snow

Snow is precipitation in the form of ice crystals that forms when water vapor deposits directly into solid ice in cold air. This typically occurs when surface temperatures are at or below freezing and humidity is sufficient for cloud formation. Snow crystals grow in clouds around microscopic nuclei and arrange themselves into hexagonal lattices, producing snowflakes that vary in size and shape depending on temperature and humidity as they fall.

Some snowflakes reach the ground intact, while others melt or sublimate before landing. On the ground, snow accumulates to form a snowpack whose properties depend on air temperature, moisture, and wind. The density of snow can range from light, fluffy powder to heavy, wet snow. Snow cover affects the landscape by insulating the ground, altering albedo, and regulating meltwater release.

Snow is measured by depth and by snow water equivalent, the amount of liquid water contained in the snow. SWE is used in hydrology and water management to estimate spring runoff and reservoir inflows. Snow and its melt supply water to rivers and aquifers and are a key resource in many regions.

Seasonal snow can influence transportation, agriculture, and tourism and poses hazards such as avalanches in mountainous terrain. Snow patterns are a climate indicator, changing with temperature and moisture conditions that affect precipitation type and duration.