Shocker? More an injection of reality... I've never known a scenario where the 12z we've just seen have been modelled consistently across the piece from 10+ days out.  All we know is that it will very likely get colder from early next week and for this cold to remain for at 4-5 days. It MAY stay colder for longer giving a top-notch cold spell, but it's too far out to have high confidence.

No, of course I am not saying that this run is any more likely than the 12Z. But the variations mean that making any meaningful forecast beyond a week out is totally foolhardy. 

The fact that inside 9 days the models can't even tell whether this block will be over Greenland or southeast of the UK should demonstrate that pretty well!

Nothing surprises me with GFS to be honest. I've seen it go from the sublime in one run to the ridiculous in the next more times than I care to remember.

My advice is to wait until the morning and see what the 00z runs bring us.

Well the control is running let's see if that follows it's leader

Indeed. I can recall occasions where people have said, "it's on the 18z" only for the 0z runs to follow suit and ditch the cold spell. I'm not saying that's what we'll be greeted with tomorrow, but.

By 300 hours it is practically an inverse pressure pattern to the 12Z run.

Remind me again why any models bother going out past T168? :)

I remember now why I chose my avatar...

No Press Release based on this evening's runs just yet then Brian? 

The Atlantic block looks much better on the Control

fwiw, EC 15 day ens keep the idea of cool weather, c/o a mid atlantic ridge, right to the end, with NE UK always most prone cold troughing.

Out to 162 it looks a lot better than the op. 

I was expecting worse based on the comments here! 

18z GFS op is disappointing in the very unreliable longer term compared with the likes of the 12z ECM , BUT its still a mightily impressive setup for mid next week. 

Snow here too if it verifies with a nice WNW'ly flow. 

Agreed David.  I've seen so much chopping and changing from one run to the next that nothing surprises me.

What was interesting and wholly different about this run was the behaviour of the low pressure near the Azores.  Instead of holding position and sitting under the mid-Atlantic high it actually drives WAA north just west of Iberia, which creates the surface high over Biscay that completely changes the pattern.  Very strange change. Whether it's an aberration or the start of a change remains to be seen but I'd discount this one run just as I would any one solitary run. 

Yep, there's so many variables in the early part of the run which could screw up the chances of prolonged cold. GEM 12z and now GFS 18z, represent 2 potential ways where things could go pear shaped. At the same time, GFS and ECM 12Zs cannot be discounted. Could go either way in the 00zs I feel.

The 18z GFS op has given the teleconnections the middle finger as it flattens the U.S. trough and ejects the cold air into the North Atlantic, triggering cyclogenesis there which further undoes the blocking pattern in our part of the world.

The disagreement with the expectations at NCEP suggests it's probably gone off on one, but as always we can't be sure about such things. Having said that, with such a strong signal for the stalled U.S. trough and powerful mid-Atlantic ridge to prevail present in the EC ensembles as early as +144, it would be a rare event if they turned out to be much wide of the mark in terms of that consensus.

I've seen it all before, with a number of possible routes tomorrow. The nicest one has GFS moving back to something like today's 12z op (or better still the 12z ECM op!). Less nice is GFS and ECM both repeating their outputs as that just means lots of uncertainty. Both outputs moving toward each other... well to be honest with the U.S. trough that looks to be out of the question - it'll do one thing or the other.

Unfortunately there has to be a chance that we see a GFS 00z similar to the 18z plus an ECM 00z similar to today's 00z. Now that would be a tough morning - despite not necessarily meaning it was all over.

Whatever comes our way, stay strong, snow seekers! 

The 18z is plausible to be honest. Looking through the GFS 12z ensembles earlier there were a million and one different variations. There's a long way to go yet, and the ECM is an extreme solution where everything goes perfectly. Back down to earth after I got a little excited over that 12z ECM 

ECM spread show lots of uncertainty WRT developments to NW

up to 180

P2 , 4 , 5 , 6 , 7 ,11 , 12 , 13 , 14 , 15 , 19 & 20 ...ish

The above all keep the blocking going quite well but with different variations of the depth of cold. Certainly a return to Westerly's are not that popular.

Overall though I'd expect to see a slight downgrade in the cold but perhaps not the general theme 

EDIT

Even some of the runs I haven't mentioned give us some v cold conditions after 180.

To me it looks as though cold weather is on the way, but as always the devil is in the detail. We should take any runs after Sunday with a degree of caution whether a milder run or cold Nirvana. Fascinating to watch though....

The 18z control is ok up to FI then it goes off on one, throwing up a stereotypical GFS bomb:

http://www.meteociel.fr/modeles/gefs_cartes.php?code=0&ech=288&mode=0&carte=0

Good to read your thoughts from down under, Kieren.

Keep yourself hydrated- sounds as though you'll need it if it's already as hot as that at 10:30 in the morning!

ECM's , you'd take that .....wouldn't you