Weather Forecasting

Can I calculate how far away a lightning strike is?
• ### Discovery Channel

1. Yes, you can calculate how far in the distance a lightning strike is. You do it by counting how many seconds elapse from when you see the lighting to when you hear the thunder. Because sound travels roughly 1,200 feet per second (350 meters per second) -- the speed varies as temperature and humidity vary, you can begin counting seconds when you see a lightning strike. When you hear the thunder, stop counting. If 10 seconds elapse, the lightning struck about 2 miles (3 kilometers) away.

Interestingly, the distance between lightning flashes is today thought to be about 5.5 miles (9 kilometers), whereas older readings told scientists that lightning flashes were typically about 1.8 to 2.5 miles apart (3 to 4 kilometers). The further-apart flashes means a relatively safe distance from lightning is really about 6 to 8 miles away (10 to 13 kilometers) as opposed to older lightning safety guidelines that said safety could be found about 2 to 3 miles (3 to 5 kilometers) away [source: NOAA].

But just because you now know how to determine how far away a lightning strike is, it's best to remember how dangerous lightning can be -- even from what looks like a safe distance. You can be hit by lightning  from thunderstorms whose centers are up to 10 miles (16 kilometers) away and it looks like a perfectly nice sky above you. The type of lightning that can strike from that far away is called positive lighting (it carries a positive charge). While most lightning forms in the lower parts of a thunderstorm cloud, some lightning forms in the  "anvil" shape at the top of a thunderstorm and is very dangerous because it can strike so far away -- either in front of or behind the thunderstorm. In fact, it's hard to believe anywhere is safe for long, given that our gentle mother Earth whips up about 16 million thunderstorms per year and about 25 million detectable lightning strikes -- from clouds to the ground -- per year on average [source: National Weather Service].

It is possible to figure out how far away a lightning strike is with some simple math. (Image courtesy NOAA)

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