What is Heat Lightning?

Heat lightning is common during the summer months. Learn what causes it and why you can see it.

At this time of year on warm, humid nights, the phenomenon known as “heat lightning” is very common. The sky will seem to flicker with light; and even on a seemingly clear night with stars, you may see flashes. No sound accompanies the flash, although if you are listening to an AM radio, you’ll hear crackles of static at the same time you see the flash.

What you’re likely seeing is the light from a distant thunderstorm that is located at too great of a distance for the thunder sound to be heard. The sound of thunder rarely travels more than 10 miles. Other cases can be explained by the refraction (or bending) of sound waves by bodies of air with different densities. An observer may see nearby lightning, but the sound from the discharge is refracted over their head by a change in the temperature, and therefore the density, of the air around him. As a result, the lightning discharge seems to be silent.

The term “heat lightning” probably comes from the fact that the effect is most often seen on warm, humid nights during July and August. So an association has been made with sultry temperatures. But when the sky is hazy, as is quite typical on warm, summer nights, the light from intense thunderstorms as far away as 100 miles can be reflected off a layer of haze and up into the night sky.

And that’s why you tend to see heat lightning as just a diffuse flash or flicker.

Watch heat lightning in action in the following video:

Join The Discussion!

Have you ever experience heat lightning?

Let us know in the comments below!

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Jaime McLeod

Jaime McLeod is a longtime journalist who has written for a wide variety of newspapers, magazines, and websites, including MTV.com. She enjoys the outdoors, growing and eating organic food, and is interested in all aspects of natural wellness.

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I’d just like to reiterate that heat lightening isn’t a separate event from regular lightening. Lightening is lightening and it’s the result of a thunderstorm. Sometimes you see lightning and hear thunder, sometimes you see lightening and don’t hear thunder. Same weather event though.


So is this why the otherwise clear night sky, on a windless but hot and humid last ditch effort from the summer season, is flashing like there is a glitch in the matrix? Mildly terrifying at first, but this really is a neat phenomenon. This is along the coast in Downeast Maine, btw.


When I lived in Southern ontario I used to see on very very hot clear days a stray lone red thunderbolt across the clear blue sky in mid day..it was freaky to see infact.. found this site just now btw about the different types of ,ightening. What I saw is what NOAA calls ‘bolt from the blue’…


Denus Williams

I’ve noticed lightning has been more quiet recently. Large bolts strking 1-2 miles away are completely silent. What is the cause?? WHO DO YOU WORK FOR JAIME?


Heat lightening isn’t real. Perhaps that should have been more clear in article.


It IS real. It’s just the definition that gets confused. People who see the lightning outside of the storm area call it “heat lightning” because it often happens on warm humid nights, and they are not experiencing any other parts of the storm, due to being outside the storms path. But the lightning IS real, and it is referred to as “heat lightning”.

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