The end of this morning's GFS run looks rather more interesting than many recent runs from that model. Still too far ahead to be taken seriously but it could, repeat could perhaps be onto something.

Nothing to get excited about for us southerners this morning although the odd long-fetch south-westerly with HP close to the SE will make things pretty pleasant at times.

A lot of scatter beyond high-res, a sure sign that people will tell us it's a sure sign that something's brewing. Aside from the GFS op, I can't see it.

Interesting that although the Euro models' idea of a stronger Atlantic ridge days 6-7 has been dropped, we now have ECM, GFSP and GFS agreeing that the low from Canada will be slow enough to permit a more amplified outcome in which it does not race NE to merge with low pressure to our N or NE, instead digging south in the middle of the North Atlantic.

It still results in a day or two of very mild SW'rlies around the NW flank of a strong Euro High, but the digging trough provides a means of eroding that in favour of another mid-Atlantic ridge around Christmas Day itself.

GFSP even suggests that the low could detach from the jet and allow a the ridge to build over the top of it.

If we get the digging trough and a decent mid-Atlantic ridge, it looks like the next steps will depend on yet another of those lows associated with the subtropical jet.

The behaviours shown by ECM and GFSP - either developing as a slow moving low separate from the main Atlantic jet (ECM, below-left) or tracking north and providing good warm air advection up the western flank of the ridge (GFSP, below-right) - are good for attempting a Christmas northerly. Obviously GFSP went off down a different road with a half-hearted Scandi High attempt but the Atlantic progression looks overdone to me.

Meanwhile the GFS run is a curious affair in lower-res (days 8-16) because it only allows the more amplified U.S. pattern to stand for a day or two before flattening it again, yet drives a rapid response to that fleeting influence in the form of a considerable Greenland High (perhaps even a full-on blocking feature), with a very interesting day 16 chart as the U.S. pattern amplifies once again.

Beyond the broad idea outlined at the top of this post, there's little if any cross-model consistency to work with this morning. Meanwhile GEFS are all over the place. A fair few feature a good push of cold from the north, but an irritatingly large number have powerful storms W and SW of the UK making a right mess of things, much like the 00z GFSP and GFS op runs.

For what it's worth, uppers below -5*C across pretty much the whole of the UK on Christmas Day is achieved by two GEFS members, with four coming very close. A larger number feature a very mild setup instead. During the following week, the number of notably cold outcomes increases markedly, as can be seen on the line graph for London:

When all's said and done though, the aspect of the output that I'm most pleased about is the major change in the Pacific pattern as the jet finally winds down over there, as the strong jet has been the main culprit behind the runs of colder conditions so far being fleeting affairs.

thanks stormchaser, a Excellent and very detailed, post, as always,

Encouraging FI again. Southerly jet and pressure rising to the NW. Probably wont come in time for the big day but perhaps we could get our once "traditional" post Xmas cold spell

can you explain that comment please?

Just a thought, I always like to look at the SLP ensembles for Reykjavik when approaching a potential pattern change.

What we really want to see is a rise in pressure over Iceland. It doesn't guarantee cold weather in the UK, but it often helps. 

I would post the latest 06z version but struggling on my phone... There is a trend to higher pressure there after Christmas, with a notable cluster breaching 1020 hPa.

Worth watching.. 

All in 'FI' of course but in 2009 and 2010 from recollection we saw a large number of GEFS runs bring very cold air across the UK at their outer limits as they latched onto a 'pattern change'. Currently there are signs of a shift but it all looks quite messy with very few runs suggesting persistent cold, and a number punching the cold shot down to the west with the UK remaining relatively mild. I'm looking forward to the watching the nwp during the coming week but it will take a LOT more evidence before I'm convinced.

Still looking poor for coldies until Christmas but tentative signs of some kind of pattern change as we head into the New Year? There's been a steady increase in more blocked charts around that period lately. The NAEFS anomaly chart is interesting for the 27th

Suggests potential for a mid-Atlantic high possibly riding up to Greenland. However at this point a full blown Greenland high doesn't look likely as the PV looks to remain around that area, so maybe nothing too prolonged.

So if we get lucky, something like the GFS 06z control. Of course its silly looking at details at this range but just musing.