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WHAT CREATES HAIL?

METEOROLOGIST JEFF HABY

Hail is large ice hydrometeors that fall out of storms. Hail is different from sleet and ice pellets in that hail usually occurs in warm season thunderstorms and hail is larger than sleet and ice pellets. Hail grows by two processes. In one process the hail grows by moving through ice and water droplets in the cloud. When liquid water freezes on the ice it forms a clear glaze. When ice crystals or supercooled water freeze on the hail they are more white in appearance with air bubbles. This is why when a hailstone is sliced open you will open see alternating clear and white ice. Another method hail can grow is by smaller hail stones freezing together to create a bigger one. A hail stone can make several trips within the updraft of a storm. The elevation that the hail grows determines the type of ice or freezing water that grows on the hail. The size of the hail will depend on how strong the storm in. The speed of the updraft and wind shear are two important ingredients for hail.

A hail stone shape is circular at smaller sizes and becomes more irregular at larger sizes. Since the shape is usually circular, a guide for reporting hail size by comparing it to circular objects of the same diameter is used for simplicity in reporting. Below is a reporting guide. Severe hail is 0.75" or greater in diameter.

Pea          0.25"
Dime         0.75"
Quarter      1.00"
Golf Ball    1.75"
Tennis Ball  2.50"
Base Ball    2.75"
Grapefruit   4.00"
Giant        4.00+ (ruler measured)