What is a Severe Thunderstorm?

Severe thunderstorms are the most dangerous kind of thunderstorms.  You hear about them in the news, but what exactly makes a severe thunderstorm different from a regular thunderstorm?

Many believe that the amount of lightning in a thunderstorm is how storms are classified as severe or not.  While lightning is a significant threat, all thunderstorms contain lightning and some weaker thunderstorms can still contain a high amount.  Rainfall rate is also not a factor in classifying a storm as severe or not, though severe thunderstorms typically do have higher rainfall rates. 

There are three things that can cause a thunderstorm to be classified as severe.  If a severe thunderstorm warning is issued, the National Weather Service is doing so because they have been notified or suspect that one or more of the following is present:

1. Hail One Inch in Diameter or More

Not so long ago, the requirement for a severe thunderstorm was hail that was only 3/4" in diameter.  More research proved that while hail this size or smaller can destroy some crops, it really doesn't damage buildings or vehicles.  Once hail reaches an inch in diameter though (about the size of a quarter) it can begin to dent cars and damage roofs.  Hail that size falls from the sky at about 50mph, so it can certainly hurt you as well!

2. Wind Gusts of 58 mph or More

This may seem like a random number, but there is something to it.  Studies have shown that this is about the wind speed that branches begin to break off from tree trunks.  It is also important to note that the winds don't have to be sustained at 58 mph or greater; they just have to be gusting up to that speed.  It's very unlikely to have winds constantly at this speed in a thunderstorm unless...

3. Tornado

Any thunderstorm that produces or is suspected of producing a tornado is automatically classified as severe.  When this occurs however, you won't see a severe thunderstorm warning issued, but a tornado warning.  This means that if you are under a tornado warning, you are also experiencing a severe thunderstorm.

Any of the above three conditions can be very dangerous, so do not take severe thunderstorm warnings lightly!

Got anymore questions about severe weather?  Let me know in the comments below!