Has winds of 58 miles per hour or higher Or produces a tornado. Keep in mind that thunderstorms may occur singly, in clusters, or in lines. Some of the most severe weather occurs when a single thunderstorm affects one location for an extended time.
Lightning is a major threat during a thunderstorm.
It is the lightning that produces thunder in a thunderstorm. Lightning is very unpredictable, which increases the risk to individuals and property. The resulting damage can equal the damage of most tornadoes.