What is a severe thunderstorm?

WEATHER: Like It or Not!
Wednesday, June 5, 2019
CHICAGO (WLS) -- When a Severe Thunderstorm Warning is issued, what does that mean? There are only three criteria that makes a storm severe. When a Severe Thunderstorm Warning is issued, one or more of the three criteria are possible for the warned area.

The three criteria are...
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1. Hail to 1" in diameter
2. Winds gusting to 58 mph
3. A tornado is occurring

As you can see, there is no threshold for how much rain or lightning are occurring in the storm. So a storm may be the loudest storm you have ever heard because of the thunder and lightning, or may be the heaviest rain you have ever seen - but unless it is capable of producing large hail, high winds or a tornado, it is not considered severe.

Of course, if a tornado is possible, a Tornado Warning is usually issued.

So the next time you find yourself under a Severe Thunderstorm Warning, know that large hail and high winds are possible.

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