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Types of Evaporation Fog

Published in Fog Types 2 mins read

What is Evaporation Fog?

Evaporation fog, also known as cold advection fog, forms when cold, stable air moves over a significantly warmer body of water or moist land. The warmer surface causes water to evaporate rapidly into the colder air. This added moisture saturates the air, leading to condensation and the formation of fog. There are two primary types:

  • Steam Fog: This occurs when cold air moves over a much warmer body of water, such as a lake or ocean. The rapid evaporation of water from the warm surface creates a visible steam-like fog. The cold air is significantly colder than the water's temperature, causing the water vapor to condense quickly. This is detailed in sources like the National Snow and Ice Data Center's definition of steam fog. (https://nsidc.org/learn/cryosphere-glossary/steam-fog)

  • Frontal Fog: This type forms when warm raindrops evaporate into a cooler, drier layer of air near the ground. This often happens in the vicinity of warm fronts, where warm, moist air rises over cooler air. (https://www.weather.gov/lmk/fog_tutorial)

How Evaporation Fog Differs

Evaporation fog differs from other fog types like radiation fog (formed by nighttime cooling) and upslope fog (formed by adiabatic cooling of air rising along a slope). Evaporation fog's key characteristic is its formation through the addition of water vapor from evaporation into cold, relatively dry air. As noted by the World Meteorological Organization, it's a process of adding moisture, unlike other processes that involve cooling the air. (https://cloudatlas.wmo.int/evaporation-fog.html) The USGS even illustrates this with images of valley fog formations. (https://water.usgs.gov/edu/gallery/watercyclekids/evaporation-fog.html)

Evaporation fog can sometimes lead to freezing fog or even frost if the temperature is sufficiently low. (https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/fog/types-of-fog)