what causes heat lightning

What Causes Heat Lightning?  

Let’s start with a different question first…

Is Heat Lighting Real?

No, heat lightning is not real!  At least not the way it’s usually presented.  It is real lightning.  Heat lightning is just regular lightning that is too far away to hear the thunder.  You may also be seeing the reflection of the lightning bolts off the clouds, rather than seeing them directly

The Heat Lightning Myth Explained

The heat lightning myth follows the premise that the flashes you see off in the distance during the warm summer months are a byproduct of heat and humidity, not a thunderstorm.  It’s also been said that heat lightning does not produce rain or thunder.  While it is possible for lightning to be present without rain, we’ll see more on this in a minute, this statement about heat lightning and thunder is also false.  The flashes we see off in the distance are simply part of a thunderstorm that is too far to hear the thunder.  We can see lightning up to 50 or more miles away, however we actually don’t hear thunder more than about 10-15 miles away.

Here is nice video explanation of heat lightning from the University of Illinois Extension:

So, what Causes Heat Lightning? 

I guess I could answer that two different ways.  The easy way would be to just say, “It doesn’t exist!”, but what’s the fun in that?  For you weather geeks out there, let’s talk about why we can see the no-sound, no-bolt lightning from up to 100 miles away.  And why don’t we hear the thunder and why don’t we see the lightning bolts?

Heat lightning is more often seen with the dark backdrop of the night sky.  This is because when combined with the bright flash of lightning, the contrast makes it easier to see it that far away.  The reason we can’t hear the thunder is because its sound is refracted through the troposphere and reflected off the Earth’s surface.  The result of the refraction is voids through which the thunder cannot propagate and the reflections help dissipate the sound.  This bouncing off the Earth is exacerbated at these great distances by its curvature.  And since we’re sometimes seeing just a reflection of the lightning in the clouds where the storm is located, we don’t always see actual lightning bolts.

Can Heat Lightning Strike You?

“Heat lightning”, I guess we’re still calling it that, by itself is likely too far away to strike you.  According to the National Severe Storms Laboratory, lightning has been documented to travel up to 25 miles, but more commonly strikes up to 10-15 miles away.    For this reason, what is thought of as heat lightning probably won’t hurt you, but storms move of course, so stay alert.  You’ll definitely want to consider shelter if you can hear the thunder since this means the storm is within striking distance. 

In fact, thunder can be a good detection method for how far away lightning really is.  The speed of sound is 340 m/s.  So, for every 5 seconds of time between a lightning strike and the thunder that follows, the lightning is approximately 1 mile away.  If you see the lightning and hear the thunder quickly thereafter, it’s very close and you should find safe shelter right away!   

Dry Lightning vs Heat Lightning

I mentioned above that it is possible to have a lightning storm without rain and that I would come back to that.  This is called dry lightning and is produced during a “dry thunderstorm”.  Dry lightning most often occurs in very dry conditions such as the western part of the United States.  The atmosphere contains so little water vapor that the precipitation that comes from the storm evaporates before it hits the ground.  Dry lightning is dangerous and can be a contributor to wildfires.  So dry lightning is lightning without any accompanying rain that hits the surface, while heat lightning is associated with lightning that does not produce thunder (or, more accurately, thunder we can hear).

I’ll leave you with this…

Heat Lightning Video


Heat lightning. (2017, December 13). In Wikipedia, The Free Encyclopedia. Retrieved 19:11, January 20, 2018, from https://en.wikipedia.org/w/index.php?title=Heat_lightning&oldid=815281914

Frequently Asked Questions About Lightning.  In National Severe Storms Laboratory, NOAA.  Retrieved 22.53, January 20, 2018, from https://www.nssl.noaa.gov/education/svrwx101/lightning/faq/

Dry thunderstorm. (2017, October 12). In Wikipedia, The Free Encyclopedia. Retrieved 23:11, January 20, 2018, from https://en.wikipedia.org/w/index.php?title=Dry_thunderstorm&oldid=805054704

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