Fog is a cloud that touches the ground and is made up of condensed water droplets. It forms when water vapor, or water in its gaseous form, condenses into tiny water droplets that are suspended in the air. There are several types of fog, including radiation fog, precipitation fog, advection fog, steam fog, upslope fog, valley fog, freezing fog, and ice fog. The most common types of fog are:
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Radiation Fog: This fog forms when all solar energy exits the earth and allows the temperature to meet up with the dew point. It is most common in the fall when nights get longer, and airmasses begin to cool.
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Advection Fog: This type of fog forms from surface contact of horizontal winds. It can occur with windy conditions, and warm, moist air blows in from the south and comes in contact with snow or cool moisture on the ground. This contact between the air and ground causes the air blowing in to become cool, and the dew point rises, creating high humidity and forming fog.
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Steam Fog: This type of fog forms when cold air moves over warm water. When the cool air mixes with the warm moist air over the water, the moist air cools until its humidity reaches 100%, and fog forms. This type of fog takes on the appearance of wisps of smoke rising off the surface of the water.
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Frontal Fog: This type of fog forms when warm raindrops evaporate into a cooler drier layer of air near the ground. Once enough rain has evaporated into the layer of cool surface, the humidity of this air reaches 100%, and fog forms.
Fog can also form when water evaporates from the surface into the air, raising the dew point until condensation occurs.
