Giant Hailstone

Giant Hailstone

Hail develops in most mid-latitude thunderstorms, often melting before reaching the ground. Severe hail is officially defined as being .75 inch or more in diameter -- or bigger than a dime. [A dime is slightly less than .75 inch across.] But even most hail which is technically "severe" measures an inch or less across -- too small to cause personal injury or serious damage to chasers' vehicles. On the other hand, extremely severe hailstones -- like the one held here by long-time storm chaser and hail aficionado Jim Leonard -- can total a chase vehicle, ruin roofs, break windows, kill animals and seriously hurt or kill humans. For this reason, most chasers avoid falling hail like a bad disease.

The costliest thunderstorms in history have been supercells producing very large hail over metropolian areas -- such as Fort Worth, TX, in 1995 and Sydney, Australia, in 1999. Such giant hail falls from supercell thunderstorms. The rotation of a supercell's updraft dynamically strengthens the upward wind motion a great deal, helping to hold larger ice particles aloft for a longer time. The longer a hailstone can remain suspended in a growth region -- where supercooled liquid raindrops hit it (coalesce) and freeze on impact -- the bigger the hailstone will grow.

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