Yet again we see pressure rising towards Greenland post day 10. Could happen sooner, maybe in time for Christmas but good consistency emerging. The most interesting run up to Christmas for 4 years

interesting synoptics but still nothing of confidence from Exeter....yet?

Yes a massive snowfest to end the GFSP. Some sort of snow event between Christmas and New Year is definitely possible.

http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=360&mode=2&runpara=1

The vast majority of the GEFS tonight at 384 still do not support a long cold spell. You can step through them all here:

http://www.theweatheroutlook.com/twodata/datmdlout.aspx

Nonetheless there is some twitching taking place and I expect MOGREPS is similar. The best guidance during the coming week is likely to be the MetO extended range forecast and the GEFS. They both need to begin firming up otherwise I'd still back a continuation of the present pattern with high pressure to the south putting a brake on any potential. 

 A level headed summary, thank you Brian 

Edit: My forward guidance for taking note of FI with regard to a possible cold spell and the end of the year is to wait and see what the models are showing by next weekend before drawing too many conclusions.  Nevertheless, the possibility of a pattern change does make for more interesting model watching than we have been used to of late, even if it may, like so many other situations in the past, end up being a red herring. 

Keep Calm and Carry on Watching

GEFS do not have a clue what will happen after the 20th 

http://modeles.meteociel.fr/modeles/gens/runs/2014121412/graphe3_1000_283_88___.gif

The smart money would be on what the ECM is showing with a continuation of the standard UK winter borefest

http://www.meteociel.fr/modeles/ecmwf/runs/2014121412/ECH1-240.GIF?14-0 

Until we get to all that, it does seem that fresh to strong westerly wind associated with a zonal-type set up is going to be the dominating weather feature over the next few days . . .

Ouch ECM -  the Christmas Grinch of the models this evening!

There is one major point at which it chooses the pretty much the worst option on the table if you're looking at cold conditions around Christmas Day.

This happens days 6-7, when instead of having a low linger off the coast of Newfoundland such as the GFSP (below-left), GFS and GEM runs do, it totally removes low heights from the area (below-right).

This ECM solution favours a trough NW of the UK with the northerly taking place on the other side of the North Atlantic while we're in a mild SW flow. It's essentially amplification in the wrong place to do the UK any good within the target period.

By day 10, the U.S. pattern is becoming seriously amplified and as a trough digs down west of the Azores, a high would be able to rapidly develop just NW of the UK and at least attempt to draw up the Euro High in the process. Not the most secure route to take!

GFSP does a great job tonight of showing how the highly amplified upstream pattern can allow a strong Euro High to be transformed into a well amplified mid-Atlantic ridge in the space of two days:

Some fascinating output from that model, the likes of which has been long awaited by the likes of myself 

I daresay ECM would at least show similar potential if it ran out to 384 hours like GFSP does - the strong East Pacific ridge and trough digging down across the East U.S. is almost identical across the two.

This from Fergie on NW:

12z EC-EPS awaited, but nothing surprising in broad output... the DET remains in keeping with Exeter's thoughts from today's earlier analysis looking into the 10-15d period:

"... 00z DECIDER products still indicate remarkably low levels of (Shannon) entropy throughout the f/c period, corresponding to relatively high levels of confidence in the associated forecast (zonal) pattern. Examination of latest circulation biases indicate some weakening of the strong westerly component into the trend period, although mobility from the western quadrant is still indicated."

Not Gospel, but giving a guide out to around 29 December, I wouldn't bet against this. 

The 12z ECM op run's day 6-7 handling has support from the 12z JMA op run.

Of the other op runs, GFS and GEM go with a flat pattern days 7-9 before amplification brings a northerly day 10.

GFSP is alone in having such a prominent Atlantic ridge to our NW by day 8.

5 GEFS runs follow a similar route to the GFS op run.

Nearly all runs go on to develop large storms around the Azores which prevent what is often extensive high latitude blocking from bringing Arctic or Polar air to the UK. Again similar to the GFS op run in that sense.

The amplifying Pacific/U.S. pattern is gaining more and more support for days 8-16 (i.e. the second week of the forecast period) but we need to hope that the GFS and GEFS output to be displaying their usual over-progressive nature. The GFSP 12z op run does a fair job of showing what the GEFS would look like with the progressiveness turned down a bit.

Bringing it all together, the pattern for the final week of December currently looks like being the most favourable for a significant incursion of Arctic air that we've had in the past two months. I must stress 'currently' because all I'm doing here is working with recent model output and trends.

There seems to be a chance of a transient northerly before that period, which may coincide with Christmas if we are extremely lucky (or unlucky depending on your situation!), but this is really just another version of the various chances we've been having of late, in which we need the timing and placement of various features to be just right in order to get anything much. If we saw a significant cold spell arrive that early, it would represent a very fast result from the Pacific/U.S. amplification, not something I would bet on at this point in time.

amazing post again stormchaser just like others on here i cant thank you enough for your posts they are so detailed and intresting and exciting to read.thanks alot matey, [  i have read else where some artic change over xmas post xmas into the new year, and gavins blog flash is  a VERY intresting read to, which he has just updated a while ago,  [ sorry if im off topic ]

Thanks James. Seems that something with a bit more interest may develop as we move nearer to the end of December- we shall see!

