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7. Thunderstorm Hazards

a. Turbulence
(1) All thunderstorms are turbulent, and some are potentially destructive to aircraft.
Almost any thunderstorm has the potential to produce "severe" turbulence and some may
produce turbulence classified as "extreme."

(2) Turbulence should also be expected outside of the area of the visible cloud and in
the case of severe thunderstorms, "severe" to "extreme" turbulence can be encountered
several thousand feet above and 20 miles laterally from the storm.

b. Hail
(1) Hail is a ball or irregularly shaped piece of ice ranging in size from approximately

.6 centimeters to 13 centimeters in diameter. Large hailstones usually have alternating layers
of clear and white ice. In general large hail and severe turbulence occur in the same storms.

(2) Hail and turbulence are nearly equal in being the greatest hazard to aircraft
produced by a thunderstorm. Hail can cause severe damage to surfaces such as the front
edge and tops of the wings. In extreme cases hail has broken out aircraft windows.