Eagle Eye

Sort of 2 wave Stratosphere with a dominating wave 1 amplitude event increasing pressure on the Stratospheric vortex and is now a trend that I'll be monitoring as a potential SSW pre-cursor . I'm a bit behind @chionomaniac as I forgot to look at the Strat in all this excitement till a few days ago .

ICON showing a decent evolution, that low could (and hopefully will) help to re-enforce WAA back towards Greenland and allow deep cold to be entrenched further on.

Look how cold we are compared to continental Europe (away from mountains), coldies have envied them before, maybe we won't be envying them so much this time

Our first proper taster is at 90 hours and closing in now on the ICON.

Poor mid Atlantic fish (I know that makes no sense). Swim a couple hundred miles and they are freezing and then Swim towards the Azores and find themselves flying back towards the cold.

Just a little bit messy.

Every time someone says that I'm convinced they curse the next runs

England are winning and I'm sure the 18z runs will have the snow winning all the way till +384 hours , that would be the jackpot anyway .

This is what forms into our disruptive low (stronger low in the upper part of the image), the initial tropical wave getting forced up with a moisture stream lifting up from the south and becoming a more natural December low but with extra moisture input. I think the main problem for the models is that we're still in a +VE AAM state and how they handle the -VE EAMT is probably going to end up in quite a messy solution, as we have seen already. I don't think we'll see an evolution that seems a bit more natural until closer to time. We could see a few runs show the more natural evolution over the coming days but it's clear that the models are mostly struggling on how to evolve this low.

Interesting 120 hours chart, that low clearly not as strong as yesterday initially but the forcing takes over and the stream of moisture clearly intensifying it but I think it's dynamics beyond that we don't really know as it'll likely change positioning quite a lot as it comes closer to time.

Both ends of the Strat doesn't matter too much as far as I can tell although it's not the perfect scenario which could be if 2 warnings were perpendicular to each other. It increases pressure on the Arctic vortex at thr 10hPa heights and the chances of a split increase. What that would do would be to weaken the zonal winds with the Arctic warming and that can potentially get transferred downwards, weakening the westerly momentum in each layer of the Atmospheric it goes down to. I'm not sure of the exact threshold of zonal wind weakening for it to get down to our 2nd most important layer of the Troposphere though.

Away from this upcoming model confusion and we can move to the Stratosphere. Clear signs of increasing distribution of Eddy's in the Stratosphere allowing an increase of warming values. Wave 1 amplitude clearly increasing in the upped Stratosphere and Wave 2 staying quite steadily above average. Clearly shown by the 10hPa values increasing for the Eddy momentum and heat flux and the Wave 1 amplification increasing and a bit of wave 2 thrown in for good measure. Decent signs away from just the upcoming spell .

Don't mention the Hurricane I mentioned it once but I think I got away with it. In all seriousness, feels like something special is brewing and I'm not talking about beer. It keeps getting closer and closer and now we can almost taste the snow (as long as its not yellow).

An evaluation of the current confidence +96 hours - Confident of cold slowly moving south (ish) Anything past +96 hours - Cold placed through the UK with spells of deeper cold I would imagine but for the Atlantic... I don't know Jeff

More shearing = tropical storms clouds change in direction with height - or to put it better veering - which slows down the development and/or weakens it, I don't know much more than that.

A lady called up earlier today and said that she had heard there was a Hurricane forming just south of Greenland in fantasy land... We can confirm that it's just the GFS going bonkers

At this point, what is going on with the observations because surely the new GFS cannot be like this it's just a very unlikely setup overall from what I'm seeing here.

If it's a warm core then it acts like a tropical system. The extratropical interaction you influence is very little in it's initial stage, moisture coming from it's south but as a warm core it still works as a convective centre influenced tropical system and the shearing will disassociate itself from it's low level circulation unless it happens to be very 'lucky'.

I know it's a bit out of date but the system forms from a tropical wave sourced roughly off just the West coast of Africa and quoting @Ben Sainsbury yesterday "That blow-up low on the ICON 12z & GFS 6z is definitely a tropical system. Obvious warm core on the models, but I just cannot see it strengthening/deepening like it does."

True but something just seems off in the models. This amount of shearing would surely have quite a lot of effect. To quote the RMet.. "Genesis is intimately tied to the magnitude of the tilt and is found to occur once the mid-level vortex has precessed into the up-shear flank. For smaller values of maximum tilt, vortex precession is comparatively rapid, aided by “showerhead” moistening provided by the up-shear advection of frozen condensate aloft. With the up-shear flank pre-moistened, rapid precession of the mid-level vortex, at smaller radii, leads to near saturation on the mesoscale and the onset of rapid intensification. When the magnitude of the tilt is quite large, precession is much slower and the showerhead effect is significantly reduced until just prior to the emergence of the mid-level vortex in the up-shear flank."

I wouldn't say it's impossible but how quickly it strengthens is essentially impossible. The flow into it from the south inducing quick moisture returns back toward the Low Level Circulation is indicative of the tropical low strengthening and moving in the flow of the upper winds but the shear around it should be enough to veer it's Convective Centre especially for it to not be able to strengthen much or at all really. It could become just a tropical wave that could enhance snowfall prospects for us if its positioning is perfect or it might die out as it enters the cooler waters and its forcing and moisture stream from the south disconnects. It needs to be monitored but its not as bad as it may initially seem.

@TamaraI think that falling on the sword, at least in my case, is more used to show a big call that the cold is favoured long-term here, I don't think it's really used in a childish manner. I suppose it's a bit childish to not elaborate further but that's the nature of making these big calls. Its more to do with living by the sword versus dying by the sword. I'm half agreeing with you, its sort of childish but more to do with passion than anything. We all see ourselves overcome by passion at some time and then will stick to our word if its backed up by some teleconnections.

My friends are already wearing things to keep them warm meanwhile there's me in my short-sleeved t-shirt,must be the northern genes in me . Even I'll be earing multiple layers on what some of these runs are showing.

Clear signs on the mid term GFS that the Eurasian feedback to the -VE EAMT combining with the +VE AAM and the slow moving nature of the weather, as long as the Eurasian feedback stays fairly strong, we should get that Scandinavian blocking propping up the -VE AO. The tropic low pushing into the North African High with +VE AAM and the Eurasian feedback will be enough for a Scandinavian high in my opinion. So in the long term, a reinvigorated blocking should form, this time around Scandinavia and increase the chances of cold again. There's still some bust scenarios but I won't go over them for now as they are for closer to time.

Was that aimed at me? Anyway, I'm going to go all in and fall on my sword as well. Clear signs on the mid term GFS that the Eurasian feedback to the -VE EAMT combining with the +VE AAM and the slow moving nature of the weather, as long as the Eurasian feedback stays fairly strong, we should get that Scandinavian blocking propping up the -VE AO. The tropic low pushing into the North African High with +VE AAM and the Eurasian feedback will be enough for a Scandinavian high in my opinion. There's still some bust scenarios but I won't go over them for now as they are for closer to time.