With the Aperge model showing temperatures of at least 36C on Friday we can now start thinking of another top five record hottest day.

1) 38.7C 25 July 2019 

2) 38.5C 10 August 2003

3) 37.8C 31 July 2020

4) 37.1C 3 August 1990

5=) 36.7C 9 August 1911

5=) 36.7C 1 July 2015

This thread is for short term model discussion which can also be used on the day itself. 

IPhone App has just upgraded the temperature for my location on Friday to 36C.

I’d like a nice clean top 5. I hate it when two dates share a record.

There will be a katabatic effect from the Downs again on Friday, but the air mass isn't as hot as last Friday. 36C looks more reasonable to me.

Blimey. What are they seeing that other models aren’t.

Not disputing what you say, but surely the Met Office know this too? They seem very confident of a rounded 38C. And they usually err on the side of caution.

The 850hpa temps are somewhat unremarkable but last week demonstrates you don't need high uppers.

Still flabbergasted by the 25C 850hpa temp in SW England last year, suprised it didn't attract more attention at the time. Must be a record for the UK.

And had it not been for the airmass being extremely wet we could have seen 40C with those uppers rather than the upper twenties we actually saw.

Looks like 850s will be about 18c Friday afternoon in the SE. So 37/38c will be top end. Just shy of the record is my guess.

That was when we had that vile North Sea undercut - what a waste of such high uppers!

I'm  not sure why the metoffice dismiss the otherwise accepted high of 38C (100f) at Greenwich back in 1911.  

Dodgy exposure, and it’s a lot higher than most surrounding stations. Then again, Gravesend was often much higher than other local stations.

If we're treating this as the general heatwave thread rather than just the Friday record one, then worth noting it's now at 28C at Mildenhall airfield (all those plane exhausts and tarmac runways no doubt). Only 2pm so a couple of hours of heating time left with 850s stable, so long as the sun stays out.

Tomorrow could be a tad disappointing on the sunshine front. BBC news just now forecasting 27C, models showing between 27 and 30 depending where you look. GFS shows largely clear whereas the more local scale ICON and Arpege show a lot of mid and low level cloud.

I think this is Ok. Specifics about Friday are most important . But as you known conditions leading up to the day are equally important as they could have an effect also.

I have also noted this increase in cloud for tomorrow. I suspect any breaks and the temperatures will quickly climb. 

What shocked me on my lunchtime walk was how brown everything is again here

I think the cloud will break, especially the further east you are.

Temps have certainly shot up today here - not surprised that Mildenhall is reporting 28. Bit of mid-level cloud making the sunshine a bit hazy from time to time.

Personally I'm not buying the 38C max at Heathrow forecast by the Met Office for Friday. I noticed that Hampton Court, just a few miles away is forecast by the Met Office to reach 33C. I could understand perhaps a 2C difference, but not 5C! There must be some human tweaking of numbers going on, as others have mentioned, probably as a result of last Friday. 

if it does break quite widely, temps will exceed 30C quite easily I feel.

I think a 37 is on though. Maybe the 38 would be a rounded 37.5.

But they seem very confident and it’s only 2 days away.

Non-standard thermometer screening, according to Trevor Harley:

"There was a remarkable hot spell, although it is quite difficult to be certain about the exact temperatures, because of (a) uncertainty about screening, and (b) temperatures were taken in F rather than C. The reading of 38.1C - 100.5F - claimed at Greenwich on the 22nd is now not accepted, as the screening conditions at Greenwich were nonstandard; it is more likely to have been about 36.1C - still quite a temperature, and the record for July (until 2006). 97F (36.1C) was also recorded at Epsom, favoured because there was shelter from the light southerly breeze."

https://www.trevorharley.com/1911.html

Actually that wasd for 22nd July. The Monthly Weather Report says the temperature was higher on August 9 1911, with 98F at Canterbury, Epsom and Raunds, 99F at Isleworth, and 100F at the Royal Observatory, Greenwich.

Even if Greenwich was discounted I am not sure why Isleworth wasn't counted.

See page 81 here: https://digital.nmla.metoffice.gov.uk/digitalFile_1f3ce836-7850-4c40-bce8-0a0ce05baacf/ and the tables on following pages.

Further info here: https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/wea.818

"A temperature of 100°F (37.8°C) was recorded at Greenwich, London, on 9 August 1911, the highest recorded there since observations began in 1841. However, this was from a Glaisher stand, not a Stevenson screen, and it is not accepted as an official record"

Note:  The Glaisher stand was brought into use at Greenwich Observatory in 1841. It comprised a vertical board on which thermometers could be mounted, which could be rotated around a central pivot to face away from the sun. It was reliant on the observer turning the stand regularly. Laing (1977) compared temperatures from Glaisher stands and Stevenson screens and found differences of up to several degrees Celsius on warm sunny days due to the Glaisher stand's design. The Stevenson screen was invented in 1863.