With temperatures rising in the coming days and the likelihood of figures in excess of 30°C over the weekend and into the start of next week, we take a look at how often this threshold is reached in May and what’s behind the figures.
While recent years have brought increasingly warm springs, a look at long-term records shows that reaching this daily 30°C threshold before June is still uncommon.
It’s important to emphasise that most years do not see 30°C reached until June or later. For example, the first 30°C of the year occurred in June in both 2024 (25 June) and 2025 (19 June), while in some cooler or more unsettled years the threshold has not been reached until July or even August. This variability highlights how unusual it is for May to deliver true summer heat.
How rare is 30°C in May?
The most recent occurrence of temperatures reaching at least 30°C in May dates back to May 2012, when the threshold was met on 25 May. Prior to that, there were similarly high temperatures reported in May 2010 (23 May) and May 2005 (27 May), demonstrating that while uncommon, summer-like heat in May is not unprecedented in the UK climate.
Looking further back into the historical record, occurrences of 30°C or above in May are scattered and infrequent. This dataset (back to 1900) shows only a handful of years in which the 30°C mark was reached during May, reinforcing the idea that such events require a specific combination of conditions to align.
Among the earliest instances in the observational record are May 1944 (29 May), May 1945 (12 May), May 1947 (29 May), and May 1953 (25 May). These dates illustrate that early-season warm spells have occurred intermittently across the 20th century.
Overall, the pattern is clear: May 30°C events are sporadic rather than regular, typically separated by many years.
The hottest May days on record
While reaching 30°C in May is rare, the UK has experienced some high temperatures during the month. Records of the hottest May days provide further insight into how marked late spring heat can become when conditions align.
The highest temperatures recorded in May is 32.8°C, with several notable occurrences. These include readings at Camden Square and Greenwich in Greater London during May 1922, as well as across parts of southeast England including Tunbridge Wells and Horsham during late May 1944.
Other significant hot days include temperatures of around 32.2°C recorded at Camden Square on 31 May 1947, and 31.7°C recorded at Heathrow and Farnham on 25 May 1953. Most of these highest temperatures are concentrated in southern and southeastern England, where proximity to continental Europe and generally lower cloud cover increases the likelihood of warmth during settled conditions.
Why does May heat occur?
For the UK to reach 30°C in May, a number of atmospheric factors typically need to align. Persistent high pressure over or near the UK is often a key feature, allowing for prolonged sunshine and light winds. This setup can enable warm or very warm air to be drawn northwards from continental Europe.
Longer daylight hours also play a role. By late May, the UK is approaching the summer solstice, meaning solar input is already strong. Under clear skies, this can allow temperatures to rise quickly, especially when combined with dry ground conditions which limit evaporative cooling.
However, despite these favourable factors, the position of the jet stream and the variability of Atlantic weather systems often prevent such setups from becoming established in May. This is one of the primary reasons why 30°C is more commonly reached in June, July, or August.
A changing climate context
While the historical record shows that May heat has always been possible, there is growing interest in how climate change may influence the frequency and intensity of such spring’s warm spells.
Recent decades have seen an increasing number of warm springs in the UK according to overall mean temperature. The three warmest springs on record have all occurred since 2017 in a series which dates back to 1884.
So, while the daily threshold of 30°C in May remains an infrequent occurrence, the temperatures experienced in spring overall have shown a rising trend.
Due to the UK’s variable climate, individual years and seasons will continue to differ markedly. Cool or unsettled springs can still delay the first 30°C daily reading well into summer, as seen in several recent years.
