Haar: What causes Scotland's sea fog, why is it happening and which areas are most likely to be affected?

The rolling sea fog that descends on the East Coast between April and September each year often reduces visibility and can send temperatures plummeting in areas immersed in the chilly coastal mist.

What is ‘haar’?

Haar, or 'sea fret' as it is also known in the North East, is used to describe a cold fog that accumulates at sea, rather than on land.

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The most common form of coastal fog occurs when warmer air meets the chillier temperatures of the North Sea.

It can often be seen rolling into areas of Scotland like Dalgety Bay, North and South Queensferry and Portobello across beaches and bridges as a dense, thick wall of mist that reduces visibility and has been known to ground flights or cause transport issues on the East Coast.

In 2013, workers on an oil rig in the North Sea off the coast of Aberdeen became stranded after dense haar grounded helicopters and flights at Aberdeen Airport.

Why does it happen?

When warmer air moves across the North Sea, cold air arising from the chilly sea’s surface cools down the warm air – prompting the warmer air to lose its moisture and condense above the sea surface.

James Mooney captured a layer of haar hanging over the Forth Rail Bridge on an otherwise bright, sunny morning in North Queensferry on May 30 2021.

It is seen more commonly in spring and summer months as while the atmosphere and temperatures begin to rise, the sea takes far longer to warm up and mostly remains cold (particularly in the case of the North Sea).

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What areas are likely to be affected?

As a typically easterly phenomenon, areas on the East Coast of Scotland and Northern England are usually the worst affected by haar.

On beaches in towns and cities like Edinburgh, Aberdeen and in the Kingdom of Fife, the dense mist is often seen rolling in across shores during the early morning and early evening.

According to the Met Office, the severity and location of the coastal fog generally depends on weather conditions such as wind strength and wind direction.

But land temperature can also have an impact on haar, with warmer land temperatures, such as those seen across the United Kingdom on the 2021 Spring Bank Holiday weekend, likely to cause the fog to dissipate faster than in cooler temperatures.

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