Snow is frozen water vapour. During the process of crystallization, these crystals are carried up and down in the atmosphere by air currents, during which they collect specks of dust or tiny drops of water on it. Gradually, these crystals become larger, so that soon there might be hundreds of crystals gathered around one nucleus.
When such a group becomes large enough, it begins to float down towards the ground and we call it a snowflake. The size of a snowflake depends on the temperature. The colder the temperature, the smaller the size of snowflakes formed. Some snowflakes are more than three centimeters in diameter.
Below Snowflake info from Wikipedia (Read More):-
Snowflakes begin as snow crystals which develop when tiny supercooled cloud droplets (about 10 μm in diameter) freeze. Snowflakes come in a variety of sizes and shapes. Colder environments lead to column-like development of the flakes, while warmer temperatures lead to thin and flat crystal development. Complex shapes emerge as the flake moves through differing temperature and humidity regimes. Types which fall in the form of a ball due to melting and refreezing, rather than a flake, are known as graupel, with ice pellets and snow grains as examples of graupel. Snowflakes are used as a symbol for winter tires, and for the 2002 Winter Olympics.
http://en.wikipedia.org/wiki/Snowflake
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