Definition
In a METAR weather report, GR is the code used to indicate hail with stones 1/4 inch (about 6 mm) in diameter or larger. Hail is precipitation in the form of solid ice, formed when updrafts in thunderstorms carry water droplets high enough to freeze, with repeated cycles building up layers of ice before the stones become heavy enough to fall.
Plain English
GR on a weather report means hail is falling — chunks of ice large enough to be a serious hazard. It tells the pilot that strong thunderstorm activity is present at or near the reporting station.
Context Anchor
Seen in the weather section of a METAR, often near thunderstorm or shower codes.
Derivation
GR comes from the French word 'grêle,' meaning hail. METAR is an international format developed under ICAO, and many of its precipitation and obscuration codes use French abbreviations rather than English ones. Knowing this helps explain why the code does not match the English word.
Why Pilots Care
Hail can dent leading edges, crack windshields, and signals dangerous thunderstorm activity that must be avoided.
Grounding Statement
If a METAR includes GR, picture hard pieces of ice falling from a storm, not just rain.
Intuition Check
GR does not mean “ground” or “gear” in a METAR. In this weather-report context, GR specifically means hail.
Example Sentence 1
The METAR included TSGR, telling the pilot a thunderstorm with hail was occurring at the airport.
Example Sentence 2
After landing, the crew inspected the wings because the ATIS had reported GR earlier.