A severe thunderstorm is defined as a thunderstorm that has one or more of the following: 58 miles per hour or greater winds, 1" or larger diameter hail, or a tornado. Severe thunderstorms form where cold air and warm air clash, and where winds change speed and direction as you go higher in the atmosphere. Storms maintain themselves partly through cool air that falls out of the storm, forming miniature cold fronts called outflow boundaries.
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