obviously on the best for cold snowy weather but will probably end up with a UK high! 
realistically see what the ENS show, then cherry pick !!

The likely outcome is probably GFS, as it shows the more mobile and more common pattern, but I just get an outside sneaky feeling this might not be done and dusted and something of a blend between the two may come to fruition....

Never has the phrase "more runs needed" been more pertinent.

Actually, GEM is a good blend so may be the most realistic. I refuse to be drawn into the ECM outcome at the moment.

GFS sadly

Upper temp EC ens for Belfast:

Op was one the cooler runs.. but, within a health cluster of cooler runs. 

Divergence between 6z GFS op and ECM00z op starts circa 5 days out as far as I can see, less robust HP build and a rapid sinking post T160 or so on GFS. I assume that's due to how both models are handling the jet - would be interesting to hear someone with more knowledge than I've got and get their take on it

Brave

Meanwhile the CFS monthly has updated and going for no signal re temperatures for the UK in January - when only a day or so back there was a a temp anomaly of 05.-1c about average over the UK:

I think I preferred the 00Z GFS - at least Christmas Eve was cold and frosty.

My head says more runs and much to be resolved, but my heart says when GFS picks up a new direction and runs with it you have to take notice.

"if you always expect disappointment then you can never be disappointed"

 I still don't know why you waste your time with CFS.

Improving GFS ens, on the 23rd the 850 mean was 0 on the 00z runs, on the 06z the mean is -2 

Its a brave call GTW but that's all it is thankfully. 

We've been here so so many times.

GFS 6z today was crucial IMO.

I can see the output surrendering to the Atlantic across the board over the next couple of days, crashing like a deck of cards.

This years chase has taken us a bit further than other years.

It was fun while it lasted. 

Onset day was 23rd just a couple of days ago. Now we're getting excited about 850 means of -2c. 

Subtle, but impactful differences between the ECM and GFS mean for Christmas morning. 

850temp_anom_20211216_00_216.jpg (1088×833) (wxcharts.com)

850temp_anom_20211216_00_216.jpg (1088×833) (wxcharts.com)

GFS more Atlantic driven, but not in a huge way.

I'm going to save these images and repost them on Christmas Eve just to see which model picked on the 10 day trend the best. 

The divergence between GFS and ECM takes place around t+138 (GFS) / t+144 ECM.

ECM has the UK high migrate northwards to join a 'true' high over Greenland, with a Siberian high then ridging to join up as well, creating a strong block to our north

At 138, GFS also moves the UK high northwards, but also begins to erode the warm uppers over Greenland from the west, and by 156, they're gone (just a nominal surface high remains). As such, the high is 'unanchored' and gets drifted eastwards, before sinking.

That's my very layman's take, anyway.

GFS Operational has been flip flopping and has mostly been a milder option over the last few runs. ECM is consistent as has the GEM and perhaps control so I would be keen to see where the Op sits in amongst it's ENS members.

Op run always appears to sink the HP where as ECM/GEM etc show the slider low and the low pressure to slide across the channel and bring in easterly air - which of course could be bitterly cold given how cold it is over the continent ATM.

One thing I have also notice is the ENS mean - at least for now the ENS has trended colder in day 8. 

In the 00z run the ENS 850hpa mean was showing -1.1c for 24th December - Only 3 members going to or below the -5c Uppers.

In this latest 06z run the ENS 850hpa mean is showing -4.0c for 24th December. - Up to 12 or so members going down to or below the -5c uppers.

MOGREPS also throws a spanner into the works with a decent number of mild runs by Xmas Eve.

Damn! Mogreps had previously been on board for a decent spell with declining surface temps

Hmm - After many days of cold options!? I still think there is too much disagreement in models - look at the ECM and GEM - show that this Xmas day could be an all time classic of a snowy spell if it came about!? Yet the Op run has been mild outlier's in the past. The 06z run of the Operational shows balmy temperatures of 12 + 13c in the south after the 25th into the New Year. Surely that's an outlier!?

Everything up for grabs! EC 30 day still goes for cold and blocked pattern as has the CFS long range and yesterday the met office were quite bullish about cold weather persisting in the south. The NAO is going negative as well so still so much uncertainty over what happens during Christmas. I guess Gavin P couldn't be more correct even if he tried when he called out a 50/50 chance that it could be a cold/snowy Christmas. A good call by Gavin and this was early December mind and now we are past the middle of the month we are still at the 50/50 mark or no more confident about weather we could see a cold easterly blocked or snowy Christmas or a milder Atlantic driven and wet one. A few days ago it was due to be mild and dry and now it appears that we could see a battle ground scenario - the question remains...!? Will the HP and colder air win the battle or will the Atlantic win?

The majority of the suite is a lot colder that it has been with decent clustering towards Christmas.

The operational run was generally an outlier towards the end. This has a few days to run yet.

Wait! Sorry to go OT but remember the Met Office's update yesterday: - No suggestion of a return to milder Atlantic driven weather. (Not for the south at least).

Monday 20 Dec - Wednesday 29 Dec

At the start of this period it will be settled and predominantly dry with large amounts of cloud, though cloud may well be thick enough for the odd spot of drizzle at times. In general, cloud amounts will tend to reduce with time, with a corresponding increase in the risk of overnight fog and frost, which may be slow to clear by day in some areas. Towards the middle of the period, there is an increasing chance of more unsettled and windier weather affecting the UK, with rain, and perhaps snow, possible for some places. Temperatures will generally be near to below normal, perhaps rather cold in the south, feeling chilly where any fog persists, and locally mild in the north and northwest.

Updated: 14:00 (UTC) on Wed 15 Dec 2021

Thursday 30 Dec - Thursday 13 Jan

It is likely to remain settled for the final week of 2021, with overnight frost and fog likely in places as we head towards the New Year. Any unsettled spells are most likely for the northwest, with occasional stronger winds, and some showers or longer spells of rain and potential for areas of snow. Temperatures are expected to be around average, but milder in the north, and colder in the south at times, where frost is most likely. Heading deeper into January there is expected to be a gradual shift towards more changeable conditions, especially in the northwest, and turning milder again too.

Updated: 15:00 (UTC) on Wed 15 Dec 2021