Snow is a form of solid atmospheric precipitation consisting of individual ice crystals that grow while suspended in the air—usually within clouds—and then fall, accumulating on the ground, where they undergo further changes. It consists of frozen crystalline water throughout its life cycle, starting when, under suitable conditions, the ice crystals form in the atmosphere, increase to millimeter size, precipitate and accumulate on surfaces, then metamorphose in place, and ultimately melt, slide, or sublimate away.