The phenomenon was in no way similar to the polar lights of the northern and southern hemispheres. The polar lights are often green, but they have shapes, and the lights appear to dance in the sky. Also, according to the National Aeronautics and Space Administration, the polar lights are caused by solar storms.
When the sky over Siouxland turned green, a massive thunderstorm system called ‘derecho’ hit South Dakota and Iowa, as well as Nebraska, Minnesota, and Illinois.
According to an article published in Scientific American, “Researchers remain undecided about the exact mechanisms that cause the sky to appear green in certain thunderstorms, but most point to the liquid water content in the air. The moisture particles are so small that they can bend the light and alter its appearance to the observer. These water droplets absorb red light, making the scattered light appear blue. If this blue scattered light is set against an environment heavy in red light — during sunset for instance — and a dark gray thunderstorm cloud, the net effect can make the sky appear faintly green.”
Further, in the same article, meteorology professor William Beasley added that green thunderstorms usually occur in the late afternoon and evening, based on reports.
Nevertheless, as WaPo meteorologist Matthew Cappucci wrote, “Even by that metric, 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.”
As the mystery of the green sky continues, many people in the central US, Australia, and other parts of the world that are prone to tornadoes view the phenomenon as a harbinger of a twister — but there is no scientific evidence to back up the popular belief, according to experts.
See the fantastic phenomenon in the video below!