What is a heatwave and How is it defined?

You’ll see much talk in the papers over the coming summer months of ‘heatwaves’. The daily rags describe any thing remotely warm as a ‘heatwave’, but is there a strict definition of a heatwave?

This Met Office video sheds some light on it.

A heatwave is an extended period of hot weather relative to the expected conditions of the area at that time of year, which may be accompanied by high humidity, but what is the definition for a UK heatwave?

In Durham, the threshold for a ‘Heatwave’ is 3 days or more of 25 degC or above. The longest heatwaves in Durham have been:

Days.     Year.         Period

13         1975         2nd – 14th August*
9           1976         25th June – 3rd July
9           2006         21st – 29th July
8           1940         3rd – 10th June
8           1995         15th – 22nd August

* The 4th – 10th August 1975 was the warmest 7 day period on the Durham record. It averaged 20.8 degC. This was equalled on 16th-22nd July 2022, and 17th-23rd July 2022.