Known as “soft hail” or “snow pellets”, graupel is different from pure snow. Under some atmospheric conditions, snow crystals can encounter supercooled water droplets. These tiny droplets can exist in the liquid state at temperatures as low as −40 °F, far below the normal freezing point. Contact between a snow crystal and the supercooled droplets results in freezing of the liquid droplets onto the surface of the crystal. This process of crystal growth is known as accretion and when this process continues so that the shape of the original snow crystal is no longer identifiable, the resulting crystal is referred to as graupel. The accretion isn’t much; there’s generally a 2-5mm ball of rime prior to it falling to the ground.
To some, graupel looks like styrofoam or polystrene pellets; to others, it looks like Dippin’ Dots ice cream.
The word graupel has German origins. Grapuel is the diminutive of Graupe which means “pearl barley.”
The METAR code for graupel is “GS.”