Substitute We with i .......theres a good chap.

[swfc]

1 minute ago, northwestsnow said:

I think Blue makes a very good point .

The evolution does not have cross model consensus just yet and a few hundred miles makes a huge difference...

Only then can we be reasonably confident .

That may come this evening ,we are talking 120 - 144 now which is also I suspect ,in FAX chart  territory and it is always good to know what the pros are thinking ...

I'm at analysing every slide  on meteociel at this point!!

Surely it's not just me !!

Nope not only you mate but stop it, you'll be crackers "like me". Think the fax charts are a good bet boss

[winterof79]

If this is a sinking block im having some of it

[northwestsnow]

Just now, winterof79 said:

If this is a sinking block im having some of it

The initial attempt at a block I meant ,sorry.

 

[winterof79]

If one was to read! this thread having studied the output you would be forgiven thinking that that there was no further prospect of snowy weather if it doesn't snow Christmas day.

Small envelopes ,must shift south,etc etc.I can't recall charts showing the polar field in such distress at this juncture.

 

 

 

 

[jules216]

I am glad that the only model that Has the pattern nailed is CFS

[bluearmy]

26 minutes ago, Met4Cast said:

Apparently this problem was fixed in the most recent update

Didn’t handle the late November period too well then! 

[LetItSnow!]

As 1978 has been mentioned, here's a brief run through of the evolution that brought a severe spell and why fears of a potential southerly influence should not be feared.

23 December 1978

25 December 1978 (SWerlies!!!)

27 December 1978 (yawn more SWerlies...)

29 December 1978 (Wait a minute...)

31 December 1978 (I think they call that "boom"?

 

The rest is history.

[Met4Cast]

6 minutes ago, bluearmy said:

Didn’t handle the late November period too well then! 

True, but then again how much can that be attributed to an inherent bias in the model vs just not being able to resolve the broadscale dynamics accurately? Difficult to tell one from the other without a larger sample.. 

GEFS/EPS seem to be in broad agreement at 144, albeit the EPS is a little further north. 

[nick sussex]

Could be very wet or very white come Christmas.

You can make a reasonable case for both outcomes especially further north .

The more west based negative NAO is always a nerve shredder for coldies , low pressure tries to move ne at the weakest part of the blocking . This then phases with the Scandi troughing , what you don’t want is overly deep lows trying to move in .

 

[phil nw.]

52 minutes ago, damianslaw said:

I'll put it out there.. won't be until 22nd Dec at the earliest can begin to speculate with some confidence developments for Christmas Day. That's 5 long days of model watching still...

Yes agree with that Damian.

The strength of the Greenland block is key in how far south the Atlantic and European troughs phase.It will much nearer to Christmas for that to be decided.

It's exciting to see such a NH pattern like this though,rare for mid December with the tpv shredded.

 

[blizzard81]

I always saw Thursday 23rd Dec as the crunch day with regards to Christmas snow prospects. Just look at the difference between yesterday's ecm for that date and this morning's. That's a big change for the worse. The problem is that this is now at T144 so very little wiggle room for 'substantial' changes for the better imo. 

[Staffmoorlands]

6 minutes ago, nick sussex said:

Could be very wet or very white come Christmas.

You can make a reasonable case for both outcomes especially further north .

The more west based negative NAO is always a nerve shredder for coldies , low pressure tries to move ne at the weakest part of the blocking . This then phases with the Scandi troughing , what you don’t want is overly deep lows trying to move in .

 

Yes, big risk but big reward. Looking great for Christmas snow opportunities at the moment and I'm sure many are pleased to see the disappearance of the UK High

 

[Cold Winter Night]

The rollercoaster rides on and on.

Where do we stand after the first half of today's runs in my view?

I think splitting thinks up by lead time is helpful.

Up to 120h

The first five days we can best rely on the latest high resolution operationals.

