There is a myth that lightning never strikes the same place twice. However, in one storm the Empire State Building in New York was struck 15 times in 15 minutes.

Thunderstorms form as warm, moist air rises rapidly. On a sunny summers day, the ground is often hotter than the air. This is one reason air may rapidly rise. As it rises, the air will cool, its moisture condensing out into ice crystals and water droplets, forming immense thunderclouds, called 'cumulonimbus' clouds.

Air moving within the cloud, causes huge differences in the electrical distribution. The bottom of the cloud develops a negative charge and the top, positive. These electrical differences attract each other, so an 'electrical discharge' is produced within a cloud, between two clouds or to the ground. This discharge we see as lightning.

This discharge is just the same as rubbing your feet on the carpet then touching something. You hear a sound and feel a bit of a tingle. If you turn the light off, you will even see a tiny lightning bolt. Of course, real lightning from thunderstorms is far more powerful. One lightning bolt can reach 30,000C, five times hotter than the sun. Air can often smell 'burnt' after a lightning strike, as this huge amount of energy can alter molecules in the air. This heating also causes thunder. The air rapidly expands and then contracts, causing vibrations in the air. These vibrations, or sound waves, we hear as thunder.

As lightning is seen and thunder heard, lightning travels at the speed of light, and thunder at the speed of sound. The difference in these speeds is so great that light could travel right round the world before sound finished the 100m sprint. This speed difference provides an easy way to see how far away the lightning struck. Count the seconds between the lightning and the thunder, each second represents 300m.

It is estimated that 44,000 thunderstorms happen everyday world-wide, producing 100 lightning flashes every second. That's 8.6 million strikes every single day. Lightning, being such an enormous amount of unpredictable power, can cause great havoc; forest fires, explosions and even death. However, there is only about a one in 3 million chance of being struck by lightning, so it's not something that we need to worry about. Even so, I still wouldn't advise standing on the Empire State Building in a thunderstorm.

Other features in the Weather Basics series:

- Clouds
- Day and Night
- Fog and Mist
- Fronts
- Frost
- High Pressure
- Humidity
- Jet Streams
- Lightning
- Low Pressure
- Mirages
- Northern Lights
- Rain or Showers?
- Thunder
- Watercycle