There has not been a significant stratospheric warming so far but there is one forecast over the next week or so - but it is NOT a Sudden Severe Stratospheric Warming (SSW).. The warming is not (at present) forecast to propagate down through the atmosphere but this may well change

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/ts.php?plot=temps&alert=1&lng=eng

Morning all, seems things are more optimistic this morning. People are talking about turnovers rather than collapses.

GFSP interesting by 174.

I must have got them the wrong way round - you're right - nothing to see there.

Not on the GFS, but the GFSP has shifted towards ECM and would deliver backedge snow Sat night with a decent attempt at a Scandy block after.
The ride continues . . . .

But by the end the Op delivers widespread snow from a Westerly

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I would imagine any continental undercut will be brief with snow potential limited in that brief window of ESE'ly winds.

Experience tells me though that the air will become cold enough to support snow after the precipitation band has moved away.

Hey Brian. Looks a SW flow to me. Could you advise on why its interesting . Not intended as a dig just interested (sorry been reading to much NW....you know what its like over there)

In that setup the winds would most likely be SE off the continent (the wind direction is never along the isobars, but usually something like 15-20% from High to Low).  So, the air would be from a cold source, which is the recipe for some borderline snow where cold and warm air meet. 

Close, but not quite there.  A couple of Scandi High setups in the ensemble mix, but nothing with a look on permanence about them, yet.

As you say, potential. It shows the westwards extension of blocking to the east, propped up by lower heights over the Med, whilst that trough over the Atlantic shows signs of disrupting, with that short wave spinning out of it appearing destined to undercut the block.

Height trend 18z->6z (you can enlarge the charts by right clicking on them and click open in new tab)

The trend is poor on the GFS although there is little between 0z and 6z with 6z marginally better. 18z represented a significant improvement on the 12z and although we have taken a step backwards we are still better than that. At this stage it looks unlikely we are able to hold onto the GH so that leaves us with one last chance to maintain the cold spell; the easterly turnover. When the atlantic is weak enough a LP can stall before it hits the UK which encourages the repositioning of the high over scanadnavia. This is more likely to happen in a more amplified pattern so there is still cause to be watching that 552 isopleth even if it does not reach greenland. At the moment it is very marginal, the lows are southerly facing which means it could go either way, SW facing lows are very bad wheras SE facing lows are very good although keep in mind even a SE facing low only guarantees one stall, often there is a bigger SW facing low on its tail. 

Yeah, Gusty once gave me this as rule of thumb from an IMBY etc...

If there is a SE'ly wind off a very cold continent snow can fall up to -1c at 850Hpa and thickness can be as high as 537dam as the air is dry and very cold

Trouble is, the continent is well above average.

In March 2005 we had heavy snow here from a warm front (here being half a mile inland from the North Sea) when thicknesses were 540dam and 850s were exactly freezing. That was the last snow of what had been a remarkable cold spell! Scary to think that's nearly a decade ago now - the last proper easterly we've had here.

In 2011/2012 uppers were as high as +2C and there was snow, but this is quite unusual. And it illustrates the problem with 850 temperatures and how taking them on face value is a value is a very bad idea. 

To get this to happen you need a very strong warm front moving into cold dry air, however even a relatively weak (ana) warm front has the effect of upping the benchmark at the 850hpa level, although kata warm fronts have the opposite effect. 

In general -3C is a good benchmark for a normal ana front.

I guess that shows how hard they are to setup - everything needs to be just so to get a proper long fetch easterly.

However, back to the here and now..

Personally I don't think the models have done that bad a job on predicting all the options that could of been on the table with regard to predicting a possibly major cyclogenesis event such as the one likely after Christmas given that this was picked up on by the output quite a while back now. True it has been watered down thankfully in recent days than what was a few days back The positioning of the Low has also been changing run to run and model to model and that may continue for a while yet. The one thing that a lot here strive to see is of course is snow but this has not been shown in any way other than a blink and you miss it type affair on any output lately and that stance is maintained this morning.

It looks most likely now that the UK will be most likely be affected by a UK High of some sort delivering the heady mix of frost and fog and probably below average daytime temperatures too, particularly over England and Wales. It looks odds on favourite now for pressure to be more likely to rise to the East of the UK as we head towards and after the New Year and as I said in my report earlier this comes with a risk of shifting the High too far South later as the Jet roars over the top bringing a slow return to milder Westerly winds with rain at times to the North and West. However, there is a definite trend that each run currently seems to be exploring the chance of building any UK or near European High pressure into Scandinavia later. This could provide dividends for cold with time and is far more likely than any pressure rise across Greenland in the short term covered by the output currently. It's all a game of chess though and the pendulum could swing either way in a continuing fascinating period of synoptics this Winter.

The one thing I can say with reasonable confidence is that any chance of a severe snowy period across the UK within the next two weeks look very unlikely given the theme shown from current output runs. However, frost and ice lasting all day for some with potential freezing fog patches too could at least add to the seasonality of the period for many.

As good a summary as you'll see today. There is next to zero chance of a sustained cold feed before 2015, with the best bet stagnant low-level cold under high pressure. Snowfall may occur this Sat night IF the synoptics play ball, but apart from that chance a totally snowless year here comes to a disappointing end. Roll on 2015 . . .