“fair weather cumulus” is a kind of Cumulus with little vertical development. The formation of the cumulus with little vertical development related to convective currents.
Day time – sea breeze – over lands
Night time – land breeze – over water bodies
Over land, on clear mornings, cumulus may form as the sun rapidly heats the ground. Near coasts, cumulus may form over the land by day in a sea breeze and over the sea during the night in a land breeze.