What causes thunder and lightning? The dangerous weather phenomena explained.

Thunderstorms are one of nature's most fascinating and dangerous occurrences. We have all witnessed a lightning bolt illuminating the night sky and heard the booming crack of thunder that follows.

But what exactly is going on to cause this intense weather phenomenon?

What causes lightning?

As clouds build in the initial stages of thunderstorm development, millions of tiny ice crystals and pieces of small hail are tossed around violently, colliding at high speeds with each other.

These collisions cause the precipitation particles to become charged. The lighter ice crystals are swept to the upper levels of the cloud and are positively charged. The heavier hail falls to the lower part of the storm and carries a negative charge.

These various charges within the cloud cause the ground underneath to also become charged.

What comes next? The difference in the charges grows and eventually reaches a breaking point, causing a rapid discharge of electricity – lightning.

Related: What causes wind?

Lightning can occur between a cloud and the ground or also within a cloud.

In the United States alone, more than 25 million lightning flashes occur each year.  Obviously, it is extremely dangerous and requires immediate action whenever you are within the potential strike area. Lighting remains one of the top causes of weather-related fatalities in the U.S. and many of those who survive a lightning strike are left severely injured.

What causes thunder?

Without lightning, there is no thunder. Thunder is simply the sound created by a bolt of lightning. 

When lightning occurs, it's about 50,000 degrees Fahrenheit. That heats the surrounding air causing it to violently and rapidly expand. This rapid expansion creates the sound we hear and call thunder. 

Thunder can be heard as far away as 10 miles from the actual lightning strike. 

To calculate how far away the lightning strike was from your location, count the number of seconds between the flash and the thunder crack, then divide by 5.  The resulting number will approximate the distance, in miles, between you and the lightning strike.  The reason for the delay - light travels much faster than sound.

As a rule, when thunder roars, go indoors!