Ask Heather - how does hail form?

KNOXVILLE, Tenn. (WVLT) -- We get plenty of thunderstorms this time of year, and all too often hail can be an issue. This week's Ask Heather answers the question, how does hail form?

Actually a couple of people sent similar questions directly to Heather, Thomas Dobbins on Facebook and Chad on Twitter.

First off you need to know that the Freezing Level is the point in the atmosphere where the temperature is at or below freezing. That's why hail can form any time of year. (In the Winter, the Freezing Level is closer to the surface.)

Hail forms inside of a thunderstorm. That's where strong updrafts of warm air and downdrafts of cold air churn.

When a water droplet is carried higher in the atmosphere by the updraft, it can go well above the Freezing Level. As it falls some melting occurs, it can also pick up other water droplets and be picked up by an updraft yet again.

Each trip around adds another layer of ice. This is also why they can be jagged in shape and size. From freezing and thawing over and over.

Hail must be at least one inch in diameter to be considered "severe" when it comes to storm, and most hail is less than 2 inches across.

The largest hailstone on record fell in Aurora, Nebraska. It was 7 inches across when it was found on June 23, 2003.


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