“Why do tornadoes turn the sky green?”

Image of the Wisconsin sky by James Stutzman, via Flickr

When I was a wee sprout, I heard from someone in Tornado Alley that you only have to worry that a tornado is coming if the sky turns green. I shared this little factoid with our daughter in one of our many recent conversations about tornadoes, and was rewarded with the inevitable question.

“Why do tornadoes turn the sky green, Mommyo?”

I didn’t know. Naturally. I never seem to know. But I have an iPhone. So we asked it.

According to this article in Scientific American, it turns out there’s no proven link between green skies and tornadoes (or hailstorms) at all.

Tornadoes don’t care what color the sky is

Sure, the sky sometimes turns green when there’s a thunderstorm pending, but hailstorms and tornadoes aren’t terribly picky about sky color. They are happy to pop up whether the sky is green or a more typical stormy grey-blue. Pretty much the only thing you can count on is that the sky will be dark when that tornado drops by.

So if tornadoes don’t turn the sky green, what does?

Research on green thunderstorms is apparently prone to being called out as a waste of money by members of Congress not from Tornado Alley, making it both woefully underfunded and rather hazardous to your meteorological career. Until that situation changes, we may have to make do with scientific speculation.

Current thinking is that the water particles in the air change the color of the sky. The water particles absorb red light, making the remaining light appear more blue. Scattering that blue light across a red sunset and a dark grey cloud can make the sky look faintly green. Which explains why most green thunderstorms are spotted in the late afternoon and evening.

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