Cumulus humilis is what is commonly referred to as "fair weather cumulus". In hot countries and over mountainous terrain these clouds occur at up to 6000 meters altitude, though elsewhere they are typically found lower.
They are formed by rising warm air that has been heated by the ground, which in turn has been heated by the sun. They have a limited depth (technically known as showing no significant vertical development). This indicates that the temperature in the atmosphere above them either drops off very slowly or not at all with altitude (see Lapse rate). While cumulus humilis may be accompanied by other cloud types, when they appear in a clear sky (see picture), they are an indicator of pleasant weather for the next several hours. Though at times, these clouds collapse into stratocumulus clouds, and cover much of the sky.
Below the cloud base the air can be quite turbulent, giving occupants of light aircraft a rough ride. To avoid turbulence where such clouds are present, pilots may climb above the cloud tops. However glider pilots actively seek out the rising air to gain altitude.