Graupel

Graupel is soft, small precipitation pellets formed when supercooled water droplets freeze onto falling snowflakes, coating them with rime.

Riming: The growth of ice particles as supercooled cloud droplets freeze upon contact with them. Riming is the accretion process that builds graupel around falling snowflakes.
Hail: Layered balls or irregular lumps of ice grown by repeated cycling through strong thunderstorm updrafts. Hail grows in sustained storm updrafts, unlike graupel formed by droplets accreting on snow.
Winter storm: A storm that produces wintry precipitation, including snow, ice, or freezing rain. Graupel can occur within winter storms and signals active riming in the cloud.
Ice crystal: A solid particle of water whose molecules are arranged in an ordered crystalline structure. Graupel retains an ice-crystal core beneath its coating of frozen droplets.
Supercooling: The persistence of a liquid below its normal freezing point without solidification. Cloud droplets can remain liquid below 0°C until they strike a snowflake.
Snow pellet: A soft, white ice particle formed when supercooled droplets coat a snow crystal. Snow pellet is a common synonym for graupel, though terminology varies by region and classification.
Weather radar: A remote-sensing system that detects precipitation using reflected radio waves. Graupel's ice structure and particle size influence radar echoes and precipitation estimates.
Deposition (phase transition): The direct transition of a substance from gas to solid without passing through the liquid phase. Deposition grows the original snow crystal before riming converts it into graupel.
Snowflake: An ice crystal or cluster of ice crystals formed in a cloud and grown through deposition of water vapor. The falling snowflake supplies the ice surface that droplets coat to form graupel.
Sleet: Small ice pellets formed when raindrops or melted snow refreeze before reaching the ground. Sleet forms by refreezing falling liquid, not by riming a snowflake in a cloud.

Linked from 4 pages