Weather Whys

A: It’s a question that has been asked for centuries and is still not fully answered, says Brent McRoberts of Texas A&M University. “We know the ancient Greeks reported seeing green skies during thunderstorms, and sailors for hundreds of years have written about green skies,” McRoberts explains. “The most popular theory is that thunderstorms contain a lot of water – often in the form of hail – and this water or ice tends to scatter green light during the strong updrafts that occur in severe storms. That’s why many people say the sky appears green right before a hailstorm.”

 A: It can, says McRoberts, but not always so. “Often the sky appears almost black during a tornado, but sometimes there are greenish-looking tints to the clouds,” he adds. “Many tornadoes have hail right around them. What we do know for sure is that green skies do exist, but they are fairly rare. They may or may not contain a tornado, and they may or may not contain hail.  We do know that they are almost always an indicator of severe weather, often very dangerous weather, so if you see a thunderstorm approaching and the sky appears to look green, you should take cover immediately.”