The Enforcer

Will there be some polar air? Probably. Will it be as cold as some runs have suggested? Probably not. Will there be an immediate return to extreme mild conditions as shown by the latest 12z ECM Operational run? Probably not.

Only going from cold rain to not quite so cold rain.

Fortunately those pants are 18 runs away.

For some locations, even widespread showers moving in from the East don't travel far enough West, for example, everything the 2010 easterly tried got blocked by the Chilterns and snow only arrived courtesy of a trough coming in from the south-west. So organised fronts/troughs/disturbances can be better.

Well any sort of frost should be the first objective for this upcoming cold spell, given a total absence of frosts during the autumn season, which must be unprecedented in an inland lowland location such as this.

As if to prove your point, the BBC app T+0 forecast states 2% chance of rain here. And it's raining.

I can never figure out how the warm SSTs don't prevent snow from falling on the French coast or over the sea at 0m ASL, but do stop it falling over the Chilterns at 250m ASL.

A frost would be nice.

OK, so I am expecting some unsettled weather at some point over the weekend. But BBC have surpassed themselves this time. No sun at all at any point. Here is their current take on Sunday: Even someone with the most basic grasp of reading weather charts can see that there is zero prospect of it raining continuously for 24 hours (37 hours if Saturday is included). If they can't come up with a forecast showing precipitation of the heavy, but transitionary type, with sunny intervals in between, then just don't bother making a forecast.

That chart does demonstrate that it is a reasonable expectation for the UK to receive a polar maritime air mass for a couple of days or so, before the mobility of the overall current pattern moves it on. The good news for the UK is that the polar maritime air source in question appears to be stronger than in recent years. Therefore, whilst the time it spends here may be limited, it could still have a significant impact.

Looks even more wrong now that the timeframes match: Unbelieveably they are still in denial, referring to South Wales & the South-West:

Looks even more wrong now that the timeframes match:

Thought it was worth copying this here, as it is more relevant to your region.

What an awful nowcast - organised precipitation just skirting the southern edge of Wales: Actual situation - organised precipitation about to cross most of Wales:

Still consistently messing things up at T+144. At least it hasn't got any closer:

GFS 12z increasing the snow potential - it is going to take it to T+0 before it declares a false alarm?

00z GFS still in denial showing a mostly snow event:

Still there at T+144:

Imagine an alternate reality where models were held to account for their forecasts in Question Time type debates and phone-ins, quite unlike what happens in our reality where the next day they simply pretend the erroneous model/forecast never happened and proceed to churn out more of the same with apparent impunity.

Ah yes, the ubiquitous party-pooper mild sector, which of course is entirely absent on 12z GFS, showing an all-snow event: Don't worry, it will be corrected on Friday's 12z GFS. Yes, but only if they stand in the corner wearing a cone-shaped hat with a big 'D' on it.

The timeframe of interest is T+168, where that troublemaker first shows its hand:

No longer plumping for 'silly mild' in the period 13-16 Jan:

Close, only needs a minor adjustment:

It will be refreshing to see an ensembles chart where the operational run is not almost permanently locked in at the very upper end of the plausible temperature range like the 06z and the umpteen runs that preceeded it: Although I suspect the 12z will go to the other extreme and be a cold outlier.

Never trust hi-res GFS precipitation modelling. Snow forecast on every run until T+0: