A strong area of high pressure has been hovering over south-western Europe for days. In many places, temperatures are reaching or even exceeding 40 °C due to what is known as a "heat dome".

However, the situation is particularly extreme not only because of the high temperatures, but because of their duration. Together with a persistent high-pressure system, the heat dome sits over the affected regions like a huge atmospheric bell.

It acts like an invisible lid over the atmosphere. The air, heated by the strong June sunshine, can barely escape and is further compressed and warmed by the high air pressure. Behind it lies a stable omega block, which keeps other weather systems at bay.

As a result, the heat can linger for days, sometimes even weeks. The current heatwave stretches from Spain through France to the UK and Germany. On the TemperatureRadar, the red and purple colours clearly show that the hot air mass is barely moving.