Easterly promise still there this morning starting about 168h. GEM the pick of the bunch but GFS and Para also good.

The 18z was good enough for me! So here's round two, currently with a "start of deep cold" day of the 5th Feb.

Remember, these are for London on the Meteociel charts. The blue-haloed bit of the chart represents sub -15C runs.

Round one maxed out as 16 members below -10 (of which 2 were below -15), so we're already ahead. Will that continue, or will this potential cold spell wilt away to nothing as per the last one? We'll see over the coming days.

Oh these are wonderful. What’s you threshold for ensemble members to start thinking this is happening.

32 members going sub -10c 850s within 24 hours 

Cold cluster starting around the 5th. Lots of spread though

ECM makes it a full house of easterlies again this morning.  To early for details but could be a significant cold spell.

I no what you mean. I stayed up for the the full 18z to come out, and was very happy, but was convinced it would be gone on the 00z when I woke up. What a surprise.

That wouldn't be much fun - the thrill is in the chase!

As for the criteria, it's a number of things. A sustained signal in GEFS for one, not just one or two suites which show something good, but a couple of days' worth. A decent number of members bringing deep cold or close to it to the London area. Multiple model (if not cross) agreement of a push of cold air, too.  A decent time-frame, not just 384 but a bit closer - ideally the 10-12 day range, when we know the models can often pick up trends but not details. Consistency in other words.

I'll update the chart tomorrow morning, but FWIW this morning had 14 for London and no -15s.

If anyone cares the -10°C.t850hPa count for here on the 00z GFS suite was an impressive 25, which is the highest I have counted so far. Lots more cool or even cold rain, thanks to the easterly influence.  (And yes with -10°C t850s it can still rain here when there is an easterly component).

Encouraging signs but so much can and probably will go wrong ( if you are after a convective easterly) .240 hour charts will usually look significantly different come the day.

Personally I would like Tuesdays low to stall here and move back south delivering heavy snow . That is what I am looking out for.

Well, we’ve had that same old rollercoaster, have’nt we just, similar in its switch-backs to the last SSW event in 2018 (air brush the other non-event), and probably there are a few perturbations to come, but when you look at the average - and you see that it stays -5 (more or less) to the end of the run, you know something is up and cautious ramping can begin. This is so rare - as warrant mindful enjoyment of the ride. I love the GFS Op displaced PV spinning on a Ukraine axis and with promise of its deep cold, Catherine wheel of delight, freezing the bejesus out of the UK past the end of the run, the Jet supporting this. All models aligned more or less, and some very exciting mess in the interim...

Better prospects of cold air - enough to qualify IMO as yet another flip -  on http://www.wxmaps.org/pix/temp4 with major push across N Europe and 'patches of blue' in various parts of the UK, not just in the Highlands, in week 2. Still plenty of rain/snow in week 1.

GFS - LPs continue to run up to/ across UK for a few days yet but on ever more southerly tracks with more air being drawn in from the east/ southeast, eventually that on Wed 3rd connecting with LP over Scandi and bringing in a full NE-ly by Fri 5th. HP develops over Scotland Sun 7th pushing the easterlies down into France and then topples over the UK cutting off the E-ly flow but hints of retrogression later that week with more continental influence returning.

GEFS - chart posted by Ally  above indicates, for the S, cool this weekend, a mild blip Tue 2nd, then cold/ very cold around Sat 6th Too much variation after that date for any confidence though op and control both remain on the cold side. Less rain than yesterday but still quite prevalent to ca Thu 4th. Scotland rather different, staying consistently cold to the 6th and rain/snow only now and around Wed 3rd. Also quite variable after the 6th.

ECM - the LPs from the Atlantic briefly connect with that over Scandi briefly Mon 1st but after that stand off in the Atlantic leaving UK in slack pressure with little indication of an E-ly. Hp develops Sun 7th as above

I wouldn't say a decisive shift to cold but I would say the balance for the mid term has moved towards chilly/cold and away from mild or very mild. It's not a massive shift but enough at the moment that I'd be confident of colder weather setting in for a time. That's south centric, further North and I'd be more confident of seeing colder weather although as Doc may have mentioned not necessarily a dream set up for all!

At the moment the flow does seem to be moving towards colder weather countrywide but then I thought that a week or two back and the next set of runs removed that. If we're still moving in a cold direction on say Saturday or Sunday I'll be very interested but at the moment it's nice to see but could just reflect noise in the mid to long term. 

I’d agree that there has been a big shift, but there are subtle changes that peak the interest. It’s painful, but I do think we’ve move ever so slightly forward. For me at least, it was the 0z at least holding onto changes we have seen from the 12z and 18z. 

I think the general pattern is there, I think I want to jow see upgrades. The next four days for me are pivotal, if we are still seeing cold ‘lite’ by Sunday, my interest in this winter will be finishing rapidly. 

Tend to agree. The signals for something cold is certainly still there in 00zs but model to model there seems no consistency as to how we get there and in what shape or form it takes.

The famous phrase 'more runs needed' has never been more apt. 

There's a clearer signal for a cold incursion. Whether it lasts or not is a different question and I suspect things could be quite messy. 

At least now is 6 days countdown for the drop than over 10 days away, if wasn't the interfering mild blip it would be today the last day of mild weather.

Obviously nothing is ever certain but an easterly is looking likely this morning.  ECM mean at day 9.

https://www.wetterzentrale.de/en/topkarten.php?map=1&model=ecm&var=2&run=0&time=216&lid=AVG&h=0&mv=0&tr=24#mapref

If high pressure does start to become the main factor wouldnt bet against a 2006 repeat....UK under a benign Rex high daytime max 6 ,while Eastern Europe gets the sort of freeze where my Polish friend said " spit frozen " !!!!

It's looking good for you Jiries for Saturday and perhaps again Sunday.  ECM giving the west Midlands another 10cm or so Saturday and again Sunday but more marginal.