ShinyDave

I already did, and I've gone full Brenda from Bristol over it. "You're joking. Not another one?!?"

Indeed. And the continental heat isn't going away is it? So if and when the plume setup does emerge...

I might genuinely move to Lerwick one day, especially if I get (even) more heat-sensitive as I grow older. Wonder if Rightmove has seen a spike in searches for such a move?

Was going to say that the breakdown/relief was trending slower on recent models by the looks of it - bodes ominously for Tuesday night at the very least.

That's how it's looked (and is certainly the most widespread, entirety of England and Wales with a tropical night forecast by the looks of this 12z!) but a slower breakdown would set up a lot more places to have a second such night even if it then doesn't hang around long enough for a third straight historically hot day.

At the very least this has to increase the risk of Tuesday night being oppressive for a wider area if the breakdown slows up. GFS 12z already has 27C minimum for Humberside (I still can't calculate that registering as a real thing that might really happen) and 24C for basically anywhere along and east of the A1 corridor.

More westerly peak than this plume too if it plays out precisely like that, which of course is an elephantine "if" at that range - the 40s are on the M4 corridor rather than the A1 corridor.

The lowest run there is 21.6. The lowest!

I'd guess the main question mark over the cold front timing is going to be if entire swathes of England get a Tuesday run at the record or if it's just going to be the East Midlands/East Anglia that realistically get enough time for historic maxima. The macro setup is locked, and it's locked into the pattern that make the "edge cases" of a few days ago look legitimately possible bordering on likely. Monday is locked as a historically hot day. Realistically it's just down to how far into Tuesday the pattern holds, which by the sounds of it will be almost a nowcasting situation.

Certainly 40C with British infrastructure is disruptive enough to warrant substantial intervention. Of course, the difference between this and COVID - or even storms like Eunice, the red warning for which caused one high-profile Twitter conspiracist to complain about the idea of a "weather lockdown" - is that for millions of people, this danger is actually worsened by staying at home. That is another complicating factor in any emergency response plan.

Worth noting the details of the warnings. There's now three areas with warnings. The red one is essentially a London-York-Manchester triangle ignoring the Peak District; that's for Monday and Tuesday. Then there's two separate non-overlapping amber areas - one for Sunday-Tuesday covering almost all of England and some parts of Wales, one for Monday-Tuesday covering essentially the rest of England and Wales plus parts of southern Scotland. The second of these only projects medium impact, the first has high impact and therefore could be upgraded to red with higher confidence. Not surprised the Heat-Health Alert upgraded to level 4 at the same time - figured it would be a coordinated move. Notably, it applies to all regions - wondered if there might be an exception or two, but no, every region has the same comments: "Emergency. Hot weather returns this weekend, peaking Monday and Tuesday, with very warm nights likely."

That is indeed some way past the record minimum. Literally only one run - which has the cooler air pushing in way ahead of any of the others - doesn't have a >20C "tropical night" minimum for London. Even the other low-end runs do! Sea temperature influence mentioned as a factor for the minima coming later; how much of that is offset by there being more daylight and hence less nocturnal cooling time in July? And that minimum record was set on 3 August 1990, which is: a) very early in August; b) the same day as the then-record maximum. So I don't see why a historically hot spell in the third week of July shouldn't be capable of producing record minima.

And if it goes all the way to 40 - which would only need the same size leap that the record took in 2003 - then there's a deeply symbolic power about that. (The 2003 record had its own symbolic power as the first 100F day but even at that point Fahrenheit was basically "the thing the Express uses for Big Scary Numbers" in this country, I think.) It's true that the press "cry wolf" and run articles based on edge cases, but the trend is real. Two of the hottest days of all time came in consecutive summers in 2019/2020 - by local maxima the #1 and #3, by CET the #1 and joint #2 per Squeakheart's post - and the summer before that might actually be more remembered for its heat because of its longer duration. It seems like every year there's the threat, often realised, of a Spanish plume randomly dropping a day hotter than any in mid-C20 British history. (To say nothing of what that implies for the level of heat in Spain itself...) The press bring an awful lot of noise, but there's an alarming signal too.

Not to mention how many of them are big fans (no cooling reference intended!) of government non-intervention as an article of faith. If central government aren't going to do it, other and more normally functional bodies should - the most helpful response I've seen so far is from the Mayor of London, who implemented an emergency response for rough sleepers (using a mechanism usually used/presumably intended for winter cold) as early as Wednesday. Even that is relatively generic and doesn't respond to the gravity of what could be coming.

Mine's arriving tomorrow. Very relieved. Some of these model runs look like errors but there's genuinely too many of them in that direction at too short a timeframe to rule them out as FI nonsense. Obviously the subtlety around precise placement of the upper low in particular makes modelling very complicated even at medium range, but zooming out, there's precedent for records to go by big chunks. France's went by 1.9C (44.1 -> 46.0) in 2019, and Canada's went by even more last year (via multiple consecutive record days). And the August 2003 UK record was a 1.4C leap (37.1 -> 38.5), and of course a leap that size next week gets us to... 40.1. In short, the fact we've seen 38 only twice and a non-rounded 39 never doesn't mean we can't see a 40, because record-breaking doesn't have to be as incremental as it was in 2019 when 0.2C got tacked on to the 2003 mark.

