Afterwards a return to average.. for how long? 

The GFS 06z ensemble for London suggests a sustained period of cool to cold conditions?

https://www.meteociel.fr/cartes_obs/gens_display.php?x=&y=&run=6&ville=Londres&lat=51.5085&lon=-0.12574&runpara=0&type=3&ext=1&dmode=1 

https://www.meteociel.fr/cartes_obs/ecmwfens_display.php?x=0&y=0&run=0&ville=Londres&lat=51.5085&lon=-0.12574&type=12&runpara=0&mode=1 

There’s a 6c drop in the mean between tomorrow and Xmas Day, but still a 3c spread on Xmas Day, widening to 4c on Boxing Day.

That’s not really a fair representation of the current output to be honest. It looks below average for much of the time after the next few days (in the south at least).

https://www.meteociel.fr/cartes_obs/gens_display.php?x=&y=&run=6&ville=Londres&lat=51.5085&lon=-0.12574&runpara=0&type=3&ext=1

 Beyond then in the (even more) unreliable time frame there are still strong hints of blocking around Greenland and something a bit more wintry. Just an emerging trend at this stage but one to watch.

There's a reasonable number of runs that still have that cold pool grazing the far South East/South, with the precip row spike backing this up. I don't think it's a likely outcome but it's still entirely possible and I guess globally we're talking about a tiny adjustment. Will see whether the 12zs continue the uncertainty or move more positively towards a hit or near miss scenario. 

Longer term things remain uncertain but generally the outlook remains cooler than average with 'potential' as others have already stated. One thing looking highly likely is a prolonged spell of largely dry weather, something of a mixed blessing depending on where in the UK you are (IMBYish again, we probably need more wet stuff for a while yet but appreciate most of the UK is now back at normal water levels).

6 - 10 day:

11 - 15:

Nothing notable over the next 10 days, but after that? could be something brewing. But given the timeframe, it could be brewing without the teabag in place. 

https://www.wetterzentrale.de/en/topkarten.php?map=1&model=gfs&var=47&time=294&run=6&lid=OP&h=0&mv=0&tr=6 

Which is more than this link seems to be! LOL. A bit surprising just how the cold air doesn’t make it to southern Britain despite a persistent NE flow forecast. What does it take to get -10 users to the south these days? Seems Like even in the bleak mid winter, it is still not that likely anymore. The GFS shows the -5 HPa air is struggling to make it into EA, so the snow show seems rather overcooked at this point,.

Thereafter it's a UK HP with mild to very mild uppers (got to love how the mild uppers are all over us, whereas the colder stuff does all it can to avoid us). I'd expect the surface air to be significantly cooler than the uppers suggest, providing limited mixing (and as per the last several days of ens suites I guess). 

GFS next - Edit - and it's a miss, -4 clips Kent and no precip. Doesn't look like anything clips/happens further west either. 

Not a promising start to the 12zs for the Xmas day charts fixation 😂 

Second Edit - close but no cigar on the UKMO but there is some light snow shown late on Xmas eve, just not IMBY. The cold pool grazes MBY and parts of the far south with -8c (ish). 

One thing I've noticed on the various ops is there's a signal for light precip breaking out in Wales ahead of the cold pool coming through. Not anything exciting but potentially sort of interesting for some.

Steady as she goes for the mid to long term potential. 

Edit - Just had a quick look through the UKMO run and it has the core of the HP further east, so suspect no immediate prospect of retrogression to Greenland, looks more like a slow topple through Scandinavia. Still, the GFS op looks nice!

Great run for model viewing....unusual pattern by its longevity if it comes close...the Newfoundland Low gets totally locked away by a yellow anvil.....1940 phoney war springs to mind....

The AIGFS at T168 is very similar to the UKMO run FWIW, which isn't overly encouraging. I think generally though over recent years the GFS hasn't been bad at spotting Greenie HP signals, albeit sometimes has a false start before a reboot. 

Suspect the ens won't bring much clarity but you never know I guess....

If the AI version is essentially pattern matching, how many diffluent blocks will it have in its database?  My guess is next to none, so if the forecasters are saying these features tend to be very stubborn then it won’t be in the ‘script’?

EDIT: And by 384 plenty of them have the block collapsing. It's still a fascinating period of model-watching, though, and of course there'll be lots more ups and downs to come!

See what the models are looking like in a couple of days is my take. There's a reason the Met don't update their medium - long range forecasts every 6 hours.

Not bad.

Slightly below -5 for a day or so, though I see a few runs going sub -10 between the 1st and 5th and even the odd one touching -15 for my area. 

Edit: More clearly represented on this map from the Icelandic Met Office:

Absolutely Darren, it is

also a good mention of Q comment of the modelling involved in that, years of model watching has taught me ecm really struggles the most with 500 at and around Greenland let alone any link to the possible cross flow.

We don’t get many attacks from the North like we used to but gfs was always terrific at spotting it early.

imo still very much to play for and for the less experienced don’t get to involved in anyone run be it cold or mild it’s trends and potential we want to see at this stage.

After all we have seen  much worse charts at the end of December than we have now 

I don't know about Christmas but this is 9/1/24 ( a fair bit more than a dusting, I'd say)

https://www.bailiwickexpress.com/news/watch-jersey-dusted-snow-temperatures-fall-below-0/ 

and Bonacina doesn't record snow on the mainland at that date

https://durhamukweather.com/wp-content/uploads/2018/10/bonacina.html