As we head through Labor Day, often called the “unofficial last weekend of summer”, we continue to see what we’ve seen all summer long: showers and thunderstorms. Complete with the threat for severe weather and flash flooding.
But what is severe weather? When are severe thunderstorm warnings issued?
When large storms move through, people will ask us questions about why we’re not calling the storm that’s over their head a severe storm. Usually that question includes comments about how dark the sky is, how hard it’s raining, and how much lightning there is. None of which determine if a storm is severe!
Severe thunderstorm warnings are issued when storms are capable of producing hail of an inch or more in diameter (quarter-size or larger) or winds greater than 58 mile per hour. These thresholds have been determined to be points at which storms typically start to produce damage.
Note that it’s the size of hail that’s a factor, not the quantity. If it hails long enough to produce actual accumulation, it doesn’t matter…unless the hail is quarter-sized or larger.
A quick Google search shows MANY sites that still list the old hail threshold of ¾ inch (dime-size); that was changed a few years ago as hail of that size typically wasn’t causing many problems. (A reminder to not believe everything that’s on the internet…except this blog, of course! But that’s another story for another day…)
Lighting is not an indicator of storm severity either. After all, by definition every thunderstorm produces lightning (and the subsequent thunder), even if the storm produces nothing else that might cause damage. Remember, all thunderstorms have the same potential danger to anyone who is outdoors. You should always seek enclosed shelter if a storm moves in. Use the 30-30 rule: head indoors if you hear thunder within 30 seconds after seeing lighting, and it’s safe to be outside 30 minutes after you hear the last thunder.
Rain is not a severity indicator either…but storms that produce a lot of rain can produce flooding, and we have flash flood warnings to cover that.
Of course, any storm producing a tornado is also severe…but tornadoes will always have their own warnings!
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