It's approximately 1500m above sea level, but that varies quite a lot depending on both the sea level pressure and the temperature of the air.

Warmer air is less dense so a given pressure level will be higher above sea level (that's essentially what the "thickness" values measure - the 1000-500mb thickness is just the altitude difference between the 1000mb and 500mb pressure levels.

The colours on the pressure charts show the 500mb geopotential height, which is the height of the 500mb level above sea level. That will be higher if:

(a) the sea level pressure is higher, because you are starting from a higher pressure at the ground so it will take longer to reach 500mb

and/or

(b) the column of air is warmer, because it is less dense.

The same thing applies to the 850mb height. You can find the actual altitude of the 850mb level by looking at soundings, either real or modelled.

At the moment over the southern UK is about 1500m above sea level. Over central Spain it's about 1530m. In Tierra del Fuego it's about 1350m, as it is winter there...

I'd bet Brogdale has hit it too, but we won't know for a while. The 21C dewpoints at Shoeburyness, East Malling, Herstmonceux and Wattisham are quite noteworthy too. 

After a sunny morning, it clouded up and we've already had the very odd spot of rain, with the skies looking really dark now. Forecast is for light rain on and off through the evening/night. It'll give a nice freshen-up before the warm spell's arrival.

My vineyard site peaked at just under 28C suggesting the heat was more in central and West Kent than the East, so Brogdale may not get there today.

But as we effortlessly hit 30C again, funny to reflect that back in the day there were occasional years nowhere got to 30C all summer,  and now there are occasional years nowhere gets to 33C. In a couple of decades there will be occasional years nowhere manages 35C.

We're not in Kansas any more.

Today's one of those cases where places north of the Downs (like Brogdale and indeed here) are amongst the warmest places in the country. I rue a SW'ly wind! I'm guessing your vineyard is south-facing, so you'd be on the cooler side. 

That actually has a labelled 46 in western France, and a couple of 40C pixels within the 39C isotherm over the UK. Open in new tab, zoom in and you'll see them.

https://images.meteociel.fr/im/7/15682/arpegeuk_31_102_0meh0.png 

EDIT: And if that were to come off, the amber "extreme heat" warning would surely have to be bumped to a red!

Yes I'd missed the 46C isotherm. So that would be a new French all-time record, and at least 4C added to the UK June record. It already feels pretty warm in my SW-facing home office - thermostat reading 28C, so it could get pretty toasty for work next week!

https://images.meteociel.fr/im/29/12651/arpegeuk_17_99_0znf2.png 

And people that were climate change deniers and sadly not just them are now gleefully turning all their effort into encouraging accelerating it rather than doing what they can to attempt to attenuate it.

Hey but let's celebrate "drill, drill" !

Wow!

31.3C here 3.50pm, usually pretty accurate wrt to official stations nearby.

Kent, Essex, Suffolk and Norfolk have been the hot spot today, 30.9 is the highest official reading I have seen (at Cavendish) but I am sure there are some 31s. I am not sure if Brogdale is still reporting tbh.

Looks like it might have gone, which is a blow - no reports since early March. That means the "hot zone" north of the Downs is now without representation, so we'll doubtless miss some notable maxima in years to come. (It also means we won't see just how much warming is going on down here either - Faversham, aka Brogdale, warmed by 1.5C from 61-90 to 91-20, for example).

It’s crazy, because this early peak, may actually be the first, lots of models toying with another peak after Wednesday / Thursday

Indeed,  GFS 12z.  Has gone insanely hot aswell. 

From Sunday. 

31c, 32c, 35c, 36c, 34c, 38c, 33c

My goodness. 

Thursday actually has a couple of 35C gridpoints too, so that's four straight days of 35C+. I don't think that has ever happened has it? 1976 and 1990 both managed three in a row.

The MetO 12z run (to take a random model run) is like a prolonged version of that - up it comes from the south (Monday noon), it bubbles up to the northern Midlands, the 24C isotherm moves in (Midnight Weds into Thursday), then the whole lot gets shunted eastwards - albeit lingering more than it did in 2022 (it's still covering eastern England on Friday noon).

Four days at least vs two and a half. IF that were to come off it would be a truly historic spell, and following on a month after another historic one in May... 

EDIT: The MetO peaks at 25C 850s, funnily enough in a similar area to 2022 too, just more widespread.

https://www.theweatheroutlook.com/charts/met/12_132_uk_850_temperature.png 

Looking at e.g. the Heathrow gridpoint on the GFS you can see where that idea might come from!

Mind you, even here it's bonkers. Considering there would be an onshore breeze from the sea (currently 17C, goodness knows how high by next Friday!), I can't see how we'd get anywhere near 37... but the computer clearly thinks it's doable. 

https://ukwct.org.uk/weather/fri.jpg 

Note the frankly brutal amount of time at or above 35C too - it's the "area under the curve" effect (much beloved of A-level maths students studying integration) and it's why adding a degree or two makes things much, much worse - as it pulls that curve upwards such that you endure much more heat for much longer. 

A protip for those who want record-breaking heat for whatever reason, keep an eye out for low dewpoints, i.e. below 10C and preferably below zero. That's what we saw in 2022 and it was part of the reason temperatures climbed as high as they did: dry air heats up more rapidly. There's an extra 35 minutes or so of daylight in southern England compared to the 19th July too, which will aid heating all the more.

(Can't believe I'm writing all this, considering I absolutely detest and loathe heat, but even I recognise a potentially historic event when I see one!)