Clearly the ECM has the pattern further West , but with no proper blocking and the Azores High so close, a return to milder Atlantic weather will be inevitable by day 8 or so.

Who cares at this stage?

Clearly the ECM has the pattern further West , but with no proper blocking and the Azores High so close, a return to milder Atlantic weather will be inevitable by day 8 or so.

here - http://www.wetterzentrale.de/de/topkarten.php?map=1&model=gfs&var=22&time=48&run=0&lid=OP&h=0&mv=0&tr=24 

Us Kent massive might still get a Kent-clipper type set up at any point between Monday and Wednesday but even then, it could still fail to materialise even at point blank forecasting range. Many times I've seen that happen, but for now, that's all I have to go on.

 

I'm not saying that, just highlighting a really poor pattern that looks likely from the second week of the month onwards.

Okay, so going by all available evidence it looks like a cold spell across the UK is more likely than not to happen.

 

Remember before the cold spell how we were looking at warm air advection to get things started? That looks like it actually worked (it'll be the third one that kicks it into action, so well done to the models last week for picking that up - note that this was a case of being picked up from beyond 10 days out, so those extended charts do sometimes have a use!)

So, the next step is how to a) get snow and b) keep it going as long as possible.

A) is quite simple - while some of us lucky folks exposed to onshore winds can expect some convective stuff, for most of the UK it'll be fronts that are needed. Not just that: a warm front followed by a warm sector and cold front won't really satisfy (who wants to see snow, then rain, then perhaps more snow?). No, we need trough disruption (or sliders as some call them).

As a refresher, trough disruption occurs when a low bumps into a block and - importantly - has a strong jet behind it. This effectively compresses everything, forces the fronts to occlude and - providing it's cold enough - provides a reliable source of snow (and a fair bit of it).

The first trough disruption is now almost certain to happen on Saturday, as shown by the Fax chart:

http://old.wetterzentrale.de/pics/brack1a.gif

In this case, there's a tongue of milder air wrapped around the front, so it'd be marginal at best for snow (unless you have elevation).

This low as it moves away south allows a cold feed of air in from the east, and it's this which really starts the cold spell off.

Now on to 😎...

The next trough comes along on Tuesday. This morning's GFS shows the disruption happening to the east, meaning the UK is left in a chilly northerly feed, with the fronts bringing snow across much of the UK, turning to rain as it exits the UK. ECM, meanwhile disrupts the trough over Ireland. Rain there, followed by snow, with cold air remaining in situ over most of the UK (prolonging convective stuff in the east, but denying the almost UK-wide snow that GFS offers).

Given the two, I'd opt for the ECM scenario every time, even though it's not as up front with its snow. Why? Well, once cold is in place you can always get troughs, convection etc to bring snow (and it would be snow, because the cold air is in place). With everything taking place further east, you lose the gauranteed cold, then gamble that what's left will be cold enough for snow. This morning's GFS op shows well how marginal it can be, resulting in the usual old thing of some places getting a dumping (best winter ever!) and others just seeing sleety rain (what's all the fuss about?)

Furthermore, with disruption to the east it weakens the block overall, and as GFS shows it then makes it easier for another low to move in with milder air.

ECM, meanwhile, disrupts that trough to the west of most of us. That then leads to a third low disrupting around day 9, and it's that which would bring snow and probably herald the end of the cold spell. In those extra days, meanwhile, there would be much cold weather around and an ongoing risk of troughs/convective snow (which won't be picked up until 48-36 hours out).

Anyway, to sum up: action for a lucky few this weekend, but the main course is early next week. Whether we have time for a dessert (ECM style) depends on where those troughs disrupt. Plenty to keep an eye on, anyway!

What a post! I thorougly enjoyed reading that.

And kudos to you for spotting the trend.

I do hope any cold weather we get comes with a properly Easterly. That’s better for London, and as all my draughty windows have West it’s also better for central heating.

It’s an odd synoptic pattern. There is a lot of sub-10C air in various parts of the North Atlantic both west and East. Not really a battleground as such, more general coldness with variations on the cold theme.

It's an odd synoptic pattern, only in that for the last thirty years, we've not seen it much at all. It was however more common in the 50's,/60's and 70's.

I would say it is a battleground, but, it's a battle being fought in a different dimension - vertically rather than horizontally which is the everyday arena. It's a matter of warmer air being pushed up and squeezed south, rather than out of the way horizontally at ground level.

Clearly the ECM has the pattern further West , but with no proper blocking and the Azores High so close, a return to milder Atlantic weather will be inevitable by day 8 or so.

If the charts were showing mild to day 7, then cold thereafter I somehow doubt you’d be stating that the transition to cold weather was “inevitable”, rather “it’s in FI and will almost certainly not happen”.... You can’t try and have it both ways and remain credible.

 

I'm not saying that, just highlighting a really poor pattern that looks likely from the second week of the month onwards.

With all due respect Ian, I think that comment is based on an assumption rather than actual analysis of the models. As far as I can see, none of them indicate a "really poor" pattern developing within the semi-reliable timeframe, by which I assume you mean a mild & zonal one.

