I think it has been a day at most since reaching the definition for a major SSW not a week?

As for the ECM op runs, as I mentioned earlier it highlights the lack of trend and consistency in that model’s op runs at that range.

If you define a SSW as needing both rapid warming and a wind reversal then it's only ONE day ago, not a week.

The effects have to propagate down then we need to see the impact at the top of the troposphere and then the models will start to get a better grip on how that will affect the atmosphere at 500 hPa and below.

AFAIK the signs of blocking and cold in the charts at the moment for the next two weeks are not driven by the SSW.

There has never been a clear indication of anything cold before mid-January, just a few hope casts. But if you look at the GFS 850 ensembles there is now a clear downward trend after mid January. Whilst the mean of a big scatter isn't that valid it is a downward trend and by the end of the run virtually none of the members are above the long term mean, which wasn't the case a few days ago. 

AFAIK ?

But last night the 12z ECM run end chart @ 240 set up what looked like the start of quite a block and now it's been downgraded to zonal.

The only thing I'm hoping is that things can change very quickly! 

So what you're saying is that we need to wait until we have the reversal of zonal winds to get a tropospheric response so the models can pick up on this instead of waiting for the SSW?

”As far as I know” and I’m not sure if you understand the definition of a major SSW? It is to do with threversl of zonal winds at 60degN and 10hPa not the initial temperature increase. This has been stated several times. The ECM flip in consecutive operational charts shows the uncertainty not that the one 12 hours ago was wrong.

I’m still looking to see that mid month northerly trend on the GFS.

Yes, another one bites the dust but that is normal in the modern era

Horror show again on the 06z, but I am turning into an old man now so I quite like the mildness and it looks dry in the SE too which is a nice bonus

Hi, posted this earlier.  its a little intense but will answer many of your questions.  You may have to copy and paste into your browser

https://journals.ametsoc.org/doi/full/10.1175/JAS-D-13-0349.1

An interesting choice to choose a timepoint for 4 to 7 days before the cold is due. 

To quote the well worn phrase - not all SSW's bring cold to the UK. The one niggle at the back of my mind is the now westerly QBO - which everyone seems to be forgetting.  Not a cast iron guarantee of mild weather either of course - but a player in the jigsaw non-the less. 

in our warming world mild in winter is always the form horse or default position.

Tally, one operational run from ECM means nothing. You know that what you need to look for is cross-model and ensemble support and consistency. At the moment we have none of these at all - the models are all over the place.  The GFS ensembles have been trending colder but, again, that's not anything to do with the SSW.

The people who understand this stuff are saying second half of January at the earliest. Assuming that's accurate then we have another week before we start to see charts from the high resolution models - and maybe a week more than that.

In the meantime any cold and blocked patterns will most likely just be the normal possibilities.

Me too - At least last winter (even prior to the SSW which lead to a cold end of Feb and March) - We had proper frost under clear skies and actually had some cold zonality weather - lot's of sleet and wet snow and hail etc!

Yes some colder ensembles but how do you know they are not anything to do with the SSW? WHAT MAKES YOU SAY THIS?

We have seen about 1c of warming; all that does is shift the probabilities a little, unless you think there's been a fundamental change in the behaviour of the atmosphere in favour of synoptic patterns that deliver mild weather.

You are quite right, they don't, not all SSW's are strong enough to maintain the reversal of the winds.  If they do they are major SSW's, to be truly classified as major I think they have to maintain reversal for a minimum of 5 days in the Strat.  So a few more days yet before the effects are likely to be relevant. 

Because if it was due to the SSW it would be in the operational run and supported by the ensembles.  I'm not sure that you understand what the ensembles do, although it has been explained quite a few times.

Ensembles test the stability of the evolution; they do not and cannot test something that's not in the data.

I had not read they needed to be maintained for 5 days?

It is also getting extremely repetitive and tedious re. the posting of charts in the first half of January to dismiss the prospect of the forecast and sometimes modelled cold from midmonth. 

On the subject of consistency I think the GFS has been highlighting a scenario for midmonth very clearly now. http://www.wetterzentrale.de/maps/GFSOPEU06_336_1.png 

Well let's hope the GFS op run flips cold soon because at this very stage there is little or no northern Blocking or anything coming up on the Op run which now goes up to 18th Jan.

The 6z GFS op reflects the MetO's forecast pretty well... after Beasts' chart, a couple of lows go zipping across the UK, then a blocking high builds and draws in a cold northerly flow. The cold pool over Scandinavia is being drawn towards us, too.

As for missing data, there were fewer obs than normal over New Year's Eve (as is always the case - down to 101000 or so at one stage), but not to the same scale as happens over Christmas. It would have had an effect, but against the background chaos at the moment I doubt it'd be too easy to pick up!

Tally is it an oversight or are you just intentionally ignoring what I have stated about the GFS persistently modelling a cold northerly in the op or GFSP run for days now in the midmonth period. Even on the cold northerly on the 06z op run it is unclear whether blocking would develop to our northeast beyond day 15. It is also computational-based hypothesising at that timescale anyway but do not ignore what is shown consistently.

The good news for SSW fans is that last night's 12z ECM showed reversal at 10hPa/60N for 10 days - and it'd been showing that the previous day too.