Snowflakes are formed when updrafts carry water droplets through a cloud base to heights within the cloud where the temperature is below freezing. There the droplets form ice crystals by condensing onto tiny dust particles or other ice nuclei. The crystals grow as water vapor accumulates on them and as they fall and collide with supercooled water droplets (droplets that remain liquid at temperatures below freezing until they encounter a surface on which to form ice). Snowflakes may also resemble plates or columns, depending on the cloud-level temperature and the strength of updrafts. Larger snowflakes are usually clusters composed of many smaller ice crystals.
