Another interesting piece, James. I confess I'm bring a bit grumpy about all this at the moment so please excuse the deliberate insinuation but are these 'background signals' the same ones we've been watching since November or different ones? ;)

In short, some of the things that, back in November, we expected to see happen last month, are now finally getting away this month.

One notable exception is stratospheric warming, for which there are only faint signals of the right sort of thing happening.

That's why I keep referring to the MJO at the moment - it's the only major driving force that I know of being reflected to a notable extent by recent longer-range output.

While I'm at it, today's MJO update reveals that it's continued to amplify, which defies yesterday's ECMF outlook which was stopping the amplification yesterday - but this amplification is not quite as extreme as GEFS were going for.

In response, most of the outlooks have shifted a little way toward GEFS... except for ECMF which stands firm despite the recent error. GEFS are about the same as yesterday but the bias corrected version ventures a bit further into phase 7.

Broadly, this translates to a stronger overall signal for the Atlantic jet to weaken, with amplified mid-Atlantic ridges, starting in about a week's time. Reads a lot like recent model output.

Some time next week I intend to have composed and uploaded some information about the MJO (among other things) and why, when amplified, it has the ability to drive big changes in the weather patterns we experience.

A BIT grumpy? I got that impression when you suggested I had posted a charts showing midday tempertures of -2°C here on Saturday. I didn't. It was for the Highlands, here it was in low single figures although it will probably feel colder in the strong winds. It will also be largely dry if you're that interested. 

Anyway the main issue in the model output at the minute is the very strong winds which are imminent in parts of the North. Carol Kirkwood suggested a one in three to one in five year type event.

It will be interesting to see how the charts verify for tonight and the weekend's storms as they look rather nasty in places. It remains unsettled for most of the outlook but with quite a cold westerly flow at times (which is no use here for snow but NWern parts could do very well at times).

It wasn't working on Wetterzentrale either when I last looked.

And it's no surprise to see another operational run showing a colder outlook midterm. Again, the fun stuff starts around day 8 or 9, but it's too strong a signal to ignore IMO. The parallel isn't bad either, with the odd mild sector easily countered by several cold plunges from the NW.

I daresay the ensembles will be similar too.

There were a few GFS op runs on Sunday and Monday which had more interesting FI sections in terms of a possible pattern change, but during Tuesday and yesterday that signal appeared to fade somewhat. I wonder if GFS is picking up on it again only with a little more consistency this time, perhaps.

I hope this downgrades. I think that we got more than enough strong wind/storms last year. Agree it's the main thing to look out for at present.

It is running but there seem to be resource contention problems again which are slowing it down. On TWO it's at 300.

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

GEFS look to be having problems too.

Boxing Day take 2 anyone:

Followed by a party for everyone:

its been a while ... but i think its time for the use of some:

What? You mean they had to go out to the shops to get some more crayons?

I'm sorry Michael I must of misinterpreted what you said.

I'm obviously not contributing to this forum in a positive way at the moment so I'll retire for now. I am at heart a cold weather fan and really hope the pattern changes for other like-minded people.

Actually, that's not quite true.

EPS and GEFS both picked up on a potential change to a colder, yet still unsettled outlook right at the edge of their runs just under a week ago. They've both stuck with that ever since, which is really quite remarkable! Sometimes the colder cluster has been in the majority, other times it's been an even chance or even slightly in the minority, but it's been there throughout.

And so a week on we have charts like this at just 6 days out (GFS op):

or this, followed by some rain and then back-edge snow (GFSP):

Is it a nationwide gauranteed snow-fest? Of course not. Are we going to get a change to colder conditions? Quite possibly, but by no means certain. However, with charts like the above on offer nobody can truthfully say it's staying out in fantasy land!

Hi James.

Please keep these well informed posts coming they are excellent.

It will be interesting to how things pan out after the coming week, also interesting to see that the GFS might be outwitting the ECM regards the MJO.

Plenty of wintry ppn about, obviously further North , but a better trend for sure.

http://expert-images.weatheronline.co.uk/daten/proficharts/en/2015/01/08/basis12/ukuk/rart/15011212_2_0812.gif 

Snow for Scotland

http://expert-images.weatheronline.co.uk/daten/proficharts/en/2015/01/08/basis12/ukuk/rart/15011300_2_0812.gif 

Snow for many in Scotland and parts of Ireland

http://expert-images.weatheronline.co.uk/daten/proficharts/en/2015/01/08/basis12/ukuk/rart/15011312_2_0812.gif 

Many parts of the NW have snow showers

http://expert-images.weatheronline.co.uk/daten/proficharts/en/2015/01/08/basis12/ukuk/rart/15011400_2_0812.gif 

Again Western and Northern parts seeing Snow showers

http://expert-images.weatheronline.co.uk/daten/proficharts/en/2015/01/08/basis12/ukuk/rart/15011406_2_0812.gif 

The wintry feel continues

http://expert-images.weatheronline.co.uk/daten/proficharts/en/2015/01/08/basis12/ukuk/rart/15011418_2_0812.gif 

The trend continues

J F F  of course

Long one I'm afraid.

