graupel

Graupel is a form of precipitation also known as snow pellets or soft hail. It consists of small, rounded pellets that form when falling snow crystals pass through a cloud containing supercooled water droplets, which freeze on contact with the snowflakes. The result is a fluffy, opaque particle with a rough surface.

Formation occurs as supercooled droplets adhere to the surfaces of snow crystals and freeze rapidly, creating a thick rind of ice around the original crystal. This process, called accretion or rime formation, gives graupel its characteristic soft, crumbly texture. Typical graupel particles are about 2 to 5 millimeters in diameter, though slightly larger examples can occur.

In terms of appearance and feel, graupel is usually white or opaque and can be crushed easily in the fingers. It does not bounce like hail, and it generally lacks the layered structure formed by hailstones. When it lands, graupel can accumulate on surfaces, especially during winter storms or in strong convective clouds.

Graupel commonly forms in cold-cloud environments where air is moist and there is a source of supercooled water droplets, such as in cumuliform or stratiform clouds. It is most frequently observed with winter precipitation events and can occur alongside snow, sleet, or freezing rain, though it remains a distinct meteorological phenomenon.

Distinctions from hail are important: graupel is softer, smaller, and opaque, with a simple, frozen coating on a snow crystal, whereas hail consists of larger, layered ice formed by repeated updraft-driven accretion.