Met Office issues fog warning – the 5 types of fog you see in the UK

UK weather: Met Office forecasts rain and fog across country

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Britain has woken up to a foggy landscape today. In the UK fog tends to come with cooler temperatures forecast for this week, so there’s likely to be plenty more foggy mornings to come throughout November. But what are the different types of fog, and when do they occur?

Radiation fog

Radiation fog is the most common in winter, and usually occurs when the sky is clear and conditions are calm.

It’s caused by the cooling of land overnight, which reduces the temperature of air close to the surface.

This reduces the ability of the air to hold moisture, allowing condensation to form close to the ground.

Advection fog

Advection fog is created when warm, moist air passes over a cold surface.

The air is cooled as a result, and it’s most often seen when warm air passes over icy or snowy ground in winter.

It’s most common at sea when warm tropical moves over cold waters.

Valley fog

Valley fog forms when dense, cold air forms in the lowest parts of a valley.

Valley fog is often a result of a temperature inversion, where warm air passes over the valley, trapping cooler air underneath it.

The clue is in the name – it can only occur in valleys, and unlike other fogs it can last for several days if the conditions are calm enough.

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Freezing fog

Freezing fog happens when the liquid fog droplets freeze to solid surfaces.

Mountaintops that are covered by clouds are often covered in freezing fog.

As the freezing fog lifts, the ground, the trees, and even objects like spider webs, are blanketed by a layer of frost.

Evaporation fog

Evaporation fog is caused by cold air passing over warm water and land.

When the warm water on land evaporates into low air layers, it warms the air, causing it to rise and mix with the cooler above.

The warm, moist air cools as it mixes with the colder air, resulting condensation and fog over the ground.

Met Office fog warning

The Met Office has warned Sunday night into Monday morning will see “thick fog in places, causing difficult, possibly dangerous, travel conditions”.

The forecaster warned: “Areas of fog, some very dense with visibility near 50 metres in places, and currently focused across Cheshire, Staffordshire and Shropshire, seems likely to develop more widely during the coming hours.

“It is uncertain at this stage whether the same areas will be affected during the Monday morning peak travel period.”

Learn more about the Met Office fog warnings.

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