Think the time for thundery snow showers from the NW is pretty much over, the sea is just too cold I think now for that to happen. To get thundersnow now you would have to have a raw easterly bringing <-13C uppers, perhaps even that wouldn't be enough for february. In late march 2013 the convection was limited even with -14C uppers, although that was late march.

Basically the high convection potential is all but over now.

Thinking back to Tamara's post from yesterday (or was it the day before...) and linking it to current model output:

• a strong positive mountain torque event across Asia adds a big dose of westerly momentum to the Pacific and then Atlantic (output for next 5-7 days)


• knock-on effects weaken the Azores High and displace it toward the western North Atlantic (output for 5-10 days range)


• a strong negative mountain torque vent across the U.S. removes a lot of westerly momentum from the Atlantic (now strongly suggested by ECM and GEM, less so by GFS but trended towards it 00z to 06z).


• the Atlantic sub-tropical ridge strengthens, but not necessarily in it's usual place... potentially trapped W or NW of the Azores thanks to preceding events (currently beyond the reach of most output and well outside of reliable predictions anyway).

So we can see the theory very much in action in the model output.

As ever, it's the details that can make or break a cold spell for the UK, and those are well and truly in the realm of speculation.

Why were people talking about mountain orcs a few days ago? Did they mean torque?

I've noticed over the years that TWO has few trolls...

We had thundersnow a few days ago. I doubt the sea temps have changed dramatically since then. Had thunderstorms on January 26th last year also from PM/rPM air. Just need some fairly cold uppers and an unstable airmass.

Well you still usually need a gradient of about 20C, unless all the other factors (sheer, fetch e.c.t) are excellent. But given the north atlantic is much warmer than the North sea, then I guess I was wrong about it being poor compared to an easterly (though uppers can be much colder on an easterly).

Nevertheless temps can drop by 1C during january and another 1C during February,

http://www.seatemperature.org/europe/united-kingdom/isle-of-lewis-january.htm

in the north sea they would probably drop further. All I am saying is that thundersnow at this time of year is much much harder than it is in Early december. I would say that at this point in the year, a repeat of 2010 becomes impossible, not only because the sun is stronger but the convective potential is weaker. 2010 was exceptional partly because of when it happened.

http://modeles2.meteociel.fr/modeles_gfs/runs/2015012112/6-574.GIF?21-12

GFS says some snow for the SE tonight. Yeah right!

12Z continues the trend, it didn't take long for the cold spell to get into the <192hr range. Perhaps this time we might get a height rise to accompany the weak atlantic. 

http://modeles.meteociel.fr/modeles/gfs/runs/2015012112/gfsnh-0-192.png?12

Yes, same theme just need to get the angles right and the trough to dig in more

I have a really good feeling about this one for some reason. The boxing day snap and this one required a lot of squinting at the ensembles to predict so far in advance, this one is far more obvious (although that's probably because I haven't been doing much ensemble squinting recently.

The one thing that is different here, is that the arctic air is close to the UK (in the atlantic arctic), rather than stuck in siberia with a mid latitude block between it and us. 

Upper level troughs in noya zeymbla causing a lot of cold pooling with uppers dropping below -30C, some seriously cold air that we could get access to for the first time this winter. Obviously I don't mean the uppers will be -30C in the UK. 

Very small chance of sub -15C uppers with this spell, if the cold air takes the 'shortest' path south to scandanavia and then west to the UK. By shortest I mean the path which will warm the uppers up the least. This is just a potential mind you, but definately the coldest the true arctic air has come to the UK so far this winter.

Holy tulipthis is close, this is exactly what happened in 2010, with the insanely cold air moving south over scandanavia. Obviously the synoptics will have to all come together here, and a toppler could ruin the whole thing easily, but these are the first synoptics this winter that has got me pretty excited (excepting the snap which wasn't to be back in October).

http://modeles.meteociel.fr/modeles/gfs/runs/2015012112/gfsnh-0-234.png?12

This is what we need to see. Vortex split and a ridge trying to build to stop the endless stream of topplers

I want to see that little black area move into scandanavia, that is where some of the coldest air in the northern hemisphere lies!

have to say that's loaded with potential Beast if it's cold your looking for. A few shifts here and there would make a big difference. The AZ HP doesn't seem to want to play ball though. Not mild for sure!

The Azores High is closer to our shores days 7-8, this has been the trend on today's GFS op runs so far today. Not the best, unless we can get it to build toward Greenland, which looks more achievable given that the Atlantic jet is weaker and a little more amplified in the western N. Atlantic - another trend across today's GFS op runs, this one positive.

In fact if you look at it overall, there's a move towards better mid-Atlantic ridging but a less sharp dive south of the jet into Europe. Not so good for a cold blast in 7-8 days but perhaps better for drawing down some Arctic air some 2-4 days later.

Case in point:

More like the ECM 00z. If we could just get some decent warm air advection up the western side of the ridge - doesn't quite look sufficient on this run, and that's been the story for all of our mid-Atlantic ridges so far this season.

On the plus side, the jet in the western North Atlantic has almost fizzled out completely:

...which is the expected downstream effect of that -ve U.S. mountain torque event I keep going on about 

Its also a shame that the very cold air didn't quite get into scandanavia where it could be preserved, the sub -20s are staying to the north, scandi has -16C, if that cold air could move over the land it would stay there, its so close.

Ofc we would also have to get it from scandi to the UK! This is why 2010 is so rare!

I bet there are some insane ensembles to be found on this run though. 

NAVGEM is fantastic too! Can anyone else feel that there might be something big here, or am I just mad? 

ZOMG the GEM is insane. Massive upper level trough with insanely cold air a direct Northerly away! This could be one of those situations where the polar vortex is displaced to sit close to the UK. 

I think we are going to get that northerly aswell, watch as the GEM turns the top of the meteociel maps black. 

Its toppling.

Maybe something on the cards. It's a case of once bitten for me.

How often do things verify at that range?

There is quite good agreement here, but personally I just want to see some amazing charts, regardless of if they verify at this stage. It makes for some very interesting MO watching. 

OK guys here's the plan, we go down to portugal and build a very long, high, unstable bridge that no one would ever want to walk on. Then when Gandalf next comes online we persuade him to walk on that bridge along with a choir behind him playing dramatic music. 

It can't fail.

It might just be me but the latest GFS run is very pleasing to my eyes - high pressure and it's associated heights always close by to keep it dry and mild at this end, interrupted by a brief north west polar maritime air flow which could give me the best of the sunny breaks anyway - and all without silly bombing lows going off.

I can almost already feel the warmth of the rising February sun on my face.

While this winter has actually been kind to me when compared to last year and there is still a lot of winter season to come, I'm done with all this snow/cold hunting. It's time for me to look forward to the first bit of spring-like warmth. 

Burn the heretic!

I concur. Despite that 'fizzled' jet chart James posted GFS still wants to power the lows up and across, and all controlled by the Governor Azores High. It's omnipresence has been the doing of winter so far, and for some time to come IMO.

It could be a case of all this Torque just being talk, and I will not be in the least bit enthused until a Northerly is on the cards no more than 60hrs out.

But if there is no powerful SW orientated jet then how are LPs to develop? Even if the Azores high is still present it is miles away from one of those hideous atlantic dipoles at 192hr.