On Sunday afternoon, 20,000 bathers at Venice Beach in Los Angeles were surprised by a ferocious 15-minute thunderstorm, during which lightning strikes killed a 20-year-old man and injured at least a dozen other people, at least one critically. Witnesses told Los Angeles TV station KTLA that the first lightning bolt, which struck the water near the Venice pier, sounded like a “bomb,” and actually made the ground shake.

The storm was a rare weather phenomenon, where an intense high-pressure system drove warm, moist air mass up from Mexico and the Gulf of California, creating unstable atmospheric conditions. The National Weather Service predicted isolated showers and thunderstorms throughout the southern California region today.

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Fortunately, the chance of being struck by lightning is only about 1 in 500,000 in a given year, according to the federal Centers for Disease Control and Prevention. Even so, about 35 people are killed by lightning in the United States each year. Here are some tips from NOAA and the CDC on how to stay safe.

  • If the weather forecast calls for thunderstorms, postpone trips and outdoor activities.

  • When you hear thunder, go indoors. Find a safe, enclosed shelter. If you can hear thunder, you’re close enough to be hit by lightning.

  • You can be struck by lightning in a car, but you’re safer inside a vehicle than outside. If you’re in a car, keep the windows closed. Avoid open-topped vehicles like convertibles and golf carts. The steel frame of a car offers better protection if you’re not touching metal. Rubber shoes and tires don’t offer protection from strikes.

  • Avoid shelter under an isolated tree.

  • Stay away from concrete floors or walls. They often contain metal wires or bars, which can conduct electricity from a lightning strike.

  • Don’t use a corded telephone, because it can conduct electricity as well. If you need to call someone, use a wireless handset or a cell phone.

  • Lightning can travel through plumbing, so stay away from sinks and faucets.

  • Avoid ponds, pools, lakes and other bodies of water.