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Shedding a little light on lightning

Even though we haven’t seen that much lightning around here on all but a few days this year, there is plenty to go around worldwide at any moment.

It’s estimated there is an average of 40 lightning strikes per second around the world, with as many as 2000 thunderstorms globally at any moment. NASA estimates about 14.5 thunderstorms occur per year.

There is still much to be learned about lightning, though some basics are well understood. Most showers which do not contain any ice, especially graupel - My viewers knew that term ad nauseum…sometimes thought of as soft, white hail - do not produce lightning. The strong updrafts and downdrafts in a convective cell will generally produce charge separation if there is ice, with the top of the cell taking on a positive charge, and the base becoming negatively charged.

There is no space here to go into great detail, but when hail and graupel from the frozen top of the storm coming down in cold downdrafts collide with water droplets coming in warmer updrafts, the charging and charge separation strengthen. Eventually, a positive charge begins to set up on the ground beneath a thunderstorm.

Because the air itself is a very good insulator, it takes a tremendous amount of electric charge to produce lightning. The majority of lightning occurs cloud to cloud. When the charge separation between the negative cloud base and the positive ground becomes sufficiently strong, cloud to ground lightning finally develops. The electric field between the ground and the storm is much weaker than the field within the cumulonimbus cloud itself, so it takes even more energy to make a cloud to ground strike occur. The positive ground charge begins to reach up through taller objects such as trees, poles, and houses and the negative charge in the base of the cloud sends out what’s called a “stepped leader” to meet the positive “steamer” reaching up from the taller objects. Generally lightning will tend to follow the shortest path, so tall objects such as mountains and skyscrapers get struck most often; it’s a path of least resistance.

However, fewer than 5 percent of strikes occur from the positive charge region of the top of the storm to the ground. Because the atmosphere is such a good insulator, the amount of energy to create these strikes can be 10 times greater than those from the base of the cloud, up to 1 billion volts. So, these strikes are actually far more dangerous than the more common strikes—which are dangerous enough!

Let’s cut to the chase on lightning safety. The especially dangerous positive strikes from the top of the thunderstorms can strike more than 25 miles in any direction from the storm itself. (One, in the Dallas-Fort Worth area, traveled 118 miles from the storm.) There is a common misconception that once the storm has passed your location, you’re “all clear.” Not so. Again, these positive strikes can strike in ANY direction, including to the rear of a departing storm. These “bolts from the blue” tend to be the most lethal. So, if you can hear thunder you are still in danger. This is especially important for golfers, umpires, lifeguards, and coaches to know. You CAN’T just go by what you’re seeing on Doppler radar. That just shows where the rain and hail are occurring and does not at all account for these deadly “bolts from the blue.”

Where should you go to escape lightning danger? The interior of well-constructed buildings with plumbing provide good grounding, as long as you stay away from pipes and windows. The interior of a car with windows UP provide pretty good protection. Forget about convertibles, even with the top closed. Metal shacks, buildings with large openings, porches, beach shacks, picnic pavilions, or dugouts…nope. And we’ve all heard not to stand under or near trees, especially tall trees. Stay out of open fields and avoid high ground. It used to be thought that if you felt your hair stand on end, you should crouch to minimize your contact with the ground. Now, NWS lightning researchers say there simply is no safe posture to minimize lightning danger in that situation…certainly, do not lie flat. Don’t take showers or use a tub if you hear thunder. Cell and cordless phones are safe. Corded telephones provide a pathway and so do computers. In fact, you may want to shut down computers to protect them as well as yourself. For more information, you can use a search engine for lightning and lightning safety.

One last, less critical point: there is NO heat lightning. “Heat lightning” is simply lightning from a thunderstorm too far away for the sound to reach you. Lightning always produces thunder. I dislike the phrase “end of story.” But in this case, end of story.

Meteorologist Don Paul retired from Channel 4 earlier this year after more than 30 years on Buffalo TV. His articles on weather, climate and related sciences appear at buffalonews.com.

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