Well the ECM short ensembles look pretty good this evening. The Op run tracked the ENS mean until day 10 when it became one of the warmest solutions. What is noticeable is the distinct lack of scatter on the ensembles out to T240 this evening which is also encouraging.

http://www.knmi.nl/exp/pluim/Data/PLUIM_06260_NWT.png

The GEM run at T240 also looks good this evening. 

We always see big fluctuations in the models when there is uncertainty about a possible cold spell. It is the overall trend from run to run that is worth watching. Overall the output during the past couple of days has suggested an increasing chance of a cold snap at least. The timing of such a cold plunge is bound to vary this far out.

Interesting tweets by Matt Hugo

"Amazing change to the EC Seasonal with such a strong +ve height anom over the pole for Jan/Feb/Mar. It's playing catchup once again."

"December update of the EC Seasonal model goes with a particularly -ve NAO pattern, a big change from past months!"

So far this winter have seen little to cheer up a dedicated coldie.However the above output from EC model earlier this week( if it has not already changed  )gives hope of cold conditions at some stage in January and February.

The current December model output  of occasional northerly outbreaks is  unlikely to deliver any sustained cold (reflected in  o the Meto monthly forecast) .Northerlies in this mobile situation are short lived ans any Greenland HP tends to slip south into the Mid Atlantic

Frankly to give any chance of sustained cold requires a Scandi  HP and HP build from that towards  towards Greenland.On Wednesday mornings  0h GFS Parallel there was a a good shot at building a Scandi HP but that evolution id largely absent from todays ENS.

There is always  possibility of a cold spell developing but at present  there  is not much in the current output that convinces!

I'm pretty sure that as we approached Christmas last year, many of us here would have given anything to see charts like we have at the moment back then. The main difference this time is that at least now there appears to be some hope of a notable pattern change as we go further into the winter; the model runs during December 2013, in fact the rest of the winter come to that, gave us no hope at all. We could be a lot worse off at the moment.

great post. Grounded and balanced.

Anyone expecting pronounced nationwide cold from the current output is barking up the wrong tree IMHO

Shallow low NW of the Azores looking a fair bit more troublesome on the 18z parallel, could go along a similar path to the 12z op.

Again we end up on the wrong side of the trough (as shown by this morning's ECM) and mild temperatures flood in on a long fetch SWly:

Edit - a challenging couple of days of model watching, even if the outcome is disappointing...

Lovely warm flow next weekend straight from the tropics

At least I'll get some gardening done LOL

And all this proves what? Never do what I've just done above and take one member of one run of one model as a likely outcome.

The GFS is very disappointing, but it has little support, and its completely different from the 12Z. The GFSP meanwhile is quite similar to the ECM.

Strange pattern Q gfs like a massive Dipole Pattern but we are unlucky to the south

The GFSP certainty isn't bad though, seeing -19C 2m temps on low res is really something, the back-end of that parallel run was positively 2010esque. For scotland it had an eastern sea board style low that caused a 15C gradient at the 850hpa level and dropped a good 30cm of snow, as-well as that equivalent in rain for those unfortunate enough to be south of the front. 

(I reset the colours so now the max precip rate is 8mm/hr which is about 15cm/hr for dry snow when black) which is falling here in Scotland. If this system develops anything like the ECM or the GFSP then Scotland is going to get buired  but I'm very skeptical it will.

Perhaps the models will downgrade and we will take the easy way out with the Azores winning, but I doubt it. And this stalemate seems to contrived too last, I recon the GEM and the ECM mean and possibly the JMA are the trend setters, and I'm not just cold ramping here.

Daft old GFS run - has LP west of the Azores advancing due north straight through a ridge of high pressure days 6-7!

Comparing it with GFSP which has LP in the same place on day 6, the main difference seems to be that the section of jet returning north from somewhere south of the Azores (extreme southward travel going on there!) is stronger on the GFS run:

I do like how the GFSP charts (right-side) have a higher resolution for the jet plots 

Once the LP lifts north on the GFS run it seems to somehow interfere with the blocking high over Greenland (or is it just the transition to lower-res having undesirable effects?) and from there the run flattens the Atlantic pattern in classic GFS style despite amplification remaining very much in place over the U.S.

