An excellent GFS run - a series of snowy sliders topped off with a raging easterly.

Yep, real batten down the hatches end to GFS:

Yes it is sinking south but I think it would be unavoidable for >0C 850s to cross the southern quarter of the country at least, from that chart. 

compare to GFS:

GEM is broadly similar to UKMO in terms of the track albeit a bit earlier:

and it still ends up cold for the UK

So long as the air is coming from the east, and across land, its a little easier.  Which in the case of sliders - they always will be (for the majority of us)

For the southern flank of the low- obviously in the mild sector so doesnt really matter anyway.

The event on Boxing day 2014 - although not a sliding low, allowed snow becuase it was drawing air, (not in any strength mind) over its northern flank, where it was clear and frosty.  Had it drawn that air from the irish sea, it would have stayed rain.

As modelled it's a classic case of the warm sector being squeezed out as it rides up over the cold air.  On the GFS 12z run essentially only Devon gets any 850hPa values above zero and only for a few hours.  It still shows rain to the south and west, as is almost inevitable with sliders because there's a southerly pulled up from the relatively warm Channel

A few tens of miles either side of the currently predicted track will make a difference to which areas see snow, which see rain and which get nothing at all.  Certainly one to watch over the next 4-5 days and one that I expect might give the professionals a headache or three.

GFS is quite consistent in its Easterly theme further down the line 

They might do. The wet and windy weather which brings in the drier and cooler conditions is definitely in the “realistic” timeframe. Beyond then the outlook is largely cool and unsettled. Any rain, sleet or snow potential remain to be determined.

The UK gets its best snowfall in marginal situation. I recall several occasions in 1981 where the Met Office called confidently for milder weather, for us only to get more snow due to trough disruption, followed by a splendid freeze. Oh what joy that was

wow, what insight

LOL. Don't mention Hillary Clinton or he'll go off on one

www.meteociel.fr/modeles/gefs_cartes.php?code=0&ech=192&carte=0&mode=0

Control gives us a Murr sausage

and then a proper easterly

http://www.meteociel.fr/modeles/gefs_cartes.php?code=0&ech=348&mode=0&carte=0

I remember 1981 well started properly around the 13th with a blizzard that lasted all day then cold all up to xmas with another blizzard around new year when jan started with some of the coldest temps ive ever seen here ...repeat of that would be nice .

Sunday Slider still not nailed on -roughly half of GEFS  Ens at 144h have the small depression over/close to UK.

December 81 looks at present he closest analogue.On the date you mentioned walked dog in Richmond park.The the snow was so heavy that cedar tree branches were going off like guns as they broke 

I agree that December 1981 looks to be the closest analogue at the moment. The trouble with marginal situations is that they are, well, marginal and it does not take much for the UK to lose out. So many things have to be perfect in terms of positioning of pressure systems - I guess that is why they deliver to us so rarely in this part of the world.

Yes I (we) await the ECM with bated breath! GFS was a fun run to watch evolve though out on its own in FI.

 Eyes down...

Seem to recall sliding lows give the models headaches at fairly short range - T72ish sometimes. Small tweaks in track, intensity, if any energy splits off where does it go etc. are difficult to pin down at any sort of range but can have big impacts down the line. Tis always fun in my part O the world watching a correction North and somewhere in the Midlands get snow or a correction south and I get a few flurries whilst the South West gets some snow.

Or the really fun one where it gets corrected so far south no one sees snow or it heads well North and we all get rain

In terms of the GFS run itself it's definitely a high stakes way to get snow and not one that tends to favour the far SE. It's interesting the Op is again playing with an Easterly in far FI - the Mid Atlantic ridging and brief northerlies has been a remarkably long lived pattern, going all the way back to the end of October. It'd be nice for a pattern change to be to a different (and for me) even colder set up but the cynic in me suggest a gradual collapse to more normal Atlantic driven fair is more likely. It's nice to see though and would be even nicer if it gets to a couple of days away

Before the FI and sliders fun the briefish initial NW punch still looks like delivering snow to some - I can't see -10 850s and relatively warm seas not delivering some big shower activity for the coastal fringes and maybe a bit further inland given the strength of the wind. 

Operational was coldest for the weekend on the 850 hPa ensembles for London at -10C - but hey, the mean is still -8C ! Also Op was on milder end for Aberdeen so GFS pretty much still on course.