What is a heat dome? Warnings as high temperatures set to sweep across Europe next week

Europe faces another heatwave next week as forecasters warn that a 'heat dome' is set to bring near record high temperatures to the continent. 

Spain, Portugal and Italy are among the European countries tipped to see extreme heat next week. 

In France, temperatures could peak at around 40C in the south of the country, weather authority Météo France has said. At least 19 departments are under weather warnings for hot conditions with that number likely to rise over the weekend. 

Forecasters have said it could be the country's most intense heatwave ever. The government held a crisis meeting on Thursday (18 August) to discuss measures to deal with the extreme weather. 

A heat dome, which has come from the Sahara, across Algeria and Morocco, sweeping across Europe will intensify already high temperatures. Low levels of rain also bring an increased risk of wildfires. 

A heat dome is a weather phenomenon where a ridge of high pressure gets stuck in the atmosphere. 

It traps hot ocean air like a lid or cap on a boiling pot. Hot air expands vertically into the atmosphere and high pressure pushes it toward the ground. It has nowhere to escape and compresses trapping even more heat underneath. 

Winds are usually able to move high pressure around but with the dome stretching far into the atmosphere, these weather systems become almost stationary. 

A heat dome can lead temperatures to soar well above what is normal. 

On top of this, the ground begins to warm up, losing moisture and increasing the chance of wildfires. With low rainfall expected across many of the regions the heat dome is expected to cover, experts have warned of an increased risk of blazes breaking out. 

Since 1950 heatwaves have increased in length and frequency all over the