Explaining the different types of fog

Depending on where you live, fog might be a common occurrence. There are six types of fog, advection fog, radiation fog, upslope fog, steam fog, frontal fog, and ice fog.

Fog is basically a cloud that forms at ground level. In order for fog to form, the temperature and dew point must be close to the same value. This can happen through cooling of the air or adding moisture to the air.

Fog can create hazards for drivers, since fog reduces visibility, it can be more difficult for a driver to judge distance or see hazards including other drivers.

Advection fog

Advection fog occurs when moist air moves over a colder surface. The air near the surface cools to below the dewpoint.

Radiation fog

Radiation fog forms under stable nighttime conditions when the ground emits radiation; this cools the ground, which causes a temperature inversion. Moisture may evaporate into the air if enough moisture is present.

Upslope fog

Upslope fog occurs when the terrain lifts the air and cools it to its dew point and saturation. This type of fog typically forms over higher elevations and builds downward into valleys.

Steam fog

Steam fog occurs when water vapour is added to air that is much colder, it then condenses into fog. This fog is most common during autumn and early winter when waters are still warm and colder air masses prevail.

Frontal fog

Frontal fog forms along either a warm front or a cold front. This fog is usually caused by rain falling into cold stable air that raises the dew point.

Ice fog

Ice fog is made of ice crystals instead of water droplets and forms in extremely cold air. It forms in areas where the burning of hydrocarbon fuels adds large quantities of water vapour to the air. Steam vents, motor vehicle exhausts, and jet exhausts are major sources of water vapour that produce ice fog.