Increasingly over the last year I have taken the advise of some of the more experienced members on here (and others) and used the ensembles far more, as a tool I think they are invaluable. Unfortunately we do not have acsess to the EPS which is a shame, and although the means are useful, they are no where near as powerful as the individuals or clusters. Hence the following:

This commentary is based on evidence from the GEFS, GEMS (and the other model OPs) as well but since this is as close to the individual EPS we can get I think it is important to show it. The diagram, takes advantage of the very crude method of diurnal temperature range vs airmass temperature range. If the former dominates then it is blocked type conditions, and if the later dominates then it is zonal. By this crude method, and becuse thankfully zonality has a decently strong temperature dependence (zonal=mild, blocked=cold usually) this gives an indication of the types of runs being shown.

Now the picture illustrated here has changed a little over the last couple of days, the support for blocking has actually increased, although you can see some zonal runs still being shown in the top right hand area. The transition period remains again relatively consistent, with something like the 15th at the earliest (and a small chance of a ridge of high pressure on the 13th), and the 16th on the latest. From then on there are three options:

1) Quick return to zonality; this has little support on the EPS but more considerable support on the GEFS so it should not be discarded, however like on the EPS the number of runs with zonality indicated drops off gradually over time, and something of a blocked nature is selected instead, that being said it could well be beyond the 20th before this happens.

2) Polar maritime dominance. This has become increasingly apparant on the GEFS and the OP runs in particular, with the atlantic starting to calm down but extremely low heights in scandanavia keeping the UK in a cold NW airstream. Doubtless this is a very snowy scenario for the NW. The EPS has decent support for this as-well, and I have categorised the warmer 'blocked' scenarios as probably Pm based. This is the 'low height latitude gradient' I was talking about, a weak Atlantic but nothing really to support significant blocking.

3) The Easterly block. The EPS certainty seems to like the idea! The GEFS far less so but it becoming slightly more prevelant in the distant future. The OP runs of the other models seem to like this idea more than the GEFS too. The GEM ensembles are still keen for a UK high which the other models expunged a couple of days ago.

All in all,  extremely strong support for a cold spell so high confidence here for a prediction of around the 17th. However the nature of the cold spell has no agreement with Polar NWerly, Scandi/Greenie and Inversion scenarios all on the table. As for the longevity of the cold spell: this is also very uncertain, however there is increasing support for a longer spell with periods of moderation if the GEM/GFS is right, and less so if the ECM is right. I say periods of moderation because though the situation becomes more favourable on the GEFS there is little support for <-5C uppers lasting more than a couple of days.

I'm not sure whether to be scared or be impressed by Quantum's vast all consuming knowledge. While I like to think I have something of an idea on how ensembles graphs work, anything beyond seven days is still like staring at one of those "Magic Eyes" picture until I either get a migraine or something magically pop out!

Anyway, back on topic, it's all . . . er . . . I've forgotten what I was supposed to write about. Oh yes, the way things are shaping up, I think we are going to have another January 1984 on our hands (often wintry from the Midlands northwards but staying unsettled and fairly mild over the southern half of the UK for a good couple or three months . . . I mean, weeks, which would take up the rest of January anyway). 

Nice insight Quantum, your posts are appreciated. I of course would like this to be the source of cold!

http://www.wetterzentrale.de/pics/Rtavn3842.gif

I will also add that this is quite an impressive temperature drop coming up - 18C or so in as many hours!  

http://www.wetterzentrale.de/pics/Rtavn422.gif

The run to run consistency of the overall pattern sequence on the GEFS is impressive, and the op runs are playing a similar game despite variation in the timing and intensity of lows plus how many shortwave features get in on the act.

The signal for a strong MJO progressing through phase 6 to wind down a bit in phase 7 is lending extra predictability to how the large scale pattern is likely to evolve. The theme of sliding lows relates to the high amplitude phase 6 period (not the sole driver but having a big say in things IMO), while the emergence of extensive high latitude blocking late in the 12z GFS op run is an example of what a gradual decay in phase 7 could bring about (again, in combination with other factors).

It's a similar story for the ECM ensembles, but with the consensus in those winding down the MJO in phase 6, suggestions of high latitude blocking in about two weeks time may be weaker - it will be interesting to hear about the 12z suite.

Overall, the focus remains on the jet taking on a more NW-SE trajectory (overall - some wiggling about likely) through the UK starting about a week from now, with plenty of cold air being drawn into the mix but nothing deep enough to guarantee snow on any given day... lots of marginal events here there and everywhere.

Quite a vicious option from the ECM 12z op run, that low is heading SE so a cold undercut would likely feature the following night/day.

The height chart shows high enough values over Greenland to believe that the next low in line would disrupt with a shortwave or trough extension heading SE.

As a far-southerner, I'm not getting my hopes up for much in the way of snow here during the coming week or so, but at least the weather looks a lot more interesting. Good to see the Azores High being shoved well west of us, in keeping with the NW-SE jet.

Good post Q even if all those squiggly lines do give me a headache. Cold zonality is gaining momentum with increasing cold incursions diving well South through the course of next week and beyond perhaps. All in all it may well not be a HLB or a beast from the east but at least we have some exciting weather for most of the UK to talk about.

GEFS postage stamps should be available tomorrow. I've included one which only shows snow (rather than precipitation type) for clarity on the smaller images. This shows where the parameters support snow and precipitation is forecast. For example: