Wind velocity is an important consideration in the formation of fog and/or low ceiling clouds.  The horizontal motion of the air next to the earth’s surface produces friction, which, in turn, causes the air near the ground to tumble, setting up eddy currents.  The size of the eddy currents vary with the wind speed and the roughness of the terrain.  Lower wind currents produce more shallow eddies, and stronger wind currents produce eddies up to several hundred feet and higher. When the temperature and dewpoint are close at the surface and eddy currents are 100 feet or more in vertical thickness, adiabatic cooling in the upper side of the eddy could give the additional cooling needed to bring about saturation.  Any additional tooling would place the air in a temporary supersaturated state.  The extra moisture will then condense out of the air, producing a low ceiling cloud. Adiabatic heating on the downward side of the eddy will usually dissolve the cloud particles.  If all cloud particles dissolve before reaching the ground, the horizontal visibility should be good.  However, if many particles reach the ground before evaporation, the horizontal visibility will be restricted by a moderate fog condition.
