As far as I can see the difference from the 00z Op and the 6z Op is all down to small differences in how the jet behaves as it exits the US. Shows how fragile the local pattern is for the UK.

I imagine the ens will have a similar look to the 00z set - some cold, some average to mild and hard to pick a most likely outcome.

All good fun

There are still some very decent runs in the 6z Ensemble suite.

It's not over yet! Have faith.

Yes, the Ens do give some comfort. Liverpool on Xmas Day evening have 17 members with 850's at -5c or below including the Control (-6.5c) and Op (-8.5c).

The nirvana would be snow setting in in Xmas Eve afternoon and not stopping until the early hours Xmas Day, and that broad scenario has shown on a few runs, but it's always going to be lottery-winning odds to get that just perfect. At the moment, the chances of that have very much receded per the MO.

Downgrade on ensembles. 0z there was a clear cold cluster and a clear mild cluster. Now we are back to a random spread between mild and cold from Christmas. I prefer the former because you had a 50/50 chance of cold. Now it's more like 33% cold, 33% average and 33% mild. So lower chance of decent cold but really still as much chance as the other options. Unfortunately we all know which way the dice usually falls.

Busy with other things but watching the slow motion car crash in here with some amusement.

Does anyone really think 500 miles either way is relevant 180 hours out?

If we think back to the output over the last week we’ve had all manner of options which have come and gone. The one consistent theme has been the models struggling hugely with the jet stream profile through next week. We’ve seen changes feeding through in the amount of energy in the jet and how much goes into the northern and southern arms. That’s moved on to pushing energy right through the prime meridian. This will continue to evolve as new and better signals emerge about how the atmosphere is behaving; the recent trends could continue or change again.

Whatever happens it's more exciting than the usual situation where the only thing to wonder about for Xmas Day is exactly how strong and mild the southwesterlies will be!

Quite why it is so difficult to predict the jet in a blocked scenario compared to the more typical westerly flow, is a little harder to understand, apart from the obvious that blocks are relatively rare and the data less numerous perhaps. `your thoughts on that would be of value.

It is all very interesting and a tad tantalising - even if it does crash and burn - like so many before - in slow-mo.

Will we see the Met Office long range forecast change given this mornings 06z GFS?

UK long range weather forecast

Tuesday 21 Dec - Thursday 30 Dec

The start of this period is looking to be settled and predominantly dry with large amounts of cloud. Isolated mist and fog patches developing in clearer areas. In general, cloud amounts will tend to reduce with time, with a corresponding increase in the risk of overnight fog and frost, which may be slow to clear by day in some areas. Towards the middle of the period, there is an increasing chance of more unsettled and windier weather affecting the UK, with rain, and perhaps snow, possible for some places. Temperatures will generally be near to below normal, perhaps rather cold in the south, feeling chilly where any fog persists, and locally mild in the north and northwest.

Updated: 14:00 (UTC) on Thu 16 Dec 2021

My very simplified layman's analogy would be that the flow of water in a stream is (relatively) easy to predict. Throw a big rock into the stream to disturb the flow, and suddenly the chaotic nature of all the small ripples and eddies becomes way more complex to predict or model. Chaos theory in full effect. I'm sure it was someone on here many years ago who also described it as like making a horse walk backwards. I liked that one too  🙂

Of the GFS run, there are 9 perts that bring Boxing Day cold, and the same number that deliver New year cold - some right through: Thiis is just under a 3rd, and perts at this ratio have been the only consistent factor in this unveiling mystery as to the actual Christmas weather. This means we have a 30% chance of seeing cold at Christmas, and the same for New Year. 35% deliver Meh and the remainder quite mild weather, some (like the OP) end up exceptionally mild: 

no not on one run

Not really that much difference between the 00z and 06z GEFS.

Good illustrations, those. 

meanwhile, whatever’s going on out east looks increasingly short lived..

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

They will have I pick one set of runs (trend of a couple) to make their written forecast so that written forecast will have been off the back of the last couple of runs which were rather cold

Today has changed so far….see what 12z shows soon

it will probably get re written slightly if there is a clear shift 

Mass public will have absolutely no memory of what the previous update said lol. My elderly parents will not be saying “that said cold yesterday” 

Key change in today’s update:

“ the threat of rain or wintery conditions increases”

Note the odd and unusual spelling of ‘wintry’ / ‘winter-y’

Looks like the south west will bear the brunt of any wet weather.
Remember wintry can mean cold rain as much as blizzards.

in other words, it’s looking very uncertain, although they don’t mention low confidence 

https://www.theweatheroutlook.com/twodata/gefs.aspx?modelrun=na&lg=850&lglocation=london

While the control and op don't look too good after Christmas, there's still a clear cluster of cold on the GFS spaghettis.

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

Interestingly, the cold cluster is more marked on the Dublin ensemble.

But things will quickly change if the cold arrives and becomes stubborn. I think the atlantic seems to be forecasted to sweep through Europe a bit too easily considering how much blocks alter the weather once embedded IMO

For me - thats the curve ball in all of this... makes it all quite exciting. For now the models just offer titilation

Looking at GFS 168hrs any more downgrades will be staring 

Full blown  East Coast cyclogenesis in the face 2014 style

The 12z GFS is another stinker.

By midday on Xmas Eve, all of Wales, almost all of England is in positive 850hpa territory.

Once again, the highway for lows is directly over the UK between a block to our north and a huge high pressure belt to our south.

The angle of attack for the low on this run is particularly horrible for the UK (as in, it feeds much milder air over us before it)

A pretty rotten 12z GFS and UKMO not much better.

But let's wait again till see where it sits in the Ensembles and bear in mind that things will change in a week.

GFS having an absolute mare at the moment all over the shop. Horrific 12z.