Definition
In a METAR, GS is the precipitation code reported when small hail or snow pellets (graupel) are falling at the station. Snow pellets are white, opaque ice particles, generally 2–5 mm in diameter, that are soft and crumble easily when they hit a hard surface. Small hail refers to ice particles in the same small size range. Both form when supercooled water droplets freeze onto falling snow crystals, building up a soft, rimed ice particle.
Plain English
GS in a weather report means small, soft ice pellets are falling — bigger than sleet but smaller and softer than true hail.
Context Anchor
Seen in the present-weather part of a METAR when frozen pellets are being reported at or near the airport.
Derivation
GS comes from the French word grésil, meaning small hail or sleet. The METAR code system, which is international, uses the French abbreviation rather than an English one.
Why Pilots Care
Small hail or pellets can reduce visibility, create slippery surfaces, and affect aircraft performance during takeoff and landing.
Grounding Statement
Picture small white or icy pellets bouncing off the ramp, windshield, or wing instead of soft snowflakes falling gently.
Intuition Check
Do not read GS here as groundspeed. In a METAR present-weather report, GS means small hail or snow pellets.
Example Sentence 1
The METAR for the destination showed -GS, so the pilot expected light snow pellets and brief reductions in visibility on approach.
Example Sentence 2
Snow pellets coded GS appeared in the forecast, prompting the crew to brief for possible icing during the approach.