Home › Weather › Moderate Fog Warning
Live forecasts update automatically; written guidance last reviewed 20 June 2026 by the UK Bullet weather desk. Data from national met services via Open-Meteo.
A moderate fog warning means visibility will drop below 100 metres in places, making driving and travel hazardous. The Met Office issues this alert when fog is expected to cause disruption, particularly during morning and evening commutes.
What does a moderate fog warning mean for my day?
You should expect slower journey times and potential delays to flights and ferry services. Fog can form quickly overnight and linger into late morning, especially in valleys and near coasts.
- Reduce speed and use dipped headlights or fog lights if visibility falls below 100 metres
- Leave extra time for travel and check for transport disruptions before setting out
- Avoid using rear fog lights in lighter fog, as they can dazzle other drivers
- If cycling or walking, wear bright or reflective clothing to be seen
How long will the fog last?
Fog usually clears by late morning as the sun warms the ground, but in winter it can persist all day. A moderate warning typically covers a 6–12 hour window.
Check our 10 Day Weather Forecast UK for fog trends in your area, and see the UK weather hub for live updates.
Should I cancel travel plans during a moderate fog warning?
Not necessarily, but allow extra time and check your route. Flights and ferries may be delayed, and motorway speed limits are often reduced. Postpone non-essential journeys if visibility is below 50 metres.
Is moderate fog dangerous for driving?
Yes, because it reduces reaction time and hides hazards. The Highway Code advises using fog lights when visibility drops below 100 metres, and increasing your stopping distance significantly.
Can fog affect my health?
Fog itself is not harmful, but it can trap pollutants near the ground. People with asthma or lung conditions should limit outdoor exertion until the fog lifts. See NHS advice on air quality.