advection fog

Fog that forms as a mass of warm, humid air moves over a cold surface. Advection fogs are usually maritime fogs that, driven by local winds (breeze regimes), come to extend over certain coastal strips, penetrating inland. Unlike radiation fogs, advection fogs are dynamic (they move) and do not follow the day-night cycle, so they can arise at any time of day, when the right conditions occur. Their duration is highly variable, and they can persist for several consecutive days. The physical process giving rise to this type of fog is condensation. Moisture-laden air reaches saturation on coming into contact with a sea area where the surface waters are cold, or as it moves over ground that is also cold. Advection fog can form directly over the sea and move from there onto land, or it can form only over dry land, when a mass of humid air, initially unsaturated, slides over it and reaches saturation as it cools, on coming into contact with the ground. Condensation of water vapor can also occur when a mass of cold air moves over a warm surface, in which cases an advective fog forms.