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Lightning is a giant spark of static electricity generated by a thunderstorm. The charge is created by water and ice particles moving around in the cloud. The positive and negative charges separate within the cloud (it is still not known exactly how this happens).

When sufficient negative charge has built, stepped leaders race toward Earth in steps about 150 feet long.

As the stepped leader gets close to Earth, upward positive streamers will form, often from high points locally, until one of them connects with a stepped leader.

Once a connection has been made, the lightning stroke will discharge the negative charge downward through that one lightning channel. If sufficient charge remains in the cloud, multiple return strokes can occur down the same channel.

The whole stepped leader/lightning stroke process takes much less than a second.

All thunderstorms produce lightning, but about ninety percent of it stays in the clouds. Researchers estimate there are 25 million cloud-to-ground strikes in the U.S. each year.

Lightning will generally strike the tall objects, like trees and mountains, and it is a myth that lightning targets metal objects. But there are instances where people are in danger:

 This is common in open fields and small boats where a person is the tallest object around.

 Sometimes lightning will strike a tall tree and part of the current flashes laterally to a person standing within a couple feet of the tree. This often occurs when people take shelter under a tall or solitary tree.

 Once the current reaches the ground, it tends to spread out along the surface. This ground current can injure or kill people and animals by going up a leg, damaging the body, often by stopping the heart but also potentially doing much other damage, and then moving down the other leg back to the ground. Ground current usually weakens with distance from the originally-struck object.

 Conduction can cause serious injury or death far from the original lightning strike. Although lightning does not target metal objects, they are excellent conductors and can deliver a substantial charge far away if the lightning strikes a metal fence, guard rail, bridge structure, railroad tracks, plumbing or wires. In fact, striking telephone and electric wires is one way that lightning can reach people indoors, so avoid the use of corded phones and other items during thunderstorms.

 In particular, people tend to delay getting off lakes and are struck as they head for shore. 

 Don't go out for a run, hike or bicycle ride -- or somewhere else with no guarantee of shelter -- when the upstream sky is dark in summer.

 Examples of unsafe structures would be tents, garages and bus shelters. To be protected from lightning, you need to be in a structure that is large enough to absorb the charge and, hopefully, be able to conduct the current to the ground without allowing it to pass through you. 

Rubber won't protect you from strikes above.

 Rubber tires on cars, motorcycles and bicycles do not provide any protection from lightning from above, nor do rubber-soled shoes, but could provide some protection from ground current if the lightning strikes nearby rather than directly.

Weather and Climate News

Bill Endersen

Author

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