Think many would settle for that 

I share your puzzlement to some degree.  The high N / NW needs to stand up and assert itself.  Its not game over yet but time is running out for the models to pick up on a strong lobe of that high to stick southwards to Scotland towards Christmas Eve/XMas Day.

We don't have "a few hundred feet" up in Essex 

Looking marginally better I'd say

Cold air a tad further South also 

Different at 138h , just goes to show the uncertainty 

The cold air is about 100 miles further south on this run. A tiny adjustment in global terms but hugely important if you’re somewhere in that 100 miles.

What a huge change in the synoptics by T+144 compared to the 12z. The main LP centre is stuck south of Greenland instead of off the SW of England.

Not a done deal by any means 

Yes - this is a major change. The juggernaut southern arm of the jet does reach us at T150, but has lost any northerly thrust, and dives off harmlessly to the south, leaving the cold air in place - and any little low running along the northern edge of the jet might well engage with that cold air, and a snow fest might be back on the cards...all to play for.

You might get lucky Marcus Snow into Midlands on this run

https://www.theweatheroutlook.com/twodata/gfs.aspx?run=18&charthour=153&chartname=preciptype&chartregion=uk&charttag=Precip%20type

Huge temperature gradient on the 18z

Hopefully a channel low can be achieved as shown here.

Could it be now leading the rally?

So I have come to a conclusion as to why so many models fail and hence the constant downgrades in model outputs!? - It's because we have a warmer than average Atlantic SST which is constantly fueling up the jet even more - prime example will be around +162z as seen on 18z GFS op run:

Low pressure begins to develop around the Azores at +162z despite cold air to our north and north east pushing southwards: 

By +174z this Low pressure system intensifies.

By +192z - it's into the UK and passed - thus flattening any ridge/block trying to build at the same time yet another LP system develops off the eastern seaboard of Canada. It's like we are getting cyclongenisis!? 

This is all occurring despite Greenland blocking and a -ive NAO etc.

So it's due to the well about SST's in the Atlantic which could be ramping up our storms and perhaps flattening ridges that attempt to build!?

GFS has a poor ending as it goes deep into FI, as the southern Jet powers across the Atlantic like an express train, and starts to buckle again, giving it some northerly thrust to hint at a mild start to Jan 22.   The Greenland high is modelled to be stronger than the 12z but still far weaker than last night’s pub run. The southerly thrust of the northern jet loops off to the east, and whilst the cold arrives, there seems nothing to hold it in place. The little low riding on the juggernaut jet is shown to intensify into a potential named storm and dump a load of snow over the pennies northwards. I think we could see a correction in either direction tomorrow. The BBC have now cancelled their snowy Christmas forecast in favour of a definite call for a mild and wild Atlantic driven post Christmas period. Still a mild sandwich, with a Boxing Day night frost, before a snow on northern hills event, thus far. There’s always tomorrow: However, I am used to clutching straws, I support Ipswich Town !!

Control not bad either and very different compared to the 12z 

Still some good solutions on the table for xmas outcomes still up for grabs.

https://www.meteociel.fr/cartes_obs/gens_panel.php?modele=0&mode=1&ech=144

15C in the south by the 30th. Surely this will be at the top of the ensemble?