Its about 50/50 for a cold spell at T+360 on both MOGREPS and ECM

Sounds more favourable for a cold spell than GEFS. Interesting. 

Matt Hugo only going for 30% ec ens. So maybe MOGREPS more favourable?

Matt Hugo Twiitter.

Small minority for now still but 16 out of 51 EC ENS members show a similar blocked evolution as per the GFS after approx 26th.

countryfile forecast said nothing remarkable about the weather for next ten days either average temps or maybe mild into next week

The formation of a Greenland high in low res may be something to watch, sometimes epic cold can come out of vague trends in low resolution. I'm not getting my hopes up though when it takes until 300hrs to get that 552 isopleth to greenland 

A few weeks ago wasn't it said that 50% of the EC members pointed to cold? 

You've been busy...  Hopefully you'll have many chances to put it to the test over the coming months, and see if the "red" colours really do deliver snow thunderstorms over the UK!   Based on the above, Western Greenland seems to be the place to be if you want extreme snow...  The nearest settlement to this appears to be Qeqertarsuaq, but according to worldweatheronline, its partly cloudy and cold (-11c) tomorrow....  Either convective snow activity isn't picked up on this forecast,the forecast is wrong, or other factors are at play?  Regarding this, to what extent does atmospheric stability play I wonder to your predictions... Clearly a significant air/sea difference will create some instability in itself, but whether it occurs near the centre of a windless high pressure system or in the midst of low pressure system with steep thermal gradients would have a major, possibly the major, influence. 

GFS 18z op run has shifted much closer to the GFSP 12z op run, with the jet energy tracking west to east days 6-7 rather than southwest to northeast, this taking LP away from both Greenland and the low near Canada.

It's not building the high to our NW as rapidly as GFSP did, though.

Meanwhile GFSP has also increased the separation between the low near Canada and the one passing just North of the UK. The consistency with the previous run is impressive, though that high to the NW is not quite as strong... no surprises there given that the GFSP 12z was the most positive of all runs in that area.

Given that this represents a shift further away from ECM's version of events by both of the above models, it means we have a major disagreement at just 6-7 days range to sort out tomorrow. Details beyond that aren't worth paying much attention to until this matter is settled.

I see the 18z GFS op is then too progressive with the low off the U.S. to allow the Atlantic ridge time to establish, and does the same again with the one after it as well. That's been the main troublemaker in the vast majority of GEFS runs lately. Again, hoping that's the old progressive bias showing its hand. The charts start to look more interesting again towards the end of week two, much as to be expected given the background signals at play.

The 18z GFSP is also too progressive with the first low, but not with the second.

So get this... the GFS runs have increased the room for a mid-Atlantic ridge to form days 6-7, moving further away from the ECM solution, but despite this have gone on to be more progressive, making them appear closer to ECM days 8-10.

You couldn't make it up could you?

It also highlights just how many factors need to fall into place to get the mid-Atlantic ridge and cold shot around Christmas.

Remember, this is a totally separate period of potential to the much greater one that looks likely to develop for the final week of the month. It attempts to unfold prior to the upstream Pacific/U.S. changes being able to exert much influence on our pattern.

Well lets hope that HP to our south doesn't hang on and get larger, I don't want a repeat of Bartlett xmas 2011. It felt so mild and wrong lol

As ever things can and do change quickly. Here's hoping for better charts tomorrow. 

Yeh this is only one factor (albeit a very important one!), the main thing is that the wind does need to be blowing from the sea, so if there is just a blob of high pressure over a cold air-mass it might show yellows and reds, whereas in reality there would be nothing there. For the UK it should perform better because you don't usually get insanely cold air-masses trapped under shallow highs, and if the air is frigidly cold the wind is probably from the north or east! 

All I see is Westerly , Westerly , Westerly at the moment , yes lots of time left this month for something to crop up but nothing that exciting at the moment I'm afraid

EDIT

The Ens have some interesting runs

http://modeles.meteociel.fr/modeles/gens/run/gensnh-20-1-288.png?18  20

http://modeles.meteociel.fr/modeles/gens/run/gensnh-19-1-288.png?18  19

http://modeles.meteociel.fr/modeles/gens/run/gensnh-17-1-360.png?18   17

http://modeles.meteociel.fr/modeles/gens/run/gensnh-16-1-336.png?18   16

http://modeles.meteociel.fr/modeles/gens/run/gensnh-15-1-300.png?18   15

http://modeles.meteociel.fr/modeles/gens/run/gensnh-13-1-348.png?18   13

http://modeles.meteociel.fr/modeles/gens/run/gensnh-11-1-312.png?18   11

http://modeles.meteociel.fr/modeles/gens/run/gensnh-9-1-276.png?18    9

http://modeles.meteociel.fr/modeles/gens/run/gensnh-8-1-312.png?18     8

http://modeles.meteociel.fr/modeles/gens/run/gensnh-7-1-324.png?18    7

http://modeles.meteociel.fr/modeles/gens/run/gensnh-3-1-324.png?18    3

http://modeles.meteociel.fr/modeles/gens/run/gensnh-1-1-300.png?18  1

Certainly enough to keep some interest