Cumulus clouds are characterized by dense individual elements in the form of puffs, mounds or towers, with flat bases and tops that often resemble
cauliflower. They are formed due to
convection. Buoyant, upward air currents, known as
thermals rise to a height at which the moisture in the air can condense. Because of this, they "grow" vertically instead of horizontally. Though most common in warm, summer weather, cumulus clouds can be formed at any time of year.