One thing to note is that little area of low heights and low temperatures over Europe that moves into scandanavia and then into the N atlantic is cauing cyclogenesis near shetland (and the prospect of a polar low), that is weaker on the 12Z. Without that cold air pouring into the atlantic the block would be much stronger and less disrupted. That feature is small and will not be well handled by any of the medium range models.

Note that core of -22C uppers. If that takes a small diversion and does not end up over the ocean or is slightly smaller, the impact would be important. 

This conversation finally explains the question I asked you - never looked at the Meteociel spreads and the IMO charts side by side. The spread charts is the same as this one, which does not have any mention of mslp. I guess they have just named it as it appears on the op runs.

Just to add, there is a separate chart with the MSLP deviations colour coded. The hi-res is the dashed lines in this instance.

I posted a chart recently which showed there has been a trend towards higher 500mB heights over Europe and lower heights to the northwest of the UK since the 1950s. This obviously suggests a change in the global circulation has occurred but answering whether it is temporary or permanent shift is for someone above my paygrade. 

The 12Z ensembles are very interesting, one of them full on makes it.

And a handful of others come close. I think the difference between a cold spell and not is still small, but just outside the range of the ensemble perturbations. The question is, can we get a bigger change than the perturbations? I think its possible, and we should not rule this out quite yet. 

Also how many times has a scandi high failed only for one to setup in Greenland. December could be ruled out in the 2nd week (why I was barely on the model thread then), but rule out January at your peril. 

When you discount all the ensembles that contain dartboard lows, the proportion that are close is actually high. 

And yes I think discounting dartboard lows is reasonable, how often do we see 930mb on the models, and how often does it actually come off?

Well of course I would argue that never has this been more the case since 1988, particular when juxtaposed against the 1977-87 period.

As for a post-mortem on what is forthcoming, I don't think it necessary. The NWP has never at any time given a majority verdict on cold for the UK, as a veteran of some monumental let-downs and U turns, this doesn't even make the League table.

GEFS12z update.

12Z ensemble watch:

Success (easterly in south): |||

Near miss (easterly in the north some energy SE): |||| 

Fail: ||||5 |||

Discounted for unrealistic 920mb lows: ||||5

But even the failures tend to increase heights over Greenland later.

Brian

Poor choice of words, there hasn't been a change in circulation pattern as I showed a chart from 1903 showing the mean February chart. The most that can be said is a strengthening in the circulation pattern.

Just clear this up. There has not been a change in circulation patterns. What the debate is about the strengthening and weakening of global patterns and what may cause this.

To show this here is the January mean chart from a book I have dated from the late 1950s

I think this chart is shown as a 'most common' NW Europe winter chart - plenty of winters in the fifties saw charts very different to that, certainly more variation than we are seeing right now.

Thats the mean chart back then for January. Most common is the mean, if you think about it. Yes there were variations to this but the fact remains that was even then still the mean January chart. My point is the debate should be on the strength of this pattern.

To go even further back to 1903 and here are three charts depicting on the left, a normal Feb, Feb 1903 and Feb 1895. Look at the norm Feb chart back then.

I think this is a classic example of weather v climate.  That chart shows the typical synoptic pattern for January and I agree that nothing significant has changed.  It's this pressure distribution that delivers predominantly changeable, relatively mild (for our latitide) conditions and reflects us being on the eastern edge of a huge ocean and on the western edge of a great continent.

I recall many winters where Bartlett highs were the norm and/or a rajing jet ran straight over the top and into Scandinavia.  Occasionally, as we all know, we get blocks delivering temporary Arctic airmasses but they're seldom long-lasting.  I guess that's why there's something magical about an Arctic freeze and why many of us spend time in the winter months hunting for signs of one.

Back on topic, this chart isn't a million miles from the one in your 1950s book:

Deep low pressure in our vicinity looks almost inevitable for the next week or so.

Not sure how reliable 850s are when the pressure is this low, and strong occlusions are very lenient in terms of temp requirements anyway. The point is a 50 mile shift and a slightly colder environment could mean 20cm of snow for the NE.

Wouldn't it be funny if the gfs 12z was setting a trend, with all models re-showing CAA westwards & a cold easterly spell in subsequent runs. Steve Murr would be sainted 

GFS parallel is trending cold.

Wow, thundersnow if this comes off, lake effect from the west.

OK I'll say it, shades of 1984 

Returning to my 500hpa temp analysis 

This to me says it all, in fact I don't really know where the polar vortex is, there are pieces of it everywhere. Unbelievably the strongest piece is actually over the East china sea. There is a huge chunk bitten out of it in Alaska too. Something is stiring in the dark. 

12Z parallel high res ends with heavy snow showers for the NW, and cold everywhere. 

I've always been a big believer in the saying "The proof of the pudding is in the eating of it". We can forget about any major change to the unsettled pattern for the next 10 days at least. The only change from recent weather will be the less mild feel over many areas of the UK compared to what we saw in November & especially December.

Later in January may prove to be more interesting- we shall see. Time will tell as always.

That would be brilliant for here. We had a good few hail and thundersnow events last winter from cold windy W/NW setups. Big towering clouds crashing into the Pennines.