Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earths surface. Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influenced by nearby bodies of water, topography, and wind conditions. Fog appears when water vapor (water in its gaseous form) condenses. During condensation, molecules of water vapor combine to make tiny liquid water droplets that hang in the air. There are several types of fog, including:

• Radiation Fog: This fog forms when all solar energy exits the earth and allows the temperature to meet up with the dew point temperature. It is common on clear, calm nights with high relative humidity and light winds.

• Precipitation Fog: This is fog that forms when rain is falling through cold air. It is common with warm fronts but can occur with cold fronts as well.

• Advection Fog: This type of fog forms from surface contact of horizontal winds. It can occur with windy conditions and forms when warm, moist air blows in from the south and comes in contact with snow or cool moisture on the ground.

• Upslope Fog: This fog forms when moist air is going up the slope of a mountain or hill, which condenses into fog on account of adiabatic cooling, and to a lesser extent the drop in pressure with altitude.

• Valley Fog: Valley fog forms in the valley when the soil is moist from previous rainfall. As the skies clear, solar energy exits earth and allows the temperature to cool near or at the dew point.

Fog is similar to, but less transparent than, mist. It can also be associated with freezing conditions, producing freezing fog or frozen fog (also known as ice fog), which occurs when the droplets have frozen into extremely tiny crystals of ice in midair.