An often-shared weather saying — and it's wrong — is "lightning never strikes the same place twice."

Lightning not only can strike the same place twice, but it seems to prefer high locations. The Empire State Building in New York City, for example, is struck about 25 times every year.

What is true is "when thunder roars, head indoors." Thunder is caused by lightning. It's the sound wave produced as a stroke of super-hot lightning heats the air, causing it to rapidly expand and creating the cracking and rumbling.

Lightning is a brilliant electrical discharge within a tall cumulus cloud, between clouds, or between a cloud and the ground. Thunder is rarely heard from storms more than 5 miles away. So if you see lightning and then hear thunder, how far away is the storm? A lightning flash travels at the speed of light, reaching you in less than a millisecond. Thunder travels at the speed of sound, or about 1,000 feet per second, equal to the distance of 1 mile in about five seconds. Once you see a flash of lightning, count off the seconds until you hear the thunder. Divide that number by five. The result will give you the approximate distance from you to the storm in miles. If you see the lightning flash and hear the clap of thunder instantaneously, the lightning is dangerously close, probably less than a quarter-mile. Lightning kills hundreds of people each year in the United States and claims more lives every year than hurricanes and tornadoes combined.

Four things you need to know about lightning:

• People hit by lightning receive a severe electrical shock, but they do not carry a charge. They can often be revived using CPR.

• Take cover indoors, house size or bigger. Avoid landline phones. Cell or cordless phones can be used. Indoors could be your car. Rubber tires and the metal shell surrounding your body will help protect you.

• You don't want to be in or on the water when lightning approaches. You don't want to be the tallest thing around. Avoid golf courses, open fields, metal fences or standing under tall trees.

• If outdoors and no building is available, crouch down on all fours in a cluster of small trees. Even in the open, crouching down decreases your chance of receiving a dangerous jolt.

Jim Gilbert's observations have been part of the Minnesota Weatherguide Environment Calendars since 1977. He taught and worked as a naturalist for 50 years.