Anabatic wind, or upslope winds, occur over mountain slopes on calm sunny days. As the slopes are heated, the air in contact with the surface is warmed due to convection and rises upward. The rising warm air reaches a height where it cools adiabatically to below its dew point and forms cumulus clouds.

The air over the valley at the same altitude is not as warm because of the large distance from the ground below. On the slopes as the warm air rises, a low pressure is created. The relatively colder air flows in from the valley, forming an anabatic wind.

This circulation also forces the cold air from the mountaintops to sink into the neighbouring valleys. In very large mountains, the cumulus cloud formation can often produce rain or even thunderstorms.