A radiation fog is likely to develop when there is

A radiation fog is likely to develop when there is a rapid loss of heat by radiation on clear, calm nights. During the day, the sun heats the earth and air above it, and as the air warms, it rises and cool air from surrounding areas takes its place. At night, the opposite occurs: the earth and air cool, and the cool air sinks, replacing the warm air. If the sky is clear and winds are calm, the earth and air can continue to cool rapidly by radiation, causing the temperature to drop and the air to become saturated with moisture. This can result in the formation of a radiation fog, which can reduce visibility and affect transportation and other activities.