I think we can't rule it out until this LP clears and uncertainty really falls. If the pattern is still being suggested this time tommorow its gameover, but the entropy must be higher than usual with this tricky trough still around.

Come to Kent, it happens more than you'd think! (I wouldn't put it past it tonight, either, when it will be -8C at 850 here with precipitation around).

-10C is the "usually snow" temperature I aim for here. It's also the reason I picked it as the threshold back when I did those ensemble watch charts! I would imagine it's the same for coastal areas exposed to the Atlantic.

There was a post on usw many years ago asking about cold air from westerlies. It was mentioned that even with the 510 line coming in from the west, it had been known to rain instead of snow in Northern Ireland - purely because although the air aloft was still bitter, the few thousand feet near the surface had been thoroughly warmed and mixed by its passage over the Atlantic.

Yes but the 510 line is essentially 'further up', I agree the Atlantic modifies the air massively but I reckon the 850s would be more affected than the full thicknesses. I guess being in kent you are right next to 12C waters that modifies the air so much at the surface it doesn't matter the 850s are -8C, on the plus side when it is cold enough, kent has some of the best lake effect snowfalls in the entire UK.

Stormchaser I ask of you in particular (though others feel free to answer):

I have seen constant small upgrades since xmas day, nothing enough to change the pattern, but basically every run has been a slight upgrade on the previous, and in so many ways (and this 6Z is no exception):

1) Better riding to scandi

2) Heights further NW

3) Attempt to build a siberian high

4) Stronger arctic high

5) Higher greenland heights (in particular I'm interested in superior heights when the block is collapsing)

6) Weaker svalbard low.

7) Stronger danish shortwave

Now, in your experience if these small 'micro' upgrades keep happening would the MO suddenly flip to a good pattern, or would that be gradual too?

I swear something is going on here, its very subtle, but height rises from the arctic into greenland from the north is very very interesting (far better than having height rise from the south).

Darren, Im hoping some wet snow here IF we get a shower in the period 4-9 pm with uppers around -7 because of the off shore breeze from the North.

Well for me the outlook looks more of the same  with alternating TM and PM air masses with the TM ones will be short lived affairs. So for those in elevated Northern areas a chance of more snow for sure.

There's something not quite right about this, I just get a gut feeling something about this is unusual. I don't think we are really in for the same rPm affair that we were pre xmas, I could be completely wrong ofc.

If the atlantic is so strong, why are we getting such a bizare pattern, why is there strong cyclosis across the whole atlantic? Why is the jet stream trending so far south, and why are we getting height rises to the north despite us apparantely being in zonality.

This doesn't feel right. I mean the Atlantic is starting to look like how it is supposed to look in April when the polar vortex is rapidly decaying! 

The ECM ens mean from the 22nd for the New Year period looks like it will end up being pretty close to reality. No fantasy easterlies

Current ECM mean

No covering of snow here for almost 2 years now, hmmph. A chance at least of some PM blasts which could deliver something interesting further N

ECM at day 7 - also has support in the ens mean

Changes on the GFS6z which end with a rain preceded by snow event on Jan 5th. 

The GFSP ends on a note that resembles 2010 just before we entered the freezer. Can't say I'm surprised given all the signs. Please someone tell me if I'm barking up the wrong tree, but I just think something about all this is very odd; the constant small upgrades, the weak Atlantic, and the undercutting lows. Please someone help me out! 

This is another wierd thing, the output is COLD, despite us being in zonality. It must be a combination of stagnating cold air and a southern jet, but there is nothing normal about any of this. Does anyone else see the massive potential in the MO here, or am I seeing ghosts? Please someone put me out of my misery!

Stormchaser? What do you think. Is any of what I am saying reasonable?

I have been noting this myself, the GFSP 00z being perhaps the best reflection so far of what tends to crop up in these situations - as soon as an Atlantic trough becomes negatively tilted, a sharp ridge from the mid-latitudes to the Arctic establishes and we very nearly see some proper blocking take hold to our N and NE - it was a poor time to hit lower-res in that run.

The GFS 06z nearly manages it days 7-8 but then hits lower-res with standard results.

The GFSP 06z sort of does it days 8-10 but it's not a very good effort. Things still turn interesting later on though as the jet digs further and further south (http://modeles.meteociel.fr/modeles/gfsp/runs/2014122706/gfsnh-0-360.png?6)

This signal for a lot of cold spilling into the mid-latitudes and the jet tracking a long way south is to be expected given the mangled state of the strat. vortex in 8 days time:

This should encourage a very ragged or broken-up polar vortex to develop starting about a week from now and it will then be a case of to what extent blocking highs are able to establish and interfere with attempts by the polar vortex to re-organise, and of course where exactly they locate relative to the UK.

Signs are that further warming events will continue to toss the vortex around while this is going on, mostly at the 10 hPa level with the 30hPa level looking more resilient, which will at least keep the vortex in a weakened state, with a reduced ability to drive a westerly flow in the troposphere.

The models will struggle to resolve whatever Arctic blocking establishes, which in turn makes the southward extent of the jet very uncertain from next weekend onward - and of course the track and angle of incoming troughs.

