Nice to hear your thoughts Darren after a long absence.

Ian F over on t'other channel saying there's a fairly even cluster of options for the potential cold snap but they expect normal service ( Western Mobility ) to continue thereafter. More worrying is the signal for an extended cold spell into the New Year  which has diminished further, hence its disappearance from the extended outlook.

I'm not that surprised that the MetO have altered their extended outlook tbh in view of the runs we have seen over the past few days. Having said that though, as I mentioned above they may start mentioning a cold spell again of the model runs start showing it on a consistent basis and it gets into the reliable timeframe.

I just got a tweet from Madden saying the same thing

Certainly some rather more interesting charts now appearing for next week - just when the MetO extended ease off the risk of colder weather into January.
As we all know a few good charts do not a winter make - let's see what the pub run and the 00Zs have to say.

But to be fair even the eye candy runs only show a three-day wonder before normal service is resumed with height rises to the south. My money would be on a cold snap over the Christmas weekend and then a steady warm-up into New Year. Beyon the first week of January anything could happen.

Not had chance to look through the individual runs, but the GEFS12z 850s and snow row look underwhelming and less interesting than the 6z set. ECM12z op also looks open to debate but I wouldn't be using it as security on my house.

http://www.theweatheroutlook.com/twoforecasts/ensemble-forecast.aspx

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How would I go about posting images on here?

I wouldn't like to even try and speculate on what we might have in early January at the moment, let alone later in the month. It strikes me that, far from being in the situation we were in throughout last winter where the output was pretty much the same day in, day out for weeks on end, we're in a situation at the moment where trying to forecast even 5-7 days ahead is tricky due to changes in the output, let alone further ahead. New Year is still over a fortnight away just now and very much in La La Land as far as the model output is concerned.

Just a copy here of something I posted to a friend on FB about the ECM 12z op run:

There's a west-based -ve NAO on the ECM op run at day 10, which happens because of first the western Atlantic and then the U.S. trough undercutting the mid-Atlantic ridge.

If we get to this stage it's crucial that the Atlantic LP tracks swiftly into Europe rather than developing into a rounded feature to our SW. Thankfully this run looks on course to take it straight east.

No support from the other 12z op runs for the western Atlantic LP to behave in such a way and even if it did the development is usually toned down.

So perhaps not the best of runs in terms of a 'safe' way forward, but still pretty decent going forward from day 10 as the Atlantic jet tracks well south and the Euro High looks to come under fire (the erosion of it resuming on day 11 if the ECM run verified).

As for Fergie's comment this evening, here it is directly quoted:

"Some previous EPS members showed similar developments (to NCEP-ENS) around 26-28th. Being watched, of course, albeit westerly mobility - with some NW (possibly more N'rly) phases as signalled across all suites, some more pronounced than others - characterises the anticipated broad closure of December. GloSea signals for reduced zonality by end of month has weakened, thus less confidence (which was already fairly low anyway) re early Jan. Nonetheless, we do expect some evidence for this (zonality waning) to remain but whether blocking per se emerges by/into early Jan is very unclear. That's it in a nutshell."

Now what this does is place the recent GFS and ECM runs right within the range of what they are expecting for the final week of December. they are then pretty much throwing their hands up in the air and saying they have no concrete signals to work with at all.

To be honest, I can't fathom why the signal for reduced zonality has reduced, given that recent strat. output from both GFS and ECM has been the most positive so far for reducing the zonal winds into January. Of course, GFS was insisting on a massive increase in zonality on yesterdays runs, which has since been dropped in dramatic style, and it could be that GloSea is going through similar motions but more slowly due to, it being ensemble-based. After all, GEFS, while trending colder overall today (particularly comparing today's 12z suite with yesterdays), have been shifting far more slowly than the op runs have - much as you'd expect really.

Due to the high levels of uncertainty at the moment, with some huge changes to the hemispheric setup taking place in the coming 10 days or so, there's just no way we can reliably anticipate what GloSea will get up to in the coming days, or GEFS, the ECM ensembles and the operational models, for that matter.

Taking this angle, trusting nothing much beyond the next 5 days or so, really helps to temper expectations, as must be done in order to maintain a level of sanity in these situations.

I'm not going to lie, the 12z GFS and GFSP runs got me buzzing a bit, because when it comes down to it I haven't seen falling snow since March 2013 and lying snow since January 2013 - coming up to two full years now. It has since been a case of forcing the lid back onto the keg of wonders in order to retain a realistic outlook. It's always a challenge - riding the buzz feels great while it lasts but leads to a bigger fall if the outlook then behaves undesirably.

Keep calm and forecast on

Cracking post James.  The only thing I'd say is that when the ensembles don't show a clear signal you are left rolling a dice. In the UK 4 or perhaps 5 of the 6 sides lead to an average or mild outcome with no snow over lowland Britain. Therefore, when things are indeterminate your head has to favour a mostly snowless outcome, even if you heart says otherwise.

Taken from another of Tamara's NW posts, focusing on the final week of December (she then talks about the strat. developments and January but I feel we should get December sorted first!) with a few comments by me in italics:

"There is no surprise at all to see indeterminate suggestions from G5 and ECM ensemble data for the further outlook from Christmas itself and beyond New Year as blocking signals increase and jet strength reduces across the Atlantic with a panacea of solutions appear in the modelling....  including cold pattern solutions.

This suggested upstream change, courtesy of continued modelling of GWO heading to phases 1 and 2 in conjunction with falling AAM is well advertised now across the modelling.
I must admit I only have a rough idea about the mechanisms by which Global Weather Oscillations and Atmospheric Angular Momentum play into the pattern evolution. I'm just going to take her word for it!

