Model Output Discussion - Christmas week and beyond

[ItNeverSnowsInWindsor]

The best places for Xmas day look to be Norway and Iceland with plenty of snowfall or lying snow there!

Game over for the UK by the looks of the trends.

[snowbob]

Just now, prolongedSnowLover said:

The best places for Xmas day look to be Norway and Iceland with plenty of snowfall or lying snow there!

Game over for the UK by the looks of the trends.

That’s a brave call with the way the models are behaving

could go anyway at the minute

not a done deal yet

[LRD]

1 minute ago, bluearmy said:

The thing about week 6 is that the ec46 rarely churns out a week six chart very far away from climatology. 

Mid lat sceuro high 

Indeed, that's exactly what struck me. Very unusual to have such a strong signal at 5 and 6 weeks out. Might be something, might be nothing. If it does verify or something near it (it's a long old countdown!!!), then bravo EC46!

[Bricriu]

6 minutes ago, Cold Winter Night said:

I don't know what is behind the GFS amplification signal, but the EC46 regime chart actually shows more support for Scandi heighst than for Greenland Blocks or Atlantic ridges.

Do you think the ec46 might see an SSW happening which causes a Scandi high? A lot of the background signals were pointing to a zonal January. Was glosea not calling for a mild January  too? Or could it be that rare occasion met luver spoke about of a Scandi High despite the Vortex over Greenland? 

Edited December 19, 2022 by Bricriu

[Methuselah]

37 minutes ago, BLAST FROM THE PAST said:

That potentially historic/but definitely  very notable Nor’easter.  Very influential imo

 

BFTP

Well, yes, Fred, it could be 'historic'... But it might just as easily be a damp squib?

Edited December 19, 2022 by Ed Stone

[Derecho]

I think it's going to be entertaining / funny watching the GFS come in. Anticipating a big climbdown with a mild christmas... but if it sticks to its guns we will be going into our most split model output since January 2013.

It has delayed any cold over the christmas period though!

[bluearmy]

2 minutes ago, Cold Winter Night said:

I don't know what is behind the GFS amplification signal, but the EC46 regime chart actually shows more support for Scandi heights than for Greenland Blocks or Atlantic ridges.

The greeny ridge on gfs is very much a near term feature as opposed to the ec46 which is a mid to long range tool.  ec46 shows potential blocking both nw and ne. We were musing the other day if this update would be the first for weeks without northern blocking 

[Kasim Awan]

ECM mean for boxing day. ❄

[Speedbird]

2 minutes ago, prolongedSnowLover said:

The best places for Xmas day look to be Norway and Iceland with plenty of snowfall or lying snow there!

Game over for the UK by the looks of the trends.

Game over for the whole of the UK ?

MetO beg to differ . . . for now.

[bluearmy]

1 minute ago, Bricriu said:

Do you think the ec46 might see an SSW happening which causes a Scandi high? A lot of the background signals were pointing to a zonal January. Was glosea not calling for a mild January  too? Or could it be that rare occasion met luver spoke about of a Scandi High despite the Vortex over Greenland? 

The ec46 zonal wind chart has already been posted 

there is no ssw 

[blizzard81]

Just now, Kasim Awan said:

ECM mean for boxing day. ❄

Yep, decent. I notice there are many more cold ecm members than the op just post Christmas day for debilt. That means a cold  (and possibly snowy) Christmas day cannot be ruled out in the UK as it would hit here before Holland. 

 

[BLAST FROM THE PAST]

3 minutes ago, Ed Stone said:

Well, yes, Fred, it could be 'historic'... But it might just as easily be a damp squib?

HI Pete, true/very true…..but Nope imo, it’s looking ‘at minimum’ very notable….I think this is a historic event….as in it stacks up against last 5 decades 

 

 BFTP

[Kasim Awan]

2 minutes ago, blizzard81 said:

Yep, decent. I notice there are many more cold ecm members than the op just post Christmas day for debilt. That means a cold  (and possibly snowy) Christmas day cannot be ruled out in the UK as it would hit here before Holland. 

 

Increasing support today for a post xmas cold push. 

Edited December 19, 2022 by Kasim Awan

[stodge]

Evening all

As an aside and it may be no significance at all but I do like t follow the 10 HPA charts and the zonal winds.

Most years, the "attacks" on the PV have come from the Siberian side and what they tend to do is knock the core of the PV back over to the Canadian/North American side firing up the jet and putting us back into the Atlantic dominated westerly regime.

