Fog
Fog is a complex atmospheric phenomenon. It is a visible mass consisting of cloud water droplets or ice crystals suspended in the air at or near the Earth's surface. Fog can be considered a type of low-lying cloud, and is heavily influenced by nearby bodies of water, topography, and wind conditions. In turn, fog has affected many human activities, such as shipping, travel, and warfare.
Definition
The term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated locally (such as from a nearby body of water, like a lake or the ocean, or from nearby moist ground or marshes).
By definition, fog reduces visibility to less than 1 kilometre (0.62 mi), whereas mist causes lesser impairment of visibility.
For aviation purposes in the UK, a visibility of less than 5 kilometres (3.1 mi) but greater than 999 metres (3,278 ft) is considered to be mist if the relative humidity is 70% or greater; below 70%, haze is reported.
