Except that isn't What the ensemble suite does; it only tests the stability of the evolution by minor tweaking of the position at T+0. Don't forget that T+0 is only ever an approximation because there are more data points than there are accurate measurements.

As I understand it the model is just re-run with these different starting positions; the models themselves are fixed. That means that how the SSW might propogate down isn't really going to be tested.

It's worth remembering how often we see the operational and its ensemble suite flip together; they really are only a guide to model stability and then only really in sensible timeframes.

The Met Office forecasts have for some days been firm in suggesting high pressure to the south easing away to a more changeable period before colder conditions develop.

What GFS seems to be indicating seems to be reasonably in line with what the MetO have been predicting a more generally mobile and unsettled spell for a time as we head further into January, which could be followed by colder conditions as towards mind-month. Therefore, there is no need to panic at the moment, IMO. Anyone expecting a sudden change to a colder pattern is likely to be disappointed in my view.

EDIT: See Gandalf's post just above this one.

True in some ways - Let's see what the models show when FI is mid-month (Jan) then? Fingers crossed !

A lot of people pinning their 'tails' on the GFS donkey in here....

As Martin Brundle says lets hope your donkey doesnt give up- Awsome ICON & UKMO blend overnight-

ICON -10s into Scotland 138
UKMO -8 into Scotland 144 about 12 hours behind--

GFS like the Minardi at the back...

@Retron - Icon 180...

Oh, I don't know - even GFS has a corker of a run in its ensembles, a nationwide plunge of -10C 850s from the north. It's been a long time since we last saw that and it probably still will be, given the odds of a single member coming off at that range!

http://www.meteociel.fr/modeles/gefs_cartes.php?ech=192&code=10&mode=1&carte=

To me the models are still in a state of flux, although at least they should be back to more or less the full set of data now.

As ever, it'll be interesting to see what ECM comes up with in another hour and a half - it used to share code with the old GME model, but that's been replaced by ICON. I don't know whether the relationship between the two centres has been kept up!

ECM looks interesting this morning.

ECM follows the Icon - around 80% ...- just slightly east

GEFS doesn't offer the ECM op much support, although P4 looks quite similar. I expect ECM op 850s in south eastern England will be well outside the standard deviation (clustering) in the ECM ENS this morrning.    

https://www.theweatheroutlook.com/twodata/gefs.aspx?run=na&charthour=174&chartname=ps_500hpa&chartregion=na&p=1&charttag=PS%20500hPa%20(GPDM)

Ensembles show a more disturbed period from 7 Jan, and cooling generally down to average or slightly below - perhaps a bit of wet snow on higher ground? Screaming northerlies seem to be outliers still, both in the ensembles and operational runs.

GFS Ens mean steadily declines- take away the 30 year mean line and it might look encouraging.

https://www.theweatheroutlook.com/twodata/chart.aspx?chart=/charts/gefs/gefsens850london0.png?cb=628

A click on Brian's postage stamps link shows clearly how much variation there is in the shape of the HP in a week's time, but the orientation often allows for ridging to the N or NE. That signal could be encouraging.

Pleasant ECM this morning trying to give us a Scandi. GFS awful once again 

-10c 850s just into Kent at day 8. Block looks like its fighting back at day 10 as well, 

http://www.weersite.net/?actueel&ensemble&ecmwfpluim 

Even if a cold outbreak comes from the north I don’t think it’s likely until after 20th Jan at this rate. Originally met had the turn of new year progged for a chance but whatever signal remains obviously wants to stay out in the far reaches. It may even slip into February(?)

This could be a clear example of how stat warming often plays no part in a cold outbreak for the UK

I have a suspicion (note - I can't back with evidence) that the Met Office are less inclined to make changes to their 16 - 30 day text based forecast during the Xmas period. Therefore their next significant update will be interesting. Will it keep the cold signal or push it back?

These are yesterday's 12s I would expect a significant shift to cold this morning 

I also have a suspicion that if, for example, the models they use have been consistently showing one outcome and it suddenly flips, they won't change the outlook straight away, instead waiting to see if it's backed up... sort of like how the BBC used to wait for two different sources before reporting a story.

Well the ECM means look Shiite sadly

They were out before 8 AM?

(That'd be very unusual for the full run, which is trickling out now on the usual sources.)

ECM 00z was literally off the scale for the south east. 

Yes, I agree. 

I’m surprised we’re not seeing the wild swings and options on later GEFS that a zonal reversal should in theory generate but that might still start today.

Working as office day today so perversely more time to study data 😉

Martin