JH just mentioned the possible Change on the week ahead forecast too.

Notably colder next week from John Hammond 

Doctor Who- Sylvester McCoy?

Not necessarily: on the 06Z GFS that lobe of PV over northern Canada actually served to pump up the Greenland high. It all depends on positioning and strength: the 12Z GFS showed what happens when the lobe is too strong.

GFS 18z now bringing colder air almost 2 days sooner, with -5 850s across the country by the 11th.

Is it too early now to get excited about this?

Yes 

In a word, yes. We have four days of chaos and confusion before anything conclusive can be announced about next week. The current 18Z rolling illustrates the uncertainty - however it looks like a classic 'I don't have a clue' run to me which is not a bad thing at this stage.
BUT (caveat) mainstream media are now starting to ease the possibilities into forecasts so data we mere mortals do not have access to is now supporting the cold probabilities.

Thank-You for your wisdom!

Yes I was thinking that cross-ensemble support is probably needed for atleast the next 2 days before a cold spell becomes a real likelihood.

Still probably the best charts we have seen this year or maybe since 2013?

im not one to eulogise over the Chinese model but interesting the GFS control goes the same way, by +288 it's on it's way towards a scandi high

ECM 12z ensemble for London:

http://www.weathercast.co.uk/services/ensemble-forecast.html

The Operational was in the cold cluster from Monday but well supported.  As with the chart from yesterday's 12z the longer term trend remains for cold or very cold conditions: maxima around 3C and overnight minima down to -3C

It is noticeable how the 12z GFS run was a mild run and out of kilter with the ECM suite.

Not a bad Day 8 ensemble mean chart...

It's true that the surface temps aren't as cold across the board on this run (and the op decides to evaporate the arctic high to some degree) BUT check out the final postage stamps at +384 on the ens. Lots of easterlies, greenies, northerlies. If we only ever look at that range to assess trends, then this is some trend to watch out for! 

http://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=384

edit: German ens - incoming? 

http://www.meteociel.fr/cartes_obs/gens_display.php?ext=1&x=655&y=39

First ramp of the winter I admit. It won't happen again, had to get it out of my system. 

The Op was a mild option from Day 12:

They actually mentioned it a few times this week as a possibility

Not surprising really with the atmosphere and ground as wet as it is, clear skies and no winds in southern parts.  Could be really dense in parts if its gets cold enough.

Wow its not often you get an ECM ensemble maxing out at -5C and reaching lower than -10C at night. What a corker of a run that must have been, -15C uppers from the continent presumably! 

The ECM control last night showed the high (at 216) toppling after two days. However, the pattern repeats just a couple of days later as the Icelandic low is forced south over the UK, with another northerly plunge following on behind.

EDIT: And as can be seen, the control was somewhat representative of the main cluster. It makes a change to see the low probability option being milder conditions! Also, the CAPTCHA to upload that was "snowed in"... ironic, eh?

 Meanwhile the 0z GEFS suite is backing down from the colder outlook of yesterday, longer-term the milder and colder clusters now have similar numbers of members.

ECM's noticeably less amplified (and less cold as a result) this morning. I would imagine the ensembles this morning will be a little bit milder than last night's as well.

Disappointing GFS this morning . The ECM nearly snatches victory from certain defeat at the end of its run it's certainly cold from 168h onwards. 

Looks like a toppler at 192h but then looks to be setting up a nor Easter by day 10. I'd give it 7/10 not as good as yesterday's 12z but much better than the 3/10 GFS .

http://www.wetterzentrale.de/pics/Recm1921.html

http://www.wetterzentrale.de/pics/Recm2401.html

Mixed and messy sums up the output for next week. 

Good morning Ally Pally.  for one moment I thought you said 'setting up for Easter', then I adjusted my glasses.  Well I suppose that might be an ironic view of the charts this morning anyway.  The GFS shows the worst case scenario for cold this morning. The LP in the Atlantic wont shift across into Europe quickly enough, brings milder air to the East, and lots of  cold air come south to the west of us and dilutes nicely across the Atlantic. Boo hoo. For us coldies thats like an alcoholic throwing whiskey down the plughole.

http://www.wetterzentrale.de/pics/Rtavn1621.gif

The only thing that is a certainty is that the cold air has got to come south.  Its just a question of where at the moment.

Best wait and see I suppose......