Why Does It Snow?

What You'll Learn

• Snow forms when water vapor in clouds freezes into ice crystals
• Each snowflake starts as a tiny ice crystal and grows as more water freezes onto it
• Every snowflake has six sides because of how water molecules arrange when they freeze
• No two snowflakes are exactly alike
• Snow falls when the air is cold enough all the way from cloud to ground

Words to Know

Snowflake

A tiny piece of snow made of ice crystals

"Each snowflake is unique."

Water vapor

Invisible water in the air

"Water vapor freezes into ice crystals."

Ice crystal

A tiny piece of ice with a special shape

"A snowflake starts as one ice crystal."

Freeze

When water gets so cold it turns solid

"Water vapor freezes into snow."

Check What You Learned

Fun Facts

• Snow forms when water vapor in clouds deposits directly onto ice nuclei, forming ice crystals

  Source: National Weather Service

• Every snowflake has six sides/six-fold symmetry due to the hexagonal crystalline structure of ice

  Source: American Meteorological Society

• Water molecules arrange in a hexagonal lattice when freezing, always producing six-sided crystals

  Source: Caltech, Kenneth Libbrecht research

• No two snowflakes are exactly alike — each takes a unique path through varying temperatures and humidity

  Source: Wilson Bentley, first snowflake photographer, 1885

• Snow reaches the ground only if the air temperature stays below freezing from cloud to surface

  Source: NWS

• If air warms above freezing partway down, snowflakes melt into rain

  Source: NOAA