CEDAR RAPIDS, Iowa (KCRG) - What makes a thunderstorm “severe”? Hail that’s at least an inch across (the size of a quarter), winds of at least 58 mph, or a tornado make a storm severe. Those are things that are likely to cause damage or harm people. For example, hail that size is large enough to dent vehicles or bruise a person caught out in it, or damage or destroy crops. Winds of that speed are more likely to knock down tree branches. As the hail gets bigger or the wind gets stronger, the amount of damage increases.
Flash flooding, which is the deadliest thunderstorm threat, is separated from severe thunderstorms. One important reason is that flash flooding can happen – and is sometimes at its worst – after a thunderstorm is over. Unlike wind and hail, which move with the thunderstorm, the rain that fell doesn’t go away as the storm leaves.
What about lightning? Even though lightning is dangerous in its own right, the amount of lightning a storm produces doesn’t determine if a storm is severe or not.
During a severe thunderstorm, you should go indoors away from windows and stay there until the storm passes. This isn’t the time to start thinking about what you should do – it’s the time to go do it. Thursday’s Severe Weather Awareness Week theme is about being prepared, so look for more information on safe sheltering then.
Finally, know the difference between a watch and a warning. A watch means that weather conditions could cause severe weather within the next few hours – the ingredients are coming together. You should keep watching for changes. A warning means that severe weather is expected to happen now or soon and you should take action. It’s your last warning to go to your safe place.