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When Lightning Strikes Out of a Blue Sky

Britney Wehrle was walking with a friend on a sunny, warm day when she was suddenly struck by lightning, even though the sky above her was clear and blue.
/ Source: Discovery Channel

Britney Wehrle was walking with a friend on a sunny, warm day when she was suddenly struck by lightning, even though the sky above her was clear and blue.

And while that may sound like a rare or even freakish event, it's not that uncommon for lightning to travel far from its originating cloud, experts say. In some cases, bolts have struck as much as 25 miles from where they originated. Scientists refer to these wayward streaks of electricity as "bolts from the blue," since it often seems as though the lightning comes out of a clear blue sky.

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As 11-year-old Wehrle recovers from a broken arm and a burn mark on her shoulder, it may be a good time to refresh your memory about how to protect yourself from lightning. At the top of the list: Avoid exposing yourself to it.

"When thunder roars, go indoors, and stay in there for 30 minutes after you hear the last thunder clap," said Susan Buchanan, spokeswoman for the National Weather Service in Silver Spring, Md., and a member of the agency's lightning safety team.

"Lightning is unpredictable," she added. "There's no safe place outdoors in a thunderstorm. If you remain outdoors during a thunderstorm, you are taking a gamble that you won't become one of the statistics."

And those statistics are staggering.

Every year, according to the National Weather Service, the Earth experiences 16 million thunderstorms. That amounts to an average of 1,800 storms happening at any given moment. Over the course of a year, 25 million bolts strike the ground, usually during thunderstorms but also during intense forest fires, heavy snowstorms, volcanic eruptions, nuclear detonations and large hurricanes.

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Lightning kills an average of 55 people every year, Buchanan said, but it hits and severely injures hundreds more. According to calculations on NOAA's National Severe Storms Laboratory website, there is a one in 3,000 chance of getting killed or injured by lightning in your lifetime, assuming an average life span of 80 years. The chances of lightning hurting someone close to you is one in 300.

To form, lightning requires a specific combination of circumstances, said Vladimir Rakov, an electrical engineer and lightning expert at the University of Florida, Gainesville. The recipe includes hot temperatures on the ground and moist conditions, as well as strong updrafts that propel wet air into the cooler atmosphere, where it condenses and form clouds.

With its warmth, humidity and sea breezes that blow off two coasts, Florida experiences more lightning than any other state. But even there, clouds have to get high enough for ice to form, because electrification only happens within clouds that contain water in both its solid and liquid states.

As electric charges accumulate inside cloud, sparks start to fly, much like the sparks you sometimes see as you reach for a doorknob after shuffling your feet on a carpet. Some bolts travel within clouds. Others hit the ground. But exactly where a lightning bolt will end up is anyone’s guess. And often, it ends up in more than one place.

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A flash of lightning can last for up to a second, Rakov explained, and each flash is usually made up of many strokes. Sometimes, those strokes all follow the same path. But studies show that between one-third and one half of flashes end up sending bolts to multiple end-points.

Why that happens isn't completely clear. One theory is that the first few strokes create a charge that repels subsequent strokes, diverting them elsewhere. Scientists also know that bolts can emerge from the side of a cloud and they may then travel for miles through long horizontal channels before eventually striking ground.

Whatever the cause, bolts from the blue can, on rare occasions, be deadly. The best thing people can do to avoid getting hit is to be vigilant of weather forecasts. If the radar shows storms approaching, Buchanan said, postpone outdoor activities. If you're outside and you hear thunder, go inside right away. And a pavilion doesn't count. Lightning can come in through the sides or travel through the ground.

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There are only two absolutely safe places to be during a thunderstorm. One is in a metal car. The other is in a house with a roof, four walls, and plumbing and electric systems that can absorb the electricity of a lightning strike.

Once you’re inside, don't touch anything that's plugged into the wall. And stay away from sinks, bathtubs, showers, even toilets. Electricity travels efficiently through water and metal. In a car, don’t fiddle with the radio.

Buchanan couldn't emphasize enough her urgent advice to get inside as soon as you hear thunder. The majority of people who get struck, she said, had just waited too long before heading toward safety.

If you're camping in the wilderness and inside is not an option, stay away from tall isolated trees. Get off of hills and ridgelines in favor of low-lying areas -- though you should also watch out for flash flooding. Unfortunately, tents offer no protection from lightning.

"A lot of times people who are outside run for trees because they are more concerned about getting wet," Buchanan said. "But that makes them more vulnerable."