Cumulus humilis (Cu hum) is the smallest species of the cumulus genus. It appears as flat-based clouds with slightly domed tops, wider than they are tall. They typically form on sunny mornings when surface heating generates weak convection.
Fair-weather indicator
Often called "fair-weather cumulus", their presence signals relative atmospheric stability: a temperature inversion caps their vertical growth. They rarely produce precipitation. As convection strengthens during the day, they may evolve into cumulus mediocris and eventually congestus.