Clouds that form snow crystals in the winter are made of liquid water droplet. When the temperature is below freezing the water is supercooled, meaning the droplets are cooled below the freezing point.
The shape of the snowflake is determined broadly by the temperature and humidity at which it is formed. The most common snow particles are visibly irregular . For example the most common snow flake “stellar plates” form at temperatures between -2 C (28 F) / -15 C (5 F).
Snowflake consists of roughly 1018 water molecules, which are added to its core at different rates and in different patterns, depending on the changing temperature and humidity within the atmosphere that the snowflake falls through on its way to the ground.