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WEATHER LAB | What is heat lightning?

The common misconception is that hot and humid weather causes these distant flashes.

DES MOINES, Iowa — Heat lightning is a term that gets thrown around a lot during the summer months.

Especially on summer nights, lightning flashes can be seen from a long distance even when there is no rain or thunder nearby. 

The common misconception is that hot and humid weather causes these distant flashes, however this is not technically true. 

In reality, heat lightning is simply a lightning flash produced by a distant thunderstorm.

Hills, trees or even the curvature of the earth prevent the observer from seeing the actual lightning bolt, which is why it appears to be "out of thin air." 

Lightning flashes can be seen up to 100 miles away, but thunder can only be heard about 10 miles away from a light strike. 

Therefore, it's easy to see lightning without even knowing there's actually a thunderstorm occurring in some far off place!

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One reason "heat lightning" may seem more prominent in the summer months is due to higher humidity.

Muggy air tends to make the air more hazy, and it is often this haze that causes the flashes to be more prominent in the night sky.

So the next time you're sitting on the back porch on a muggy summer night and happen to see a flash of lightning, know it is not caused by the heat, but is rather a product of a far away thunderstorm. 

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