Fog is a cloud bank that is in contact with the ground. Fog is usually the only clouds that touch the ground and it only differs slightly from other clouds in that it touches the surface of the Earth. The same cloud that is not fog on lower ground may be fog where it contacts higher ground such as hilltops or mountain ridges.
Mist is a phenomenon of small droplets suspended in air. It can occur as part of natural weather or volcanic activity, and is common in cold air above warmer water, in exhaled air in the cold, and in a steam room of a sauna. It can also be created artificially with aerosol canisters if the humidity conditions are right.
The only difference between mist and fog is density and its effect on visibility. A cloud that reduces visibility to less than 1 km (about 1,094 yards or 0.62 miles) is called fog, whereas it's called mist if visibility range is between 1 and 2 km.
In the UK for driving purposes the definition of fog is visibility less than 200 metres, for pilots the distance is 1 kilometre.
|Effect on visibility||Reduces visibility to less than 1 km (1,094 yards)||Reduces visibility to between 1 and 2 km|