My definition for down here in London has changed as the climate has warmed. It used to be 5 days of 28C+, peaking on at least one day above 30C. Now I would say the 28C measure is redundant and it only kicks in above 30C, it needs to be a string of at least 3 days above 30C and needs to peak at least at 33C somewhere.

This morning's GFS maxes for Thursday onwards are 30, 33, 32, 32, 34, 27, 28, 30, 31, 31, 32, 33, 35, 38. So it qualifies. 2 heatwaves separated by a brief cooler spell.

I am busy pre-chilling the house, making use of the cool nights and mornings to get as much air in as possible. Got it down to 19.5C so far. Then the place will get locked down.

The heatwave threshold is only 25c here in Yorkshire.   I think that is a bit low, particularly as the Vale of York is such a warm spot (E.g Bramham 39.8 in 2022, but regularly one of the warmest spots).  So by the definition a heatwave is a dead cert.  But not 100% sure how it works e.g: 

If it was just 25c for three days, in says Topcliffe  (North Yorks) and Bramham (West Yorks), it might only be 22-24c in other places in the county,  but because those are two locations in West and North Yorkshire would that mean the whole counties were declared heatwaves? If so , seems a bit ridiculous as that's just warm summer weather. 

It should be at least 27c i feel. 

I guess we should use the Met Office official definitions, so a minimum of 3 consecutive days where it reaches 28°C or further north the threshold is lower (25°C for Scotland, parts of N and SW England and Wales. 26 to 27 as you get closer to the SE).

It should (easily?) reach that threshold in parts of NE Scotland but perhaps not in Aberdeen.

We already have a date for the end of the upcoming heatwave: Friday week. According to Huff Post. Though this far out and assuming forecasts aren't reliable more than 5 days out, this could either end up being brought forward or pushed back.

Or possibly one two-week+ heatwave, depending on where the maxima fall!

Yeah that 25C threshold is quite low for low-lying areas of Yorkshire. I'm not sure how they came to that conclusion. I agree that 27C would make more sense.

Possibility of Scottish record going on Sunday. Hottest place in England  i will say Cheltenham Friday/Saturday

"Temps to rise day by day through the week" says Met Office. That's usually what happens in a heatwave!

Heatwave is not lasting long. As I said in the model thread, the pattern change has been clear for all to see, but noone wanted to listen. I am glad I stuck to my guns.

After Monday. The pattern looks much more unsettled and yes, cooler, probably for a considerable period of time.

As you are sticking to your guns, are you still going for a cool July overall?

Of course the temperature will be cooler after the (at least 5 to 6 day) heatwave, otherwise it would still be a heatwave. That was always going to be the case and I don’t think anyone has said it will not become more unsettled, for a while at least. However, the outlook continues to look much warmer than average with maybe only a brief period around the average for the time of year (and I don’t mean a few hours of rain suppressing the temperature on a single day).

This is the heatwave thread, if you need to post that anywhere it should be in the model output.  You can see why people are getting frustrated with you. 

We have forecast temps here of 27c, 31c, 33c, 31c and 28c next few days, that is a significant heatwave that we should be discussing in this thread.

I am going for a cool second half of July yes. By cool, I mean temperature below 21c in the south.

By no means do I think "cold" but yes, I think the second half of July will be much, much cooler.

Perhaps the upcoming brief hot spell may tick up my CET prediction for July to 18c in the end, but it will not be much higher than that in my view.

I've mentioned the heatwave, in the heatwave thread.

If I posted that in the model thread, it would be instantly deleted, as there's no free speech allowed, sadly.

My views are every bit as valid as everyone else's. 

The 06z GFS, like the 00z run has temperatures in places back up above the heatwave threshold by next Friday.

Views are fine, but criticism of those views when they are based solely on hunches and in opposition to the body of evidence is also fine. The data continue to not show a cool second half of July. Do you think the models are wrong?

I have not criticised anybody, ever. I give my views. And I read and digest other people's views. Respect is key, and I respect everyone's right to have a view, and always will.

One thing about me is, if I'm wrong, which admittedly, often, I am, I never hide away, and take the comments on the chin.

Likewise, I wish others would too.

Anyway, to stay on topic, I accept the next 4-5 days look hot, and yes, a heatwave of sorts is incoming. The longevity is not what some media outlets and commentators have suggested, and after a few days of pretty high temperatures, they do drop back down to more normal values, maybe still slightly above average in places, but with good chance of some useful heavy rain. Regarding the models, they are definitely trending towards this pattern change. How long that lasts, who knows. I've also never said the models are wrong, but merely that they have trended more changeable.

Blistering heatwave incoming for East Wales and the Marches over the weekend if the UKVMet is on the money.

Infact the all time Welsh record (37.1c) could well be under threat. As things stand it's likely to be amongst the hottest Welsh days on record. 

An exceptional period of weather (in terms of heat) for this part of the World. 

There are a couple of things worth bearing in mind with the UKV:

1) It has been overcooking temperatures at times recently 

2) The relatively sparse reporting network means the chance of a weather station sitting on the highest temperature grid points is quite less, particularly when the core of the heat is a tad farther west

I don't rate the UKV model , Arpege is much more reliable and has 33c/34c as the peak temps which seems much more realistic.  I'd be surprised if we go above 35c this heatwave. 

It'll be interesting to see how it (UKV) performs - it did fairly well in the last heatwave if I recall correctly but happy to stand corrected. It's certainly out ahead of the pack this time so it may well be overcooking it.

I'd be interested to know if there is any data out there on model performance for temperature alone (or indeed any of the parameters). I suspect that some models are prone to overcooking certain parameters (GFS and wind for e.g.) but I've nothing to prove it.

The only other thing to note is that Arpege only goes our to Friday at present and at that point it's in line with the UKV - the peak of the heat is Saturday and Sunday so it'll be interesting to see what Arpege has for then.

The Arpege 12z will go out to Saturday so will be interesting. 

It's a fabulous "workhorse" model, in my opinion, hitting the sweet spot in terms of range, domain size and resolution. On balance it's probably my favourite of all the numerical models we have access to, even if it doesn't necessarily come out on top in any single category.

The 12z is out and it is indeed very different to the 3z UKMV in that it keeps the temperatures for Sat and Sunday much lower - 30 to 32c and also much less widespread - predominantly Gloucestershire area and surrounding counties. I wonder what the next update will bring!

As Dave suggests it looks like the highest values will be around the Gloucestershire area.

Looks like 36C could be the max temp, but I've not had chance to look through in-depth.