See the green, swirling storm clouds above you? Run! This means that the storm is especially strong and dangerous, and perhaps a tornado is approaching.
Green clouds have long been considered a signal of an impending tornado or hail storm on Tornado Alley, a huge region of the United States that runs through northern Texas, Oklahoma, Kansas, Nebraska and beyond.
Popular wisdom says that the green color of the clouds is due to frogs and grasshoppers that are sucked into the sky by tornadoes. In reality, the situation is somewhat different.
So why are the clouds green? Storm hunter and blogger Pecos Hank explains that it's about how objects absorb and reflect sunlight.
Severe thunderstorms can produce concentrated heavy rain and hail that look like waterfalls. The storm hunters call it the core. Sometimes storm clouds provide a glimpse into the core in flight. If you are under the base of a storm, the core is often bluish or turquoise at about noon. But in the late afternoon and late evening, when most of the storm activity occurs, golden and reddish sunset light can mix with the blue sedimentary core, and the result is a greenish light.
Green clouds are a sure sign of a severe thunderstorm. Such clouds are often high, and high clouds are an important ingredient in potential hail storms and tornadoes. So, while green clouds do not mean that a tornado is approaching, they do mean that a tornado may be approaching. Therefore, if you want to avoid heavy rain, strong wind and lightning, green skies are a sign that you should pack up and leave a dangerous place.