This week parts of the UK are set to be hit with soaring temperatures as a shocking heatwave causes the mercury to rise.

Red weather warnings are in force across the country warning of extreme heat, with some areas seeing temperatures as hot as 40 degrees.

As Brits prepare for the weather, what causes heatwaves and why are we getting so many? The Met Office explains.

What classes as a heatwave?

A heatwave is an extended period of hot weather, relative to the expected conditions of the area at that time of year.

The current temperatures far exceed those normally, therefore we are experiencing a heatwave.

The UK also has its own conditions to be met for a heatwave to be declared.

A UK heatwave threshold is met when a location records a period of at least three consecutive days with daily maximum temperatures meeting or exceeding the heatwave temperature threshold. The threshold varies by UK county.

The Met Office says: “The Met Office heatwave threshold has been updated ahead of summer 2022.

“The initial heatwave thresholds were calculated based on the 1981-2010 climatology of daily maximum temperature at the mid-point of the meteorological summer (15 July).

“The revised thresholds will use the 1991-2020 averaging period introduced in January 2022. The geographical differences reflect the differences in climate across the UK.”

What causes a heatwave?

Heatwaves are common in summer when high pressure develops across an area, the Met Office explains.

High pressure systems slowly move cand can persist over many days or weeks. They can occur in the UK due to the location of the jet stream, which is usually to the north of the UK in the summer.

This can allow high pressure to develop over the UK resulting in persistent dry and settled weather.

What is the difference in heatwave warnings?  

The Met Office has several warnings it can issue during periods of hot weather. They are explained below:

Extreme Heat Warning – an impact-based warning designed to highlight the potential impacts of extreme heat to protect lives and property, helping people make better decisions to stay safe and thrive.

UK Health Security Agency (UKHSA) Heat Health Alert - An England-only service considering the impact of prolonged extreme heat on public health, especially those with long-term health conditions.

Heatwave definition - a threshold-based meteorological definition designed to provide the media and public with consistent and reliable messaging.