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Storms form in cumulonimbus clouds like the one pictured above. These clouds produce rainfall, lightning, wind gusts, and large hail. Many places on the earth depend entirely on cumulonimbus clouds for rainfall.

According to the National Weather Service, 1,800 thunderstorms occur at any given moment around the world. Three conditions must be present for a thunderstorm to form: cold air over warm air, unstable air, and a source of lift for the storm. These storms most often form in cumulonimbus clouds. Thunderstorms, Thunder, and Lightning Each year, 16 million thunderstorms occur around the globe. About 100,000 occur in the US each year, with about 10,000 (roughly 10 percent) being severe. The National Weather Service defines a severe thunderstorm as one with winds greater than 58 mph, hail

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The New Weather: Extreme Weather