Looks like 24.5 is the form horse at the moment.

Neil- you're a Torro member; you must have known about that link!

Northolt 24.6C

2nd September 35.6

9th October 27.8 (the latest recorded date where 80F has been exceeded)

What you say is true, but for the purposes of this enquiry, 80F is an arbitrary threshold: that date record is unlikely to fall on the potential absolute line as only 3 days before, 28.9C was recorded, a full 1.1C more. For the line to be quite that steep is a bit hard to register.

To illustrate this further, following the 9th, there is about a week and a half of PAMs around 25C, with no real drop-off. I suspect that hitherto, this time of year has not produced its best. I estimate that 26.7C (about 80F) is possible up to about 14th. 

Some of the dates quoted earlier may indeed be close to PAMs.

2 things to remember, that sort of oppose one another:

• accuracy of earlier apparatus, conformity of sites and integrity of readers; and:
• warming in the last quarter of the 20th century.

1921 was a quirky year!

And if we want a date record that has a good chance of being broken, how about tomorrow?

The record is 25.3C but with 25C predicted over much of eastern England, this one looks very vulnerable indeed.

I had previously tried to do that for the record breaking 38.5C recorded on 10 August 2003

The only way I could get a handle on it was to do a statistical analysis of all the daytime maxima for that area to see if a calculation based on standard deviation / return period would give the answer

I used the CEDA Daily Maxima data (1960-2016) for the 5km grid square that included Faversham. Kent where the max was recorded

I found that day's max was a significant outlier (and I suspect it should not have been verified) for that grid square and that data set was not useful

I went to the next highest reading (Kew Gardens, London at 37.9) and this one had a much more consistent history with many readings between 34.0 and 37.9C in the date range 15 July to 15 August for 1960-2016

Unfortunately, the data is not "normally" distributed and has an increasingly "fat tail" at the high end but not the low end. The mean max is 23C for this grid square and date range but there are 13 occurrences of days 10C above this mean (33C or more) but no occurrences of 10C or more below this mean (13C or less)

After some adjustment, however, the nearest I could get (with some interpolation) was for a return period of about 90 years for a temperature of 38.5C to occur somewhere in the UK and about 270 years for 40C or more. If the long term UK mean temperature rises, however, these return periods will be shorter

Agree- some models offering 26C around The Wash area tomorrow.

Here in the extreme SE the incredible run of high temperatures continues.

The past 7 day maximum temperatures are as follows, for our coastal location these temperatures are on a par or slightly ahead of mid summer maxes. On most days this week we have been challenging maxes nearly as high as they can get around these parts at this time of the year:

The mean maximum for the month stands at an incredible 19c (66f).

Somewhere in the UK has managed at least 20C on every one of the past 9 days. Quite impressive for this time of the year. 

Apart from the date record on the 13th, we were only 1.1C off the date record on the 14th and 2.1C off the date record today. 

We may not see 20C again this year although I would not rule it out. There are still likely to be some pleasantly warm days in the SE over the next week or so. At the moment the best chance of hitting 20C again appears to be on Sunday in East Anglia.