Graupel are soft, small pellets formed when supercooled water droplets (at a temperature below 32°F) freeze onto a snow crystal, a process called riming. If the riming is particularly intense, the rimed snow crystal can grow to an appreciable size, but remain less than 0.2 inches.

If the pellets are greater than .2 inches in diameter, it is referred to as hail. Both hail and graupel can form from convective precipitation (thunderstorms)