The first since Dec 1996./ Jan 97?

I remember that spell very well.  Not much snow here but it felt like an 80s cold spell

This one will feel like an Ian Brown cold spell. 

To get one of those would require a Scandinavian High (which it looks like we're going to get), with east/ENE/NE'lies over much of the UK, an upper cold pool ejected from the continental mainland, passing westwards over the UK, and -10 (or better yet) -12 850s. That sets up convection down here, even if further inland it's colder but dry. The Scandinavian High should then ideally move westwards towards Iceland/Greenland, allowing a cold plunge over Scandinavia, only for the high to move eastwards again and drag that cold air over us. This latter step is very rare these days!

This morning's MetO output is very close. We have a Scandinavian High on Christmas Eve, which moves westwards for Christmas Day. There's a cold pool over the south and a telltale kink in the isobars showing a trough crossing England and Wales.

https://images.meteociel.fr/im/4/17309/ukmo_0_144upz3.png 

The 850s are what lets the side down, although -7/-8 might be cold enough for some snow flurries inland:

https://images.meteociel.fr/im/99/26630/ukmo_1_144bjq1.png 

Of course even at 6 days out much will change, and it's unlikely the 850s would be exactly that temperature anyway, let alone the rest of it! Nonetheless, for a rough guide it's very encouraging. 

A quick look at the ECM-46 shows it's doubled-down again on the cold, showing cold anomalies in the south for five weeks in a row! By week five they're confined to the SE, but before then we keep our widespread -3 to -1 anomalies for the week after next. There's been a slight downgrade in the extent of the deep cold air over France - maybe 30 miles further east from Calais - but the picture remains a solidly colder than average one.

https://charts.ecmwf.int/products/extended-anomaly-2t?base_time=202512180000&projection=opencharts_europe&valid_time=202601050000 

The pressure charts continue to show high anomalies to the north for a couple of weeks, suggesting we may well see the high migrating westwards with time, but not scooting off tout de suite to Canada as has happened in recent decades. There's a weak signal for higher pressure to the NE in week 3, and that'd imply a good chunk of the ensemble members are showing that ping-pong effect I mentioned yesterday.

https://charts.ecmwf.int/products/extended-anomaly-mslp?base_time=202512180000&projection=opencharts_europe&valid_time=202512290000 

All in all, it's still very encouraging. If nothing else we'll all notice the change, and Christmas Day is shaping up to feel absolutely perishing down here. The MetO raw, for example, has 5C at noon, overcast, with a biting ENE'ly wind (biting due to the relatively low dewpoints). The current balmy weather will seem a long way away next week!

The great Southwest blizzard was probably the most snow I have seen in this area.In one night the snow fell and drifted to the tops of the hedges and gates , most roads impassable and the power off for a week.

Loved it then but now I am not so sure 🤔

The AIFS shows widespread snow on Christmas Day, driven on by strong ENE'lies from a Scandinavian High. This is an accumulated by 150 chart, but the snow over England and Wales appears during Christmas Day.

https://images.meteociel.fr/im/12/15080/ecmwfuk_45_156bkp3.png 

https://ukwct.org.uk/weather/enswatch2.jpg 

We must be due a very cold Op run soon. 

I'll have a look at the gribs later, but the TWO AIFS plots aren't showing much snow on Christmas Day.

Thanks for clarifying Brian. I was wondering what I was missing with Darren's post. Cold, dank, easterly yes, but definitely next to zero snow opportunities. 

FAX: today's W-lies clear the recent rain out of the way. New trough by late Saturday being stretched out SE-wards as it comes up against a Scandi HP 1021 mb. The trough develops a centre 999mb as it passes Cornwall to become a complex (sc. Messy) area of LP over Biscay and begins to bring in light E-lies for Britain, assisted by the Scandi HP which grows to 1034mb Tue 23rd.

GFS Op : a less potent Scandi HP, and a delay in moving the the trough on from Cornwall means that winds are more SE-ly  on the 23rd and (probably) less cold than shown in FAX. But eventually things move on and on Christmas Day HP is 1035mb Norway ridging to Scotland and LP is 1000mb Sardinia with light E-lies for Britain. The HP persists ca 1035mb near NW Scotland and blocks both Atlantic fronts and Euro cold pools so a long spell of quiet anticyclonic weather for Britain, at least to Sun 4th when the HP starts to move S-wards.

ECM: similar to GFS with a day or two's difference in timing, and at times the HP is a little further north which allows stronger E-lies in the Channel.

AIFS: London - a little rain this week but the major feature is the decrease in maxima to around 3C from Christmas Day onwards, dry, NE-ly winds setting in and persisting. Edinburgh - similar but only dropping to about 5C and the wind at New Year swinging into the north.

GEFS: temps near norm to Christmas Day, then a week with mean temp 5C below norm (3C in N), well supported by ens members (all below 0C in S), ens agreement breaking up at new year esp in N with some much milder members appearing but not enough to raise the mean back to norm. Only small amounts of pptn, snow row figures in many places suggest a 50% chance of flurries/dusting in the week after Christmas, highest values 20/33 in Norwich

Great to see this posted and my pick is -18 please. Last time that low was -17 in Feb 1991 gave me nice -5 max for 2 days.

What strikes me is the huge difference between the ensemble mean 850mb temperatures for the 0Z GFS and ECM. The GFS is around -5C for a number of days where the ECM is around 0Z.

That's what strikes me too. The 2m temperatures differences are less marked, with GEFS only looking slightly colder in the south. GEFS could be the winning card, but when a divergence like this has happened recently it has usually been the European ensembles that have won out.

We are talking about very small subtle differences at this point that make a large difference. So we may well end up with a rollercoaster of upgrades and downgrades. Still, even if we don't get that initial cold surge from the east, there are further opportunities down the line as long as the northern blocking holds.

It's very much an opinion and not backed by any stats but my perception of the ECM ens set is it rarely shows low 850s until a few days before hand. No idea why, just something I've noticed in previous cold spells where it's noticeably warmer in the run in, then corrects down. 

That said on this occasion I think it's more the noise of competing signals re HP placement, seems to be a lot more options in ECM on that front vs GFS, so uppers are correspondingly spread and the mean much higher.   

https://modeles16.meteociel.fr/modeles/gfs/runs/2025121906/gfsnh-13-204.png?6 

P14 is a highlight, that one is brutally cold.