At 120h (114h for GFS 6z) GFS is best for cold prospects, the High is stronger and the Norwegian Low pushed more Southeast.
UKMO is worst, as it sends the Norwegian Low on a higher latitude track SW and ECM is in between.

This immediately shows that even among the high res runs in a usually more reliable time frame there is disagreement on a feature that is crucial for the way forward. We have to keep that in mind when we watch what follows, and look at ensembles for help.

120h-168h

This period shows a step up in uncertainty, compared to the 5 days before.
Yesterday's 12z EPS ensemble showed a marked shift towards a weaker, more NW placed Greenland High, with more Southwesterly influence for the South of the UK (and Holland).
This corrected somewhat on the 0z ensemble, with heights lingering in our area on two clusters. This could mean colder temperatures, under the High.

The EPS regime chart now shows a rapid progression to moderate NAO- as was obvious on the clusters above as well.

192h-240h

The end of the regime chart takes us to FI and the Christmas days.
There is not too much scatter on that progression to NAO- and negative blocking (BLO-). This would indicate a Scandinavian trough, combined with Greenland heights.
On the 192h-240h clusters we see two clusters that stay on that page, meaning that the UK will remain on that border between colder NE influence and milder SW winds, and one cluster that returns heights into the Scandinavian sector.
That gives a very wide spread for Christmas.

The general setup is something we would like to see around Christmas, and as many have stressed, the detail will decide what our Christmas weather will look like and we'll have to wait for a couple of days to get more clarity.
However, what coldies enjoy in the end is actual snow and cold on their doorstep, not a nice synoptic Northern Hemisphere view on a chart on a screen. Emotions surrounding this are therefore understandable.

264h-Rest of the winter

After Christmas, to the New Year and into January, the outlook is fantistic for a coldies POV.
The clusters agree with those crazy GFS runs that the tPV seems to get shattered, putting us in a place of great opportunities with heights all over to our North.

The pessimist will undoubtedly conclude that we will miss out on those "as always" and the optimist will conclude that a 1947/1963 winters is still a possibility.
And you know what? They both could be right and that is more than we could say in many previous Decembers!

Finally, the De Bilt EPS 2m plume for 0z is decent. It stretched the y-axis to -25c to accomodate for some crazy members in the ENS.

I said a couple of days ago that I expected that we would see some members where the bottom falls out and here they are.
Now let's hope that group will grow in size. That's how many a great cold spell started!

[chicken soup]

26 minutes ago, jules216 said:

I am glad that the only model that Has the pattern nailed is CFS

Good model that according to some on here.I

[GSP]

9 minutes ago, nick sussex said:

Could be very wet or very white come Christmas.

You can make a reasonable case for both outcomes especially further north .

The more west based negative NAO is always a nerve shredder for coldies , low pressure tries to move ne at the weakest part of the blocking . This then phases with the Scandi troughing , what you don’t want is overly deep lows trying to move in .

 

Exactly. We are still a whole week away from Christmas Eve, and goodness knows what changes the models will go through until then!

It’s always been about ‘potential’, and nothing more. How this is playing out has us glued on every run, and certainly another period of interesting model watching.

If it happens it happens, if it don’t…..

We don’t get snowy Christmas’s anyway, so we should not be too disappointed.

[Midlands Ice Age]

Speaking of Northern Hemisphere profiles (SLP and min temp)for the GFS for today -

 

       

 

and for 10days time.

 

     

As can be seen  between now and then -

the Arctic is expected to be dominated increasingly by high pressure.

The temperatures (unlike during a SSW) are actually still cooling over the Arctic.

This is becoming more and more interesting.

 In our area of the world  we go from above average to below.

Even now the anomaly for the Arctic is below normal at -0.6C. This has not happened consistently for a good many years.

MIA 

 

[winterof79]

Mustn't grumble

GFS Mean

25th

 

 

[Mark Parsons]

No mention of the white stuff in the sensationalist tabloids yet, that could be a good omen !

Edited December 17, 2021 by Mark Parsons