The sky turned green during the derecho storm on July 5 in Sioux Falls, located in the US state of South Dakota. According to experts, the primary reason of the phenomenon is that the clouds tend to emit blue light as they bear rain, and the sky turns green when blue light is combined with red and yellow light coming from sunset.
On the other hand, about 30,000 people were left without power for hours in South Dakota, Minnesota and Iowa, where the derecho storm was effective, National Weather Service stated.