The belief that “heat lightning” is a real thing, is simply not true, but rather a misunderstanding of the term. Most commonly, people think that heat lightning is lightning that occurs in the clouds when it’s hot outside. When, in fact, the term heat lightning or silent lightning is used to explain cloud-to-ground lightning that occurs very far away.
Cloud-to-ground lightning occurs within a thunderstorm when lightning comes from the clouds and touches the ground - it’s pretty self-explanatory - While sound travels through the lowest layer of the atmosphere, the troposphere, with height, the temperature and density change which results in the sound of thunder being refracted or bent. When thunder is refracted in the troposphere, the sound waves are bent by bodies of air at different densities. Thunder also reflects off the Earth’s surface. Since Earth is round, when it reflects off the surface it sometimes doesn’t make a noise in places that we see lightning. With refracting and reflection, we are left with places that don’t hear any noise when they see lightning. You’re most likely to hear thunder if you are within 10 - 15 miles of the lightning strike.
When you are observing “heat lightning,” you are usually more than 10 - 15 miles away from the storm. In fact, you can see it from up to 100 miles away! The lightning is still visible because light travels faster than sound and isn’t refracted in the troposphere. It is easily seen during the hot, humid nights of July and August. When the sky gets hazy on a hot night, the light from intense thunderstorms can be reflected off this haze, which lights up the sky and can be seen from miles away. Since the sound of thunder doesn’t follow the lightning, we tend to label it as “heat lightning.”
Always remember, that within a thunderstorm, if you can see and hear lightning and thunder respectively, seek shelter and remain cautious. Even though “heat lightning” isn’t exactly real, it’s completely safe to watch since the storm is very far away. One of the most common places this phenomenon occurs is in Florida over the water at night. The remnants of storms that could have formed during the day coming from the opposite coast causes thunderstorms above the oceans and water.
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