By here I just mean the whole UK. The tropospheric polar vortex nearby to the east of us and ridging in Canada and Greenland gives us the best chance of a very cold outbreak from the NNE.

That doesn't mean it will happen though as there are lots of other things that need to be right too. The upshot is that I'm seeing potential for NYE onwards for cold weather in the UK.

Aint that true!

Before then it looks like a pretty mobile setup with cooler conditions tomorrow then milder then cooler and potentially very unsettled over the weekend.

The 06Z update was a significant "downgrade" for cold on the London grid point used by TWO. 

Is the drop significant?  Looking at the ECM chart for 10hPa winds the mean sits above the top decile over Xmas before dropping back towards the mean.  I’m far from an expert on this but that doesn’t look sufficient as it stands?

GEFS35

GFS Op 00z: NW-lies for Britain today under influence of LP Scandinavia, relaxing briefly before new LP arrives Sun 22nd 985mb Denmark with NW gales back in force. HP then comes in from the SW - by Xmas day 1035mb E France, a little further S than shown yesterday, still close enough to keep British weather settled but SW-lies are stronger so frost and fog less likely. This HP persists to Sun 29th, intensifying for a while, before LPs from Iceland and mid Atlantic combine and develop as a N-S trough covering Britain 975mb Wed 1st, importing rather cold air from N Scandinavia. This deepens 950mb (sic) Fri 3rd E Scotland still importing air from the NE. A lot of snow on the hills?

ECM: similar to GFS but HP not so intense, allowing more of a W-ly rather than SW-ly for the w/e Sat 28th.

GEM - similar GFS but HP retains its strength, positioned a little further north and dominates Britain to Sat 28th

GEFS - as yesterday, temps down -up - down to Tue 24th, a mild period over Christmas to Sun 29th, then mean returns to norm with a good spread of outcomes above and below. Mainly dry in England to Sun 29th, wetter or snowier in Scotland, then increasing chances of rain or snow everywhere with some big totals in N& W. 

This is the reality for the South that even when the Canadian vortex gets shunted over to Siberia very few ensembles bring a cold spell. It may turn average or even stay mild. At least it's pretty dry is the best that can be said.

Spare a thought for Churchill, on the western shore of Hudson Bay, where the forecast for New Year’s Eve on the latest 06z GFS run is rain and temperatures above zero, and an 850hPa anomaly of +20c.  Don’t look at the anomaly over Hudson Bay - it’s off the scale.

Theres always a hope that LRFs that have gone mild winter, go spectacularly wrong..

We live in hope.

No major snow since the 2xBFTE 2018. 

Keep watching around NYE, my guess is that we will start to see some good ensembles soon.

Never read or bother or get worked up with long range forecast as all are virtually hopeless and very wrong all the time.  If they predicting mild winter we should be seeing temps well over 10 to 15C during 90 days of winter. Latest ensembles show yo-yo temps so not very mild all the time.  

Would be nice just to get some decent ensembles to look at over Christmas.  

Let's hope it's a back-loaded Winter then even though most LRFs pointed towards more of a front loaded Winter.

Mighty need to look north as we move towards new year. And quite a stormy weekend coming up again! ( 2 week cycle)

https://www.theweatheroutlook.com/premium/weather-analogues.aspx?dt=30days 

I think the ensembles are underspread. The anomoly over canada is so huge and so high confidence that I can't see a little chunk of cold core low in the greenland area scuppering the whole thing. I kinda feel that chunk of cold core low may delay or accelerate cold conditions depending on where it goes but ultimately we are seeing a large scale pattern change that is going to become very favourable for cold conditions. I'm still thinking around NYE is when we should be watching.

Look at those bonkers T anomolies over Canada at the 850hpa level. Sooner or later its going to end up with a monster ridge over greenland which then will propagate down to the surface. The position of the ridge is self amplifying where warm air advected into E canada strengthens the 'dome' and weakens the jet. Its a great pattern with so much potential.