After a strong storm last Tuesday, the sky above Sioux Falls in South Dakota, USA, turned a strange and almost frightening shade of green. Images of the seemingly unreal sky attracted widespread attention on social media.
https://twitter.com/jkarmill/status/1544422037078294532
Fortunately, this sky was not a doomsday omen. At least we can say that the green sky is a completely natural phenomenon, albeit rare. As frightening as it may seem, this is due to the scattering of light by ice.
“Water/ice particles in storms with depth and water content primarily scatter blue,” NWS meteorologist Cory Martin said on Twitter. “When reddish light scattered by the atmosphere illuminates blue water/ice droplets in the cloud, it appears to glow green. It takes an enormous amount of water content in the cloud to achieve this color, which usually means that there must be a significant amount of ice (large hail).”
https://twitter.com/eddiedevonne/status/1544483626515107843
So, just as the many different colors the sky takes on have different meanings, a green sky also means that a large hailstone is likely to appear soon. “This event is typically a visual warning sign that the storm is capable of producing very large hail,” says Martin.