Snowy L

The signs were there for this weeks cold spell, the stratospheric charts showed low pressure into Europe and a ridge getting as far as Iceland but not penetrating into the polart vortex, which inevitably leads to mid-lattitude blocking rather than high-latitude blocking. This time the vortex is splitting with each lobe moving away from the North Pole. This should enable Northern blocking for a time Edit: Example of this:

Northern Hemisphere pattern is the encouraging part, no point talking about specifics 200 hours away.

I'd say it's pretty representitive of what's going to happen over the high lattitudes. The things that will win it or lose it for us in the mid-lattitudes are shortwaves.

Arctic high completely in control of the North pole, the only logical solution after today's stratospheric charts. ECM very much leading the way.

Yep definitely a more positive swing from the ECM. ECM will always be the first to catch on to weak vortex events with GFS trailing behind in typical fashion with a 100-150 hour handicap. I expect further upgrades and we should see the undercut happening in the next few runs. That atlantic shortwave was a nice addition that almost got us the undercut in this run.

Refer to +192

Need that azores high to back off a bit though, it's preventing a complete undercut.

Shortwave could actually help us if it manages to move east and link up with the Scandi Low

That's the thing I don't think it will sink, it will just move over towards Northern Russia. I think we will end up with a set up similar to last January with a weak high between Greenland and Scandi. PV just isn't quite in the right place to set up a Greenland High. I'm just happy we're finally starting to see two distinct PV lobes, I'm shocked it's taking the models so long to get to this, with GFS still way out.

Indeed, finally we have a model that appears to be in sync with the stratospheric ones.

Yes vortex splits are usually indicative of zonal weather...

Still pretty similar to the 06z, more elongated low though which is good to see.

12z GFS coming up, I expect a far better run than the dreadful 06z. It has to start taking this vortex split into account. I expect to see a much slower west-to-east movement of the Atlantic lows (vortex over that area actually moves east-to-west on the stratospheric charts) and subsequently a much better opportunity for the nearby high pressure to build North. A zonal pattern in the next couple of weeks just wouldn't fit with any of the background signals. The increasingly likely pattern is some form of blocking in the high latitudes, that's not to say the UK will get a cold spell though and it's pointless to look for something as specific as affecting our tiny island. The Northern Hemispheric pattern as whole though should become more blocked in 7-10 days time.

GFS couldn't be further from what everything else is pointing at. A North Siberian high FI, really? This when the bulk of the vortex is likely to be in that position. And then they show the area to our North filled with low pressure systems....exactly where the split in the vortex is expected to happen. ECM 0z is far more clued up imo and anything is possible until mid-december.

High pressure building over Greenland that wasn't on the 12z. I have a feeling we will see something similar to the ECM, only it's looking like the low will undercut on this run.

http://www.wetterzentrale.de/topkarten/fsavneur.html Wetterzentrale seems to be working and is on 60 hours. Looks like we have a very slight shift west looking at the 850 temperatures, which is good news.

Doesn't look like we'll get the undercut based on t144, though ECM is keen to get that vortex into russia/Scandinavia.

"Indeed Joe, Thanks. I just want to keep the flow of the thread going rather than personal debates amongst members," It was hardly personal, it was two members giving differing opinions on what a model was showing, exactly what this thread should be about

I think this first shot at cold will get away from us and we will end up with high pressure too close to the UK. However, it's good to see that most models still keep low pressure to our South. This could help in the coming days as a further burst of wave breaking is expected which will help to push the bulk of the Polar Vortex to the Southeast of the Pole and into Russia. I actually think this FI run is a good shout at what will happen, with high pressures making their way towards the Pole from the Canada region, let's hope we end up in a favorable position for a block.

PV starting to look very stretched, maybe a build of high pressure towards Scandi is on?

The event is 80 hours away, and a clear signal has been given again and again - widespread upper temperatures of -2 and dew points above zero for most.

Larger warm sector with this low pressure, snow event for lower ground looks very unlikely.

I think one thing that will prevent us from getting a good block is that the PV is clearly reluctant to sink too far South. We need solid low pressure in Southern Scandinavia to force a block to our Northwest. I still hold hope for something better in early December though. Still more disruption to the lower stratospheric vortex being forecast with warmings expected over Greenland. Could orientate the vortex more in our favour and get it to sink into Scandinavia.

Good shout, Greenland High building based on t168

GFS gone shortwave crazy again, it's sending way too much energy over the top of the high. That high pressure is looking very weak, I hope this is just a poor run from the operational and we see it changed at 18z. One alternative is that we could see a Greenland high earlier than expected of course...