Snowflakes start off as ice crystals formed in clouds high above the Earth’s surface. If the temperature of the cloud is below freezing, the droplets can freeze to form tiny ice crystals. As the crystals move through the air, they grow by the condensation of water on their surface and by collision with water droplets. They may also join with other ice crystals to form snowflakes.
It is often said that no two snowflakes are identical. There are, however, four common types of snow crystals:
Stellar crystals are star-shaped and flat. They are also very complicated in detail. They form in clouds with temperatures between about -13°C and -18°C and can grow as big as a dime;
Hexagonal plates form in clouds with temperatures between about -10°C and -13°C and about -18°C and -20°C;
Hexagonal columns form in clouds with temperatures between -7°C and -10°C and below -20°C;
Long, slender and cylindrical, they usually form in clouds with high moisture content and temperatures warmer than -7°C.
Sometimes you will see snowflakes with irregular shapes. This is caused by the crystal passing through clouds with different temperatures and moisture content. A plate-type crystal falling through clouds with temperature and moisture content suited to dendrites will develop star-like extensions. Strong winds and/or turbulence, causing crystals to collide and break, can also result in irregular crystals.
The best way to ‘capture’ snowflakes is on a dark background such as construction paper, a dark snow jacket or a dark blanket. The key is to make sure that your chosen background is cold or else the snowflakes will melt!