More commonly known as ground fog, it is the most common problem
for air traffic control. Usually forms at night and dissipates before mid
morning. Best conditions for formation are a cool clear night, light
wind, and high humidity.
Because advection fog covers large areas, it is considered the most
dangerous to aviation. Forms when air moves over a land or water
surface that is colder than the air mass that is passing over it.
Forms when air is forced to ascend a gradual slope. Forms in very
deep layers and requires considerable time to dissipate.
Forms when cold air moves over warm water. Evaporation from the
surface of the warm water saturates the cold air and causes fog to
Table 1-9 -- Four types of air mass
Frontal fog is another hazard that must be added to the list of weather troubles
associated with fronts. There are two classes of frontal fog: warm-front fog and cold-
front fog. Each is described in Table 1-10.
Much more extensive than cold-front fog and a definite hazard to flight
operations. Formed by rain falling from warm air into cold air along the
Cold-front fog is rare. It forms in the cold air mass just behind the cold
front. This type of fog dissipates rapidly due to the fast movement of
Table 1-10 -- Two classes of frontal fog