By the way, I think that's what did for our recent cold spell.

The odd thing this winter so far the bulk of the warmer 10 HPA temperatures are on the North American and European side and, as you might expect, this has the effect of sending the core of the PV back over to Siberia enabling our Greenland HP. 

Tonight's 12Z GFS OP (hideous outlier as it no doubt is) illustrates this and what it also shows is, contrary to the normal pattern, the strongest zonal wind pattern is over the Siberian/Eurasian side - the storms are there while under the lighter zonal winds, the Greenland HP is able to survive and occasionally exert its influence leaving the Atlantic its less than zonal stuff and keeping the real storms well away.

Just an observation, may mean nothing.

 

[damianslaw]

Someone mentioned not many examples of a clash between polar and tropical maritime air of such depth in the run up to christmas. Two years spring to mind, showing the extremes, 1995 - after a lenghty cold period with high pressure and some snow, we lost the cold air around this same time, and a clash took place, mild air moved in briefly around 21-22 and then the cold came back with resurgence, heights to the NW.. 

Last year the other example, again heights to the NW but an extreme negative west based NAO, there was an attempt to pull in cold air Christmas Eve, but by Boxing Day it failed and instead the SW blowtorch took hold.

Not saying either of these situations will verify this year, but interesting to view the synoptics of both years to see what can happen. We are probably in the middle of both extremes, which makes this year exceptionally hard to call for christmas weekend.

[Methuselah]

Just now, BLAST FROM THE PAST said:

HI Pete, true/very true…..but Nope imo, it’s looking ‘at minimum’ very notable….I think this is a historic event….as in it stacks up against last 5 decades 

 

 BFTP

We'll see, Fred... I don't know!

[Eagle Eye]

I think the connect with the Trop and Strat vortex amplifying both into largely zonal patterns was an over-estimate based off pretty unfounded Ocean-Atmosphere coupling. I'm not saying they can't I just don't think that it will, we should stay largely around average and not dip too deep into the -VE AAM for now and some +VE torque events could cause a rebound pr two setting off unstable inertial patterns propping up unstable Rossby Wave thermal transfer. What this means is that, Rossby Waves should be more likely to propagate vertically and they impart a slight Easterly forcing where they propagate so as long as we keep getting these mini rebounds into +VE AAM (or even better hold an unstable inertia pattern in +VE AAM) then the Trop and Strat shouldn't go into the distance of large +VE zonal patterns. Eventually, I would imagine the unstable inertia stops propping itself up but when and how is anybody guess. For all we know, we could technically keep this going on all Winter however unlikely. The more favoured solution is for a better first half of Winter and that's my thoughts, December through mid January for now remain the beat times for a proper cold pattern but let's see how this all evolves.

[Dancerwithwings]

1 minute ago, prolongedSnowLover said:

The best places for Xmas day look to be Norway and Iceland with plenty of snowfall or lying snow there!

Game over for the UK by the looks of the trends.

Well that’s standard or familiar patterns that’s a thing that we all know…Norway YES, Norwich No…Iceland for sure, Inverness yes maybe…

Probably or more historically that’s the usual thing that’s us with the regular hope that we strive or struggle with…but “game over” is not a thing that’s done and dusted… not just yet !

 

[Methuselah]

10 minutes ago, BLAST FROM THE PAST said:

HI Pete, true/very true…..but Nope imo, it’s looking ‘at minimum’ very notable….I think this is a historic event….as in it stacks up against last 5 decades 

 

 BFTP

Well, I do hope it's notable, Fred... But my cat tells me otherwise!

[feb1991blizzard]

6 minutes ago, Ed Stone said:

Well, I do hope it's notable, Fred... But my cat tells me otherwise!

It is going to be surely - you can't tell me that -28c uppers practically into the deep south of America isn't notable?/

[snowbob]

If I remember correctly.

and I’m sure someone will correct me if I’m wrong,

wasn’t this the other way round last year 

ecm was modelled to give us some cold for after Xmas and gfs was having none of it.

I seem to remember as I had my mum last year for Xmas and was worried about getting her to my sisters on 27th

maybe I’ve jumbled a year or two

But I’m sure this was the case

if I am corect ecm failed big time

just saying could be failing now to

Edited December 19, 2022 by snowbob

[goosey007]

5 minutes ago, snowbob said:

If I remember correctly.

and I’m sure someone will correct me if I’m wrong,

wasn’t this the other way round last year 

ecm was modelled to give us some cold for after Xmas and gfs was having none of it.