I would say that from all I can see, a cold spell lasting beyond next week looks just as likely now as a quick return to milder weather.

 

If the charts were showing mild to day 7, then cold thereafter I somehow doubt you’d be stating that the transition to cold weather was “inevitable”, rather “it’s in FI and will almost certainly not happen”.... You can’t try and have it both ways and remain credible.

To most, his credibility went out the window a long, long time ago. Round about the time that people sussed out his agenda.

Anyway, pleased and relieved to see broadly a continuation of the pattern that's been emerging over the past couple of days. Darren (in his typically superb post) talks of GFS and ECM differing on the location of the trough disruption; a halfway house of the two would be ideal...

PS - anyone else get that feeling of impending dread when you look at the MO in a morning? We've been led up a fair few blind alleys this winter and it's hard not to fear the worst.

Hints of a prolonged cold spell now.

 

 

 

 

Ian Fergusson Twitter

 

 

 

with potential for significant risk of snow across parts of the UK by Tuesday, albeit detail impossible at this range. Longevity of colder weather also v uncertain: global influences (MJO; & weakening stratospheric polar vortex) likely influential thro Feb

Sounds interesting!

 

Sounds interesting!

 

 

To most, his credibility went out the window a long, long time ago. Round about the time that people sussed out his agenda.

Anyway, pleased and relieved to see broadly a continuation of the pattern that's been emerging over the past couple of days. Darren (in his typically superb post) talks of GFS and ECM differing on the location of the trough disruption; a halfway house of the two would be ideal...

PS - anyone else get that feeling of impending dread when you look at the MO in a morning? We've been led up a fair few blind alleys this winter and it's hard not to fear the worst.

 

Hands up from me. You go to bed having dived deeply into the evening output, and wake up with a dread that overnight it's all unravelled.  We've all been there many times, so it's not an irrational fear.

UKMO extended

 

Looks good to me - the Azores is positioned to prevent the usual mild crud from coming our way, so whether the prevalent pattern is from the east or the NW, it will still be cold. With the Azores in that position, super cold air is crossing the Atlantic from Canada, without getting modified by TM incursions.

Looks like GFS has sifted everything a couple of hundred miles east this morning. The mild sector is mild enough to bring rain into East Anglia by 144 on this run, but the extra "warmth" means much more in the way of snow for the majority of England, albeit increasingly slushy and wet snow in the SE. The further east the warm sector gets the warmer the air within is likely to be, as it's being "squeezed" less (for want of a better term - the more it's squeezed, the colder it'll be.)

Last night's amazing 18z run was the result of everything being west enough early on to allow the deep cold to the east to gain a foothold over the UK - as ever, tiny differences on a global scale would result in quite different conditions on the ground.

This morning's MetO run also seems to have moved things east. Hopefully just a wobble, as it's not a trend I'd want to see continue. As it is, down here the GFS now brings snow, followed by slushy wet snow, followed by rain (138>168). Yesterday's 18z, with everything further west, instead had 12cm of snow, with it snowing pretty much constantly due to showers blown in from the sea.

 

Of course we have to remember that we were informed yesterday that the 06z run isn't up to much 

Just to remind people that in a warm occlusion situation uppers of around -2C are cold enough for snow whilst uppers of 0C can still often give snow (and in 2010 we even managed it with positive uppers). In fact bands from the north west stalling into cold air from the SE often reduce the lapse rate further meaning you would be looking at 0/-1C rather than -2/-3C as you would expect from a band from the west.

Point is as long as the uppers are subzero there is a good chance of snow. This all being said this only applies for the classical ana warm occluded front. It does not apply to weak shallow (kata) fronts or fronts undergoing frontolosis. In my view the determining factor for whether or not that band is snow or rain (by the time its across England) will be its coherence not the airmass temperature. Provided the front does not show significant decay I'd expect 100% snow by the time it reaches England. If, however, the front decays and fragments then drizzle becomes more likely than snow.

Clearly the ECM has the pattern further West , but with no proper blocking and the Azores High so close, a return to milder Atlantic weather will be inevitable by day 8 or so.

Well I'll be happy with the 8 days you've now allocated us :-)

 

What a post! I thorougly enjoyed reading that.

And kudos to you for spotting the trend.

 

Yes, indeed. Well articulated as usual and it helps with the emphasis on the snow starved South! My main concern with these charts is that there has historically, and often, been a movement East then south of the really cold air as we get closer. On the rare occasions when it doesn't we usually get something special. Fingers crossed but don't hold your breath - the form horse is against us!

With regards to snow - Tuesday looks like the best chance for the south and south west - looks like that front stalls over the UK around the +126hrs with temperatures close to freezing over many parts of the UK - even the south coast then dipping below by 1800.

From 0600 am until around 1400- Looks like there will be a period of sleet or snow moving in from the North west with many waking up to a dusting or covering - but who knows this could just be rain or sleet or cold rain depending on the positioning of the Azores HP and LP etc.