Most people have heard the saying “red sky at night, sailors’ delight, red sky at morning, sailors take warning.” But what about when the sky turns green? There’s no catchy saying, but it’s closer to the “red sky at morning” warning.

What You Need To Know

  • Green skies usually indicate large hail within a storm

  • It happens when storms move in later in the day

  • This phenomenon is extremely rare

In early July 2022, a powerful derecho swept through the Midwest, bringing severe storms with tennis ball-sized hail and damaging wind gusts over 90 mph in South Dakota.

Not only did it bring severe weather, but it turned the skies bright green. It’s not the first time it’s ever happened, but it is rare.

Here’s another look at the storms and green sky as the storm moved toward the NWS office in Sioux Falls, SD.

While most of us are familiar with dark storm clouds, few have seen these bright, green skies. So how does it happen?

Think of how the sky turns reddish around sunset. It’s because when the sun is near the horizon, the light has to travel through more of the atmosphere and scatters the light more.

(Credit: National Weather Service)

When that reddish light travels through powerful storms late in the day with high amounts of water content (hail), it turns the sky green. Usually, it’s an indicator that the storm can contain very large hail.

So if you ever see green skies and dark clouds approaching, it’s probably a harbinger of large hail and powerful storms, and it’s best to get indoors to a safe shelter.