Nafgem/gfs same thing really.

I can't see any difference at all between the 9Z ICON and the 6Z.

I've seen it before, and we saw it many a time in e.g. 2010 - the ensembles do sometimes shift en masse, and when they do it's usually because they've picked up on something which turns out to be key for the future evolution. For example, the low I'm worrying about on New Year's Day isn't critical, as whether it's deep or not doesn't matter in terms of the following few days - there will be something else that sets half the members off on a different track.

Usually once a "spoiler" has been found the ensembles then stick with and develop it, again 2010 being the odd one out - there were several times when something appeared to derail most of the members, but they then flipped back to extending the cold.

Who knows what'll happen this time!

I think its similar to what we've seen before with this cold spell in general. The big picture is pretty high confidence and has been for a while; but small (admitadely crucial) details are making a big difference.

I think it boils down to excellent high latitude blocking is working in our favour yet a chunk of polar vortex is in the wrong place and puts the UK near the battleground. The big picture is still good though so I don't see any reason to be any less optimistic as a result of the 6Z set.

I do. I can’t remember the year but it was a decade or so ago. Super Cell will recall if it he still visits. Heavy snow was forecast for the north and a prolonged cold spell. Not only was the snow forecast wrong only 24 hours out, but the entire ens suite flipped at 48 to milder

The AIFS 06z bears little resemblance to the GEFS 06z data in the medium to long term for what it’s worth.

GFS is often the first model to pick up on trends. Regardless, it is still considerably cold on the 6z, with running 7 day averages running at up to -4.0c or even less. (or is that 'more'? don't know how to measure that when in negatives)

Exactly 100cm at one gridpoint in northern Scotland on the 03Z run. 

The UKM high-res chart has a couple of -23C gridpoints at 129 hours too.

"Best charts for cold I've ever seen at T+x", "I never trust the GFS "00xz" "Probably the Christmas data" " All gone Pete Tong" "The north will get a good dumping" "I'll never trust the GFS again" " Biggest turn round I've ever seen between runs" "what a flip". "It's on a knife edge, more runs needed". "A definite downgrade"

Such fun and can be read every single year on TWO because there is always at least one such event every winter. But we will end by saying it is all because of climate change and we won't be fooled next year - but we still and always are 😀

It's another beauty from our robot overlords.  It's been very consistent.  Consistently wrong? Find out soon enough. 

It's automated pattern matching, and it'll be interesting to compare it in the years ahead to the traditional methods. I note it's already having to backtrack on the New Year's Day low, unfortunately! Here's the 6z (left) vs the 0z (right).

https://images.meteociel.fr/im/62/17064/ecmwfuk_0_78wos3.png 

https://images.meteociel.fr/im/73/19526/ecmwfuk_0_84zam9.png 

That chart is a correct representation of the UKM global. However, I've spoken to people in the past who have advised me to stick to UKV (or ensemble ones) temperature forecasts if using UK Met data.

I'm sure you're right, but my memory isn't good enough to remember the 2010 ensemble output wobbles. That aside, it will be very interesting to see what this evening's output shows.

I can't remember that. There was a winter about a decade ago when the long-range forecasts from the UKM were predicting cold weather, but it was constantly pushed back IIRC.

Here's a longer version of the clip I posted yesterday - you can see a few times when the suite flipped, only to flip back again:

https://i.postimg.cc/BbCwHzJ0/ani.gif 

And agreed, I'll be watching the 12z with interest. The ICON is rolling out right now, and even at 24 hours the first of the lows is a bit deeper, etc.

Thanks. I'd missed that animation showing the 2010 GEFS. 👍

The other side effect is that the cold air sinks further south, and faster...

We don't really get a proper cold feed in the south though - the trend seems to be for a straggling lobe of high pressure reaching southeastwards to cut off any decent northerly before it gets established.

It has a decent snow event in parts of central and southern Britain. I think we had an Arpege run recently (yesterday perhaps) which showed something similar.

It even has some snow on the ground here, on the paradise Isle of Sheppey! Impressive, and shows what can happen if that troublesome low doesn't deepen as much (and thus takes a southerly track). Snow and lighter winds, what's not to like! 😁

Not in this universe