In a climate now capable of over 40C, the resilience of the June 1976 heat record is remarkable. Despite recent near misses, the 35.6C benchmark has held on, but for how much longer?
The UK record temperatures for July and August have been set relatively recently - the overall record is 40.3C at Coningsby, Lincolnshire, set on 19 July 2022. A recent study from the Met Office, using UNSEEN models, has determined that even higher temperatures than that are possible in the current climate. This was also reflected by some runs from the GFS medium range forecast model prior to that record breaking heatwave, which had some parts of eastern England reaching as high as 42 or 43C, which was toned down to predictions of 40 or 41C as we got very close to the event.
This infers that temperatures of around 40C are probably also possible in late June. But the current UK June temperature record still stems from the late June 1976 heatwave, 35.6C at Mayflower Park in Southampton on 28 June 1976. It is clear that substantially higher temperatures are possible in June in the current climate, but although there have been several recent approaches in recent years, the old record has so far remained intact. There is an outside chance of the record being broken today, but it looks most likely that the highest temperature in the UK today will be around 34C, allowing the old record to hold on for another year.
The late June 1976 heatwave was an extraordinary event, especially as it occurred in what was, averaged globally, one of the coldest years in the second half of the 20th century. Global temperature anomaly maps have most regions cooler than average in June 1976, but with a marked warm anomaly covering north-western Europe. The first two-thirds of June 1976 had featured a northwest-southeast split in the weather, with plenty of dry sunny weather in the east Midlands, East Anglia and south-east England, but often cloudier and more changeable weather further north and west, especially in western Scotland and Northern Ireland, with a persistent east Atlantic trough. Many areas had a hot southerly around the 8th/9th.
The main heatwave started around the 21st/22nd as high pressure built to the east of Britain and pulled warm air masses in from a long way south, and the dry sunny weather over the south-east spread to cover most of the country. Many areas averaged well over 10 hours of sunshine per day during the last third of the month. High pressure then remained over or close to the British Isles until early July, maintaining hot weather. It was one of those heatwaves that gradually subsided through early July, rather than ending in a thundery breakdown.
There was a notable near miss in 2015, when June had been dry and sunny but rather cool for much of the country, but Heathrow Airport (London) recorded a high of 36.7C on 1 July, which at the time was a new record for July, and it would have comfortably beaten the June 1976 record had it occurred a day earlier. The intensity of the heat spike was reflected by the fact that, officially, the highest temperature for June 2015 was recorded at Heathrow just before 0900 on 1 July (a consequence of the long-standing system of recording the daytime maximum from 0900 to 0900).
Since then, there have been several near approaches, but nothing has broken the old record. In June 2017, England had a hot spell from the 17th to 21st, which recorded 34.5C at Heathrow on the 21st. June 2018 ended hot, with record temperatures in parts of northern and western Britain, but nothing really challenging the June 1976 record, with a peak of 33.0C at Porthmadog in Wales. June 2019 ended up with some exceptionally hot air at high altitudes - at 850 hPa (about 1.5 km above sea level), the temperature exceeded 20C for a time over parts of southern and eastern Britain, which in many cases translates to surface temperatures in the high 30s Celsius. However, on that occasion the surface airflow allowed the English Channel and North Sea to have a considerable cooling influence, and so surface temperatures did not get that high. Again the June 1976 record was closely approached, with 34.0C at Heathrow and Northolt, but not exceeded.
More recently, June 2022 had potential to become exceptionally hot around the 15th-17th, ultimately recording a high of 32.7C at Santon Downham (Suffolk). June 2023 ended up as the warmest June on record for the UK as a whole (in records going back to 1884), but was characterised by persistent rather than outstanding heat, with temperatures no higher than around 32C.
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