One big difference to early December that the models all agree on is the total absence of high pressure from the Azores to Europe this time around. Though this doesn't establish until day 8 so not a given - but a strong signal.

I'm glad you see it too, I was starting to think I was completely barking up the wrong tree with this.

Wrg to the 6Z I think its in many ways superior despite not having quite as well developed Siberian high. Have you noticed the backing of the isobars on our collapsing domestic system? Every single run they have backed more and more without exception, and the 552 isopleth is moving further and further west, I thought on the 6Z it was about to link up with the siberian at one point! Also the greenland high is more developed on the 6Z and the shape of the lows are more elliptical. 

I guess my point is, the output is not what we want to see, but the trend definitely is. I for one will await the 12Z on tenter hooks.

Very much enjoy the posts from yourself and Stormchaser - great to have analysis of what is going on and adds an extra dimension to model watching. 

Yes, interesting set of GFS runs this morning. Proper cold zonality, 80s style. The pressure rise over the pole is causing the models a few issues

Typical example of uncle Bart in this chart? - is this right Gooner?

Interesting GEFS runs again this morning. The Vortex comes under increasing attack with several showing splits and arctic highs. Few if any look well positioned to benefit us in the short-medium term but interesting synoptics nonetheless. With warming forecast in the strat on this side of the Atlantic we may be lucky enough to see the emphasis of any HLB shift towards Scandi or Greenland in the coming days and weeks, though it will be a long process if this transpires. Still interesting stuff to chew over, particularly with lying snow of much of central northern England as we speak.

The effects of "cold" zonality can be shown quite nicely here:

www.weathercast.co.uk/services/ensemble-forecast.html?eps=london

(ECM ensembles for London)

There's a marked sine-wave effect in the new year, suggestive of zonality. And the temperatures from it are a degree or two down on what you'd normally expect in a zonal flow. However, with the vast majority of runs showing highs of 3C or higher throughout the risk of snow down here at least is vanishingly small. I'd love to see some snow from the west - zonal style, rather than breakdown style - but alas, I don't think it'll happen down here any time soon. Further north and west though it's a completely different kettle of fish!

In the meantime there's some continental-style cold weather which, although not snowy, promises to be seasonal (and pleasant enough to be out and about in too).

I believe the influence of the block out to the North East will become stronger and Atlantic weather systems will stall close to our shores.

http://www.wetterzentrale.de/pics/Rtavn2041.gif

We could end up in a no man's land situation between weather systems though any air cold air from the continent over us may make it interesting if any Atlantic systems try to make any inroads.

Usually in situations where Arctic blocking is intruding on the mid-latitudes, we see a train of lows being modeled on run after run before eventually there starts to be signs that one of them will be disrupted, attain a negative tilt (orientated SE to NW) and then slide southeast (or send a shortwave SE).

I have often seen such a development remain largely absent from the op runs and ensembles until a sudden materialisation somewhere within the 5-8 day range, so even seeing it on just the odd run here and there is encouraging. Interesting that it's the newest model (GFSP) exploring the idea most readily at the moment.

GFSP 12z out to +120 hours so far, not much change apart from the continental cold pool being a little further east by Wednesday - a trend that has been in place over the past 48 hours, allowing higher uppers in which threaten to bring about some persistent fog.

Flat jet powering NE by Thursday with a milder southwesterly wind starting to take over, though struggling to make itself felt at the surface across much of England and also NE Wales. SW England and southern parts of Scotland are mildest at 8-10*C.

For those preferring colder conditions, the flat jet actually has a positive effect at this point, as it rapidly squeezes out the mild air through Friday morning in favour of a colder polar maritime air mass.

Meanwhile, GFS is out to +156 and has managed to slow the pace of things a little and mirror the GFSP run very closely, having been a bit more progressive in the Atlantic on the 00z and 06z runs.

http://www.wetterzentrale.de/pics/Rtavn2161.gif

http://www.wetterzentrale.de/pics/Rtavn21617.gif

http://www.wetterzentrale.de/pics/Rtavn2164.gif

No shortage of wintry ppn for more Northern areas

Not nearly as much of an Atlantic ridge for day 8 on these 12z GFS and GFSP runs, but there is a negatively tilted trough south of Greenland on both representing the potential for a sliding low - check out GFSP at +204 hours (http://modeles.meteociel.fr/modeles/gfsp/runs/2014122712/gfsnh-0-204.png?12) and you can see the trough extending SE, funny thing to see given that there's a vast trough covering Scandinavia and Siberia as opposed to a blocking high.

Again, a reflection of the polar vortex becoming very untidy indeed.

Perhaps of greater interest than the GFS and GFSP output is the day 5-6 charts from UKMO:

Here we see the Atlantic shortwave tracking further south than on any previous run while the pattern further west becomes a lot more amplified. Of course there's the usual shortwave preventing a ridge to Greenland from the Atlantic, which raises confidence in this output 

I think stormchaser, that monster arctic high is having a real impact. I know I always said NAO dominates over AO, but I think its one of those times that the oscilation in the arctic is so negative that its starting to impact the jet stream on both sides of the arctic, not just the pacific.