How Does Fog Form?


Quick Answer

Most fog forms as a result of the combination of moisture in the air and an influx of cool air that causes the moisture to fall below its dew point and condense. Meteorologists consider fog to be a type of a cloud that forms just above the ground.

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Full Answer

Radiation fog, or ground fog, is the most prevalent fog, and it forms at night or in the early morning. Radiation fog is common in valleys. Steam fog occurs when a mix of cool air that lowers the temperature of warm air over a body of water. Ice fog, a rare fog that exists in extremely cold environments, forms when the moisture in the air consists of ice. Advection fog is the only type of fog that forms with warm air over a cold surface. This is common on northern coasts and in colder climates with a large amount of warm air over snow. The movement of advection fog is visible. Warm rain and cool air creates frontal fog. Fog that moves on an incline is upslope fog. The cool air and moisture from hail also produces fog.

The sun warms the surface of the Earth to dissipate fog. Typically, this process begins on the outer edges and works into the more dense fog.

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