Fog is a meteorological phenomenon defined as a cloud with a vertical depth of less than 1,000 feet and an opacity sufficient to significantly reduce visibility. It forms when the air cools to its dew point, causing water vapor to condense into microscopic suspended water droplets or ice crystals. The primary mechanisms of formation include radiation fog, which occurs when terrestrial surfaces cool rapidly overnight; advection fog, which forms when warm, moist air moves over a much cooler surface; and steam fog, which results from the rapid mixing of very cold air with warmer vapor sources. Fog layers can impact physical processes by altering thermal gradients, affecting atmospheric transmission of radiation, and creating unique local microclimates.