https://images.meteociel.fr/im/4/6494/gens_31_0_192udg4.png 

Recent weather has reminded me a lot of the very wet November of 2009. Prior to the very end of that month, if someone had said to me that a month-long freeze would be starting just after mid-December, I probably wouldn't have believed them. However, when the models first started to pick up on the change in pattern which ultimately led to the start of that freeze at the end of Nov/start of Dec, they stuck with it consistently and never wavered from it to the best of my recollection. December 2012 was another wet month (after many wet months previously that year) which preceded a change in pattern to a much colder period after the start of 2013, and just as in 2009 and 2010 there was a great deal of consistency across the model output of the pattern change for quite a while before it came along.

Looks like the models are struggling with the positioning of this HP post xmas with the runs last night and this morning collapsing and sinking the ridge now  latest 12z shows the models retrogressing the ridge to the NW to bring in colder weather and keeping us cold for longer. Nice to see those colder runs back. 

The 06z 850hpa ENS for London on 25th Dec showed a mean of -1.8c at 12pm midday but the 12z 850hpa ENS for London shows a mean of -4.5c at 12pm midday. Not bitterly cold but quite a jump to colder airmass uppers.

All eyes on ECM 12z and 18z .

It’s very much on the cold side of the ensembles, although to be fair I’ve never really rated the GEM ensemble set.

So I posted this a day ago, and things have firmed up since then.

Looks like that arctic ridge is alot weaker now, so as a result the greenland ridge is ending up in Scandanavia. So it looks like we will see an initial cold surge around xmas day, I suppose the thing that will determine how interesting this gets is how much of that siberian polar vortex gets dragged into the circulation. The more the better, not only does it mean more cold air, but it eventually ends up in the azores and stops sinking.

18z control @ 240z retrogresses the HP Towards Iceland and Greenland:

It is interesting how mild the near continent so often has been in winters within the last One or two decades, when there is little benefit for cold weather fans from short fetch easterlies, especially with warmer sea surface temperatures.  To get true cold Weather to UK shores, we Do seem to need that Siberian Vortex or Arctic incursion to deliver true cold, especially to the south, which of course, makes getting true cold weather (cold enough for precipitation to fall as snow and snow to settle) An ever more rare event.  So Fingers firmly crossed that you are right and the HP retrogression to Greenland or a Greenie-Scandi Connection pulls in the Siberian air mass, With a flow of mini lows or disturbances from the east, running east to west, as happened in 1995, and then the warmer sea anomalies could act as a benefit in convective snow, rather than As recent experience - a party-pooper - warming sufficiently to deliver just cold rain and sleet.

https://images.meteociel.fr/im/45/16397/174_779UKttn6.GIF 

The ECM-46, meanwhile, has doubled-down on the cold spell - extending it by a week, so four weeks of colder than average conditions for southern areas. The really cold anomalies have expanded and become closer on the nearby Continent, with -6 to -3C anomalies as close as Calais. The -3 to -1 anomalies now cover a much larger part of the UK, extending all the way to central Scotland.

https://charts.ecmwf.int/products/extended-anomaly-2t?base_time=202512170000&projection=opencharts_europe&valid_time=202601050000 

It remains the most interesting run up to Christmas for a number of years, albeit it's still at that "just out of sensible modelling" time span! 

The SSTs are a bit of a red herring IMO. In 1993 there was 6 inches of snow here from an easterly in late November, with SSTs of 12 or 13C (and they're only half a mile away from here).

Get cold enough 850s and the lake effect kicks into action and the greater the temperature differential the greater the convection, the deeper the snow.

SSTs only really kill snow chances if it was marginal to start with. 

I continue to use -10 at 850 as a decent chance of snow marker but prefer -12. We can still get those these days but you need the easterly in place first! Even in 2018 there were corrections right up to the last minute: I went to bed one day with the models showing an overnight low of -5, woke up to see the MetO raw showing -12, it ended up as -14.8.

https://www.wunderground.com/dashboard/pws/ILEYSDOW1/graph/2018-02-28/2018-02-28/daily 

Further aloft the 850s were shown to be -12 or so right up to the night before IMBY, they ended up as -14 or -15 depending on source.

Apologies for the lack of evidence to back up my musings (I must work out how to add images/data sets to posts!), but the GFS 18ens had that 'look' about them, plus appreciable snow-rows even as far south as London! (maybe 30% on several days towards the end). 

Whatever happens from here, it's been fantastic to have so many possible options on the table pre-January. Perhaps we'll luck out and someone will be able to recreate that Dickensian Xmas picture postcard scene for TWO's gallery? I'm guessing even a hard frost would excite many after the turgid mild-fests of recent times?

Anyway, here's to another days interesting model watching 😊 I have a feeling a full-on beast may be able to stir....

I'll update these at least once a day.

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

Ensemble watch is back and England bring thrashed again in the Ashes - quite a nostalgic morning 😉

It's beginning to look a lot like Christmas....

Yay, I had a feeling this might be coming. These are becoming as rare as red weather warnings, so you know you have to sit up and take notice. 

Just need some polar bears…..

LOL, love it Neil 

Meanwhile, much of the Alps which are bare of snow and above normal temps finally look like turning more seasonal for Christmas.