http://modeles.meteociel.fr/modeles/gfsp/runs/2018122400/gfsnh-10-6.png?0 

ECM still says yes. A huge shift in the zonal winds coming up if the output is to be believed.

Here are the actual conditions at 12z yesterday. Key area to focus on is 60-90N between 1hPa and 30hPa (top right hand quadrant). Yesterday there was a very strong positive zonal flow in this area which is not unusual for the time of year

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_u_a12.gif

By day 10 a complete flip to a fairly strong negative zonal flow indicated by the blue colours.

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_u_f240.gif

Latest GFS parallel run suggest the polar vortex in the stratosphere will not split. It had been forecasting a split consistently for some days. By the end of the run the vortex has regained its circular shape, albeit it is still displaced with the centre on the Norwegian coast. Ideally you want a split to get the maximum impact from the SSW. 

Whether there is ultimately a split in the vortex or not, it looks as though this is another pretty notable SSW.

Here is the GFS forecast for zonal winds which also shows a strong reversal

Day 10 http://www.cpc.ncep.noaa.gov/products/stratosphere/SSW/gif_files/lat_pres_gfs_UGRD_NH_f240.png

Day 16 http://www.cpc.ncep.noaa.gov/products/stratosphere/SSW/gif_files/lat_pres_gfs_UGRD_NH_f384.png

The first one shows a reversal (albeit a weak one at the all-important 60N/10hPa), but it doesn't last - by your day 16 chart the 10/60 winds are positive again. Still, better to have a weak, shortish reversal than none at all!

If you look at winds at 50hPa, not much variation on a day by day basis throughout the GFS run:

http://www.wetterzentrale.de/en/topkarten.php?map=2&model=gfs&var=39&time=234&run=6&lid=OP&h=0&mv=0&tr=3

I am really beginning to wonder if sudden stratospheric warming events are really all that they are cracked up to be. 

I   see the spike in warming  has peaked.

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/STRAT/

Excuse my ignorance, but how does the amplitude peak compare  to past events.

That's because its just updated to today's run! When I posted it the figures were still from the run on 23 Dec. Quite a big change on the latest output.

It has/will have reached its peak today, beating in mind the warming is not directly over the pole http://modeles.meteociel.fr/modeles/gfsp/runs/2018122406/gfsnh-10-6.png?6 

On a related but diametrically opposed point, I wonder if there is a nacreous cloud risk today given the notable cold in the stratosphere in our part of the world?

If that was to happen, I would be very concerned about the resulting lack of rainfall and possible water shortages which could arise from that, especially since there are still a number of locations which could really do with getting some rain right now because of what has already happened during this year, and which are still not getting that rain.

That spike had nothing to do with the SSW as the SSW had not started at that point. The SSW has not peaked, even at the 1hPa level and in fact has only just started impacting the 10hPa level.

See this chart. Third box down (blue line) is the 10hPa line which is starting to move up now and is forecast to peak shortly.

http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/index.html

This URL should go directly to the image http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/ts.php?plot=temps&alert=1&lng=eng 

Copied across from the MO thread

Given the nature of the definition of a SSW you cannot pinpoint it to a specific location, as it focuses on temperature and zonal wind speed latitudinally across the globe. You could identify the location where the warming started but that is entirely different to how the SSW is defined. So it is important to be clear on that point.

What we can do is look at how the polar vortex responds to the SSW in terms of its geographical location. The site linked below does that really well using interactive graphics for all SSW events between 1979 and 2013. You need to be patient as the graphics at each link take some time to load. A quick look at some of the years where we had cold weather in the UK following a SSW, it is not unusual for the PV to be displaced towards Europe initially in these situations.

http://birner.atmos.colostate.edu/ssw.html

Does it need to be directly over the pole to have an influence? Would the warming over Siberia not have an equal amount of influence, if such an influence is to be have? 

There’s still uncertainty iin whether we see a split or displacement the ECM going for the latter whislt the GFS the former which it sees it quickly reform over Greenland thereafter. Personally I think we’ll see a week or so in which we’ll see its effects work in our favour thereafter I foresee a west based -NAO as the main core of height anomalies transfers more over to the Canadian side of the globe.

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

Worth a read- page 60 something and if you know your UK data for the years listed, you'll be able to do some correlating...or not.

Yes, I started a new thread a few weeks ago with a post containing a link to this paper, but it didn't seem to attract much notice.

Latest EC model kicks down the road the date of the Stratospheric warming induced split vortex, now supposedly due 3rd January. This as tropospheric energy transfer eases... pic.twitter.com/tk6o3QHZj2

— Chris Fawkes (@_chrisfawkes) December 25, 2018

Thanks for that

I have monitored the SSW on the ECM pretty much all the way through & -7 M/S is now the lowest ive seen in terms of the zonal wind -

Its only a matter of time before the blocking comes...

The Sudden Stratospheric Warming may struggle to effect the troposphere, interesting to watch... pic.twitter.com/rN3xO8sfpG

— Chris Fawkes (@_chrisfawkes) December 27, 2018

Cold and snowy weather fans on Twitter and in weather forums when reading your tweet... 😄 pic.twitter.com/PWuibARkYQ

— Liam Dutton - Weatherman (@liamdutton) December 27, 2018

I don't know if this has been posted but I happened across  this  RMS meeting report.

The section on SSW begins at about 20 minutes into part two of the report.