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At any moment, 1,800 thunderstorms are in progress somewhere on Earth.

Meteorologists know the cloud conditions necessary to produce lightning but cannot forecast the location or time of the next stroke of lightning but cannot forecast the location or time of the next stroke of lightning from a storm, says the National Weather Service.

A thunderstorm forms in air as a result of moisture, instability and a trigger, such as a cold front to cause the air to rise.

Continued rising motions within the storm may build the cloud to a depth of 35,000 to 60,000 feet - six to 10 miles - above sea level.

Temperatures higher in the atmosphere are much colder, and ice forms in the higher parts of teh cloud. The formation of ice in a cloud appears to be a very important element in development of lightning, the NWS says.

Within a storm, many collisions occur between the ice particles. This causes a separation of electrical charges.

Positively charged ice crystals rise to the top of the thunderstorm, and negatively charged ice particles drop to the middle and lower parts of the storm. A moving thunderstorm gathers positively charged particles along the ground, and these travel with the storm.

As the differences in charges continue to increase, positively charged particles rise up taller objects, such as trees, houses and telephone poles.

Have you ever been under a storm and had your hair stand up? This is one of nature's warning signs that says you may be a lightning target.

At this point, it is important to find shelter immediately. The negatively charged area in the storm will send out a charge, known as a stepped leader, toward the ground. The charge is invisible to the eye and moves in steps in less than a second toward the ground.

When the charge gets close to the ground, it is attracted by all the positively charged objects, and a channel develops.

You see the electrical transfer in this channel as lightning. The lightning channel heats rapidly to 30,000 degrees. The rapid expansion of heated air causes the thunder.

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Since light travels faster than sound in the atmosphere, the sound will be heard after the lightning.

If you are ever in a storm when you see the lightning and hear the thunder at the same time, that lightning is in your neighborhood. Some lightning originates in the cirrus anvil at the top of the thunderstorm. This area carries a large positive charge, and lightning from this area is called positive lightning.

This type is particularly dangerous for several reasons. It frequently strikes away from the rain core - either ahead of or behind the thunderstorm. The lightning can strike as far as 10 miles from the storm in areas that most people do not consider to be a lightning-risk area.

The other problem with positive lightning is that it typically has a longer duration, so fires are more easily ignited.

Positive lightning usually carries a high peak electrical current, which increases the lightning risk to an individual.

This information about lightning was provided by the National Weather Service for Lightning Safety Week. Watch billingsgazette.com Wednesday-Friday for more information about protecting yourself from lightning.

For additional information on lightning awareness, go to the National Weather Service Billings home page at http://www.wrh.noaa.gov/billings and click on Lightning Safety Week.

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