What Do Green Clouds Indicate?

Some may have witnessed green clouds from time to time during strong thunderstorms. What does this mean? Can it signal a tornado is coming?

Having witnessed this myself on a few occasions, I know how eerie and ominous this can be. Green clouds can in fact be an indicator of severe weather.

When a thunderstorm builds higher and higher into the atmosphere, the updraft of the thunderstorm grows stronger. The updraft of the thunderstorm is the part of the storm where warm, moist air is ascended vertically into the storm letting it thrive. As the updraft gets stronger, it suspends water droplets in the cloud, preventing them from falling.

As it prevents them from falling, these water droplets freeze. As they freeze, they get larger and larger as more and more droplets freeze to it. This is how hail is formed. When the hail becomes large enough it will fall from the sky.

While the hail is suspended in the cloud, it refracts sunlight differently from drops of water. As sunlight hits ice it scatters the sun’s rays in a way that will reflect green light.

If the storm is a supercell thunderstorm, and the trajectory of the storm is just right, green clouds could be a sign of an imminent tornado. The bulk of the precipitation and hail precedes a tornado if the supercell is moving directly northeast. However, this is not usually the case, so be sure to take cover during a severe thunderstorm regardless of what the sky looks like.

In summation, know that green clouds in a thunderstorm could indicate the presence of large hail. This is because hail refracts the sunlight, making it have the appearance of a green color.