The turn of the year and early part of 2015 is going to be very tricky to predict I think, and we should be prepared for quite possible sudden and significant changes of travel for that trend period in the lead up to Christmas.
I swear I have seen blocking disappear suddenly at 10 days range only to re-emerge in an altered guise at 7 days range. Just to give a sense of how crazy it can get! Obviously on some occasions the blocking goes poof all together and crying into cornflakes becomes a nationwide epidemic...

Falling tendency in angular momentum suggests that frictional torque overall is negative over mid latitudes and the sub tropics. This, aligned with a retrograded Pacific jet stream also backs-up the quietening trend in the Atlantic.

Slower flow leaves room for better jet amplification. However, taking into account present conditions over the polar field with zonal winds only just set to start falling once again over this period in response to fresh wave activity on the vortex, then calculating amplification equations is going to be difficult. Much easier for the models to handle much more predictable faster zonal flow.
I suppose this translates to the models having a very hard time pinning down the resilience and poleward extent of ridges, and the positioning and shape (for want of a better word) of the troughs.

If WAF really ramps up, as it may well do in the days to come - then the calculations will increasingly become more and more in our favour and the type of alluring GFS output we are currently seeing in FI may become more and more plausible sooner rather than later. Caution advises, as reasoned later in this post, that it might be a little premature at this time - but all bets are off as stated in the extended period."

What is WAF...?! That's a new one to me. Her words imply that the models may not do a good job of seeing any 'ramping up' before it takes place. I can't give an informed comment on the odds of that one.

What a read... Tamara's posting represents what I aspire to be capable of after a decade or so more experience in the field 

Let's all try not to over analyse. Specifics are impossible at this stage.

Its all about trends.

Today has been fairly significant and a step in the right direction for those looking for a pre New Year cold snap with at least a chance of some snow.

Firstly we managed virtual agreement between the 6z GFS control run and the parallel at 264 hours to build heights over Greenland. Retron's snippets of the ECM control run data sounds tasty too.

We all know the difficulties of getting cold to the UK, no doubt shortwaves will try their level best to delay, stall, cancel or divert our dream setup but compared to where we were this time last night things are looking pretty good for now.

An interesting few days of model watching coming up..made even more special due to Christmas approaching. .

Ho Ho Ho

Sound words as usual Brian, though perhaps an extra side is needed for below average temperatures but no snowfall... 

For me it's the trend in GEFS which is most important, and that is basically absent at the moment, as can be seen from my crude analysis of recent GEFS line plots for London:

Here, 'runs to [a given threshold]' are the total number of times a line crosses heading downward except in cases of a line wobbling around the threshold resulting in numerous crossings in a short space of time, while 'mean to [a given threshold]' is how many times it crosses heading downward while duration is the total time spent below the threshold value.

Ignore the 'Duration -15*C') entries for future GEFS runs - they're just there to get the chart space to display properly (I was ending up with ridiculously fat bars even when I shrunk the chart size right down).

It's actually highly unusual to see such apparent stability in the GEFS when the pattern is on the change, though what's hidden by the above measure is to what extent blocking has increased or decreased in frequency. I haven't got the spare time to go through all of that each day 

A very interesting read, thanks James!

Been amusing myself trawling through the GFS ens - there's some odd looking charts in there, particularly from T240 onwards. Would be fun if some of them verified even if they weren't cold, simply because they look so weird

Whilst it's all FI with the usual caveats, the one below (assuming I get the post/picture thing right) does flag up the 'issue' with Greenie HPs - you really need some troughing over the continent to set in or a lot of the country get's stuck in a frustrating middle ground. Still, it's nice to see the HP to our North West signal is still bouncing around and moving closer to the reliable timeframe too, although still a minority solution at the mo in my eyes. It's certainly interesting, if nothing else

Edit: Pressure does fall in the next chart, really should have looked at that first

Defying what I just said, a rapid flick through the GEFS gives me an estimate of 40:60 cold to mild (slightly optimistic though as I placed a couple of 'very nearly cold' outcomes on the cold side), with every single one of the mild runs being down to low pressure powering NE from somewhere around the Azores starting between 8 and 10 days from now.

So, further restraining of expectations there. I wonder just what it is that's caused the op runs cause to explore the other options today after all those 'power NE' runs we had to put up with?

Completely uninformed speculation but could be that as the modelled critical period for those changes get closer to t0  the model is better able to get the solution right (right if you want a colder outcome that is).

Any pattern change, particularly with HP moving North seems to cause the models grief and you often get some big adjustments as things get closer to the day.

Seem to remember GFS (and the other models) constantly screwing up sliding LPs, with mild being the general modelled outcome, only for things to be corrected come the day.

I'd assume the physics for West to East of varying descriptions is better known and easier than wandering jet, HP inflating North and shortwaves firing all over - seems logical that one can be modelled ok quite a way out and the other won't.

The real trick is telling when the models are getting the pattern wrong and thus looking like a genius I guess

What is WAF...?! That's a new one to me

No Idea perhaps Peter or Darren might know thanks for the read intresting.

Yes it does Kev a bit spooky.

WAF - wave-activity flux. But in this context I can't see why it's not called simply wave activity. It would make the posting just that little bit more immediately accessible to non-scientists such as myself.

Oh botheration hope that's at sea level and the moors get in on the action! Not that anything at that range is set in stone! 

The pub run looks like it's been on some early Christmas sherry with a weird slack regime on Xmas Eve and what looks like a tropical storm off Newfoundland. I think this may be best put with the old teabags and potato peelings on the compost heap.

Yes, the 18z certainly looks a strange run. Don't think I've ever seen a chart like the one for Christmas Eve at 12z - looks like a kid has been given some coloured pencils and scribbled Ts and Hs wherever they fancy. What a mess. I agree one for the bin. Eyes down for tomorrow morning's runs.