Severe Weather Awareness Week: How hail forms and hail sizes


KNOXVILLE, Tenn. (WATE) – Before learning how hail forms, you need to know about the basic structure of a thunderstorm. 

Any strong thunderstorm has a strong updraft. Eventually, that updraft will weaken as colder air builds in the center of the storm.  The storm collapses and a surge of air from the storm hits the ground and spreads in all directions. 

Microburst and macroburst

If the downburst is 2.5 miles wide or less, it’s called a microburst. When it is greater than 2.5 miles, it is called a macroburst.

How hail forms

In terms of hail formation, the stronger the thunderstorm, the larger the hailstones that can form. Raindrops are carried into cold parts of the atmosphere and freeze into small hail.  Hail is bounced up and down inside the storm. Hailstones grow by colliding with supercooled water droplets in a cloud. The hailstones fall when the updraft weakens or the hail is too heavy to be supported in the storm. These chunks of ice continue to grow inside the storm before falling to the ground as hail.

Hail is classified as severe if it is 1 inch in diameter or greater. Remember to always send your hail reports when it is safe to do so.

(This is one of a series of stories by the WATE 6 Storm Team for Severe Weather Awareness Week.)


Flooding and flood safety

Lightning formation and lightning safety

Tornadoes and tornado safety

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