Most of the models are going for a disorganised or even split polar vortex by T240. GEM and GFS op show this best although even on ECM we have high pressure close to the Pole.

GEM

GFS

CMA

ECM

The T240 charts are looking not too dissimilar to what we saw on the same date (2 December) in 2012. The pressure pattern near the UK is quite different so it will not be anywhere near as cold as it was in early December 2012. It is more the positioning of the polar vortex that is of interest.

Is the PV shrinking?

GFS and GFSP are starting to play around with various solutions to the polar vortex taking a hit sometime during the first week of December.

The 18z op runs both have a split taking place that leaves one half in the Atlantic:

This is the GFSP version, with GFS keeping some lower heights over Canada so the split isn't as clean as shown here.

I'm hoping these interesting runs with broken-down polar vortexes start becoming more frequent and also more exciting for the UK over the coming week or so, so that we can at least have a bit of fun speculating about them 

GEM the pick of the bunch again this morning -10c uppers nearly make our shores prob some snow around as well by day 10. 

http://www.wetterzentrale.de/pics/Rgem2402.html

At a glance the signal this morning from the GEFS and ECM op is for a stronger Azores high and a more defined west or south westerly flow as we head into December.

A link to a site?

Welcome TW. We have a winter thoughts thread further up the main page that might interest you. 

GFS ens very mundane. Barely a single member dips into -5 territory over the entire run. 

Agreed 

The GEFS mean at 240 hours is a lot more consistent than it has been recently after the clearance of the trough at the end of this week.

Despite being a lesser model the GEM continues with a signal to pull some cold air westwards at 216 hours, bringing the risk of wintry showers to some eastern coasts for a time..less than a 5% of achieving verification of course but unwise to ignore it totally at this stage. 

I concur. Those taking GEM as a flag for their cause are misguided as it's now almost totally isolated. The concensus is pressure building to the south and an Atlantic-dominated period into the first week of Dec.

The current and modelled strat warming isn't going to help because a) it's not 'sudden' and b) it's not breaking down below 7mb. According to the theory the warming needs to permeate down to 10mb and above to start to promote PV erosion and block formation.

The OPI predicts a colder than average winter and as winter has not started yet it's unfair to comment, but looking at the first half of December at a stretch the patterns will probably need to undergo a rapid switch sometime soon.

That's how it is at the moment.

In the absence of much interesting during the coming week (aside from a potential strong storm, but which has low support), it seems like a good time to be looking further ahead. If you're not bothered about the statosphere and/or don't give it any credit as a forecasting tool then maybe give this post a miss 

Both the GFS and GFSP shift the polar vortex out of Greenland by the end of their runs, and send it on a route to Siberia while giving the UK a westerly flow that turns increasingly cold on the GFSP run. The GFS run plays difficult, building a strong Euro High, and would need some 4-5 more days to get us onto the cold side of the jet as the polar vortex becomes established to the east of the UK.

Sure, this is all well outside of the reliable in terms of detail in the troposphere, but it's well supported by developments in the stratosphere:

GFS displaces the strat. vortex toward Siberia and has warming pressuring it from both sides. From what I understand (I still have a few holes in my knowledge to fill), this setup favours a progression to low heights Scandinavia-Siberia and high heights across Greenland, Canada and much of the high Arctic.

GFSP gives the strat. vortex more trouble than that - it not only maintains the split that we have at the moment, but increases its magnitude, weakening the daughter vortexes (or vortex lobes) in due course:

There's also strong warming pressuring it, which could potentially cause at least one of the lobes to fall apart completely.

The setup shown above favours low heights south of Greenland and through the UK, and also towards Siberia. The vortex over Greenland drifts slowly SE days 10-16, hence the increasingly chilly Atlantic flow for the UK, as the storm track shifts south and the area of peak low pressure development shifts east.

A key caveat here is that these outputs can only be considered a rough guide that indicates a strat. vortex in a lot of trouble, with a signal for the Greenland lobe to finally pack its bags and take a trip somewhere else.

