For me, the most exciting weather event is a good thunderstorm. It doesn’t have to be severe. I just like lots of lightning and thunder. Ironically, I was afraid of storms when I was small. As I got older, I had a sense of the amount of power within a storm that was needed to create thunder. Intuitively, we understand there’s power involved, and Ben Franklin was kind enough to demonstrate that it is electrical power. But why does it happen to begin with?
Lightning is actually an outward sign of the atmosphere trying to find balance. It’s defined as a sudden and violent electrical discharge, and it’s created when negative and positive charges build up separately. Imagine a pool of negative charges collecting inside a storm cloud above a tree, for example. At the same time, a pool of positive charges is collecting near the top of the tree. Opposite charges attract, so they move toward each other. When enough of each type of charge is built up, a connection is made between them through a channel. We see that connection as lightning.
The channel allows the charges to move and become more evenly distributed between the cloud and the tree. In the meantime, charges may be building up elsewhere in the storm and on the ground level. So, the process sets up again in a new place, and the connection doesn't have to be between the cloud and objects on the ground. It can also be within the cloud or between clouds.
There are a few interesting notes about lightning. First, it can strike twice in the same place. In fact, it often does. The charges that build up on the ground level tend to climb to the highest point before the connection with the charges in the cloud is made. That’s why there are so many photographs of lightning striking the Eiffel Tower, The Empire State Building, and even the dome of St. Peter’s Basilica in the Vatican. Those buildings are all some of the tallest things in their vicinity.
Second, thunder always follows lightning. It’s the sound created when the channel is made. It follows lightning because sound travels slower than light. The old rule of counting seconds between the lightning and thunder to estimate the distance the storm is from you holds true because sound takes about 5 seconds to travel one mile.
If you see lightning in the distance on a summer night, but don’t hear thunder, it isn’t “heat lightning.” It’s just lightning that is too far away to hear the thunder. Heat lightning is a misnomer. Thunderstorms are more likely to pop up on hot, humid days late in the afternoon and early in the evening. As the sun goes down, the lightning is more visible from far away, but the storm is too far from you for thunder to be heard.
There are so many cool facts about lightning that I can't cover them all right now. If you have any questions about lightning, thunder, or any other weather phenomena, please ask!
An image of lightning captured with a cell phone camera during a storm over Raleigh, North Carolina.
Photo by Doug Casteen, used with permission.