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Posted at 11:00 AM ET, 06/20/2008

Beware of Bolts From the Blue

By Steve Tracton

You've just discovered the email announcing that you've inherited $5 million is not spam.
You've just received a Dear John letter from your loving significant other.
You've just been promoted from intern to company CEO.

You're standing outside under clear blue skies and suddenly the tree across the street is hit by lightning.

Courtesy NOAA. Credit: Al Moller.

It's no wonder these totally unexpected events are known as bolts from the blue, which refers to lightning that typically emerges from the back side of a thunderstorm, travels a relatively long distance through clear skies, and then angles downward and strikes the ground. Such bolts have been shown to travel more than 25 miles away from the originating thunderstorm cloud.

Keep reading reading for more on bolts from the blue. Also, see our full forecast through the weekend and beyond, NatCast for tonight's game at Nationals Park, and Beachcast if you're headed for the shore this weekend.

D.C. experiences an average of almost 800 cloud-to-ground lightning flashes per year. Summer is peak lightning season -- we're certainly off to a fast start around here -- and in 2007, 45 people were struck and killed by lightning in the U.S. In fact, most people struck by lightning each year are in rain-free areas in the vicinity of thunderstorms.

It's not known what proportion of these strikes qualify as bolts from the blue. But clearly this type of lightning is quite dangerous, for it can strike when least expected. Trying to explain the phenomenon to my 4-year-old granddaughter is tough, especially when she's anxious to jump back into the pool as soon as skies have apparently cleared following a "boomer."

Courtesy New Mexico Tech/NCAR/NOAA.

Bolts from the blue can be detected by networks such as the Washington, DC Metro Area Lightning Mapping Array. A good example from another network in Colorado is shown to the right. The sequence of blue dots indicates the lightning path emerging from the rear of the thunderstorm as seen on Doppler radar.

I'd bet Ben Franklin could have used this type of information when planning his famous kite experiment. Then again, he still might have been fried by an unexpected bolt from the blue.

By Steve Tracton  | June 20, 2008; 11:00 AM ET
Categories:  Thunderstorms, Tracton  
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