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29 August 2003

It's Lightning Season

by Forrest M. Mims, III
Geronimo Creek Observatory
Seguin, Texas

South Texas can experience electrical storms any month of the year. Most lightning occurs during May, when cool air from up north runs into moisture saturated air from the Gulf of Mexico.

That's what happened Sunday evening just south of Seguin and Monday morning just north of the city. The Sunday storm was a supercell, a giant, isolated thunderstorm that spewed hail and apparently spawned a tornado. It's top blossomed into a giant cauliflower shape than blanketed the southern half of Guadalupe County.

These two simultaneous lightning bolts were among hundreds produced by two powerful storms. Photograph by Forrest M. Mims III. Click image to enlarge.

The Monday morning storms were caused by a batch of cool air that arrived in advance of a cold front. One of these large storms passed midway between Seguin and New Braunfels. It was soon followed by a second storm along the same path.

Both these storms produced hundreds of lightning bolts, often several at the same time. The nearby photograph captured two bolts during a single exposure.

Each year between 1992 and 1994, lightning killed an average of 51 people. Another 345 people were injured by lightning strikes each of those years. In short, lightning is a natural hazard that must be taken very seriously.

Chances are that South Texans will experience more electrical storms before summer. So let's look at some lightning safety precautions.

People have been struck by lightning while fishing, boating, swimming and playing soccer and golf. These incidents provide important clues about where not to be when an electrical storm arrives.

Fortunately, the thunder and flashing from lightning storms provide plenty of advance warning. It's always best to heed the warning and seek shelter well before the storm arrives. That's because lightning bolts can be more than five miles long. They can sometimes strike well away from the cloud that caused them.

If you're outdoors when an electrical storm is in the area, be sure to stay away from metal fences and gates. The voltage from a lightning bolt can travel miles along an ungrounded fence line. Also, avoid solitary trees or other objects that project upward.

Florida has by far the most lightning of any of the 50 states. The Florida Department of Community Affairs urges that people follow "The 30-30 Rule."

The rule provides that if the time between a lightning flash and the arrival of thunder is 30 seconds or less, then you should seek shelter. You should not leave the shelter until 30 minutes after you see the last lightning flash.

Cars are generally considered relatively immune to lightning bolts. But the best place to be is indoors. Yet even there you must take precautions.

People taking a shower or talking on a phone have been seriously injured or killed by lightning. There have even been instances of people being struck by lightning while standing on a front porch or by a window.

Besides protecting yourself, it's a good idea to protect your expensive electronic appliances. That especially goes for computers. I know two men who lost all their computer equipment to lightning strikes.

Lightning can strike both power and telephone lines. Surge protectors that are connected between your computer and the power and telephone lines will help. But even they may fail. So its best to unplug your computer from the electrical outlet and to remove the telephone cord from its modem.

The best way to appreciate the power of a lightning bolt is to compare it to the electricity available at the wall sockets in your house or apartment. Most such outlets provide up to 15 or 20 amperes of current at a potential of 120 volts.

Household current can kill. But it's next to nothing when compared to lightning. A typical bolt from a moderately sized thunderstorm has a potential of several hundred million volts. The electrical current in the bolt can reach 100,000 amperes.

The two storms that passed between Seguin and New Braunfels produced ten or more such bolts each minutes. That's more power than the output from a nuclear power plant!

There are a few million Californians who would sure like to figure out how to capture and use some of the power in thunderstorms before summer arrives. But so far no one has been able to come up with a safe and practical way to tap the power of electrical storms.

That's all the more reason to treat lightning with the respect it deserves. For the power of lightning is really quite frightening

Forrest M. Mims III is an independent scientist, writer and photographer.

This feature was originally published in Forrest Mims's weekly science column in the Seguin Gazette-Enterprise, Seguin, Texas. The column is written for a general audience.