Having read through here before looking at the charts I feel underwhelmed by what the reality is. As Brian has said ECM is poor and I see a very rocky road in sustained cold for the UK within the framework that the cold charts are shown.. I'm not saying that there aren't windows of opportunity for cold weather from Christmas on but they are just that and while some move on to develop things further a lot don't and in my mind (and I hope I'm wrong) the synopses still look biased towards less cold solutions than not.

I'm not sure why people are saying ECM is poor?

By t+240 it shows high pressure in the vicinity of Greenland and the Mid Atlantic - this is the trend that matters. 

Focusing on minor details such as upper air temps is fairly pointless at that range. 

Amateur mistake 

Another minor point - it's always worth being careful with 850 ensemble graphs.

When a cold period becomes established, the best and most severe snow events can often occur when uppers are in the region of -1C/-2C (battleground scenarios).

Therefore an 850 ensemble graph that shows several members creeping up towards freezing point aren't necessarily totally devoid of interest. In this respect 2m temp ensemble graphs and dewpoint projections are more useful. 

The trend of blocking over Greenland/mid Atlantic is what to focus on for now.. Details of localised snow events/surface conditions should be looked at nearer the time. 

So tonight the trends are looking promising, but given the range, there's still time for the blocking signal to go wrong/change to something less favourable. 

This guy knows what he's talking about 

Joe is a legend

In days gone by when looking at GFS for a pattern shift we always used to say 'when the control follows the OP the rest of the pack will follow'.
Early days and all that but it's a notch-up tonight that's for sure.

Well we all know how these situations often go pear shaped, more often than not they downgrade nearer the time. We still have a long way to go before anything is nailed on. Certainly not getting my hopes up. Think I will leave any self optimism until Monday at the earliest haha

Looks alright to me - WAA up West of Greenland, stable (ish) mid atlantic ridge, reasonable cold air to our East, meandering jet. I'd agree it's not or anything but given a correction south of the LP, more of an inflation of the HP over Greenland and it's weather Bingo time imo.

Of course the form horse would probably be a slightly better version of the toppling ridge ahead of next LP we've had so far in December.

That said I do think a pattern change of sorts is unfolding, just not convinced it'll be cold enough for widespread snow away from the North.

At least with this approach I'll be pleasantly surprised if it upgrades

Brian,

Pleaae take it easy on me a blind? OAP, but this is my first forray into the MO thread. I think!!

I do not seem able to magnify your charts to enable me to read them properly. Is this my problem? I am still on Windows XP with IE.

On the charts as far as I can see it looks to me like  a good deal of back-edge snow would move down the country on the 216, and the new depression moving up from the SW (I think it does anyway!) would enhance the cold ahead of it  to give most areas some snow, maybe turning back to rain.

Anyway if I am wrong I can always blame my eyesight!

I reduce the size of the charts in these threads to reduce the amount of scrolling. Full size versions are available on the chart viewer page:

http://www.theweatheroutlook.com/twodata/datmdlout.aspx

One thing I just noticed is the GFS op is currently verifying slightly better than the GFSP:

http://www.emc.ncep.noaa.gov/gmb/STATS/html/new_acz6.html

The ECM mean charts are excellent for cold. Much better than the Op. 

http://www.wetterzentrale.de/pics/Reem2401.html

http://www.wetterzentrale.de/pics/Reem2402.html

I know these charts paint half a picture at times but tonight's ECM 10 Day Mean Chart illustrates my problem well as the High over the North Atlantic shows the Jet flow riding over the top which would force the High SE and back winds off from North to West soon after with Westerly winds and the risk of a return to the status quo of Low over or to the North of the UK and High to the South.

http://www.wetterzentrale.de/pics/Reem2401.gif

As far as I'm aware, I don't think that many, if any, forecasters were going for us to get a major cold spell this side of New Year, so even if we do get this cold "snap" as currently suggested by the models, it will be something of a bonus IMO. Going by many of James' (Stormchaser) posts, he is not expecting anything of great significance until sometime in January, if I understand them correctly.

Both Gibbys & GTW have a highlighted a possible route back to mild, however the amplitude in the wave looks pretty good, A toppling high where the 552 line has found its way into Greenland (just in this case )always has the potential to topple in Scandi allowing Deep cold to filter west ( rather similar to the GFS p.)

The ridge moving North out of Eurasia at 240 is also one to keep an eye on as it will help to slow progression down .....

THE MEAN is a halfway house, which would mean some more amplified members & some not so...
http://www.meteociel.fr/modeles/ecmwf/runs/2014121712/EDH1-240.GIF?17-0

finely balanced - At least we have some great charts to discuss..........

Wise words... There's a trend towards high pressure around the Greenland area a week or so from now.  Given how fickle the models are at that range, that's about all we can say with confidence.  I'd be suspicious if all models were showing a winter nirvana at that range... A long way to go on this... 

Watching how the U.S. trough moves, ECM would most likely go on to be similar to GFSP but the flattening upstream would take a bit longer to occur as the LP hasn't made it as quite as far toward Greenland as of day 10.

Anyway, I reckon the real issues lie with the behaviour of the jet stream in the 5-7 day range.

You see, GFSP is consistently going for the jet riding up the western side of the mid-Atlantic ridge with no real attempt to cut underneath it (see below-right, little in the way of LP to the south of the ridge). This results in a huge meander in the jet which on our side favours a push of low heights into Europe from Scandinavia.

