Methods of Cooling Air to the Dewpoint

1. Conductional Cooling

(a) Air flows over a cold surface and is cooled by conduction (This process is termed "advective cooling.") If the cooling is sufficent to take the air parcel's temperature to the dew point, the resulting condensation will produce a layered cloud on the ground.
APPLICATION:  California's coastal summer advection fog

 (b) Air "sits" on a surface that gets cold overnight. (This process is termed "radiational cooling"). If the cooling is sufficent to take the air parcel's temperature to the dew point, the resulting condensation will produce a layered cloud on the ground.
APPLICATION:  California's Central Valley winter "tule" or radiation fog

2. Expansional cooling

Air expands, molecules get "further apart", do not strike each other as

often, do not "vibrate" as much. Air expands when pressure around

moving air parcels decreases markedly. Best example---air involved in

vertical motion.

APPLICATION: rising air experiences cooling at "dry adiabatic rate"

of 5.5^oF/1000 ft. This is one of the ways in which the air is cooled to

the dew point.