The Washington PostDemocracy Dies in Darkness

Bolts from the blue: Here’s how lightning can strike when a storm is tens of miles away

Lightning strikes ahead of an approaching thunderstorm in downtown Washington. It originated in Silver Spring, more than nine miles away. This photo was taken from inside the Jefferson Memorial on June 25, 2014. (Kevin Ambrose)
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Ah, summer. There’s nothing nicer than firing up the grill, cooking a few burgers and sitting on the porch as a distant storm flickers and rumbles against the backdrop of a dusky starlit sky. Nothing more than a gentle breeze stirs the air, as fireflies dance and occasional growls emanate from the storm cloud. You estimate it to be at least 15 miles away. It sounds like a serene scene, right? You’re safe. Or so you think.

Suddenly, an arc of electricity launches out of the top of the storm, propelling upward and outward at 20,000 mph. The mega lightning bolt shoots horizontally from the storm cloud; it targets a field just 100 yards away, and suddenly a flash brighter than the sun illuminates the landscape like day and blinds you. Your hair stands on end, your teeth chatter, and your ears are deafened as the thunderous roar shakes your house and rattles the window panes. A second later, it’s over — yet every electrical device in your home emits a cicada-like hiss as the electrical field propagates outward from the blast. A foot-deep hole, three yards across, marks the spot where the lightning struck.

This fascinating map shows where you are most and least likely to get struck by lightning

Strange as it may sound, “bolts from the blue,” as they’re known, are not as rare as one may think. In fact, they’re a relatively common across the United States during the summer months. As severe thunderstorms tower nearly 10 miles high, a process known as “triboelectrification” imparts electrical charges onto moisture in the atmosphere. Liquid water takes on a negative charge, and ice becomes positive. Because it’s colder in the upper atmosphere, the top of the cloud is home to the most ice and hail. That’s why the top of the storm cloud becomes positively charged. The lower portions of the cloud tend to be more negative. Each charge region initiates different types of lightning — and the results can be truly shocking.

Lightning’s job is to balance the charge differences within the cloud and between the cloud and the ground, which has a positive charge. We call this a potential difference.

Once in a while, an exceptional amount of positive charge builds up in the upper levels of the cloud — so much charge that the atmosphere has no choice but to attempt to balance with the ground. After all, the change in charge — potential difference — is super, super high. When this happens, an incredibly powerful “super bolt” can ricochet from the top of the cloud downward. Because of how far it has to travel, it must be extremely intense. After all, the cloud top to the ground is oftentimes as much as 10 miles!

The large potential difference also means that positive bolts don’t necessarily need to stick around near the storm. They’re big, powerful, and can go basically wherever they want to — within reason. The farther they travel from the storm, the greater the difference in charge has to be to sustain the bolt. That’s why if you’re 10 or 15 miles from a storm, the odds of lightning crashing down are slim — but they’re not zero.

Mapping a “bolt from the blue”: Behind a rogue lightning flash near Silver Spring from a storm in Falls Church

On March 19, a powerful line of storms was approaching the Atlanta area from the west. It was about 30 miles away from the city around 9 p.m., with sparse clouds above the suburbs. Wayne Verno, a meteorologist at the Weather Channel, was home at the time.

“I knew the storms were in the distance, but suddenly I saw an immense flash and heard thunder,” he said. “Sure enough, I checked out the data, and we had had a lightning strike not too far away.” With clear skies overhead, it’s no surprise these remarkable events are dubbed “bolts from the blue.”

“I went to my back porch and waited, and sure enough we had two more a little while later,” recalled Verno. “You could see the bolts shooting out way ahead of the line. There was no rain — nothing! Some of the bolts leaped nearly 30 miles.” That would be like a storm over the Chesapeake putting out a lightning bolt that hits the Washington Monument. It’s crazy!

Superbolts can be up to 100 times as powerful as a typical lightning strike and are a force with which to be reckoned. One such bolt on May 31, 2012, woke people in Tulsa with earthquake-like shaking. As far as a half-mile away, car alarms were set off, and picture frames fell off the walls.

There is no safe place near a thunderstorm. It used to be believed that 10 miles away was a safe zone, which is relatively true — but not always. Your risk of being struck diminishes exponentially with distance from the storm cloud, but historically regions 50 miles out away from a storm have found themselves the unlucky destination of a strike. This may be to a storm’s anvil being blown downwind, and carrying with it just enough charge to touch off a sporadic bolt.

This year has already seen five lightning fatalities in the United States and numerous injuries.