Records from the Reading University Atmospheric Observatory show how exceptional this hot spell of weather has been.
Yesterday (Monday 25 May), Reading experienced its hottest May day on record, the maximum temperature reaching 32.8 °C, more than fifteen degrees above the May average of 17.4 °C. The previous May record, on records back to 1908, was 31.9 °C on 29 May 1944.
Today (Tuesday 26 May) looks to be as hot, if not slightly hotter, and is the third consecutive day in heatwave conditions (meaning a temperature of 28 °C or more). The last time this milestone was reached was in May 1922.
Another record has also been set at the University of Reading this month: the greatest range in temperature yet recorded in any month in Reading in almost 120 years of records.
A year’s temperature range in one month
Dr Stephen Burt, of the University of Reading Department of Meteorology, said:
“You might remember that the first half of May was rather cold, with a cold northerly wind and even night frosts. This month has now set another new record, for the greatest range in temperature yet recorded in any month in Reading.
“From the minimum of -0.1 °C (air frost) recorded on 12 May, to yesterday’s maximum of 32.8 °C less than a fortnight later, a monthly range (so far) of 32.9 degrees. The previous highest monthly range of any month was in May 1944, at 32.8 degrees. There have been several entire years having a smaller range in temperature – back in 1974, the annual range in temperature in Reading was just 28.3 degrees.”
Causes of heatwaves
Explaining why the last week of May has been so hot, Professor Richard Allan, Professor in Climate Science at the University of Reading, said:
“Heatwaves in the UK are often occur when a stubborn area of high atmospheric pressure blocks the usual cooler, moister weather systems. When the atmosphere gets stuck in a rut, this can cause a build-up of heat as the sun bakes the already parched ground and it becomes difficult for the hot air to escape. Trapped air is forced to sink and heat up like a pressure cooker, under the increasing weight of the atmosphere aloft. This lid on the lower atmosphere, sometimes referred to as a heat dome, also stops the uplift of air needed to form cloud and rain.
“The sustained sunshine rapidly dries the soil meaning less of the sun’s heat is used evaporating moisture and the full force of the sun bakes the ground.
“It is well known from the science that as greenhouse gas levels continue to rise due to human activities, it is becoming increasingly difficult for Earth to lose excess heat to space. A warmer, thirstier atmosphere is more effective at drying soils, intensifying heatwaves and drought in one regions while channelling this excess, stolen moisture into storm systems elsewhere. This means human caused warming of climate is intensifying heatwaves and droughts as well as extreme rainfall and associated flooding.”
Seeking relief
Dr Akshay Deoras, climate scientist at the University of Reading, said:
“In addition to extreme daytime temperatures, nights are offering little relief, with temperatures failing to drop below 20°C in some areas. This is creating tropical nights that prevent homes from cooling down, leaving indoor spaces warm and uncomfortable well into the early hours. This is particularly significant in the UK, where housing is largely designed to retain heat rather than release it. Well insulated buildings, limited cross ventilation, minimal use of air conditioning, and urban heat retention from concrete and brick all contribute to trapping warmth indoors. As a result, indoor spaces can remain uncomfortably hot long after sunset.
“What was once considered a distant scenario is now becoming reality, with the UK increasingly exposed to extreme heat events. The 40°C threshold, once thought highly unlikely, was already reached during the July 2022 heatwave, and early heatwaves this year have further reinforced how quickly such extremes are becoming more plausible.
“This heatwave is also affecting much of Europe, with temperatures forecast to reach 40°C in southwest France later this week.
Whilst the holiday season may tempt people outdoors, the risks should not be underestimated. It is essential to stay hydrated, seek shade during peak hours, and take early signs of heat exhaustion seriously. These include dizziness, headaches, nausea, rapid heartbeat, excessive sweating followed by sudden cooling, and confusion. If symptoms worsen, medical attention should be sought promptly.”
