With summer in full swing, the topic of lightning and thunderstorms are fresh on our minds with outdoor activities happening in abundance. According to the National Weather Service, lightning kills about 20 people each year in the United States, with hundreds more injured, and an average of 20 million cloud to ground flashes are observed each year. Because of this, it’s important to know about the different types of lightning as well as some safety tips when outdoors this summer.
Lightning is a spark of electricity between opposite charges, which occurs between the clouds, the air, and the ground. The result is a quick flash of light followed by a very lound rumbling sound called Thunder. This occurs when lightning heats up the air very quickly and causes a sonic boom type of sound. Lightning is most typically observed in thunderstorms, but it also has been observed in volcanic eruptions, intense forest fires, and during heavy snowstorms as well.
Thunder can be heard up to 25 miles away from where a lightning strike has occured, according to the NSSL, which is a good way to estimate the distance you are from lightning. To do this, count the number of seconds from the time you see a flash of lightning to when you hear thunder. Divide that time by 5 (sound travels about ~1/5 of a mile per second), and you will have the number of miles between you and the lightning strike. There are multiple ways lightning can strike as well, which we will dive into in the next section.
Image of Spider Lightning (Cloud to Cloud) with a Cloud to Ground Strike in the Background. Courtesy of NSSLCloud to ground lightning (CG) is the most harmful kind of discharge that is responsible for hundreds of injuries and deaths every year. Like the name says, this lightning occurs between charges that develop between the thunderstorm cloud and the ground. Within this category, there are actually two ways CG can form; Negative CG (-CG) and Positive CG (+CG)
This is a more common way for CG strikes to occur, which forms initially as a negative charge steps towards the ground (known as a "stepped leader"). As the negative charge nears the ground, positively charged particles or "streamers" from the ground move upwards and make the connect with the negative charges. When these connect, a flash of lightning occurs, which is really up to as many as 20 quick strokes of electricity and can make lightning appear like it's flickering.
This is another process of CG strikes and forms in a similar fashion, but only with a positive charge lowering to the surface instead. Positive CG strikes also typically only have one return stroke and are more likely to have a sustained current flow. Positive CG dominated storms are not as common as Negative CG ones. You may have heard of the phrase "bolt from the blue," which is when a cloud to ground lightning strike begins inside of a cloud, but travels horizontally away from the cloud before interacting with the ground. The sky may be blue, but lightning can still occur with a storm nearby. This is why even when a storm is 10 - 15 miles away, it can be dangerous for outdoor activities to occur and is also why we have the phrase "When Thunder Roars, Go Indoors".
Cloud flashes are types of lightning that do not interact with the ground at all! The most common type of cloud flashes are Intra-Cloud (IC) lightning flashes. These are lightning bolts that remain safely within the clouds. A common example of IC lightning is "sheet lightning," which occurs within the cloud and give the appearance of a sheet of light in the sky during a storm (see image above). There are also Cloud-to-air (CA) flashes, which begins from a cloud and extends outward into the air around the storm. Despite extending out from a thunderstorm, this lightning still does not make contact with the ground (see image below)
Cloud-to-cloud (CC) lightning may sound similar to IC lightning, as it happens between clouds. However, this kind actually occurs on the outside of the clouds where the bolts almost seem to "jump" from one cloud to another. You can be seen what we mean by the first image in this blog, which shows classic CC lightning. This is also known also as "spider lightning", thanks to it's long and horizontal bolts that extend across the cloud. Spider lightning can also be linked to +CG lightning.
Now that we've gone over the various types of lightning, how can you stay safe from it? Remember "When Thunder Roars, Go Indoors"? This isn't just a catchy slogan but actual good advice to take when a storm is nearby. If you do find yourself outdoors, keep moving to find a safe indoor shelter as there is no real safe place outside during a thunderstorm. If no option is available, stay away from tall objects, hills, trees, and metal poles. Seek shelter within a car if you can, as lightning can pass through the metal frame and into the tires when reaching the ground (a form of a Faraday cage).
When you're inside, you still may not be 100% safe from lightning. Stay away from plumbing or electrical equipment and refrain from coming into contact with any running water water. You can find more information about lightning safety and some lightning safety facts in our Lightning Awareness and Safety blog.
