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Here's how lightning works.

Lightning is an electric current, and just like the electricity lurking in the outlets in your house, it can be deadly. Have you ever gotten a shock by shuffling across a carpet and then touching something made of metal? Then you've experienced the same process that makes lightning.

Within a thundercloud, many small bits of ice bump into each other as they swirl around in the air. All those collisions create an electrical charge, just like the one that built up in you when you crossed the carpet.

After a while, the whole cloud fills up with electrical charges (usually with a negative charge closest to the earth). Since opposites attract each other, that causes a positive charge to build up on the ground beneath the cloud. The ground's electrical charge concentrates around anything that sticks up, such as mountains, lone trees, people, or even blades of grass. The charge streaming up from these points eventually connects with a charge reaching down from the clouds, and--zap!--lightning strikes.

The intense heat of the lightning bolt causes the surrounding air to explode outward with a gigantic boom--thunder.

How much lightning is there?

Lightning flashes aren't all the same shape or size, and they don't all carry the same amount of electrical current. And two clouds that are about the same size may create very different amounts of lightning. It depends on how much electrical charge the cloud has, and that depends on a lot of other things, like how fast air is moving in the cloud and how mny ice crystals have formed in the cloud.

Satellites looking down at the earth have shown that there are more than 3 million lightning flashes each day around the world. That works out to about 40 flashes each second. This includes flashes within or between clouds as well as the ones that strike the ground. It sounds like a lot, but it's less than scientists used to think there were.

In the United States, the state of Florida and the Rocky Mountain region get the most lightning. Worldwide, the countries near the equator get hit the most.

Lightning is dangerous. Stay away from it.

Lightning kills about 100 Americans each year. That's more deaths than result from tornadoes, hurricanes, or any other kind of weather except flash floods. About 400 other people each year are struck by lightning and live through the experience. Those who survive a lightning strike often have serious health problems as a result, such as losing control over some parts of their body or losing their memory.

The best way to keep from getting struck by lightning is to go inside before an electrical storm gets too close. Light travels extremely fast, so the lightning's flash reaches your eyes instantly, but the sound of thunder travels much slower--one mile in five seconds. If you hear thunder, it means the storm may be close enough to strike your location, so you should go into a house or car until at least 30 minutes after you no longer hear thunder.

"If the thunder roars, get indoors!"

If you're not close to shelter, here are some things to stay away from:

More lightning facts

More on lightning

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Written by:
Carol Rasmussen
UCAR Communications

UCAR Communications UCARWeb

Created by Bob Henson, UCAR Communications
Last modified: 4 April 2000