Start counting when you see a lightning flash. If you hear thunder five seconds later, the lightning is a mile away; 10 seconds later, it's two miles away.

On the average, around 40 million lightning strokes hit the ground each year in the United States. And all thunderstorms generate lightning, the USA's second biggest weather killer.

Ways to avoid becoming a victim of lightning

In the United States, lightning is the second biggest weather killer, next to floods. Most victims are struck in the open, such as on beaches or golf courses, or when they take shelter from the rain under a tree. But lightning can be dangerous in your home.

1. If you are outdoors, you should rush to safety at the first flash of lightning, crack of thunder or even a darkening of the sky.

2. Hazy skies, especially in the East, can often hide thunderstorms.

3. All thunderstorms are dangerous. Forecasters can't tell, even with the most sophisticated instruments, whether a storm will produce hundreds of lightning flashes or only a few.

4. Never take shelter under a tree.

Cars offer lightning shelter

1. Lightning hits car.
2. Current flows through metal toward ground.
3. Lightning jumps from wheel to ground, can blow out tire.

Lightning can reach inside to kill

1. If lightning hits a house or other building...
2. ... it can flow through plumbing, electrical or telephone wires.
3. Lightning has killed people talking on telephones.
4. It has also killed people in showers or bathtubs.