Definition
Solid pieces of ice that form inside thunderstorms when supercooled water droplets freeze onto a nucleus and are carried up and down through the storm by strong updrafts, accumulating layers of ice until they grow heavy enough to fall to the ground. Hailstones range in size from small pellets to several inches in diameter and can cause severe damage to aircraft structures, windscreens, and engines.
Plain English
Lumps of ice that form inside thunderstorms and fall from the sky. They can be anywhere from pea-sized to bigger than a golf ball, and they can seriously damage an airplane.
Context Anchor
Seen in thunderstorm and severe-weather discussions, weather briefings, and decisions about avoiding storm cells.
Derivation
From Old English 'hagol' (hail) plus 'stan' (stone). The word literally means 'hail-stone' — a stone-like piece of hail — which is exactly what it is.
Why Pilots Care
Hailstones can dent or penetrate aircraft surfaces, shatter windshields, and create immediate safety hazards when encountered in flight.
Grounding Statement
Picture a thunderstorm acting like a powerful lift that keeps tossing water drops upward until they freeze into hard ice and fall out of the cloud.
Intuition Check
Do not treat hailstones as just “cold rain.” They are solid ice, and in aviation they are a warning sign of a strong thunderstorm that can damage an aircraft.
Example Sentence 1
The pilot diverted around the thunderstorm to avoid hailstones, which can cause severe airframe damage even at small sizes.
Example Sentence 2
Post-flight inspection revealed dents in the leading edges caused by hailstones.