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AUBURN, Feb. 21---Spring is the peak season for thunderstorms in Alabama. Thunderstorms are generated by temperature imbalances in the atmosphere. When warm air near the earth's surface collides with cool air above, turbulence occurs, resulting in thunderstorms.

The United States has about 100,000 thunderstorms annually. It's estimated that at any given moment nearly 2,000 thunderstorms are in progress over the earth's surface and that lightning strikes the earth 100 times each second.

A thunderstorm may extend several miles across its base and often towers to altitudes of 40,000 feet or more. Some thunderstorm clouds stand alone while others can be seen in groups. These groups are known as a squall line.

Lightning always accompanies a thunderstorm. Electricity produced in a thunderstorm can be as strong as 100 million volts. Lightning strikes before it thunders. Thunder is the sound of air suddenly expanding due to the heat of the lightning. When lightning is near, thunder sounds like a sharp crack.

Thunder from distant lightning sounds like groaning and rumbling by the time it reaches you. Because the speed of light is about a million times that of sound, we see a lightning bolt before the sound of thunder reaches us. You can estimate the distance (in

miles) of a lightning strike by counting the number of seconds between lightning and thunder and dividing by five.

Hail storms often accompany thunderstorms. Hailstones are lumps of ice ranging from pea- to grapefruit-size, that form during some thunderstorms. They're usually round but can be cone-shaped or irregular in shape with pointed projections. Hail often devastates crops but can also cause heavy damage to aircraft, automobiles, roofs and windows.