There are a few theories as to why these green skies occur, with the predominant hypothesis having to do with the way heavy raindrops and hail are able to scatter and reflect light.

As Scientific American explains, thunderstorms often happen in the late afternoon and evening, when the setting sun casts shades of yellow and red across the daytime's blue sky. Water is exceptionally good at holding the color blue, and it's thought that raindrops of a certain diameter can disperse all but cerulean light. Thus, meteorologists posit that if a storm has enough liquid power behind it and hits at the perfect time of day, competing yellow and blue light will combine into green.

Yesterday's storm, however, pushed this conjecture to the brink.

"Even by that metric," WaPo meteorologist Matthew Cappucci wrote, referring to the prevailing theory, "the colors exhibited by storms over Siouxland and along the Interstate 29 corridor of South Dakota, the James River Valley and northwestern Iowa were unlike any in recent meteorological memory."

READ MORE: Derecho turns sky green, sweeps through 5 states with 90 mph winds [WaPo]

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