Have you ever seen tall, dark puffy clouds forming on a hot humid afternoon?  These are called cumulonimbus clouds, sometimes nicknamed "thunderheads."  They can actually form any time of day when the temperature falls rapidly higher up in the sky.  These tall dark clouds are full of moisture and contain strong up and down air currents. Cumulonimbus clouds may tower more than 50,000 feet, and cover from just a few square miles up to two hundred square miles. 

What is Lightning?

To put it simply, lightning is electricity.  It forms in the strong up-and-down air currents inside tall dark cumulonimbus clouds as water droplets, hail, and ice crystals collide with one another.  Scientists believe that these collisions build up charges of electricity in a cloud.  The positive and negative electrical charges in the cloud separate from one another, the negative charges dropping to the lower part of the cloud and the positive charges staying ins the middle and upper parts. Positive electrical charges also build upon the ground below.  When the difference in the charges becomes large enough, a flow of electricity moves from the cloud down to the ground or from one part of the cloud to another, or from one cloud to another cloud.  In typical lightning these are down-flowing negative charges, and when the positive charges on the ground leap upward to meet them, the jagged downward path of the negative charges suddenly lights up with a brilliant flash of light. Because of this, our eyes fool us into thinking that the lightning bolt shoots down from the cloud, when in fact the lightning travels up from the ground. In some cases, positive charges come to the ground from severe thunderstorms or from the anvil at the very top of a thunderstorm cloud.  The whole process takes less than a millionth of a second.   

Kinds of Lightning

There are words to describe different kinds of lightning.  Here are some of them:
In-Cloud Lightning: The most common type, it travels between positive and negative charge centers within the thunderstorm.
Cloud-to-Ground Lightning: This is lightning that reaches from a thunderstorm cloud to the ground.
Cloud-to-Cloud Lightning: A rare event, it is lightning that travels from one cloud to another.
Sheet Lightning: This is lightning within a cloud that lights up the cloud like a sheet of light.
Ribbon Lightning: This is when a cloud-to-ground flash is blown sideways by the wind, making it appear as two identical bolts side by side.
Bead Lightning: Also called "chain lightning," this is when the lightning bolt appears to be broken into fragments because of varying brightness or because parts of the bolt are covered by clouds.
Ball Lightning: Rarely seen, this is lightning in the form of a grapefruit-sized ball, which lasts only a few seconds.
Bolt from the blue: A lightning bolt from a distant thunderstorm, seeming to come out of the clear blue sky, but really from the top or edge of a thunderstorm a few miles away.

What Puts the Thunder in the Thunderstorm?   

Lightning bolts are extremely hot, with temperatures of 30,000 to 50,000 degrees F. That's hotter than the surface of the sun! When the bolt suddenly heats the air around it to such an extreme, the air instantly expands, sending out a vibration or shock wave we hear as an explosion of sound. This is thunder.  If you are near the stroke of lightning you’ll hear thunder as one sharp crack. When lightning is far away, thunder sounds more like a low rumble as the sound waves reflect and echo off hillsides, buildings and trees.  Depending on wind direction and temperature, you may hear thunder for up to fifteen or twenty miles. Thunder is only a noise and is nothing to be afraid of.  But lightning can be dangerous.  Head to the next page to find out how to stay safe from it.

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