What is a heat dome? Temperatures reach 30C in the UK

People enjoy the hot weather on Bournemouth beach in Dorset, as forecasters predicted a “last dose of summer”  (PA)
People enjoy the hot weather on Bournemouth beach in Dorset, as forecasters predicted a “last dose of summer” (PA)

With the hottest day of the year in the UK on the horizon, thousands have flocked to parks, bars and outdoor swimming pools this week.

Temperatures have climbed towards 32C and are set to continue into the weekend, with figures of at least 30C forecast for Thursday, Friday and Saturday.

Economic experts said the September heat would help boost spending after a soggy summer that depressed sales on the high street.

The UK is having a late summer burst of hot weather but what is causing it? Forecasters say this phenomenon is known as a “heat dome”.

What is a heat dome?

The Royal Meteorological Society says a heat dome takes place when an area of high pressure stays over the same area for days (sometimes weeks). Warm air then gets trapped underneath like a lid on a saucepan, pushing temperatures above what is normal for the time of year.

The heated air expands upwards into the atmosphere, then high pressure from above acts as a barrier, meaning it can't escape and causes the air to subside or sink. This creates a dome effect.

The warm air sinks and compresses and heats up, which then traps more heat underneath. Clouds are pushed around it, trapping the heat even more.

However, meteorologist Dr Chris England told Sky weather that the phenomenon “doesn't really apply to the current heat of the UK”, and that the flow around the high pressure comes from the south over the UK, bringing heat up from the Mediterranean and north Africa.

Is heat dome a new term?

The term first came into general use in 2011.

Oklahoma City weatherman Gary England told the New York Times: “I’ve used ‘heat dome’ off and on over the years, but I think it’s a little bit misleading; it’s not shaped like that.”

What is the difference between a heat dome and heat wave?

The terms “heat domes” and “heat waves” are often used interchangeably but heat domes are just one of the atmospheric conditions that can contribute to the formation of a heat wave.

A heat wave is a period of excessively hot weather for a prolonged period of time, often with high humidity.