I seem to remember as I had my mum last year for Xmas and was worried about getting her to my sisters on 27th

maybe I’ve jumbled a year or two

But I’m sure this was the case

if I am corect ecm failed big time

just saying could be failing now to

Defo pointing that way around 7 to 10 days before Xmas last year …..but can’t remember who was first to sniff out the eventual outcome …..

[snowbob]

Just now, goosey007 said:

Defo pointing that way around 7 to 10 days before Xmas last year …..but can’t remember who was first to sniff out the eventual outcome …..

No same but I do remember this same situation 

not as complicated just more a garden path sort of thing

this year way more going on in terms of model confusion 

[phil nw.]

The 2 mean charts at t168 show the 850hPa forecasts NH view.

Interesting to see how the deep cold trough over N.America meets the mild sub tropical air to it's east and creates the WAA up to Greenland.The jet splits and the northern arm goes over the top of Greenland and this sends a cold trough south towards the UK.

Meanwhile the Iberian high is doing it's best to stall the cold over the UK.This creates the battlezone of lows around our latitude .The models are still to agree on the development and movement so i think it could be as late as Wednesday before we get a better handle on this.

The main point being there is pretty decent agreement on the overall NH pattern over Christmas but the devil is now in the detail over the UK and where the 2 airmasses battle it out.

[SqueakheartLW]

What will Christmas Day bring?

This is the big question and recent output suggests we are likely to be very much in a battleground scenario between mild sub tropical or central N Atlantic air and cold Arctic air to the north trying to get in and where they meet it's going to be fun and games for white Christmas chasers

GFS 12z

Using the GFS 12z and its ensembles as an example we have the extreme range on 850hpa temps from this:

The mildest outcome     P16     Scunthorpe 850hpa temp = +0.8C

To this:

The coldest outcome     P20     Scunthorpe 850hpa temp = -11.7C

Basically the path of the trough here varies from the most northerly path in P16 where it passes over Scotland with only Shetland really in the colder air and the rest of the UK very much in the boring mild Christmas territory wondering what could have been if things turned out differently.

Then we have the other extreme in P20 when the trough passes so far south that it is a barely noticeable feature in southern France. This leaves the whole UK in the colder air and those of us away from the north also wondering what could have been due to the trough tracking so far south of us we miss out on any potential snow event. Those of us on exposed coastlines and in northern Scotland would still do well out of this for snow at least but the majority over England and Wales would be dry and cold under that ridge.

The 850hpa mean and anomaly for the same time frame as both the P16 and P20 runs shows that colder 850hpa temps are favoured but where the mean boundary between the mild and the cold is is yet to be decided. The 500hpa chart would suggest northern England is the boundary.

Will this correct south or north or will it get watered down and removed completely?

Corrected south years

This is the big question and which way will it go. Most previous examples of these sorts of setups usually see things get corrected southwards as the time approaches until the potential snow event ends up so far south that we all basically miss out. The perfect examples I can think of where potential Christmas battle zones and possible snow events that corrected south in the end were 1995 and 2000.

I remember the build up to 1995 and how mild air was trying to push north in the few days before Christmas and I do believe there was a snow event a few days before Christmas as the mild air tried to push in. I could imagine the nightmare on here if a repeat of the 1995 situation were to happen again and based on recent output are we about to see another repeat where we have a will it or won't it turn cold for Christmas and beyond. In some ways it looks like a repeat of 1962 where the severe cold was due to push in from the east and imagine how the model output would have been handling that. Another possible candidate for the current situation is 1978 where low pressure was pushing in from the Atlantic combining with increasing northern blocking until the jet stream pushed far enough south that the cold air came in.

The other main year with this kind of situation leading up to Christmas was 2000. I remember this one a bit more and how heights were building over Greenland in the days before Christmas and the trough and jet stream were getting pushed further to the south. The big one was where the band of rain and potential snow was going to be on Christmas Day. As it turned out Christmas Eve was the wet day for most of England and Wales and Christmas Day ended up with the fronts off the south coast and the whole UK in the cold air with scattered snow showers.

Corrected north or removed

Of course there was last Christmas when things were looking so promising then at the last minute the cold spell was first watered down and shortened significantly before it was then finally removed completely with only a glancing blow from the cold into the north before we then reverted to the usual mild muck before we went on to produced the warmest New Years Day on record and the warmest start to any year on the CET record with a mean January 1st CET of 12.7C, well clear of 2nd position, 1916 at 10.5C.