In short, the run is pretty much garbage... in theory. As in, only if the likes of Tamara are correct in their predictions (so far, the performance from Tamara in particular has been really quite good).

Now GFSP... well, having ditched the flatter day 7 U.S. low, it follows ECM's 12z effort really rather closely, then briefly does a great job of showing where that run was going, only to fall apart as a ridiculously broad low over Newfoundland drives energy east to trash the party.

Is it just me or did I say the same thing early this week about a GFSP run for the festive period? If so, we've seen that low both consolidated into a more compact feature and adjusted quite a long way west.

Anyway, what actually happens is basically a big increase in jet stream strength over the eastern U.S. removing the split jet in the far-western N. Atlantic. Much of that strength boost happens just after crossing into lower-res. So suspicious for the usual reasons.

Despite the mild interlude 27th-28th December, I would be happy with similar ECM and GFSP runs out to day 10 tomorrow morning, but the odds of that must be through the floor at the moment 

My take on the models at the moment is that there is fairly good cross model agreement on what happens out to T150 (0z on Christmas Day). Beyond that we are getting a multitude of different solutions with no consensus at all really. So it really is impossible to say what might happen beyond Christmas Day at the moment.

The general synoptic situation at 0z on 25 Dec sees the UK in a run of cool north to north-westerly winds as low pressure moves east across Scandinavia. Pressure is high over Greenland and also over Portugal with low pressure to the west of the Azores. The following describes the evolution from this point for the various models.

GFS 18z  http://modeles.meteociel.fr/modeles/gfs/runs/2014121818/gfs-0-150.png?18

A fairly active low pressure area to the wet of the Azores is already showing signs of drifting north which it does gradually forcing the high pressure over Portugal to drift NE towards the SE of England. The low then elongates east to the north of the UK over the top of the high pressure bringing in a mild S/SW flow. The Atlantic then takes over in low res.

GFS 18Z P http://modeles.meteociel.fr/modeles/gfsp/runs/2014121818/gfs-0-150.png?18

Very similar evolution to the 18z op run out to T192

http://modeles.meteociel.fr/modeles/gfsp/runs/2014121818/gfs-0-192.png?18

Beyond that a ridge does develop temporarily again from Greenland to Portugal allowing some very cold air to flood south over the UK for a time

http://modeles.meteociel.fr/modeles/gfsp/runs/2014121818/gfs-0-252.png?18
http://modeles.meteociel.fr/modeles/gfsp/runs/2014121818/gfs-0-288.png?18

Eventually the Atlantic express rolls back in

ECM 12z http://www.meteociel.fr/modeles/ecmwf/runs/2014121812/ECM1-168.GIF?18-0

ECM has a little area of low pressure just to the west of Iceland at T150 which is different to GFS. This suddenly develops into a complex and deep system of low pressure within the following 48 hours bringing mild south westerly winds to the UK. This seems a somewhat unusual evolution. The low to the west of the Azores stays put and fails to engage with the low developing to the south of Iceland.

http://www.meteociel.fr/modeles/ecmwf/runs/2014121812/ECM1-216.GIF?18-0

By the end of the run the Greenland high is ridging strongly SE towards the Azores and the main low is sinking south east to the west of Ireland. If the ECM ran on for a couple more days we might find the UK ends up in a run of N or NE winds. So the run is not without interest but I am not convinced by the evolution it shows.

GEFS 18z Control http://modeles.meteociel.fr/modeles/gens/run/gens-0-1-150.png?18

Also has a small low close to Iceland at T150 similar to ECM. Unlike ECM this low moves east but does still result in a SW flow over the UK by T180 http://modeles.meteociel.fr/modeles/gens/run/gens-0-1-180.png?18

Beyond that it looks like the next area of low pressure will try to move in from the Atlantic.

GEM 12z http://modeles.meteociel.fr/modeles/gem/runs/2014121812/gem-0-156.png?12

The low to the west of the Azores remains in situ due to the jet stream in the vicinity diving south east. The pressure patterns remain locked in place with little change out to T240 and the UK remaining in a cold northerly airstream. Low pressure remains blocked off the Canadian Maritimes.

http://modeles.meteociel.fr/modeles/gem/runs/2014121812/gem-0-240.png?12

So a real mixed bag of options beyond Christmas Day offering anything from mild south westerlies to potentially a very cold spell for at least a time. That says to me that everything beyond T150 at the moment is FI and pure speculation.  

