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.
Golf Ball 1.75"
Tennis Ball 2.50"
Base Ball 2.75"
Giant 4.00+ (ruler measured)