Definition
A form of frozen precipitation consisting of very small, white, opaque grains of ice. Snow grains are the solid equivalent of drizzle: they fall in small quantities, do not bounce or shatter when they hit the ground, and are usually associated with stratus clouds or fog rather than active storm systems.
Plain English
Tiny grains of ice — much smaller than snowflakes — that drift down quietly, usually from low cloud or fog. They are the icy version of drizzle.
Context Anchor
Seen in airport weather reports, weather briefings, and cold-weather surface observations, where snow grains may be reported as SG.
Derivation
“Grain” comes from an old word meaning a seed or small particle. That helps here because snow grains are tiny seed-like ice particles, not the larger branching flakes people usually picture as snow.
Why Pilots Care
Signals possible reduced visibility and the chance of light ice buildup on the aircraft.
Grounding Statement
Picture tiny white ice specks falling out of a low gray cloud or fog layer, more like fine pellets than soft snowflakes.
Intuition Check
Snow grains are not just small snowflakes. They are tiny ice particles with a grain-like shape, and they usually fall in light amounts rather than as a snow shower.
Example Sentence 1
The METAR reported SG, so the pilot expected light snow grains and reduced visibility under the low overcast.
Example Sentence 2
The forecast called for snow grains, so the crew watched for any ice forming on the wings during taxi.