Weather: What is a 'heat dome' - and how long is it set to affect the UK?

Most of Europe is right now baking in a so-called "heat dome" - conditions a bit like a pizza oven, which are scorching Spain, France, Italy, Greece and beyond.

Meanwhile, temperatures in the UK peaked at 33.1C at Heathrow on Monday - with hot conditions also expected on Tuesday.

So, what's going on with our weather?

Follow latest: Amber heat health alert extended to more areas

What is a heat dome?

A heat dome forms when an area of high pressure lingers over a region for days or weeks.

This pressure traps hot air - like the dome of a pizza oven or a lid on a saucepan - and bakes the air and land beneath.

As the ground parches, it absorbs heat - making conditions hotter still.

The dome of high pressure also blocks out clouds and cooler air, resulting in clear skies and persistent heat.

Find out the latest forecast for your area

What effect is the heat dome having on the UK - and how long could it last?

The current heat dome is hovering across most of Europe, while the UK sits just on the cusp of it.

That means the same high pressure bringing plus 40C (104F) temperatures to southern Europe is also roasting southern and eastern England on Monday and Tuesday.

Temperatures had been expected to hit 34C (93.2F) in London and the South East on Monday. They peaked at 33.1C at Heathrow.

But, these regions are due to sweat through a "tropical night" on Monday evening - when temperatures do not drop below 20C (68F), making it much harder to sleep.

Northern and western Britain sit outside the area of high pressure, hence conditions there are cooler and wetter.

The heat will be pushed away to the South East on Tuesday night, as a cold front moves through southeastern England.

Cooler air has already started to move into the North West, bringing rain, and that will move across all of Ireland, Northern Ireland and Scotland overnight, mostly clearing into northern England later.

Tuesday will be hot and humid in the South again, but it will be cooler elsewhere.

Wednesday will bring nearer average temperatures, although still higher in the South East.

Are heat domes becoming more common?

The (scientific) jury is still out, says climate scientist Dr Michael Byrne, from the University of St Andrews.

"Some research suggests heat domes will become more common as climate warms, with more frequent heatwaves as a result" but there is no scientific consensus yet, he says.

"But what is crystal clear is that climate change is loading the dice such that when a heat dome does occur, it brings hotter and more dangerous temperatures," he adds.

The 'game-changer'

While heat domes are nothing new, their more intense impacts are.

Europe is already more than 2C warmer than in pre-industrial times, and the fastest warming continent in the world, making every heatwave and heat dome hotter than they would have been.

That's because greenhouse gases released from burning fossil fuels are trapping more heat in the Earth's atmosphere, raising the average temperatures.

Read more:
'Tropical nights' soar in European holiday hotspots
'Most effective' protection to avoid sunburn (and it isn't suncream)
Tips to stay cool in the heat

Dr Friederike Otto, a senior lecturer in climate science from Imperial College London, says: "Countless studies have shown that climate change is an absolute game-changer when it comes to heat in Europe, making heatwaves much more frequent, especially the hottest ones - and more intense."

Prof James Dyke, an expert in climate science from Exeter University, adds: "The only way to avoid even more extreme heat is to rapidly phase out fossil fuels."

But we must also adapt to the hotter world, experts say, which means making sure people and buildings can keep cool to avoid the dangerous side effects.

Baroness Brown, from the Climate Change Committee (CCC), told Sky News in April: "It still seems to feel like it's tomorrow's problem… and if we don't tackle it today, it becomes tomorrow's disaster."

The 'silent killer' and the side effects

Scientists call heatwaves the "silent killer" because they drive significant excess deaths, particularly in those who are already vulnerable.

They are also dangerous for small children - whose small bodies heat up faster - and pregnant women, and risk premature births.

The side effects hit not just our health but land and buildings too.

Heat fuels the conditions for wildfires, and can cause crops, railways, and power lines to fail.

Dr Madeleine Thomson, from the Wellcome Trust, which supports health research, says we need a longer-term approach to coping with longer and hotter heat.

"The strategy of reacting to each crisis is failing, and the science tells us it will get worse," she says.

"We need to shift to proactive, rapid and coordinated action to mitigate and adapt to climate change.

"The tools exist. The evidence is clear. What's missing is the urgency. We must act and we must act now."

(c) Sky News 2025: Weather: What is a 'heat dome' - and how long is it set to affect the UK?