The GFS and GFSP have both gone with the shortwave low shoving its way NE toward Svalbard days 8-10 that ECM has been consistently modeling, but unlike that model, they continue to avoid trough disruption to our west in during that period.

That means we end up looking for the Greenland vortex to dive SE as per recent runs, but it takes longer to do so on the GFSP 12z op, while the GFS 12z op still has a go earlier, but seems to redevelop a stretched out vortex to our NW late on in the run.

The slower trop. vortex disintegration in the GFSP run is a result of the strat. vortex taking longer to shift away from Greenland. That's a trend that I've seen in past winters when we've been waiting for strat. events to change the game - it seems that a tendency to be over-progressive applies at that level as well as nearer the surface. The run finishes with a good setup for a notable cold spell going forward but it sure is a long road to get there.

The redevelopment of low heights to our NW on the GFS 12z op run is an unpleasant sight, hopefully that won't have much ensemble support. If it does, I'll start to wonder if the strat. vortex is really going to do much shifting at all during the leading third of December.

Having said all this, the forcing of low heights NE beyond day 6 is far from convincing on the GFSP 12z op run, as it barges right through an area of high pressure extending from Scandinavia to the Arctic Ocean north of Siberia, which has been looking stronger with each new run:

Note how the heights in green extend further north/northeast from Scandinavia on the 12z run.

A look at the jet chart shows a complicated setup with three streaks to resolve at that crucial timeframe:

Just a thought - but I'm not betting on anything, as UKMO is even more aggressive with firing energy NE. I'm still thinking that unless we see some trough disruption to the west in the 8-10 day range and the polar vortex dropping south in the Atlantic, we're heading down the long road rather than taking any shortcuts.

Well it the GFS and the UKMO projected forecast to next Sunday T144, the SE diving Low affect SW Europe, Cold with High Pressure for Central and E Europe, and SE Greenland- Iceland N Atlantic Low P. Quite a Potent Vortex, and Northeast E Norwegian Sea and just on to NW of N Russia Arctic Sea area PV Low also being cold weather same goes in SE Greenland And farther  North Atlantic.

Cool SE flow for Britain Thursday and mostly cloudy, then SE winds and Mild on Friday to Sunday.

Next Week A Low could pass near North and NW UK, bringing cool and bright sunny weather for SW Central and W to SE parts of UK.

Then Upto Thursday next week GFS has High  pressure bring from Monday p.m/ Tuesday settled weather with overnight frost possible and near average daytime CET Temperatures. 

By Late Thurs. into Friday we could see an area of Low P. Move from N Atlantic heralding GFS suggests another following spell of Wet and windy weather by the Weekend Sunday/ Monday with Colder NW flow with some wintry showers possible.

I hope No errors are in post- fingers crossed, but the GFS and UKMO and ECMWF predictions are only reliable Upto Max t168 at the moment any my forecasts for following period are I am not really convinced will be true to happen so there goes any criticism!.

hey stormchaser you can never ever belive to amaze me with your absolute fantasic post brilliant total awesome, thanks for your post above there buddy enjoyed that,. sorry off topic, but had to say this,

ps, hope this cold is not a red herring, lol 

ps steve murr over on net thinks it can go either way,   ?    

btw  steve murr is very tecnical,  i get lost, but he knows his weather. i rate him as i do alot of others,

GEFS12z look the coldest set we've seen so far this season but i've not had time to look through them this evening:

Certainly looks that way,  Brian. Interesting 

Just had a quick glance and despite the lower 850s and 2m temp spread most of the runs don't have synoptics which make a 'big freeze' look likely although a few do. I wonder whether we could end up with 'coldish' and fairly stagnant conditions bringing the possibility of some snow during the first half of December. 

Yes, nothing to get the sledges out for but at least a cooling trend is apparent. 

Ties in with Ferguson's comments on Points West just now. No cold air to tap into, but a cooling trend. 

Seems about right for December then?

Malcolm
Wakefield & Gothenburg, SWE

Just taken a good look at the models and I reckon we are in pretty good shape. 

The Scandinavian Block is now well into its second week and shows little signs of shifting southwards any time soon. Certainly here in East Kent its influence is being felt with much of the forecasted rain recently either stalling before arriving here or sliding SE'wards into Europe.

As a child in the 80's it was always an encouraging sign to see a Scandinavian High in situ so early in the season. I remember Jack Scott back in the late 70's saying that the cold will eventually come if the block sets up early enough.

We need to be patient. The feed will turn easterly soon and it will get progressively colder the longer the pattern persists. To introduce a noteworthy severe spell of cold weather we will need to see the Arctic High come into play allowing a west Siberian trough to feed Arctic air around the periphery of the high pressure..get this in place and the cold will arrive 3 or 4 days later.

There is some evidence in the form of outliers but the majority of output wants us to become colder due to the continental feed but not much else..for now.

