UK hot spell: Are we experiencing a heatwave?

High temperatures are in the forecast this week, but does that mean its a heatwave?

The definition of a heatwave varies globally, but in the UK it's defined as when daily maximum temperatures reach or exceed a given threshold for three consecutive days.

Across the UK this threshold varies too, with different counties and countries within the UK having different criteria. For example across Scotland, Wales and Northern Ireland the criteria is 25°C, ranging between 25°C and 28°C for England.

The highest threshold is found across counties such as London, Bedfordshire, Buckinghamshire, to name a few. The threshold is based on maximum temperature climatology between 1991 and 2020, at the mid-point of meteorological summer - the middle of July.

This week, some of us may be seeing a heatwave by definition, but not all of us. Monday 24th June to Thursday 28th is when the high temperatures are expected, with the UK Health Service Agency having issued a yellow heat-health alert.

Temperatures will be soaring into the high-twenties, particularly across central, southern and eastern England, reaching a peak of around 30°C on Wednesday 26th. The average daily maximum temperatures during this time of year are around 20°C - 21°C across these regions.

From Thursday onwards, fresher air will be introduced from the west, bringing a gradual cool-down by the end of the week.