A light or thin fog is usually called a mist. Fog may occur when the moisture content of the air is increased beyond the saturation point.
Fog also occurs when the air is cooled below a critical temperature called the dew point.
Fog commonly found in valleys and depressions in the morning, especially during autumn, is of the radiation type, which because of its shallow nature is dissipated by the sun's heat as the day progresses. The extensive fog banks frequently occurring along the coasts of Newfoundland and Labrador are of the advective type and, being generally quite deep, often persist for days at a time, hindering shipping and aviation activity. Licensed from Columbia University Press. All rights reserved.