GFS Op 00z; last of the NW/N winds today as a cloudy HP move up from the SW and intensifies 1035 mb Christmas Day over the near continent (best chance of any sunshine in the NE)  persisting to Sun 29th, and positioned  a little further north, near Britain, than yesterday. LP arrives rapidly Mon 30th from Iceland, first to W Ireland then moving to N Sea and deepening 970mb with N-lies setting in. This relaxes its grip and a brief ridge develops but another LP moves up the W coast and resumes the N-lies from a position near Shetland 970mb Tue 7th.

ECM ; the coming week's HP persists beyond the 29th, at least to 31st when deep LP is well north somewhere near Iceland ad SW-lies develop over Britain.

GEFS ; soon becoming mild and this lasting to Sun 29th when the ens members split into two camps, well above and well below norm in the S, more scrambled in the N, so that the mean, near norm, means little. The op and control alternate between the mild and the cold in the S, tend to be on cold side in N. Dry until 29th then moderate rain in most runs, heavier in W, possibly as snow in the far N

I too never understand the misguided assertion that models somehow don’t ‘factor in’ ground truth. The ground truth was modelled (however accurately) and so any iteration going forward had already included effects from whatever came before it.

Of course the model can and will and often does change its prediction to adjust for differences between truth at Z0 and predicted at Z48 for instance (it feeds on current data to project forward) but a rough idea of the ‘truth’ (in this case the significant warming at 850hPa over Canada) was already in the mix. The same can be said for things like ‘the model’s confused with the high SST’ or ‘it doesn’t know about the large iceberg near Svalbard’. There’s bias of course, and performance stats show this model to model, but to suggest it doesn’t consume and use data in advance is foolish.

I buy both arguments. That warming in Canada was relatively easy for the models to predict given the split Pacific jet. From what I've seen, it isn't unprecedented, even if it is rare. What may be harder for the models to project is the direct and indirect effects this may have on the north Atlantic pattern in the medium to long term. We'll see anyway, but what they are holding onto is the near constant cold between Greenland and Norway. The broad model consensus is for that hyper warmth over eastern Canada to keep blowing warm ridge bubbles over towards our side of the Atlantic, keeping this cold air at bay. But one small, minor tweak could change everything between now and the new year. All speculative of course, but it is fun to speculate on this unusual northern hemisphere pattern, even if there is nothing unusual being felt on the ground. 

To be replaced by something relatively similar (just not as wintry). 

https://www.wetterzentrale.de/maps/GFSOPEU06_282_1.png 

Experience should remind us that once the Euroslug takes up residence, it's hard to shift. At least its not stormy. And we can save on heating bills. 

https://www.meteociel.fr/modeles/gfse_cartes.php?ech=318&code=0&mode=5&carte=1 

Quite an impressive Northern Hemisphere pattern as well:

https://www.meteociel.fr/modeles/gfse_cartes.php?ech=318&code=0&mode=0&carte=1 

A huge snowstorm on New Year’s Eve for much of the Midland and south, with over 30cm for some.

Always seems to be potential 10 days away with these effing models!  And we always let them sucker us!

Copied over from the Christmas thread, here's what Christmas Day looked like at the same time range as the above, and how it now looks (bearing in mind it's still just over 2 days away):

https://images.meteociel.fr/im/50/24088/gfs_0_240jch4.png 

https://images.meteociel.fr/im/62/12148/gfs_0_60pwi4.png 

I wouldn't regard the snowy wonderland as shown on the 12z with anything more than the briefest of raised eyebrows... it does, however, add to the growing sense that a spell of less mild / colder conditions may well be on the way for the turn of the year. Maybe that ridiculous warmth over Canada will have the traditional effect (i.e. a cold plunge further east, over us), maybe not. Hopefully in another 3 or 4 days we'll have more consistency and a better idea. Of course there may be a bit of a wobble as is traditional on Christmas/Boxing Day...

(FWIW, G(E)FS settled on what looks like the overall Christmas pattern at 8 days out).

https://www.theweatheroutlook.com/charts/gfs/12_252_uksnowdepth.png 

PS - Is Wetterzentrale down?

Much crossing of fingers still needed, Snow Row figures out of 33 runs for 1st Jan - Birmingham 7, London 4, Brighton 2.

It is very early days, but hopefully New Year's Day onwards looks much more interesting. 

A couple of members with -15 850s for the far north aside, there's not anything dramatically cold on offer and there's a lot of scatter in the ens for more southern locations, suggesting it's as likely to be significantly milder than average than colder but at least there's some potential.  When you look at the Aberdeen ens versus the London set, there's more of a cold theme which suggests a greater chance of cold air pushing far enough south to cover Scotland with the milder members for the south mainly being ones with HP over the continent still too close to allow the cold air to cover the whole country. 

People keep mentioning high pressure to the south but I am not seeing that on current output??

If you're talking about a persistent HP cell or repeating ridge to the south I'd say it's not really there, but there's definitely periods where HP is just to the south of the UK as the snapshots below show. The milder ens members on the GFS, broadly speaking have that HP the dominant feature in the mid to longer term, the colder ones don't (as with the Op this time round although it's fine margins at points). 

Edit: Quite a fun end to the extended ECM, albeit that too flirts with HP to the south spoiling things before it comes good:-

ECM only goes out to 240hrs where do you get this pls?