As the air rises is becomes saturated and the water vapour begins to condense and hence clouds are formed. Air flowing up slopes. Air is cooled adiabatically as it rises up the slopes of hills and mountains. If the air rises enough when the hills or mountains are sufficiently high or when the air is sufficiently moist, cloud will be formed. Air being forced to rise in the vicinity of cold or warm fronts.
Warm air is forced to rise over a mass of heavier cold air.
As the warm air rises it cools, and then clouds may be formed. The forced ascent of air, which results from the convergence of high and low pressured air. This convergence occurs over a large area, but again the type and extent of cloud formation depends on the nature of the low pressure system. This is also related to low-level clouds being produced via the turbulent mixing of the air underneath a temperature inversion. In the past, there were four main groups in which clouds were classified.