Among the planets in the Solar System, Earth is unique in possessing large quantities of water, and water’s properties are highly significant in determining weather. This is because water readily exists in three different phases (ice, liquid water, and water vapour) at temperatures frequently encountered on Earth. ‘Water in the atmosphere’ explains humidity and saturation: the number of molecules of water vapour in the air is determined solely by temperature. Unstable conditions lead to the formation of cumuliform clouds and precipitation is created by either glaciation or coalescence. There are three groups of clouds—cumuliform, stratiform, and cirriform—with ten types of cloud identified based on their altitude and structure.