Snow crystals grow in one of two designs—plate-like and columnar.Plate-like crystals are flat.They form when the air temperature is about fifteen degrees below zero Celsius.Columnar snow crystals look like sticks of ice.They form when the temperature is about five degrees below zero.

　　The shape of a snow crystal may change from one form to another as the crystal passes through levels of air with different temperatures.When melting snow crystals or raindrops fall through very cold air，they freeze to form small particles of ice，called sleet.

　　Groups of frozen water droplets are called snow pellets.Under some conditions，these particles may grow larger and form solid pieces of ice，or hail.

　　When snow crystals stick together，they produce snowflakes.Snowflakes come in different sizes.As many as one hundred crystals may join together to form a snowflake larger than two and one-half centimeters.Under some conditions，snowflakes can form that are five centimeters long.Usually，this requires near freezing temperatures，light winds and changing conditions in Earth’s atmosphere.

　　Snow contains much less water than rain.About fifteen centimeters of wet snow has as much water as two and one-half centimeters of rain.About seventy-six centimeters of dry snow equals the water in two and one-half centimeters of rain.

　　Snowfall helps to protect plants and some wild animals from cold，winter weather.Fresh snow is made largely of air trapped among the snow crystals.Because the air has trouble moving，the movement of heat is greatly reduced.

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