The hottest summers in Britain from 1900
"Summer" is defined meteorologically as June, July, and August. Several make a good summer (e.g. temperature, sunshine, and amount of rain), and not all of these things are too everyone's liking. And of course it can be too hot for most people.
Hottest summers
The hottest summer of the twentieth century was 1976, by a considerable margin. Here are the means (taken as mean CET [Central England Temperature series] temperatures (in º Celsius) for the three summer months) for the top thirteen:
1976 17.67
2018 17.40
1995 17.27
2006 17.27
2022 17.27
2003 17.20
1983 17.03
1947 17.03
1933 17.00
1911 16.97
1975 16.83
1959 16.57
1997 16.53
1955 16.53
1949 16.60
Honorary mention should be made of 1826, at 17.60, 1846, at 17.10, and 1899, at 16.9.
In case you're interested, the coldest summer of the twentieth century was 1907 (13.60), fllowed by 1922 (13.70); 1954 and 1956 were poor too, and more recently 1972 (14.17), 1977 (14.37), 1978 (14.40), and 1988 (14.67) and 1993 (14.90). Since then the only poor summer (< 15.0) has been 2011 (at 14.83).
Of course there is more to a good summer than high overall mean temperatures; sunshine and rainfall also matter. On a compound measure, the best summer for England and Wales is still 1976. In decreasing order the best summers are:
1976, 1995, 2022, 2018, 1911, 1983, 2006, 1975.
The worst summer on the compound measure was 1927. The best summer in Scotland was 1995, and the worst 1985.
Hot summer months
Are "summers not as good as we remember them"? No: they're better. Consider this table of the distribution of the number of hot summer months (with CET equal to or greater than 17.5C) across the decades of the twentieth century:
Here are the hot months (more than 17.5C):
July 1900, July 1901, July 1911, August 1911, July 1921, July 1923, July 1933, August 1933, July 1934, August 1947, July 1955, August 1955, August 1975, July 1976, August 1976, July 1983, August 1984, July 1989, August 1990, July 1994, July 1995, August 1995, August 1997, July 1999, July 2003, August 2003, August 2004, July 2006, July 2013, July 2014, July 2018, July 2019, August 2020, July 2021, July 2022, August 2022. Note there are no Junes.
And here are the very hot months (more than 18.5C):
July 1921, August 1947, August 1975, July 1976, July 1983, July 1995, August 1995, August 1997, July 2006, July 2018, August 2022.
And the extremely hot months (more than 19.0C):
July 1983 (19.5), August 1995 (19.2), July 2006 (the hottest of all, 19.7), July 2018 (19.1)
So the only really outstanding British summers, with two consecutive hot months, have been 1911, 1933, 1955, 1976, 1995, 2003 and 2022. So much for the great British summer! Note also the scarcity and pretty random distribution of these hot months. I have written about our nostalgia for non-existent weather of yore elsewhere (Harley, 2003, "Nice weather for the time of year").
Interestingly, although extremely hot days often occur in early August (without exception until 2019), the extremely hot months are often July.
Before the twentieth century, summers were worse. the only very hot month before 1921 were July 1783, with a mean of 18.8C, and 1852, with a mean of 18.7C from when records began in 1659).
Warm summers have become much more common since 1990, even if some of them have been wet.
Consecutive days over 30C
1976 was clearly exceptional on other measures: in the summer of 1976, somewhere reached the 90s (32C) for 15 consecutive days from 23 June and 7 July (before or since there has been no such spell longer than give days over 90F in a row). There were 3 consecutive days over 35C (26-28th June).
In 1995, in addition to 7 days over 31C, on 32C was reached on 6 consecutive days from 29th July-3rd August .
1983 had 6 days over 32C from 11th-16th July.
1990 had 4 32C+ from 1st-4th August, and like 1976 and 2020 only, had 3consecutive days over 35C.
1906 had 4 32C+ from 31st August-3rd September.
Heathrow had 16 consecutive days over 30C between 23 June and 8 July 1976, a record.
There were 14 consecutive days over 30C in August 1947, and there had also been 6 in a row 26 May to 3rd June.
In August 2003, from the 5th to the 13th, there were 9 consecutive days where somewhere in the country exceeding 30C, the longest such run since 1976, and 29C was exceeded between the 2nd and 14th - the longest run since August 1997, and 10 consecutive days over 30C in from 3rd - 12th. 32C was exceeded on 5 days.
In 1975, there were 8 consecutive days over 30C from 2nd-9th August which was preceded by 4 days from 28th-31st July and then followed by another 4 from 11th-14th August.
1983 saw 7 consecutive days over 30C from 11-17th July.
The end of June 2018 saw 5 consecutive days over 30C at the end of the month, Porthmadog in Nort Wales doing particularly well.
August 1997 saw at least 5 consecutive days from 8th-12th recording over 30C.
July 2006 saw 30C reached each day between 16th-29th apart from 23rd.
August 1997 saw 5 consecutive days from 8th-12th recording 30C+.
July 2006 saw 30C reached each day between 16th-29th apart from 23rd.
"Heat waves"
A "heat wave" has a Met Office definition for the UK. It's when the temperature exceeds a threshold for three consecutive days, that threshold being 28C in parts of the south, 27C (old 80F more or less) for much of the south and east, and 25C for the southwest, north, Wales, Northern Ireland, and Scotland.
By that definition heatwaves are surprisingly here. Take July 2022 when it reached 30.7 in my garden in Angus. No heatwave! Two days over 29, but the days either side didn't exceed 22.