The "who" is apparently Steve Barclay. He was previously the Downing Street Chief of Staff and called it "a priority to restore a smaller state both financially and in taking a step back from people's lives" when he took that post in February, which would be consistent with your theory he might be skittish in calling an emergency. But with so many moving parts at play (and numerous relevant stakeholders as you say) I don't know how much a reticient Health Secretary would stand in the way of this; needless to say, we're in unknown territory here. We've already seen an emergency activation from the Mayor of London seemingly targeted at supporting rough sleepers, and I believe one local ambulance service moved to their highest level of alert specificially citing heat alongside COVID absences in their own staff, so there's evidence slowly gathering that relevant individual stakeholders not bound to central government declarations are prepared to take their own action as needed. I'm sure we'll find out more about which stakeholders have which powers in such a situation as it develops!

I did wonder what the exact mechanisms might be, knowing that these two aren't the same systems and aren't for the same purposes. I would presume that as the model runs keep coming in with historic-level predictions, that reinforces any decisions to initially lock in the red warning (because that's already at maximum for impact and just needs the confidence increased to go red), and then to activate Level 4. But the latter is an unrelated system and as you say has different decision-makers involved, because it's serving a different purpose (of readying health and social care). If the relevant decision-making mechanism is a Cobra meeting, apparently there was one on Monday - presumably the situation then was too fluid to lock in a decision. I don't know if there would need to be another Cobra meeting before locking in Level 4, or if some sort of agreement was made along the lines of "we go when UKMO go" on Monday. Obviously Cobra meetings are inherently secretive, and there's no direct precedent for this - because there weren't specific UKMO heat warnings pre-2021 - so I guess we'll find out. But as you say, UKHSA co-runs the Heat-Health Watch with UKMO, and it would make sense that they make the actual operational decisions, using UKMO as the provider of the data they need to make said decisions.

That has to be new territory. If we get anywhere near those we're going to see an unbelievable number of localised records going; have even the previous historically hot days (10 August 2003, etc.) been quite so widespread in their intensity?

And the very dry winter leading into such a summer will have reinforced the infrastructural impact - reservoirs, farming, etc.

I know there's technically two separate mechanisms at play - the colour-coded weather warnings (which only got used for heat for the first time in 2021) and the Heat-Health Alert system (that IIRC was introduced as a direct response to the 2003 heatwave and is aimed at mobilising health and social care). I would presume that some formal decision makers (at UKMO and possibly beyond) are looking at these models as intently as we are here, and planning for what type of interventions might be needed and when. The Heat-Health Alert updates are always around 9am, and the updates/extension to the public-facing amber warning have been aligned with this. The latest round of modelling does seem to suggest further confidence in this being a historic heat event into at least Tuesday. Most of them break up during next week, I think. Birmingham City Council schools (which I looked up as the largest single council and because it's also in the warning area) end term only on the 21st. Sussex/Kent/Surrey schools are also open until at least then.

I don't like thunder at all (because of the unpredictable noise, the flashing light that comes with it - genuinely disturbing for me at night - and the actual danger that can come with it, although between the hill in one direction and the gigantic metal bridge in the other my house isn't much of a lightning magnet...) but I end up following along with the storm chasers/enthusiasts on here because sound is a lot less scary if I'm already anticipating it. I'm normally more sensitive to high-pitched noises too so I guess it's specifically that aspect of danger (and the fact they usually follow a hot spell that's already worn down my sensory defenses) that makes me particularly anxious about thunderstorms.

I'm guessing that would also lead to some very weird mixed messaging from individual readings if patchy cloud is thrown into an otherwise historically hot mix?

If the front movement is from the SW does that imply a more northerly and easterly potential maximum on Tuesday if the front arrives at a marginal time for records? But that UKMO run suggests Cheltenham might be the station to watch (and of course it's put up a record before with the 1990 mark). Certainly looks like the macro setup is very much getting consensus (potential for the UKMO warning to go red based on that growing certainty?), and it's just the fine details that remain uncertain. Considering the subtlety of the moving parts that have to happen, I'm surprised there's this much consensus 5-6 days out... a sign of improving modelling as the march of computing power goes on?

Sensitivity can definitely go the other way too (though in that particular sample it was less prevalent). I've definitely got a couple of cold-sensitive autistic friends to go with my penguin pals! Sometimes I wonder if I actually like/tolerate the cold or if I just like using heavy clothing/blankets/duvets/my partner (they're also a Penguin Autistic) for pressure stimming Certainly the cold seems to have more and better ways for me to deal with it.

If it sparked action to slow down the impacts (by reducing emissions) and alleviate them (by improving infrastructure) then I would also like to see it happen. I'll always be worried first about people in general and vulnerable people in particular but I can't lie and pretend I'm not interested in "numbers go brrr like they've never gone brrr before" either...