How locked into pattern are we?? when you look at that is that 3 omega blocks or would you call those 3  omega ridges?

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

ECM full ensembles show massive scatter after day 10. Plenty of cold runs including the control which is one of the coldest but also plenty of very mild runs as well. Anything is possible post Christmas.

http://www.knmi.nl/exp/pluim/vijftiendaagse/index.php?run=12

Thanks GW

GFS 216 Mean

You'd take that all day long

For London the average 2m temp is about 2C which is unbelievable, the ECM mean is a proper cold spell in itself, saying nothing of the cluster of runs below the mean. All or nothing gambit.

http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=6&ech=216

Have a click through some of these.....not that bad

Nice analysis GW, good to have further angles on the model output at the moment 

I just took a moment to think about what makes ECM's 12z run particularly special days 8-10 - it's the fact that there's still a weak transfer of energy over the top of the East Pacific ridge which prevents it from strengthening to the point that it draws the main focus of the block toward Alaska (GFSP 18z) or disrupts the Greenland High and takes over proceedings (GFS 18z).

The GFSP run has a particularly large blocking system by this time, which allows it to hold on until day 12, but the high heights over Alaska shove the U.S. trough further east to the Atlantic border, which is not the case on the ECM run:

See how ECM has kept the Pacific High more or less in situ and has trapped much of the U.S. trough between that high and the vert strong one over Greenland.

The different focus in the blocking system emerges at around +168 hours and guess what... it seems to be a Canadian shortwave that does us so much good on the ECM run! Something to watch out for on the 00z runs, though it will take something special for things to keep falling into such ideal positions.

I guess we have wave 3 activity when we want wave 1 activity?

Indeed Marcus looks better

I guess today has been a bit disappointing for some, given the withdraw from the eye candy synoptics on show yesterday on various operational outputs. Having said that, the ECM mean has if anything got better and better, the GEFS suite is still at least equally split between the cold and milder options, GEM is stonking along and from what I can gather from Matt Hugo's tweets, the ECM monthly anoms have suddenly switched to +ve anomalies over the poles for Jan through to March. Given this, and the ongoing weakening of the strat vortex, it's hard to paint a solemn picture RE cold potential at the moment. It might not come in the stonking fashion suggested in the last 48 hours, nor may it come that quickly, but not only is all that still possible, the long term signals have arguably improved too. Plenty to chew on - though, as ever, it could all go the way of the pear. Usual caveats apply...

Last night's ECM ensembles were again the coldest we've seen this year - there's no change as I see it in the chances of a cold spell (as opposed to a cold snap), despite the traditional wobbles. As is often the case in these setups the ensemble mean is utterly useless, clusters are the way to go (and the majority of members are in the cold cluster).

FWIW, last night's ECM control went as follows:

168 (Christmas Day): Cold front moving SE'wards across UK, -5C 850 air spreading south

192: Weak ridge over UK, eastern and northern areas under sub -5C 850 air

216: Trough over Scotland, warm sector over UK (850s still below zero though!)

240: Deep low over North Sea, strong NW'lies and westerlies for UK. Most areas under sub -5C 850 air.

264: Low fills over London, with northerlies for most. Cold (sub -5C 850) air remains over the UK.

288: NNW'lies, cold air remains over UK.

312: Ridge builds to west, northerlies and cold air for UK.

336: Ridge moves over northern Scotland, northerlies and cold air elsewhere.

360: Warm sector (still below zero 850) moves southwards over UK, with northerlies and NW'lies.

By 240 all of the UK except areas south of the M4 and a few coastal fringes in the east and SE are shown to have seen snow.

By 288 all of the UK except Cornwall and the far SE of Kent has seen snow.

Make no mistake, it's a snowy run. The snowiness comes, of course, from the low crossing the UK being entrained in unusually cold air.

Don't look at the GFS 00's. Its a complete run of nothingness