SIOUX FALLS, S.D. — The sky in one South Dakota city turned an ominous color earlier this week.
On Tuesday, Sioux Falls residents saw it turn green just before severe weather moved in.
The National Weather Service said a derecho swept through much of the state, with winds reaching 99 mph in some areas.
According to the agency, a derecho is "a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms."
The storms toppled trucks, flooded roadways, and knocked out power to thousands of residences.
According to AccuWeather, green skies often accompany severe weather.
Scientists believe if a thunderstorm coincides with ambient red light, like a sunset, airborne water particles can bend the light, so it appears green.
No injuries were reported.