Man With Beard

Knife edge stuff at T192. That low in the Atlantic needs to keep coming!!

From a quick look at the 51 individual ECM ensembles for January 15th, I suggest around 70% get a cold pattern across the UK by this date, and the other 30% are a mismash of synoptics that prevent the cold. Interestingly there's not much difference at T144 between some of the runs that eventually go cold and the op run. Must be a close run thing. To be honest, these kind of synoptics before a cold spell are nothing unusual - I think the problem for NetWeather junkies has been that the ensembles were just so ridiculously strong 48 hours ago, that even a return to a normal build up to a cold spell, where there's a bit of scatter, looks like a huge downgrade.

Once the cold is in, a different pattern can maintain the cold. The chart for December 25th 2010 doesn't look too cold yet delivered max temps of -5C across some central areas, because the synoptics held in place the cold delivered earlier in the week. This is particularly true in January when there is less daytime heating. But as you rightly say, the current issue is getting the cold in to begin with!

Really not sure where we go from T168 chart, and totally different to 00Z

GFS12Z - the cold is still going to win at around D9 but a closer call - with the low stalling west, any increase of heights from the south may have kept the cold from pushing too far south - however, it doesn't happen and a front is allowed to hold across France keeping mild tucked far away.

It slides into France, mild air stays to the SE of it. Wouldn't want it to stall in Biscay though.

That low running into France T150-T180 locks us on the cold side of the incoming northerly. Definitely something to watch for in the next 48 hours, as this would be a key ingredient for ensuring the cold gets south and no nasties from Iberia/Azores can get in the mix.

It kind of feels wrong to post this on a day John Holmes of all people is bigging up the cold, but it must be mentioned that a really firm Greenland block signal doesn't last more than a few days on the ECM clusters - doesn't necessarily mean the end of cold and snow as the overall pattern remains pretty messed up beyond 17th January, but chances of a prolonged cold spell would be a bit more doubtful. Still, of course these are D11-D15 charts so much could change particularly in the absence of agreement. Original post: https://community.netweather.tv/topic/99706-model-output-discussion-into-2024/?do=findComment&comment=4997558

It kind of feels wrong to post this on a day John Holmes of all people is bigging up the cold, but it must be mentioned that a really firm Greenland block signal doesn't last more than a few days on the ECM clusters - doesn't necessarily mean the end of cold and snow as the overall pattern remains pretty messed up beyond 17th January, but chances of a prolonged cold spell would be a bit more doubtful. Still, of course these are D11-D15 charts so much could change particularly in the absence of agreement.

Wow, John Holmes going for deep cold, that is a collectors item! Have to agree about the NOAA, they are really bullish about the block to the NW. Thanks for your insightful analysis John, we all appreciate it

North Scotland totally buried ... and the south coast gets fractionally clipped by a low sliding into France. But the run goes on...

The anomaly is actually slightly less but that's only because it was ridiculously high. It still is ridiculously high.

Latest ECM mean definitely not as hot with the Greenland High. But I'd still have bitten your hand off for the chart a week ago. Flow is still from north for UK.

Amazing model viewing at the moment. The GFS in particular is like a Christmas special on "Best British Winter Synoptics"! Each run is severe in an ever so slightly different way

Great update Mike. I note there's a lot of low pressure running into cold air in the D11-D15 period, either over us or just to the south. Whilst that eventually threatens the security of the NW block, it would bring a substantial snow risk into play. All fun and games for the moment though!

Yes, I think you've spotted the way out of this cold spell. The Greenland High would still verify but a blast from the Azores might create a dividing line between cold/mild - all speculation at the moment.

I'm not really bothered about the ECM op tonight beyond D6 - it's all about the mean

It's a weird thing - over the past 15 years, most of the significant cold spells have been picked up well before arriving - 2018 beast from the east was remarkably counted down literally from D15 by the GFS mean and 2010 was fairly well signalled aside a slight wobble just before the infamous Christmas freeze-up. Occasionally there's a late surprise (Jan 2013) and a massive fail (Dec 2012). But when the signal is really strong on the mean charts (not ops), it tends to deliver even if that signal is beyond D10. I'm starting to think we're in that category for the period Jan 15-20. But I'll be nervous all the same until D4 .

Please, do not even think about calling this chart marginal! (but feel free to call it FI )

Regulars on here know I'm not prone to overstatement but this really is the most wintry T300 ECM mean chart I have ever seen. Incredible signal at that range. I had to check about 10 times to make sure it was the mean and not an outlier member!

2 ECM means on the bounce going for an Icelandic High at least for a short time - this type of high has led to some of our best freezes in recent decades:

Actually, it's snowing properly now. Light and a bit sleety, but settling on some cold surfaces. Just a little more intensity and we could get a covering. That's fine lol! Glad to hear you have something to report in the snow desert of Paulsgrove

Heaviest snow here since 2018. Translation: A few bits of dandruff observed falling when using a microscope

Cold and snow lovers, let someone slap you across the face if it means the ECM D10 verifying. It's the real deal - Scandi High with a cold train incoming and instability likely to produce white stuff.

I completely agree. The model is quite incomprehensible tonight. T0 charts are rarely so complex. I wouldn't trust it. There again, there are times when bizarre GFS run are a sign that a shift is coming in the modelling, so although I don't trust the run, I can't completely ignore it either.