On the plus side, Gfs 18z suite looks like taking a dive mid month onwards. Late Feb would be last chance saloon for any meaningful snow however, especially in southern England. 

Indeed, everything on the table. It’s clear that GFS overplayed any snow from today’s feature, as is often the case with GFS. I like ICON and ARPEGE for short term snow output. Absolutely no clue from a scientific perspective what we will be looking at in a weeks time, but I’ll stick to my narrative that whatever the least exciting option is from a weather forum perspective, it’ll have little problem eventually becoming that, most of the time. 

Some exceptionally cold 850s (sub -10c's) but also some milder runs. 18z Control plunges us into the freezer.

For London the ECM Op was not an outlier. It’s somewhat annoying when people misuse that term. Only at Day 15 was the Op unsupported by any of its ensemble suite for both 850hPa and 2m temperatures.  The 2m temperature in the Op was in line with the mean out to Day 5 and then  only 2-3c below the mean for the next week.

https://www.meteociel.fr/cartes_obs/ecmwfens_display.php?x=0&y=0&run=12&ville=Londres&lat=51.5085&lon=-0.12574&type=2&runpara=0&mode=1 

Essentially there are two groups - a cold one and a mild one. The Op manages to start on the cold side before ending up in the mild one in FI.

Fair analysis 

As you know, the reality is that what happens next depends on what happens next…

Referring again to the 850’s, EC 12z op was barely supported with its going off the rails characteristics. 

 https://www.wetterzentrale.de/en/show_diagrams.php?geoid=49069&model=ecm&var=2&run=12&lid=ENS&bw=1

GFS ensembles getting better but still show a short lived cold spell.

https://www.wetterzentrale.de/en/show_diagrams.php?geoid=50893&model=gfs&var=2&run=00&lid=ENS&bw=1 

GFS Op 00z: HP over Baltic and/or Norway typically 1040mb to Sat 15th with SE-lies for Britain bringing in cold-ish weather for Britain from SE Europe. The HP then moves north to Greenland and/or Iceland with much colder and more direct easterlies originating in N Russia. This E-ly push gives up just as it reaches the N Sea Tue 18th, and the Atlantic steps in with a large LP gradually approaching Ireland, the wind switching to S-lies but still rather cold, drawing on the cold air deposited there by the foregoing E-ly. Final chart has 960mb Brittany with Britain under a mixture of air from both Greenland and a cold continent.

ECM: the Scandi HP moves to Iceland earlier leaving Britain Thu 13th to Mon 17th in a no-man's-land between LP Atlantic and Russia and HP Iceland but looking cold, before converging with GFS on Tue 18th.

GEM: also a pattern change from Thu 13th but in this model the Atlantic wins easily and Britain is under milder SW-lies from Sun 16th onwards

GEFS: first a little below norm then a little above, to Sat 15th when ens members divide; the majority incl op and control extremely cold (8 to 10C below norm) though a significant number stay mild esp in the W. The freeze ends for most around Fri 21st but by this time a wide spread of outcomes. Small amounts of most likely rain in the S fair chance of snow in the N, dry for a few days around Sat 15th in the S, dry for a few days now in the N.

https://www.wetterzentrale.de/en/show_diagrams.php?geoid=50893&model=ecm&var=2&run=0&lid=ENS&bw=1 

Agree. Doesn't look impressive on the grid point used by TWO, but there is a big split as you say.

You did say ‘outlier’, so at least you’ve backed off that, I suppose.  As for ‘going off the rails’, that could describe your attempted analysis, I think… 🙂

https://charts.ecmwf.int/products/aifs_opencharts_meteogram?base_time=202502080000&epsgram=aifs_classical_10d&lat=51.3973&lon=0.921564&station_name=Leysdown-on-Sea 

(Other locations are available, of course).

Things seem to still be wandering slowly towards a colder solution in the medium to long term, with both GEFS and ECM ens featuring a noticeable uptick on colder solutions versus a couple of days back. It's not a convincing signal though and the mild scatter suggests that's still an entirely possible outcome (worth noting there's very little mild in the GEFS at T2M level from 17th -21st). 

ECM ens are still less keen on colder 850s which just highlights how finely balanced the pattern and if you looked at MOGREPs you'd assume a bit of chilly air might be on offer but not a lot else, albeit they only go to the start of where the colder spell looks to potentially set in, so I guess not surprising. 

Promising baby steps towards cold but quite possible for the signal to reverse with minor changes. More runs and all that.

Annoying thing is it wouldn’t take much adjustment but the trend at the moment is too SE’ly for the south and south east. Will feel bitter

>200m: Rain

100m-200m: Mix (rain more likely for higher, snow for lower)

<100m: Snow

0m: Snow is guaranteed to settle (though could quickly evaporate) and will be extremely dry and powdery.

Even before the proper deep cold arrives, you can see well below 200m for most parts Monday onwards.

*Technical details

The wet bulb zero level is the temperature at which the wet bulb temp goes below freezing. The wet bulb accounts for the cooling potential of non saturated air and usually sits half way between the dewpoint and the temperature. A snowflake forms a bubble of humidity around itself that is going to be more saturated than the environment so evap cooling won't cool all the way to the dew point (unless the temp and the dew are nearly the same). So the height left over is essentially the distance the snowflake has to travel before completely melting once evaporation has been taken into account. Its not zero because melting also cools the snowflake (though to a lesser extent than evaporation) and it also takes time to fully melt the snow flake.

**

The time period we’re interested in however is 7-10days so lots to resolve and even though the result is far from decided, we’re in the game.

It's on TWO here:

https://www.theweatheroutlook.com/twodata/gfs.aspx?run=06&charthour=3&chartname=ukwbt&chartregion=uk&charttag=WBT 

Perhaps the current adjustment has not notice to anyone as now next 10 days is fully overcast wet, frostless, snowless and less cold temps.  Gone the sunny days expected later next week.  I truly hope Taylor rightfully negative post yesterday come true to get out of this pointless less cold easterly.   My knowledge that SE winds normally bring sharp clear skies and real cold are not happening.  My chase now is to get out of this set up asap.

That's wetbulb temp rather than zero height. Could you add wet bulb zero height? I'm not sure whether its best to go from the bottom or the top to find the zero level. But wet bulb height is a little better than temp for precip type since it tells you about the snowflake's journey through that low layer.

Actually you have the 0 level for temperature, so it would just be the same thing but for Wet bulb

https://www.theweatheroutlook.com/twodata/gfs.aspx?run=06&charthour=3&chartname=0c&chartregion=uk&charttag=UK%200C%20isotherm .

Mind you the 0C temp height is still a very good measure, just maybe add 150m to the figures I gave in the previous post, so 350m is the threshold rather than 200m.