Lightning is a spectacular sight to see from thunderstorms. In fact, without lightning we couldn’t call thunderstorms thunderstorms, because lightning actually causes thunder. And while it is not considered a category of severe weather, lightning can be very dangerous. But how does it even form?
Lightning is all about electrical charges and it all starts in the cloud. Ice crystals that are high up in the thunderstorm cloud, are constantly moving around. They often crash into each other because of the constant motion. As they run into each other, small negatively charged particles (electrons) are knocked off of some ice crystals and are added to another. All of this motion has now separated the positive and negative charges of the cloud. The top of the cloud becomes positively charged and the base of the cloud becomes negatively charged.
Once the charges are mostly separated in the cloud, the formation process of lightning can start. We’ve all heard the saying opposites attract, and that is very true in this case. The negative charge at the base of the cloud wants to link with the positive charge at the ground. Once the negative charge is large enough, they start moving down a “stepped leader” to meet the ground. The positive charge at the ground is also attracted to the cloud, so it begins to flow upward. When the two charges meet, a powerful electrical current flows upward from the ground. This is what we see and is known as the return stroke. This return travels at 60,000 miles per second! This flash that we see can heat the air around it to 30,000 degrees Celsius (54,000 degrees Fahrenheit). Heat causes air to expand, and this extreme release of heat causes the air to expand extremely rapidly. That expansion creates a shock wave that turns into a booming sound wave, also known as thunder!
But there isn’t just one kind of lightning. The lightning that was just described is cloud to ground (CG) lightning. The most common type of CG lightning is negative, initiated by the downward moving negative stepped leader. There is positive CG lightning, where the stepped leader is positively charged. These are typically very bright flashes, and usually associated with supercell thunderstorms.
Cloud to air (CA) lightning is when a discharge jumps from the cloud into clear air and then ends. CG lightning actually contains CA lightning, because of the branches that extend from the main CG channel.
Intracloud (IC) lightning is very common. This is actually the most common from embedded within a single storm cloud. The charge just jumps from different regions of the cloud.
Ground to cloud (GC) lightning is similar to CG, just initiated from the ground instead of the cloud. The upward moving leader orients from an object on the ground.
But no matter what kind of lightning you see, it is important to keep you and your family safe. Lightning exceeds the number of deaths resulting from both tornadoes and hurricanes each year. Lightning can strike as far as 10 miles away from the base of a thunderstorm, which is about the distance from a storm that you are able to hear thunder. If you can hear thunder, lightning is close by, and this is why when thunder roars, go indoors!