Just to emphasise the point, the 12z GFS offers up a perfect example:

Deep plunge of Arctic air into NE North America; a low develops off the coast of Virgina/Maryland and undergoes rapid cyclogenesis and then heads north to the west of Greenland.

Yet another run from the GFS that builds promising looking heights at day 10 only to quickly sink things by day 12 as the PV ramps up.

I think 10 days is about as far ahead as we should be looking with any degree of confidence at the moment with all that is going on.

No person experienced in following the model output would take any solution shown in deep FI of any GFS op run as a given, be it a cold or mild scenario.

As it is, they are just horrendous for anything remotely interesting. Merry Christmas all. Hopefully things will start to change soon because this snoozefest can't go on for ever surely?

Hi CP; the fact is, for a host of other reasons, just about any setup is possible without a SSW event. SSW, it seems, increases the probability of certain conditions occurring and persisting.

This link gives a summary of N Hemisphere SSW peaks (go to p66) and you can see that some very cold spells with Ely and Nly components, some well quoted, precede SSW peaks. 

Some are surprising: 23.1.87; 22.2.79; 28.1.63.

Others seem much closer to surface cold than the oft-quoted 2 week downward propagation period, including 4.12.81 and 1.1.85- in the latter case, the cold setup was red-carpeted on New Year's Day with an elongated Atlantic HP, and established 3 days later as LP to the NE began pumping cold air out of Scandinavia. In the 1981 case, there was a distinct line marked by a far-reaching frontal boundary behind which a very distinctly different airmass brewed.

Point here being to illustrate not the obvious- that some SSWs do not deliver, which I think everyone knows; but that some macroscale setups involving reversals in long- and broad-fetch prevalent airstreams are not SSW dependent. 

The link:https://www.earth-syst-sci-data.net/9/63/2017/essd-9-63-2017.pdf

I know what you mean and share your frustration - we have already been through 1/3 rd of the winter next week and would have had little if any frost let alone snow so we do hope to see something 'wintry' perhaps?

I guess the only comfort is the SSW and the fact that the Met Office/BBC etc have been very confident about much colder weather over the Uk  from mid month on wards (Jan 2019) and the GFS only goes until 9th Jan so perhaps we need to wait at least another 5 more days to see anything cold turning up on the model outputs? 

BCC gone for a block over Greenland and to our north in Jan as do many other models including ECMWF and Met Office Glosea 5. seasonal with below average pressure over central Europe. What we see now in the GFS esp the OP shorter range is the exact opposite! 

Displaced PV fragment over E Canada can quite conveniently lead to longitudinal HP blocking over mid-Atlantic and co-vortical attraction to quasitropical cyclogenetic features off the E seaboard.  Big Atlantic block doesn't always need full N blocking to bring the right conditions.

Not the best set-up for cold fans for sure Kieren. That said, I'd sooner take what we have now and what is being suggested for the coming week or so over almost non-stop wind and rain, like we were getting this time three years ago.

I suspect that after many years of weather watching Ian is entirely aware of that. 

At a glance there seems to be increasing disagreement on the 12z GFS ensemble data from as early as day 5.

Thanks BW for all that info.  lots to consider. 

I love this little term from the link: "SSW Compendium' 

True in some ways!

Take December 2010- well?...from what I remember, there was no SSW in November that gave us the coldest December in 100 years?

Just wanted to share this for contrasting purposes and how boring and uneventful our weather is!

Ensembles for NYC:

One day it's +10c @ 850hpa and next it's -10c @ 850hpa! 

London:  - Apart from one or two colder outliers. - boring!

NE USA looking cold after christmas....jet over States dives SE....then ridges high in Central Atlantic....(GFS).....strong jet in Pacific at 50N....Gfs models.PV strat to reform over Greenland\NECanada..hopefully not....

Agreed david and with the roof of my car iced over before 6pm tonight and fog patches forming id say its pretty wintry tbh and certainly beats wind and rain.

Happy Christmas!

Happy Christmas and fingers crossed for  some better charts for January !