Snowflakes are combinations of frozen ice crystals that fall through the Earth's atmosphere. They form when microscopic super cooled cloud water droplets freeze that are only about the size of four ten thousandths (.00039) of an inch one hundredth of a millimeter (.01 millimeter) in diameter. Snowflakes come in a variety of sizes and shapes. Complex shapes develop as the flakes fall through different temperatures and humidity. These droplets are able to remain liquid at temperatures lower than -0º Fahrenheit (-18º Celsius) because in order to freeze, a few molecules in the droplet need to come together by chance to form an arrangement similar to that in an ice lattice molecule; the droplet then freezes around this "nucleus." Experiments show that this chance accumulation of droplets around an ice lattice molecule to form a snowflake occurs at temperatures lower than -31° Fahrenheit (-35° Celsius). Once a droplet has frozen, it grows in the supersaturated cloud environment where air is below the freezing point. These large crystals fall through the atmosphere due to their mass, and may collide with others, sticking together in clusters. These clusters of ice crystals are snowflakes, and are usually the type of ice particles that fall to the ground.