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Here’s the London 12z for 850hPa:  

https://www.meteociel.fr/cartes_obs/gens_display.php?x=&y=&run=12&ville=Londres&lat=51.5085&lon=-0.12574&runpara=0&type=0&ext=1&dmode=1 

Thanks Brian, that is incredibly interesting and useful. Is this available on TWO models - can't see it? GFS shows more uncertainty after 5 days then remains fairly constant whereas ECM, as would seem more likely, increases in uncertainty after day 2 until day 7 when it becomes constant. Both seem to have an SD of about 10 after a week which would put outliers after a week at 20C, which I think means +/- 10C from mean at point of interest. If there are more up to date statisticians on here please correct me if I have this wrong.

Indeed, and there’s been a marked shift in the ensemble suite too: the cold cluster has been reduced to a handful of cold options now.  Since ECM is showing the same evolution there seems to have been a marked signal now for the block to give way.  Could all still tilt back, of course.

It never works the other way.  Unfortunately we look to be transitioning into a very wet period with the jet directing systems right at us.  Whether it was luck or physics the UK always loses. I dont think a single ensemble brings that deep cold to us. Incredible 

Everything in this county is broken. Even the weather. 

I agree - it perhaps has been one of the most frustrating winters for model watching with the ECM flips as well as GFS's each run and it's been very inconsistent. The annoying thing is that the models have shown easterlies time and time again this winter only for them never to verify. We are in a slack easterly now but +2.5c and cold rain with sleet doesn't do it. I wonder if we all need to look at the wider picture? why are models showing easterlies and bitterly cold weather only for it to backtrack? At least last winter of 23/2024 (although was mild esp Feb) - the models were not constantly flip flopping and teasing us with an easterly. I have lost track the amount of times we have seen the models flip, run after run and day after day - this occurred several times back in January when what was shaping up to be a prolonged cold spell and easterly - turned out to be a damp squib. Which leads me on to the next thing? - If the models are becoming more unreliable then why are we watching them all the time? Sorry to go OT but it's worth looking into as to why the models have been so poor each run.

I also wonder if this is happening for several reasons? 1. The colder than average airmass off the NE seaboard of USA/Canada or 2. The fact that the N. Atlantic SST's are in such a warm phase compared to 2017/18 (our last colder than average winter) The reason I think this is because warm air contains more moisture as we all know so a warmer N. Atlantic could denote more intense storms coming in and thus milder weather so maybe to get colder weather we need the N. Atlantic to cool down.

There is no shortage of cold - there have been ice days and snow on the Gulf coast of USA and Florida and there has been substantial snow in China, Japan etc - just never our part of the world.

That UKMO0Z 168h chart would bring extreme amounts of snow to parts of the UK with a stationary front lodged across the UK making no progress but with a huge temperature gradient across it.

Have you seen the dewpoints on the op GFS, Q? Incredibly dry air down here sets in over the weekend, persisting into next week. Even here xc is showing -9 dewpoints, with -12 at Heathrow:

https://www.xcweather.co.uk/forecast/heathrow 

That's a proper Arctic airmass and would be fantastic to be out in - it would also finally dry up the incessant mud that's everywhere. The only downside would be static shocks all the time!

Yeh that's pretty ridiculous. Its one of the more severe undercuts I've seen causing a ridiculously low lapse rate in some parts. The freezing rain and ice pellet risk would be very high if it came off like this. We have that ultra cold dry air extending far west of where the 850hpa level warm front is.

https://www.meteociel.fr/modeles/sondage2.php?mode=0&x1=224&y1=86&ech=120&map=0 

By gummy look at this profile:

Surface (from 2m charts): -2C

1000hpa: -1C

900hpa: -1C

800hpa: +1C!!!

700hpa: -5C

Wet bulb is well below freezing throughout and the dewpoint drops to -26!!! at the 850hpa level.

With that sort of dryness (around 30% RH, FWIW, with +2 / -12) I'm not sure there'd be much of any type of precipitation around, at least inland! Those are the sorts of figures we used to see in the proper easterly spells in the 80s, although as snow showers moved in the dewpoint would inevitably rise closer to the air temperature. Seeing snow magically vanishing via sublimation as a kid sticks in the mind - sunny with snow on the ground, temperatures well below freezing, dewpoints close to -10... the nearest we've come to that was in 2018, with the Beast bringing similar conditions.

https://www.wunderground.com/dashboard/pws/ILEYSDOW1/graph/2018-02-28/2018-02-28/daily 

(My back garden WS records at the peak of the spell show afternoon temps below freezing with dewpoints around -10).

One to keep an eye on, anyway. The GFS has been alternating between an Arctic and modified maritime airmass over the past few days, sometimes with dewpoints in the -5 range, but this is the first time I've seen what I'd call an 80s style airmass to be forecast. Hopefully it'll become a bit of a trend!

Yeh good point, though I suppose it doesn't preclude low level precip under that ultra dry layer. ARPEGE is interesting, it has an upper level low remaining in the north sea which increases the negitive tilt and pushes the cold air further inland earlier.

Was supposed to be this week cold snowy with sun but completely disaster with all week less cold wet easterly so really need an exit out if no proper 80s styles.  

Is that the Woodcock comment? Are you declaring it over? 

Yes, definitely if it has the same result. 

Similarly the ECM ensembles are overwhelmingly on the cold side for the next 10 days down here, the median max from yesterday's 12z struggling as high as 4C here by day 10. I doubt this morning's output will be greatly different. (EDIT: It's crept up to 6C, and the scatter has increased too - so you still can't conclude anything, really!)

I'm also reminded of the way how even when we're in a cold spell (and we're in one now, albeit not a very exciting one), you'll seldom see agreement out to day 10, let alone further afield.

It's simply too early to call it, although obviously going down the "Sod's Law, it never happens so it won't happen this time" route will be too tempting for some!

Southern England / South east England would of had a Feb 1991 the last few days down here  - 30 years ago, what a waste!

Here are the main deterministics at t+168.

Getting to the point where I want to see strong heights to the south west now....Nice 18 degrees C for me now...

Yes. For ECM ENS the London link is:

https://www.theweatheroutlook.com/twodata/ecmwfens.aspx?run=00&lg=850&lglocation=london 

For GEFS35 the link is:

https://www.theweatheroutlook.com/twodata/gefs.aspx?run=na&lg=850temp_35day&lglocation=London&charthour=006&chartname=ps_500hpa&chartregion=na-region&p=1&charttag=PS%20500hPa%20 (GPDM)

or

https://www.theweatheroutlook.com/twoforecasts/gefs-35-day.aspx 

The temperature profile has been much as I expected, but the amount of precipitation has been significantly greater. I was also secretly hoping to see some snow falling (not accumulating) but that hasn't been the case.

ECM: Similar to GFS to Tue 18th but HP then intensifies over Britain rather than staying to the south

GEM: like ECM with an even more marked tendency for the HP to intensify over Scotland in the later stages.

GEFS: mean temps soon back to norm and staying there with good support from ens members to Tue 18th; mean continues near norm with the majority of members mild but weighted by  a few very much colder (op mild, control cold; in the N the support breaks up a day or two earlier). A little rain at first esp in S, continuing in small amounts in the N, then resuming generally and heavier around the 18th. 

Thought that was the angle you were going for, ECM the hope today as it shows Atlantic fizzling away and HP building. Still a crumb of hope