Snow

Snow is precipitation made of ice crystals, often joined into flakes, that forms in clouds and falls when atmospheric conditions allow.

Ice nucleation: Ice nucleation is the formation of the first stable ice crystals from supercooled water or water vapor. Snow formation begins when cloud water freezes or vapor deposits onto an ice nucleus.
Cloud: A cloud is a visible mass of suspended water droplets, ice crystals, or both in the atmosphere. Snow crystals form and grow inside clouds.
Snowpack: Snowpack is the accumulated layer of snow resting on the ground over time. Repeated snowfall builds the seasonal store of snow on land.
Sleet: Sleet is precipitation that reaches the ground as small ice pellets, formed when falling snow melts and refreezes. Unlike snowflakes, sleet consists of hard pellets created by melting and refreezing.
Nakaya diagram: The Nakaya diagram maps snow-crystal forms against temperature and water-vapor supersaturation. It summarizes how cloud conditions influence crystal shapes, while leaving complex growth unresolved.
Deposition (phase transition): Deposition is a phase transition in which a gas becomes a solid without passing through a liquid state. Water vapor can add ice directly to growing snow crystals.
Supercooling: Supercooling is the cooling of a liquid below its freezing point without its becoming solid. Supercooled droplets provide liquid water that can freeze onto ice crystals.
Snowmelt: Snowmelt is the liquid water produced when snow warms and melts. Melting snow supplies rivers, reservoirs, and soils.
Freezing rain: Freezing rain is liquid precipitation that freezes on contact with surfaces at or below 0 °C. It falls as liquid drops rather than as ice crystals.
Snowflake: A snowflake is an individual snow crystal or an aggregate of snow crystals that falls from a cloud. The variety of snowflake forms raises questions about how tiny growth differences arise.

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