What is a severe thunderstorm?

WEATHER: Like It or Not!
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...

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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