GFS  Op 0z- slower to move the trough S-wards but by Christmas Day 1000mb Balearics while HP has settled N of Scotland 1040mb with strong E-lies for England (bit not connected to a source of deep cold). This set-up persists to New Year, though the E-lies weaken, and something much colder is pushing s into E Europe. By Fri 2nd this n-ly blast has retrogressed and the fringe of it is affecting the North Sea coasts while the HP has taken up a position NW of Ireland thus blocking any Atlantic LPs.

ECM - like GFS but any deep cold even less likely as source is SE rather than S. The HP cell moves S and allows something milder across Scotland before, as in GFS, setting up a block with N-lies for the 2nd (which, however, do no persist as the HP takes more control of British weather

AIFS both London and Edinburgh show a cooling down for the Christmas - New Year period, London to about 3C while Edinburgh a touch milder around  5C. Some rain this week, especially today for London, but mainly dry from Christmas onwards

GEFS - in the S rain and milder today, near norm to Christmas Day with a little rain , then 2 or 3 C below norm and dry through to New Year. In the N similar but the rainfall emphasised for the 23rd rather than now, and mean temp only 1 or 2 C below norm.

Snow row indicates perhaps a few flurries in the S for Xmas (10/33 in places) and some chances of snow around the New Year in the east (10+ / 33). Cold-ish for Christmas but hopes of any severe wintry weather seem to depend on an FI northerly.

Looks like some kind of Southerly from that view but with colder uppers then the rest of the output shows?

No, that clearly shows an easterly flow.

Here 

https://www.theweatheroutlook.com/twodata/aigfs.aspx?run=06&charthour=168&chartname=mslp500&chartregion=na-region&charttag=500hPa%20GPDM 

^ hours on from that (midday Xmas Day) has temps across E&W widely at 3-4c (a degree or two colder in Scotland) and a moderately stiff breeze. Will feel really chilly.

Surely you know to follow the direction of the isobars and then adjust for the  pressure gradient?

With regards to xmas itself, details are difficult at this stage and the options range from 'chilly and dry' to 'heavy snow showers'. Its too early to say much more than that, though I do note that while the models tend to be overly optimistic about the pattern (the model with the worst pattern tends to be right) they are conversely pessimistic with how cold the airmass is so I wouldn't be surprised if we see a big downward trend in those uppers provided the HP doesn't sink further south.

Plenty of detail to spin up within this that the low res models cant produce.  If those charts were to verify as is, there would be flurries pretty much country wide, albeit little to no snow cover away from immediate eastern and southern coasts.  Probably the best festive and seasonal charts in years!

Indeed despite the Op the ensembles are the coldest yet.

https://www.wetterzentrale.de/en/show_diagrams.php?geoid=50893&model=gfs&var=2&run=6&lid=ENS&bw=1 

https://images.meteociel.fr/im/76/346/gens_4_1_288lyo6.png 

(Of course it's negative zonality, and that's what makes it special! Just one of many options in the GEFS 6z suite.)

Tbf I'd not quite call this fully negative zonality. 

I'd reserve that for the vanishingly rare cases where you get coherent upper lows moving from east to west along a upper level jet. It is happening a bit in the longitude of Iceland, but west of Iceland the jet is west-east, and east of Iceland the jet is non existent. 

The chart in question would suggest more a NE flow. Isobars are a guide only, and wind direction rarely follows the isobar flow perfectly, except in very stable conditions. A straight south to north isobar flow for example more often than not brings a SE'ly wind flow.

Edit: Example below from the current set up. SSW isobaric flow over the Irish Sea and adjacent lands, but wind direction is more S to SE. 

https://www.theweatheroutlook.com/twodata/aigfs.aspx?run=06&charthour=0&chartname=windvector&chartregion=uk&charttag=Wind 

And. 🙂🙂🙂🙂

Yes, from 26th into the New Year- just (ATM). The set up looks to me like a proper pattern change rather than a week-long blip, with HP hopping about a bit but always nearby and keeping an essentially cold 850 regime at hand.

ECM ENS 00Z 2m temps for Christmas Day below. They are readable if you open in a new tab or pinch on smartphone.

Yes but the zoomed in chart view and the colder uppers pushing northward made it look more like the air was pushing up from the South.

Anyway it's all still to play for after the solid 6z GEFS, however the other models are less convincing. If the GFS starts to wobble then it will be time to start worrying.

Better start worrying then, as sooner or later it'll wobble! 😁

ICON is out now and it wasn't worth the wait - the high is further south.

Yup, ICON is pretty terrible for the cold prospects. 850s barely drop below freezing, let alone significantly so. A mild mush fest Christmas would be likely if ICON is anywhere near right.

Thankfully it's the op run of one model amongst many. Ensemble watch now until at least the middle of next week.