What is a severe thunderstorm? | CNN

Harsh weather of all kinds is often called severe, but the word takes on a very specific meaning when it comes to thunderstorms. About 100,000 thunderstorms rumble across the United States each year, but just 10% intensify into a severe thunderstorm, according to the National Oceanic and Atmospheric Administration. A storm’s threats must be fierce enough to check at least one of three criteria boxes before the National Weather Service issues a severe thunderstorm warning or a tornado warning. Some storms check two or all the boxes at once. This first criterion is the most straightforward: Producing a tornado of any strength, size or duration automatically makes a storm severe. It’s the ferocity of a storm’s hail and wind where we have to dig a bit deeper. If a thunderstorm drops hailstones that are at least quarter-sized, it’s officially severe. This 1-inch diameter is the size at which hail can start to cause damage, like denting cars, siding or cracking windshields, especially if strong winds increase the force of its impact. The damage really escalates once it reaches the size of golf balls, and especially baseballs and softballs. Forecasters describe hail that is 2.75 i