OPI signatures and forecasted Strat events are encouraging in the longer term..if these do come to fruition then the building blocks being placed now will make for an interesting period of weather..should it all verify.

Exciting times but we will need to be patient and not be too disappointed if this first early potential gets swept aside by the atlantic because the evidence is mounting that there will be more opportunities for cold outbreaks further down the line.

Time will tell.

Sounds about right to me 

Mid-December has long been my 'hopecast' for a significant cold spell hitting the UK - in other words, what we have a good chance of ending up with if everything works out the right way, which as we know is nearly always a long road in this country (and sometimes the end is a mirage!).

Having said that, ECM again teases with a quicker route to a Svalbard block or thereabouts, in fact it has the best day 10 setup so far from that perspective:

This is about as good as it can get within such range following a flattening of the blocking to our east into a mid-latitude block across the UK.

UKMO seems geared up to follow the same sort of route as ECM considering the day 5-6 progression. 

JMA doesn't flatten the block anywhere near as much, but begins to dig the Atlantic trough south on day 8:

As I've said very recently, if there's one thing we can count on GFS and GFSP doing, it's having a bias towards a flatter jet that doesn't allow troughs to drop south. As I've seen the likes of Steve Murr state, there also seems to be an issue with GFS capturing split jets, which lead to some low heights getting carried N or NE and the rest dropping S or SE.

Case in point - GFS predictions for 28th November as of 15th, 18th and 20th November GFSP 12z op runs, then current +72 hour chart:

In all forecast cases, there has been no splitting of the jet, with the trough remaining a single, potent feature. The reality has turned out very different.

Funnily enough, the 12z GFSP runs of 16th and 17th were a lot closer to the mark, though the split of energy happened further west. The model should be kicking itself! 

...so I do think there's a good chance that the disrupting trough to the west turns out to be the right way forward, even if the strat. vortex doesn't move along as quickly as originally predicted - after all, that only really has the potential to help us out in the longer term - with impacts starting about a fortnight from now.

OMG super post stormchaser, your an elite poster, full detail with charts, what a trooper. thanks buddy, enjoy your posts,, 

No, not necessarily. There have been many years where there has been severe cold to tap into even in November. It's just down to the current setup. 

Many thanks to you and others who have posted along similar lines - it's great to know that my enthusiasm is providing some interesting and informative reading for others 

Just had a quick read around on another forum and it seems the tilt of the trough at day 4 remains uncertain to the point that it could still potentially change the whole outlook going forward; GFS and GFSP are very close indeed to having enough of a NW-SE slant to the trough as to allow the blocking to the NE to take full control of our weather.

GEM has just a little more tilt and ends up bringing a wedge of cold from the east late on in the run - and that's despite it throwing the whole polar vortex at Siberia days 8-10, which flattens the block.

On the other hand, ECM and UKMO are less tilted than GFS and GFSP so we are talking about a pretty significant correction for such short range. It is, though, the sort of adjustment that you might not even notice if it wasn't so critical to proceedings!

I have to admit, I'm afraid to try and call it one way or the other and don't envy the position of the official forecasters right now!

OK thanks. I should do well to have a read through James' post I think 

Malcolm
Wakefield & Gothenburg, SWE

It certainly got pretty cold up here in late Nov 2010, just as the severe wintry spell that went on to dominate that December was getting underway.

Further to my post last night I have been exploring the model verification stats a little more. The stats are available for different time periods. The ECM model performs the best at all time intervals.

The following charts are verification of sea level pressure

3 day forecast http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day3_PMSL_MSL_G2NHX.png

5 day forecast http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day5_PMSL_MSL_G2NHX.png

8 day forecast http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day8_PMSL_MSL_G2NHX.png

10 day forecast http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day10_PMSL_MSL_G2NHX.png

Worth noting that at 10 days out (T240) the ECM model verification is way ahead of GFS (0.361 compared to 0.274). So on average the ECM solution will be much more reliable than GFS if you are looking at T240 charts.

The data also shows just how much the forecast accuracy drops off between days 5 and 10. ECM gets the sea level pressure patterns right 89% of the time on a 5 day forecast but only 36% of the time once you get to 10 days out.

After doing a bit of digging I understand that the PRHW14 data is the one that is providing the parallel GFS charts that we are able to access. The PRX data is another slightly different version of the GFS parallel run being overseen by a different branch of NCEP. I also notice there is a new run appearing now on the 3 day chart being PRHW14N. I assume this is a "new" - hence the "N" - version of the parallel run. There are only three days of data at the moment on this new run so too early to tell whether it will perform better than the existing parallel run.

Worth noting that at day 10 the original parallel run is performing much better than the current operational GFS (0.293 compared to 0.274). 

Current timetable for replacing the existing GFS op run with the new GFS model is 7 January 2015 but this could be pushed back again.