Bruegelian

Good to see that the GLOSEA update seems to favour the cold in north america going to the south eastern states, and no big Aleutian high.

Hey ho indeed, I think at this time of year us weather nutters start to get impatient about winter arriving, and are totally ignorant of the Autumn weather. Hey Ho!

Hello all and hope you have all enjoyed the snow and nothing unpleasant has happened to any of you, There has been quite a lot of snow here, with some immense drifts, some i would say about 8 foot deep. There was some freezing rain which is a slight annoyance, since it kind of detracts from the purity of the event, but 2-3 days before the event the models were going for mostly rain for SW so can't complain. It's good that low levels in SW have had decent snow not just high ground, and cool that the river tone froze in Taunton. Anyway today it is melting, but having said that it is snowing now. My weather station temp says 0.8 C, but I'm not sure if its right because the batteries are low.

I thought it was interesting what Catacol said about the teleconnections that caused this cold spell were just too perfect/powerful and it's all got overcooked. Like the lead guitar turned up the amplifier to 11 - it was incredible for a while, but then the amp blew up. If the amp had been set at 10 or 9, it might have lasted longer!

Is there anything that could stop the block scooting off to Canada? As has been said, a few days ago it looked like it might settle around greenland.

I think that it's easy to spend too much time looking at and worrying about the future, instead of enjoying the present. Even without snow, the next few days should be bitterly cold, and this on it's own produces interesting effects.

Thanks for that knocker - interesting how that paper theorizes that Antarctic sea ice melt would cause the opposite effect i.e. a trough in NE Pacific. Ever complicated as you say, any effects of AGW seem to usually have another conflicting effect, from what I have read. I think it might be good one day to have a thread about the Aleutian Ridge - We could call it "We need to talk about the RRR".

This has been a strange winter - the snow back in Dec happened without much blocking, and the models are going for something similar now - this winter we seem to have had less problems with HP to south. But really, we need to be reassured that the blasted ridge/trough pattern over North America that fires up jet, won't be around forever!

I know it's rare for us to get cold when there is a strong polar vortex over NE Canada, but didn't it actually help us in Feb 1991, with vigorous LP over Greenland helping to "pump up" a Scandi high?

Have been wondering recently what has been causing the "Ridiculously Resilient Ridge" (RRR), the ridge of high pressure in the Gulf of Alaska, that has been so dominant in the last 5 years or so. This article http://www.sfgate.com/weather/article/high-pressure-ridiculously-resilient-ridge-rain-12404417.php suggests this: "We've know for a long time that cool water temperatures in the eastern tropical Pacific Ocean associated with La Niña can produce a ridge in the Gulf of Alaska, which often tilts the odds in favor of winter high pressure near California and drier than average conditions especially in Southern California," Swain said. "But there's new, emerging evidence that the tropical west Pacific is just as important — and that unusual warmth there can produce a rain-blocking high pressure pattern right over California. "This year, we have both conditions in play: cool eastern and warm western tropical Pacific. That would suggest an increased likelihood of winter ridging this year, and an increased chance of drier than average conditions especially across the southern half of the state." There's also this: (from here: http://www.sciencemag.org/news/2017/12/vanishing-arctic-ice-could-drive-future-california-droughts) In modeling runs with the low-ice condition, the Arctic’s global influence quickly became apparent. With less ice, the Arctic reflected less of the sun’s energy out into space, leading to a surplus of heat there. Within just 20 years, that had disrupted the usual flow of energy toward the Arctic from the tropics, leading to warmer-than-normal waters just north of the equator. That excess tropical energy fueled rising air in a process known as convection, creating rain, releasing heat, and forming large-scale atmospheric patterns called Rossby waves. Those waves, in turn, led to the formation at midlatitudes of high-pressure systems, or “ridges.”

Why is it that it seems whenever we have a chance of HLB delivering cold to UK, it seems we get a ridge & trough over N America bringing cold there and firing up the jet stream. I suppose maybe it because when there is a negative AO, the high pressure can spread there as well as here. Anyway I think hopefully this winter is a transition period between cold going to US fading, and going to Europe instead, just a 'funny feeling'.

Thx for the replies, yes I remember cold and lots of snow in Feb 1996. Also I think there are a few others such as 1956, 1985. I have been talking to Tamara on here, and she says that most of the winters that had a La Nina designated, and featured significant UK cold weather, had some kind of atypical La Nina circulation going on, of course every La Nina is different. She says that 95-96 and 55-56 are in this category.

Hope this is right place to post this, if not then move, I was wondering, have there been any past winters, where there has been a La Nina, let's say moderate strength or below, and there has been a 'proper' cold spell in later winter i.e. from around this date onwards? Thanks Brug.

Thanks for the responses - Also I think Steve Murr's idea that AGW is changing the landscape faster than computer models can keep up with, may have some credence. But getting into pretty deep water now....

It is a worry that seemingly all of the mid-long-range models are going for a largely mild & wet January with high pressure to south,that is JMA, CFS, EC, presumably Glosea as well. However today Gav P did a video saying that he thinks that possibly it will not pan out like this, because of the jet stream wanting to keep south of us. Does anyone know why exactly, the jet stream has been behaving like this - is it the pressure pattern, or perhaps even lower-than-average temps in Africa reducing the thermal gradient, or something else? Thanks.

Isn't it the case though, that we have had some very potent cold spells when the polar vortex was strong/fairly strong, e.g. Jan 87 and Feb 91? Apologies if this is incorrect. Edit: Chart for 1 Feb 1991: I know that generally a strong polar vortex is not good for cold here, but I think there are few cast-iron rules with the weather.

Ridging over E Canada has hinted at by the CFS weeklies recently. I know this model gets a lot of stick, but I think it isn't too bad really. Hope everyone has had a great Xmas Day!

It is fascinating the way the weather always takes us by suprise, even if it is want you don't personally want. I remember in late Nov/Early Dec when there was a lot of HLB in the troposphere, but the stratosphere was pretty cold, and most people thought that the strat would propagate down and obliterate the blocking. However, that didn't happen, and in fact the reverse happened with the trop changing the strat. And then more recently, we thought that things were looking odds on for blocking, but there has been a suprise flip in proceedings. It can always catch us out!

It would be super funky if we could 'steal' the Alaskan ridge from US/Canada, over the top of the world and into Greenland!

Is it too late or not for UKMO to side with GFS/ECM, in member's opinions? Thanks

Thank you, all very interesting.

So after the strat couples with the trop and we have a westerly dominated period (as seems likely), then what? What are the possible routes back to cold? Thank you, I have only a basic understanding of these matters

So having a La Nina suppresses amplification and hence HLB, but surely there must be plenty of winters where we had a Nina, but had some HLB episodes giving cold weather. I suppose its a matter of degrees like everything else.

Yes, IIRC GLOSEA long ranger was showing strong zonality for this autumn, so I'm taking the DJF prediction with a little salt.

But it wasn't too far off the mark - last winter was painfully close to being proper cold at times. There was a lot of HP around, just never "locked in" to our north.