Really some strong trends showing up on the CFS, all the runs seem to be showing something interesting now. They all manage blocking of some description by the end of the year but some go a good deal further than that and somewhat sooner (blocking generally beginning sometime between the 20th and the new year). The most recent CFS run has cold Nerly by xmas and the beast from the east by the start of January, and its a real screamer on this particular run.
In fact (and I'm not exaggerating) this is the coldest run I have ever seen on the CFS.
Originally Posted by: Quantum
That's a huge flip from what was a persistent tendency across the preceding three days to bombard the UK with Atlantic storms until a reformation of the polar vortex to the NW of the UK.
Goes to show you can never put much faith in that model even when it's consistent for several days.
Now, on to the morning output... I'm going to focus on the output following the consensus solution regarding the U.S. low which is ECM/UKMO/GEM as opposed to GFS.
Both the ECM 00z op run (above) and the GEM 00z op run (below) show low pressure favouring a position just NE of the UK out to day 7 or 8.
ECM absorbs the U.S. low into the midweek trough and maintains it as a gradually weakening feature, while GEM bombs it out but not before the midweek trough has 'captured' it i.e. directed the jet such that the storm is drawn to the UK rather than heading NE.
Both models then show the jet digging further south, towards the Mediterranean. This looks like a response to a combination of the steadily increasing heights over the U.S. (looks like a major blocking high) and the disruptive influence of the Siberian High.
This is all good for maintaining two strong areas of blocking that can drive wave breaking into the strat. Really it's no wonder that Matt Hugo, among others, are reporting significant strat. warming events at the longer range.
So what about GFS then? Well, it's transport of the U.S. low NE as a deep trough is only temporary, with a route towards the UK soon following, which brings it close to the ECM/GEM output. The main difference is that the jet hasn't been able to track so far south across Europe within the next 10 days, instead taking until day 16 to get as far as the others have it by day 10.
The good news is, this doesn't prevent the Siberian High from doing it's work, and despite lacking the U.S. block that ECM and GFS have, the increasingly strong warming is still present for days 10-16.
You can already see the strat. vortex beginning to stretch at the end of the run as the warming takes effect:
After a long run of rather tedious model output, things are finally starting to look up if you like the idea of a cold end to the year or start to the New Year.
I will admit that my original idea of mid-late December cold, with a good chance of encompassing the Big Day itself, now looks to be a bit fast. That's largely due to a persistent low in precisely the wrong part of the Arctic which has prevented the Siberian High from driving wave breaking for the past week or so. Good thing it's on the way out! 
Briefly on the MJO - it could still give an extra boost, though perhaps not by much, with the consensus now showing a phase 7-8 path but at increasingly low amplitude. GEFS continues to show a more amplified MJO and ECMF has trended that way so who knows... but at the moment it looks as if it may spend the crucial period close to neutral, having not much of a say in things after all.
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