Why Has It Been So Foggy in the UK This Week?

UK fog and air pollution this week, Digi Mart USA News (United Kingdom): Many parts of the UK have woken to thick fog over the past few days, with some areas seeing visibility reduced to a short distance ahead. In London, the city’s mayor has put a high air pollution warning in place.

Forecasters at Imperial College London advised Lord Sadiq Khan to trigger the alert after “dense fog and very light winds allowed pollution to build up”.

BBC Weather’s Simon King says fog is essentially a cloud that has formed on the ground. Fog forms when the air cools after sunset, causing water vapour to turn into droplets.

If visibility is more than one kilometre, it is called mist; if it is less than one kilometre, it is fog.

Simon King told Newsround that bonfire events last weekend added to the poor visibility. When winds are calm, fog can get worse.

Fireworks and bonfires for Bonfire Night and Diwali added tiny smoke particles to the atmosphere, which act as seeds for water droplets, creating a thicker cloud on the ground.

While the fog is thick, travelling to school by car, bus, bike or on foot may be harder because roads, signs and buildings are harder to see. Drivers are being told to take extra care and may use fog lights to help them see and be seen.

Pedestrians and cyclists are advised to wear high visibility clothing and take extra care when crossing roads.

Outdoor activities such as football, rugby and hockey training can also be harder to run safely if players and coaches cannot see clearly across a pitch. An FA Cup tie between Altrincham and Notts County was heavily affected by fog at the weekend.

The fog is expected to clear and give way to cooler, frosty weather later in the week. Fog itself does not normally make healthy people ill, but some people with asthma or other breathing conditions may find symptoms worsen when extra particles from smoke or pollution are in the air.

People with asthma should follow medical advice and keep inhalers close by.

Forecasts show the weather becoming changeable in the second half of the week, with winds picking up and thick fog less likely to form. Some foggy mornings could still occur in Northern Ireland and Scotland, and frosts look more likely across the UK as a colder weather front moves in from the north.