From Free net encyclopedia - For other meanings, see Fog
(disambiguation) Fog is a cloud in contact with the ground. It
occurs when moisture from the surface of the Earth evaporates;
as this evaporated moisture moves upward, it cools and condenses
into the familiar phenomenon of fog. Fog differs from cloud only
in that fog touches the surface of the Earth, while clouds do
not. All types of fog form when the relative humidity reaches
100% and the air temperature drops below the dewpoint, pushing
it lower by forcing the water vapor to condense. Fog can form
suddenly, and can dissipate just a rapidly, depending on what
side of the dewpoint the temperature is on. Fog reduces
visibility. Although some forms of transport can penetrate fog
using radar, road vehicles have to travel slowly and use more
lights. Localised fog is especially dangerous, as drivers can be
caught by surprise. Fog is particularly hazardous at airports,
where some attempts have been made to develop methods (such as
using heating or spraying sa