Moderate Fog Warning

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By Amelia Grant, Technology & Media EditorReviewed by Oliver ReevesForecast data: Open-Meteo & national met services

Live forecasts update automatically; written guidance last reviewed 16 June 2026 by the NewsPrism weather desk. Data from national met services via Open-Meteo.

A moderate fog warning means visibility falls to 100–200 metres, making driving and outdoor activities hazardous. Issued by the Met Office during autumn and winter, it advises extra caution and allows extra journey time.

What does a moderate fog warning mean?

A moderate fog warning, often classed as a yellow-level alert, indicates dense fog that reduces visibility significantly. It can cause sudden patches of zero visibility, especially near rivers, valleys and coastal areas. The warning is typically in place from late evening until mid-morning.

How should you travel in moderate fog?

If you must drive, use dipped headlights or fog lights, reduce speed sharply and increase your stopping distance. Avoid using full beam — it reflects off the fog and worsens visibility. Listen to local radio for updates and delay non-essential journeys until fog lifts.

Visibility100–200 metres (moderate), can drop below 100 metres in patches

Warning levelYellow (be aware) – Met Office

Typical durationForm overnight, clear by late morning; can persist all day in sheltered valleys

Most affectedCentral, eastern and southern England; valleys and coastal plains

Fog and your health

Fog can trap pollutants near the ground, worsening asthma and other respiratory conditions. If you have a lung condition, limit time outdoors when a moderate fog warning is active. Keep windows closed and use a HEPA filter indoors if possible.

When does fog normally clear?

Fog usually clears within a few hours of sunrise as the sun heats the ground and breaks the stable air layer. If cloud cover remains thick, fog can linger until early afternoon. Check the 10-day forecast for local timings.

What is the difference between fog and mist?

Fog reduces visibility to less than 1 km; mist allows visibility above 1 km. Both are made of tiny water droplets suspended in the air. A moderate fog warning is only issued when visibility drops to 200 metres or less.

Is it safe to walk or cycle in moderate fog?

Yes, with care. Wear reflective or high-visibility clothing, use a torch or bike lights, and stay on pavements or cycle paths. Cross roads only where you can clearly see approaching traffic. Avoid exercising near busy roads due to trapped pollution.