This type of fog is inherently dependent on longwave radiative cooling and high moisture contents at the earth's surface. Occasionally, west coast fog episodes partially owe their existence to radiative cooling; in addition, nocturnal radiative cooling contributes to the depth of hot spell west coast fogs.

Radiative cooling is cooling primarily in the longwave portion of the electromagnetic spectrum (i.e., longer wavelengths than solar radiation). It is maximized at night during dry, clear conditions. The radiative cooling rate increases rapidly as the temperature of the land surface increases. During the daytime, radiative cooling is typically more than offset by solar radiation absorption.

For additional information on radiation cooling and fog formation, visit the Radiation Fog Web Module