Something amazing could happen this week – summer may reappear, for a few days at least. Warm sunshine, few clouds and little sign of rain is on the cards, just in time for the school holidays.

The improvement in weather is thanks to a visit from the Azores High, a huge high-pressure system often anchored over the Azores islands. The story of this anti-cyclone actually begins at the Equator, where intense sunshine sends warm, humid air billowing upwards. That generates huge thunderstorms towering upwards until they hit the invisible ceiling of the stratosphere. The tropical air then spreads outwards until it sinks at about 30 degrees latitude. As the air falls it gets squashed and warms up, much like a bicycle pump grows hot when inflating a tyre. The sinking air is also dry, leaving skies clear. And as high pressure systems like this straddle the globe at about 30 degrees latitude, they create some of the world’s deserts, such as the Sahara.

In the summer the Azores High also pushes further north, towards Portugal and Spain, and sometimes reaches the UK with its magnificent weather. As long as this ridge of high pressure is in control it sends wet and windy low pressure systems skirting around the top of the anticyclone. But if the Azores High slips southwards, the foul weather can return again.