Severe Weather Preparedness Week: What’s the criteria for a severe thunderstorm?


RALEIGH, N.C. (WNCN) — This week is North Carolina Severe Weather Preparedness Week — what makes severe thunderstorms different from “ordinary” thunderstorms?

About 10 percent of thunderstorms are classified as severe, and it’s a short list of criteria — one-inch diameter hail, winds of 58 mph or stronger, or a tornado.

Tornadoes are, of course, the one thing that everyone thinks of when it comes to severe weather. North Carolina is far from tornado alley, but our state averages 26 tornadoes, three tornado fatalities, and 39 tornado injuries each year.

Tornadoes occur most frequently in the late afternoon and early evening hours, however, many killer tornadoes occur during the overnight hours when they’re more difficult to see and people are asleep.

The gusts of wind from a thunderstorm, called downbursts or straight-line winds, are also a serious danger, and one that many people don’t take seriously enough. Those straight-line winds can be just as strong as the winds of a tornado and can result in similar damage. During the past five years, there have been 16 fatalities and over 70 injuries in North Carolina due to straight-line thunderstorm winds.

Finally, when it comes to hail, anything larger than a quarter is big enough to do some serious property damage. Most of the hail that falls in North Carolina is typically that size or smaller, but in just the past five years, hail the size of golf balls or larger have occurred over 200 times, and baseball-size hail has occurred eight times.

Tornadoes, straight-line winds, and hail. That’s what makes a thunderstorm severe, but those aren’t the only hazards that thunderstorms bring — we’ll have more information about lightning and flooding later this week.

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