Fog
Fog forms when a small temperature-dewpoint spread exists.
Radiation Fog
Radiation fog forms over land area when the Earth is cooled due to energy radiating into space. This cooling reduces the air temperature the dewpoint or below, and often occurs on clear, windless nights. Radiation fog is generally a nighttime occurrence and often does not dissipate until after sunrise.
Advection Fog
Advection fog forms when moist air moves over a colder surface. This is common in coastal areas, where moist air from the water is blown onto the relatively cool land.
Advection fog can move deep into continental land area. Strong winds can push the fog into a layer of low stratus clouds.
Upslope Fog
Upslope fog forms as a result of moist, stable air being adiabatically cooled to or below its dewpoint as it moves up sloping terrain.
Frontal Fog
When warm, moist air is lifted over a front, clouds and precipitation may form. If the cold air below is near its dewpoint, evaporation (or sublimation) from the precipitation may saturate the cold air and form fog.
Steam Fog
When very cold air moves across relatively warm water, enough moisture may evaporate from the water surface to produce saturation. As the rising water vapor meets the cold air, it immediately recondenses and rises with the air that is being warmed from below.
Because the air is destabilized, fog appears as rising filaments or streamers that resemble steam.