Within a cloud where temperatures are below freezing, ice crystals may be encircled by supercooled water droplets. In instances where ice crystals and liquid droplets are in proximity, water vapour molecules transition from the liquid droplets to the ice crystals. This process results in the ice crystals increasing in size, while the water droplets diminish.

Once an ice crystal attains a considerable size, it commences its descent. During its fall, the ice crystal can expand by colliding with and adhering to other ice crystals, or through encounters with supercooled droplets that freeze upon contact.