"The only consistent element in latest longer-term forecasts is the unusually strong SPV signalled to remain throughout January, which - taken in isolation - would imply a leaning to +ve NAO. However, longer-range predictions aren't so clear-cut on NAO and the sudden lack of almost any useful signal in ECMWF beyond 1st week of January is, in itself, considered very unusual.

If basing prediction on GloSea5 alone, the anticyclonic theme remains dominant - but weakening - further into extended range (ie by d15), with this sinking south to allow a mean westerly flow across us and a gradual upward turn in temperature. However, given that a conspicuously colder phase looks set for first few days of 2017 (scope/longevity/severity uncertain) and signals then suddenly vanish thereafter, forecast confidence beyond week 1 of Jan remains much lower than normal."

Yes, once the data issues are out of the way the zonal ghost train will be back on its tracks

How do you propose this loss of data results in a blocking bias in the models (forgive me if I've got the wrong end of the stick, but this seems to be what has been claimed earlier in the thread)? A reduction in accuracy, almost certainly (although the level of which I've not seen any evidence for), but a specific bias?

I haven't ever said there is any bias. All I have said is that there is lack of data be it zonal conditions or blocked ones. How that manifests into model output is at best a guess, though I would think it may slightly perpetuate whatever conditions prevail on Christmas Eve if I were a betting man  😀👍

Darren (Retron) and I were exchanging thoughts on this earlier today.  It is a puzzle why - if it's true - a loss of data should favour blocking patterns.  I did ponder whether it was the coarser opening position (i.e. lacking some detail) that caused the models to miss minor developments.  It's also possible that as it is the upper level data that is not complete that events in the upper atmosphere become less certain - and we know that blocking is dependent on height rises in the upper atmosphere.

I'm still not convinced and it's probably best to treat all the output as slighly suspect for another 24 hours.

Hence my earlier comment ...............and it isn't ignorance Jacko as Darren is well clued up on data ...no doubt.

But to have an increased showing of blocking due to missing data .....really ?

Those old models just love us weather watchers eh ?

Very sensible

Good downward trend there

18z still dangles the carrot

Good cold plunge over us in deepest FI

-9 lowest IMBY so far , be good to go lower

It means that the longer range models are not picking up what the deterministic output is showing and there are no clear signals going into January.  That means, essentially, that it's guesswork what happens into the New Year, beyond the first few days.

GFS 18Z keeps the theme of a deep southerly tracking jet in FI

http://modeles7.meteociel.fr/modeles/gens/runs/2016122518/gens-4-1-348.png

some crazy ens members! Must be the lack of data

Having had a rude awakening with a poorly daughter in the early hours I thought I'd sneak a look at the models... lack of data or not, GFS seems quite consistent run to run with blocking to the north west. No sign of any zonal train here... http://old.wetterzentrale.de/pics/Rtavn2641.gif

0z GEFS ensemble for London - a drier cooler period up to NYE.  Then there appears to me to be the signature of 2 topplers in succession in the New Year, with pM and tM air alternating.  Things could turn out differently of course, but 2 topplers to start the year is my interpretation of the most likely outcome from the displayed GEFS this morning, though the ECM could bark up another tree...   In the short term I would welcome an air frost, but locally that may prove  hard to achieve.

UKMO 144 is a decent chart though, but isn't that jet going to separate and slice the high at 168?

ECM ends this morning on a true Fantasy Island classic.  More runs needed (though I doubt they will be of this quality )

ECM the pick this morning, along with the GFS control. Steady as she goes for a New Year cool down with the chance of something much colder.
Now go and do some boxing.

Edit: ECM 240 isn't the chart of the day but the chart of the year. The PV is completely rent assunder.

ECM 240 should be framed.  Shame its so far off, but a nice Boxing Day Surprise for model watchers.  Enjoy the jam.

GFS is consistent with its topplers and more jam tomorrow post 240 hours. ECM is a classic but at 240 hours its too far away to take seriously.

Pick of the bunch today surely has to be UKMO 144 ? A declining European High, falling heights over the Azores, an impressive Atlantic ridge with an arctic arm extension and plenty of cold air to tap into to our north and north east. 

Looks like it's not just the Gfs that's been on the sherry lol

It's certainly getting interesting... increasing likelihood of a cold blast for New Year... plus chances of sustained cold increasing to my untrained eye.  Ian F mentioning PNA has changed the MetO outlook to blocked/anticyclonic for Jan...

http://climate.ncsu.edu/climate/patterns/PNA.html some info on PNA here

A transition to a pattern which has more "wintry" potential is in the bag. The question is whether we end up with a toppler then changeable and chilly regime or a more substantial cold spell.