Cumulus humilis is formed when the atmosphere is quite stable and the air is fairly dry. If the air were much drier or more stable, cloud would not likely form at all.This picture shows a rare day when both conditions are met, there is little wind, and there are no upper-level clouds to lighten the sky. Near the horizon, some 100 km away, is heavier cumulus congestus, which will likely go on to produce showers or thundershowers later in the day.