In an amazing turn of meteorological good fortune, at least for those of us in south and east England, a heatwave has aligned with the late May bank holiday weekend.
We don't normally get temperatures of 30°C and above in May, even late May, because it's still officially spring no matter how you classify it.
The last time England reached 30°C in May was 25th May 2012 and the time before that 27th May 2005. That's only twice this century and just once in the last 20 years. In the 20th century there are reports of hitting 30°C on 21st May 1922, 29th May 1944 (a week before D Day), 12th May 1945 (just after VE Day), 29th May 1947 (after a punishingly cold winter) and 25th May 1953 (a week before the Coronation). 30°C in May is rare and highly intermittent but not unheard of.
The earliest that 30°C has ever been recorded in the UK is 12th May, whereas June is more likely, July is more normal and in some years it never happens at all. If we take the modern definition that a 'heatwave' requires three consecutive days of elevated temperatures, then Britain's never seen one in May until this weekend.
Over the last decade we've averaged twelve days over 30°C each year - fifty years ago it was only four. But it's not all about recent climate change... the only year when 30°C has been recorded from in every month May to September is 1947.
If you tot up all the 30°C days in the last fifteen years, about 45% of them were in July, about a quarter were in August, another 20% in June and just 10% in September. May doesn't really get a look in, even with this year's heatwave factored in.
Today may be the hottest UK bank holiday of all time. The current record holder is August Bank Holiday Monday 2019 when the temperature reached 33.2°C at Heathrow, beating the previous record of 32.8°C on the Late Spring Bank Holiday Monday in 1944. The absence of bank holidays between late May and late August is mostly responsible here.
More extremely, today should break the record for the UK's hottest day in May. The current record is 32.8°C, first achieved on 22nd May 1922 and then equalled on 29th May 1944. That is a very long time for a temperature record to have stood, and at time of posting maybe has ten hours left. It's also a fairly complex record shared between four locations - Camden Square in 1922 and Horsham, Tunbridge Wells and Regent's Park in 1944.
Meteorologists keep records not just for months but also individual days of the year, so we can also list the maximum temperatures ever recorded on 23rd, 24th, 25th and 26th May.
23rd May: 31.7°C on the Isle of Grain in 1922 24th May: 32.2°C (90°F) at Camden Square in 1922 25th May: 31.7°C at Farnham and Heathrow in 1947 26th May: 29.5°C at Inverailort (Highland) in 2010
Nowhere on Saturday beat the daily record for 23rd May, with Frittenden in Kent reaching only 30.5°C. But Kew Gardens yesterday reached 32.3°C, becoming (marginally) the warmest 24th May ever recorded. Somewhere today is almost certain to beat the daily record for 25th May, and the daily record for 26th May also looks like being smashed tomorrow, probably by several degrees.
Unlike many warm spells, this one's not due to hot air blowing north from Africa. Instead it's classic high pressure behaviour, a huge blob of air being compressed as it moves downward leading to warming through a process known as adiabatic compression. The great heatwave of 1976 occurred for much the same reason, but that was in late June/early July, not at the end of May.
Here are the years in which the UK's monthly temperature records were last broken. For May that's currently 1922 but is about to be 2026.
When the UK maximum monthly temperature record was last broken
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
2024
2019
1968
1949
1922
1976
2022
2003
1906
2011
2015
2019
Years in the 21st century are underlined. There are seven of these, and are about to be eight, i.e. two-thirds of our monthly records have been broken since the millennium. Five have changed in the last ten years. Every month from October to February has been upgraded since 2011, suggesting that winter extremes are being affected more than summer extremes.
The elusive monthly records that haven't been broken recently are as follows.
Mar: 25.6°C Mepal (Cambs) 29 Mar 1968 Apr: 29.4°C Camden Square 16th Apr 1949 Jun: 35.6°C Camden Square 29th Jun 1957 / Southampton 28th June 1976 Sep: 35.6°C Bawtry (South Yorks) 2nd Sep 1906
The monthly record being broken today is older than all but one of these.
Meanwhile at the cold end of the spectrum...
When the UK minimum monthly temperature record was last broken
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
1982
1956
2018
1917
1979
1975
1978
1964
1915
1973
1919
1995
Years in the 21st century are underlined. There's only one of these, indeed the monthly minimum temperature record has only been broken twice in the last 40 years, whereas in the same period the record for maximum temperature has been broken eight times.
In summary, when it comes to monthly temperature records we've been breaking a lot more maxima than minima recently. It doesn't prove the climate is heating up, not in itself, but it is self-evidently the direction of travel you'd expect if it was. I wonder which monthly record will fall next.
