Parts of Wiltshire have been covered in a thick blanket of fog in recent days.

Drivers have reported low visibility on the roads due to the misty weather.

But why is it so foggy and what causes so much mist to build? What does it mean for drivers? 

Here’s the answers to some of those questions. 

What causes fog?

Fog is essentially a cloud at ground level that causes visibility to reduce to less than 1000 metres.

Fog is caused by tiny water droplets suspended in the air.

The thickest fogs tend to occur in industrial areas where there are more pollution particles in the air.

These conditions allow water droplets to coalesce and grow, the Met Office said.

What is the difference between fog and mist? 

The Met Office says fog, mist and haze can all affect visibility in different ways - from driving conditions to shipping and aviation.

Fog and mist differ by how far you can see through them, according to the weather agency. 

Fog is when you can see less than 1,000 metres away, and if you can see further than 1,000 metres, it is called mist.

Severe disruption to transport occurs when the dense fog causes visibility to fall below 50 metres.

Can pilots fly aeroplanes in foggy weather? 

Airports often choose to delay or cancel flights if foggy conditions are not ideal for take off or landing. 

But, according to aviation news website Simple Flying, fog can massively impact pilots looking to move an airplane while it's on the runway. 

This situation means crews have to rely on maps and visual communications in the cockpit, instead of views of the airport through plane windows.

Driving in fog 

Drivers are advised to use fog lights to make it easier to see and be seen in misty conditions.

The Highway Code says motorists must use headlights when it isn't possible to see more than 100 metres in front of the car. 

Drivers can also use front or rear fog lights but this is optional.

Fog lights should be turned off when visibility improves. 

The AA has several top tips for driving in fog:

  • Use dipped headlights, wipers and demisters.
  • Use fog lights when you need to.
  • Beware of other drivers not using headlights.
  • Only drive as fast as conditions allow.
  • Slow down so you can stop in the distance you can see clearly.
  • Allow 3 seconds instead of 2 between you and the car in front.
  • Check your mirrors before you slow down.
  • Open your window to listen for traffic at junctions if you can’t see.

What does the fog light symbol look like?

The front fog light symbol shows a lamp with slanting lines of light in front of it, pointing left. The lines of light are intersected by a wavy line which represents the fog.

The rear fog light symbol is the same as the front fog light symbol but in reverse. The light and fog lines appear after the bulb, pointing right.