We are facing probably our best prospect of widespread wintry weather in years... with the chances of snow on snow events for quite a wide area of the country.  Theres a real chance that this Cold air could lock in and be topped up.  

The GEFS are probably the lowest ive seen them - on a grouped scale - for the extended period that they are.

A word of caution- that we know how fickle our weather is, I hate to ramp.  But you cant deny the below is simple brilliant.

Headline: Ian forecasting a week of cold weather for the whole of the UK (excluding Shropshire)

Surely downgrades will start appearing now

Thanks Darren for a great post

6Z GFS looks to keep Tuesday's event as snow right down to the south coast.

There's then a second similar event on Thursday into Friday which doesn't have quite such cold air and turns to rain for a while (although down here the uppers never dip below about -2C).

Milder air doesn't really get in until day 9 (Saturday), and even then it looks fairly brief.

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!

Brilliant analysis Darren.

More please.

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.

Without wishing to ask a "will it snow in my backyard" question, what do you think are the prospects further West. i.e. Ireland. We shouldn't have any difficulty with front decay this far West, but will it be cold enough here?

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.

 

Seems to be rain showers, then dry then rain here.  Just saying.

 

Without wishing to ask a "will it snow in my backyard" question, what do you think are the prospects further West. i.e. Ireland. We shouldn't have any difficulty with front decay this far West, but will it be cold enough here?

Its looking a little bit too mild imo for most of Ireland. I'd expect it to convert to snow as it hits mainland Britain.

Quite some Strat warming by 300h. Second half of February could be even colder than the first half.

http://www.meteociel.fr/modeles/gfse_cartes.php?ech=204&code=0&mode=10&carte=1

Can't find the other link but notice how PV get's split by the SSW on the 06Z run The strat warming starts from Iceland and then moves northwards into the Pole whilst another area of warming from Siberia moves into the N. Pole. This could all change but if this comes about then we could see blocking end of Feb and maybe a negative NAO as well as AO! - That being said the AO and NAO have been out of sync this winter.

Quite some Strat warming by 300h. Second half of February could be even colder than the first half.

http://www.meteociel.fr/modeles/gfse_cartes.php?ech=204&code=0&mode=10&carte=1

 

doesnt it always warm at this time of year? Don’t follow it close enough. Wondered how it looks to previous years??

 

 

doesnt it always warm at this time of year? Don’t follow it close enough. Wondered how it looks to previous years??

PV get's destroyed. It does warm yes but not so suddenly. Some parts of the Arctic show the strat warming to +4c at 10hpa that's a major SSW and something we haven't seen since Jan 2013:

 

 

doesnt it always warm at this time of year? Don’t follow it close enough. Wondered how it looks to previous years??

I dont think it does quite this early nor as quickly . It should definitely help blocking to our north.

 

 

Seems to be rain showers, then dry then rain here.  Just saying.

We shall see. This could either provide a substantial amount of snow as the front stalls/moves slowly or it could be hours of cold light rain or maybe sleety stuff. If the precipitation is heavier it will turn more to snow and settle because there is colder air behind this front! At the moment with daytime maxes of +1 or +2c for the far south and the very close to -10c isothem this will be falling as snow right down to the south coastal areas.

 

Its looking a little bit too mild imo for most of Ireland. I'd expect it to convert to snow as it hits mainland Britain.

Thanks for the reply - it happens that way all too often for us unfortunately.

 

We shall see. This could either provide a substantial amount of snow as the front stalls/moves slowly or it could be hours of cold light rain or maybe sleety stuff. If the precipitation is heavier it will turn more to snow and settle because there is colder air behind this front! At the moment with daytime maxes of +1 or +2c for the far south and the very close to -10c isothem this will be falling as snow right down to the south coastal areas.

Thanks

Just need it all to move 20 miles further East and I'm happy. 50 miles would be better. 

Quite some Strat warming by 300h. Second half of February could be even colder than the first half.

http://www.meteociel.fr/modeles/gfse_cartes.php?ech=204&code=0&mode=10&carte=1

 

I tried to point this out yesterday, but nobody wanted to buy it. In answer to ballamar - there is a Spring Strat warming every year as the sun rises above the horizon, but it does not occur in mid-February - this looks like a genuine Strat warming (if it comes off), rather than a purely seasonal one.

http://www.meteociel.fr/modeles/gefs_cartes.php?code=0&ech=102&mode=1&carte=1

Amazing looking chart with a very narrow slither of warm air and a compressed scandi high

Quite a few GEFS maintain an easterly so this is an evolving situation

Of course, its the 06z which Liam Dutton says is rubbish! LOL

Headline: Ian forecasting a week of cold weather for the whole of the UK (excluding Shropshire)

Surely downgrades will start appearing now

Not really because Saturday will be wet with average temps

Easterly still looks like it may re establish itself after Tuesday - Hopefully first week of February will be clearer soon: