Here's everything you need to know about sea fret.
What is sea fret?
Sea fret, known in Scotland as a haar, is a coastal fog.
They're much more common on the east coast than elsewhere in the UK because the North Sea is so cold.
What causes it?
It might seem counterintuitive but the fog is caused by warm weather.
When a pocket of warm air passes over the freezing sea, the moisture in the wait begins to condense.
The air in the pocket then starts to cool down and forms a fog.
When this happens at the same time as a light wind, the fog is blown over the coast and, sometimes, more inland areas as well.
When does sea fret happen?
Coastal fog usually happens most in the spring and summer months when conditions begin to warm up but the sea (which warms more slowly) stays relatively cold.
The impact, location and movement of coastal fog depend on a number of conditions, including wind strength, direction and land temperature.
When does sea fret disappear?
Sunshine generally burns the fret away after a while but if it is too thick and winds continue blowing east towards the coast, or temperatures on land aren't high enough, it can persist for several days.
The danger of sea fret
The sometimes sudden nature of this type of weather can be dangerous by causing disorientation as it dramatically reduces visibility.
Industries such as fishing, shipping and oil can all be affected.