Definition
The process by which a hailstone grows larger by being carried upward through a thunderstorm by strong updrafts, where it encounters supercooled water droplets that freeze onto its surface, adding another layer of ice. Each trip up and down within the storm can add a new layer, producing the characteristic onion-like ring structure seen when a hailstone is cut open.
Plain English
Hail gets bigger when a storm's rising air pushes a hailstone back up into very cold, wet air. Tiny water droplets freeze onto it, coating it with another layer of ice. The more times this happens, the larger the hailstone becomes.
Context Anchor
Seen in aviation weather discussions about thunderstorms, hail formation, and why hail is a sign of dangerous storm strength.
Derivation
Hail comes from Old English hægl, meaning frozen rain or icy pellets. The layered growth process is what makes hail different from other forms of frozen precipitation — each layer marks a separate trip through the freezing zone of the storm.
Why Pilots Care
Growing hail poses a direct risk of damage to windshields, leading edges, and engines, requiring pilots to avoid areas of strong updrafts.
Analogy
Think of dipping a candle wick into wax repeatedly — each dip adds a new layer. A hailstone gains layers the same way, except the storm's updraft does the dipping, and ice replaces the wax.
Grounding Statement
A hailstone grows by being lifted again and again through freezing wet air, gaining a new layer of ice each trip.
Intuition Check
Hailstones are not simply normal raindrops that froze once on the way down. In strong storms, they can grow layer by layer inside the cloud before they fall.
Example Sentence 1
The pilot avoided the towering thunderstorm by a wide margin, knowing the powerful updrafts inside could lift hailstones high enough to gain another layer of ice and grow to damaging size.
Example Sentence 2
Radar returns showed the storm cell where hailstones were likely to gain another layer of ice before falling to the surface.