Cloud and Precipitation

When air is cooled below its dewpoint the water vapour therein starts to condense out into water droplets. The water droplets form either fog or cloud, depending on the process by which the air is cooled. It is generally understood that the fog is formed when the cooling of the air takes place at the surface by conductive processes, whereas cloud generally forms above the surface due to the adiabatic cooling of the rising air. The cooling of the air occurs as the air is forced to rise as follows: a

at a warm front

b

at a cold front

c

by convectional processes

d

by high ground

e

by turbulence