How do snowflakes form in clouds ?
Snow flakes are frozen water, that is, ice, that forms in clouds. We have an online graphic that shows why snow crystals form in different shapes. For snow to form in a cloud, the cloud has to be below 32 degrees F and has to have very tiny particles, called freezing nuclei such as tiny bits of clay, to encourage water drops in the cloud to turn to ice. Once a cloud has a mixture of ice crystals and water droplets, the ice crystals will begin growing as the water droplets evaporate. The ice crystals grow into snow flakes as water vapor in the cloud turns directly to ice instead of condensing first into water and then freezing. Rain drops that freeze on the way down are ice pellets, which are also called sleet. Our water in the atmosphere index and our winter weather index have links to a lot more information on what goes on in winter clouds.
