Fog characteristically resulting when radiational cooling of the earth's surface lowers the air temperature near the ground to or below its initial dew point on calm, clear nights.
Fog formed as the ground (and objects on the ground) cool by losing long- wave infrared radiation. Conditions favorable for formation of radiation fog include light winds, clear skies, and high humidity at the surface (near or at 100 percent).
A common type of fog which forms overland on nights characterized by light wind, clear sky, and moist air in the lower levels of the atmosphere.
Fog resulting from the nightly cooling of the ground and adjacent air. This is the main type of fog that plagues the Central Valley each year.
Fog produced results from the air near the ground being cooled to saturation by contact with the cold ground. The cooling of the ground results from night time loss of heat from the Earth to space (terrestrial radiation). Favorable conditions for radiation fog are clear sky, little or no wind, and high relative humidity. It occurs in stable air and is primarily a night time or early morning phenomenon. As the Earth and the lower layers of the atmosphere warm during the day, air that was stable during the early morning hours may become unstable - at least in the lower levels. For this reason visibility usually improves as the temperature rises during the day. Mixing in the lower levels disperses the fog into a thicker layer, and eventually it evaporates into the warmer air. When cloud layers form aloft over a radiation fog and retard heating from the sun, visibility improvement is very slow. It is also known as Ground Fog and Valley Fog.
Fog produced over land when radiational cooling reduces the air temperature to or below its dew point. It is also known as "ground fog" and "valley fog".
See ground fog.
a cloud of water droplets formed when the cooling ground lowers the temperature of the air above it to its condensation point
A common type of fog, produced over a land area when radiational cooling reduces the air temperature to or below its dewpoint. Thus, a strict radiation fog is a nighttime occurrence, although it may begin to form by evening twilight and often does not dissipate until after sunrise. Factors favoring the formation of radiation fog are 1) a shallow surface layer of relatively moist air beneath a dry layer and clear skies, and 2) light surface winds. It can be most confusing near sea coasts with cold coastal water. It can be difficult at times to differentiate between this and other types of fog, especially since nighttime cooling intensifies all fogs. Radiation fog is frequently and logically called ground fog, but in U.S. weather observing practice, the latter term is defined only with respect to the amount of sky that is obscured by the fog.
Fog that is created when radiational cooling at the earth's surface lowers the temperature of the air near the ground to or below its dew point. Formation is best when there is a shallow surface layer of relatively moist air beneath a drier layer, clear skies, and light surface winds. This primarily occurs during the night or early morning.