Rolling haar: A sea of fog on the Ligurian coast

Can't get to the coast this Bank Holiday? Check out this sea fog instead which affected large stretches of the Ligurian coast earlier this year.

Sea fog, known also as haar in the UK and Ireland, forms under certain conditions and is best observed between late winter and late spring.

This is because during spring, the sea reaches its lowest temperatures, while warmer air moving in becomes more common. Sea fog requires the movement of a warm air mass over a cold sea surface.

The warm air passing over this colder surface then cools and condenses, like when a person breathes warm air onto cold glass, forming a dense layer of fog or low cloud.

If there is a strong anticyclone (high pressure system) in place, which suppresses convection and forces air to subside, the fog that forms will be more robust.