Each winter there are about 1 septillion (1, 000, 000, 000, 000, 000, 000, 000, 000 or a trillion trillion) snow crystals that drop from the sky.
The unique and complex features of snow crystals are very much affected by unstable atmospheric conditions. Snow crystals are sensitive to temperature and will change in shape and design as they fall from the cloud and are exposed to fluctuating temperatures. To have two snow crystals or flakes with the same history of development is virtually impossible.