The ECM and GFS models insist otherwise - they have the jet undercutting, with lows developing SW of the UK (ECM above-left, with notable LP development south of the ridge). This is great for getting a proper cut-off high over Greenland which can draw a lot of deep cold air south toward the UK... but that's of little use if the LP to the SW develops too rapidly and tracks too far north (stronger lows typically track further north). 

The GFS 12z was kind enough to keep the first LP from the SW as a weak feature until reaching the UK, with rapid development as it crosses our lands. This results in a sequence of events that's far from ideal but could easily deliver a widespread rain-snow event (I'm not taking the precipitation charts at all seriously at that range).

The ECM 12z is a tale of poor fortunes, as the weak LP on it's way over from the SW meets with a shortwave in the cold, unstable northerly flow that just happens to be in the right place at the right time for the two systems to interact in the most unfavourable way that could be achieved - the low from the SW being drawn on a more northerly track, but also fails to absorb the shortwave which is left out west of the UK on day 10, interfering with the cold air mass. Beyond day 10, the next LP to the SW is positioned right for following a track further south but it's questionable whether there would be enough cold air to our N and NW for a snow event across the SE'rn half of the UK.

Now it is true to say that the earlier phasing of the Atlantic and Scandi lows on the GFS and GFSP runs does help to bring more of the cold air our way within the 10 day range, but I think this mid-Atlantic jet stream issue is far more important. The GFSP 00z had the slower phasing and that worked out just fine.

Speaking of which, something between that run and the GFSP 06z is what the UKMO 12z op run bears close resemblance to for day 6. Going by the positioning of LP, the jet beneath the mid-Atlantic ridge appears to be weaker and further south than what ECM has.

GEM's a curious case, developing LP to the SW as early as day 6 but then whizzing that NE and going down a line more like the GFSP 12z from that point onward.

JMA offers it's own variation on the theme in which the Scandi trough digs south by day 8, while the jet thinks about undercutting but then seems to change its mind:

Posted just for fun as it's among the best charts on offer for Christmas Day synoptically, though the magnitude of the cold conditions is nothing to write home about on the day itself.

I suppose what we have is GFSP and GEM versus ECM and GFS with UKMO and JMA somewhere in the middle. Typical of highly uncertain situations!

Funny how the two 'upgrade' models are both on the same side. Their track record has yet to really be established so it has no effect on confidence levels.

I feel that the main thing to take from ECM is that we can see very unfortunate shortwave behaviour in these situations, but the op run itself does seem like a worst-case scenario (yet it's still alright for a [probably] short-lived cold spell to end the year).

Hi Gandalf you are right the height of the 552 line on the ECM is sliding ESE at 240

http://www.meteociel.fr/modeles/ecmwf/runs/2014121712/EDH1-240.GIF?17-0

However first & foremost the energy is split so its no a sinuous flow moving east. There energy going over the top ESE towards NW Norway & a burst of energy moving SSE over Winnipeg indicating that the high will eventually shear & become cut off somewhere over scandi.

The exact location may well ensure that the UK could get a very cold feed of continental air.

As it stands I think we have just enough amplitude in the forecast to stay in the cold air & it not turn into a 2 day cold snap as you & Gibby intimate.

ECm extended ensembles currently agree with this scenario rather than the full blown toppler assessment

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

the control has a MAX of -3 on day 12 which is extremely unlikely unless the flow is continental...

remember as soon as the top of the ridge is flat it will stop toppling- hence why the initial wave is vitally important.....

True that those De Bilt ensembles are heading in the right direction for an easterly signal, but they still have some way to go really. Not that such things are the main concern at this time, just a potential super-bonus if we get really lucky as 2014 hands the baton to 2015.

Meanwhile my latest observation of GEFS shows an increase in occasions where runs reach -5*C or below but a drop in the number making it to -7.5*C (though a fair few stop at -7*C, revealing one of the main the limitations of this crude measure):

After all of what we've seen today, there's still nothing on offer that can justify a confident prediction one way or the other. This is often the issue when the models start reacting to signals at such long range - many days of limbo in which a level head and open mind is essential to the sanity of cold weather enthusiasts.

we seem to be progressing nicely into winter proper, despite some not so keen to see it. to be fair, there are potential spoilers out there but i have a funny feeling that this next week will be one of upgrades to the cold spell rather than the opposite. (hope i haven't ruined it now)

Nick! How could you?! 

Anyway... just because it's such a nice thought, I remember how in the cold spells of early and late 2010 there were several situations in which the models showed powerful storm systems tracking NE into cold air across the UK to bring widespread blizzards, and yet the end result was a weaker system tracking into France leaving us cold but largely dry.

This thought entered my head upon reading about and even having a glance at the ECM ensemble clusters (generously offered up on another site - behind a paywall usually), which showed the op run to be in the cluster taking the LP furthest north, with at least 40% of runs taking it further south and 17% not featuring it at all (so more in line with GFSP).

..and finally, the ECM 12z ensemble mean, which shows an excellent synoptic pattern but with the coldness of the mean 850's diluted by the runs that are near to the ECM op run:

Perhaps of more importance, the mean for the previous two days gradually lowers the -5*C from the north coast of Scotland and under a northerly flow it looks favourable for lowland snowfall in Scotland but no further south than that. So for the Scots that's pretty good going given that it's the average of 51 members.

Excellent discussion in here this evening. Hope the 18Z continues to buoy the optimistic mood.

OT  Apologies

D Bett talking about 24th / 25th & 26th ..........saying Xmas Eve likely to be the coldest day of the three with a return to Atlantic winds on Boxing Day