Fog is a cloud that forms at or near the Earth's surface when water vapor (water in its gaseous form) condenses into tiny liquid water droplets or ice crystals suspended in the air
. There are several types of fog, including:
- Radiation Fog : This type of fog forms at night under clear skies with calm winds when heat absorbed by the earth’s surface during the day is radiated into space. As the earth’s surface continues to cool, provided a deep enough layer of moist air is present near the ground, the humidity will reach 100% and fog will form
- Advection Fog : This type of fog forms from surface contact of horizontal winds. Warm, moist air blows in from the south and if there is snow or cool moisture on the ground, it will come in contact with the warm, moist winds. This contact between the air and ground will cause the air blowing in to become cool. Then dew point rises and creates high humidity and forms fog
- Evaporation Fog : This type of fog forms over bodies of water overlain by much colder air. It occurs when water evaporates from the surface into the air, raising the dew point until condensation occurs. Lake effect fog is an example of this type of fog
Fog can also form when rain is falling through cold air, which is common with warm fronts but can occur with cold fronts as well
. Fog often dissipates with daylight as the air and ground warm up, causing the fog droplets to evaporate