ECM has a similar tropospheric pattern evolving so perhaps the strat. evolution is also similar - that information can usually only be obtained by people with special access, and even then only from the 12z runs I think, so I can only speculate for now.

I know it's a long waiting game, with the above evolutions probably on the way to a mid-December cold outbreak of some form or other, but that's always been the case when depending on developments in the stratosphere to influence the troposphere - December 2010 was different because that event went from the troposphere to the stratosphere.

It is a shame that what we get in the meantime may well just be a boring westerly flow with some drier spells, some spells of rain, and perhaps some strong winds to contend with on a few occasions. Having said that, a mobile flow usually brings more in the way of broken cloud than the battleground setup we've been having of late, and signs of high pressure tracking across from the southwest are welcome if you desire some more useable weather.

Thanks James, very interesting!

There remains, at time of writing, NO clear/definitive signal towards calling the west-v-east outcome into at least next 10-15 days and I'd urge folks to sit tight on this (perhaps confusing) period of NWP to-&-fro, which may continue for some time yet. Add some of the possible background hemispheric drivers described well by Tamara and others, and the complexity moving ahead - and caution needed interpreting daily model output - should be very apparent.

The tedium from last winter continues. We seem locked in this awful pattern while the US gets all the fun.

It's still Autumn

An interesting few days ahead I think with regards to the first week of Winter, At least some signs that it will turn more seasonal but whether that's from the East or the NW remains to be seen.

Apart from another lot of Rain on Tuesday it looks like it will start to turn drier in the SE which  will be welcomed by many I'm sure as we see out the end of Autumn.

Some really good posts from the guys this morning in here Stormchaser with a great in-depth post and Gusty giving a tease at a hint of something 

Link

Oh if only it were July. The GFS run would have a humid thundery breakdown on Tuesday and an airflow on Thursday and Friday from a long way south in North Africa... Bit of a waste in late November really.

An interesting comment by Fergie, considering how much the momentum in the output seems to be towards low heights overrunning the blocking high to our east on its journey to Scandi/Siberia.

Perhaps a more meridional route (by which I mean the jet tending to track north-south or south-north rather than east-west) is possible. Attempting to envision what this might look like, I can see the Greenland lobe sinking south and becoming trapped in the mid-Atlantic, where it eventually disintegrates. Blocking to the east maintains the status quo from current conditions for a while longer, before having the opportunity to retrogress to the northwest, encouraged by the strat. forcing driving lower pressure over Scandinavia and/or Siberia.

That's by no means a forecast, just a theoretical evolution which at this time hasn't got much support from the models or their ensembles... at least, not from the ones I've seen. Perhaps the Met Office are seeing a good number of more meridional solutions in their own model output behind closed doors.

There does also remain a small chance that the Atlantic trough aligns in the right way to drive low pressure underneath the blocking high later this coming week (as advertised by GEM, which I'll refrain from posting for the sanity of this thread), but the odds seem to be heavily against that.

With Fergie talking about the 10-15 day period in this comment, I imagine the Met Office are thinking along the same lines, as the critical period for the GEM run is in 4 or 5 days time.

It's a good thing the model runs change then!

I can well understand where he's coming from tbh. The model output that we have access to here has been varying considerably at times over the last couple of weeks or so.

Interesting things are happening in the strat. Here are a couple of height charts from the 1mb level which is right at the top.

The first is +144hr but about 80% of the entire model run looks almost identical. The displacement is going to happen very soon (within the next few days) and the polar vortex (1mb) will sit on greenland for the forseeable future. It certaintly is a major displacement with the centre closer to the UK than the north pole however I'm not sure we really will benefit from a polar vortex on greenland; in fact this happened an awful lot last year. Its not until right at the end of low res that things get really interesting, with the polar vortex weakening and migrating towards scandanavia. There is a deep trough visible in N america, if this sort of pattern propagates down then America could really get hammered with sections of the 500mb votex visiting the E again, but for us the future is far less clear.