Snow forms in clouds when the air temperature up there gets below freezing. Water molecules come out of the air and stick together in special patterns of little ice crystals. Then the ice crystals keep getting bigger or tangle up in little clumps to form snowflakes.
Snowflakes have very intricate crystal patterns. There was a scientist who learned how to catch snowflakes and keep them cold long enough to take photographs. He photographed more than a thousand snowflakes without finding any two that were exactly alike. The scientist was called "Snowflake" Bentley.
Now that you know what snow is made of, let's hope we don't see too much of it at any one time.