As a derecho rolled through the northern Plains Tuesday, the sky turned green. A derecho is a powerful wind storm, but this cluster of storms brought more than just the intense, destructive wind. The ominous green color in the sky is caused by the water and ice inside the storm clouds and is an indicator that the storm is producing large hail. 

The National Weather Service office in North Platte, Nebraska, put together this great info graphic explaining what happens inside the cloud. In a very general sense, it's the same reason we get rainbows.  The light we get from the sun actually exists in the colors of the rainbow (red, orange, yellow, green blue, violet), and the water in the atmosphere can scattered that visible light into those different colors under the right circumstances. 

FW7rDDxWQAItghi.jpg

"Water/ice particles in storm clouds with substantial depth and water content will primarily scatter blue light. When the reddish light scattered by the atmosphere illuminates the blue water/ice droplets in the cloud they will appear to glow green. It takes a tremendous amount of water (...) to achieve this color, which usually means a substantial amount of ice (large hail) has to be present!"

There were dozens of pictures like these online when it happened. Some have been edited, so choose carefully which ones to believe. To the best of my knowledge, the photos included here do not appear to be edited. This is the color the sky appeared to be Tuesday afternoon.Â