This week's question comes from Morning Brief reader Rose: "Why does the sky turn a yellow-greenish color before a tornado?"

We often hear from readers like you that they saw green skies before a tornado touched down in their neighborhood. The horrible hue shouldn’t be taken as a surefire tornado warning, but there is some science hidden in the clouds. 

A turning of the skies to yellow or green or even blue indicates that the atmosphere is holding a tremendous amount of moisture and ice crystals, sometimes hail. Moisture is one of the most significant ingredients that storms need to become severe and, possibly, produce a tornado. 

The shading of the clouds comes from how much light is scattered out by the particles in the clouds and by the rest of the atmosphere.

Raindrops tend to absorb warmer red or purple light while letting blues bounce around in a cloud. The depth of the clouds, often 40,000 feet tall or taller, also adds a shading effect to the space below them.

But it isn’t just the precipitation that turns the sky funny colors. 

Thunderstorms often are near their peak strength near or just after sunset, meaning that the sun is already low to the horizon and the light from the sun has to travel thousands of extra miles through the Earth’s atmosphere before it gets to your eyes. This scatters away the blue light and leaves the oranges or yellows. 

Combine the yellows from the late-day sun and the blues from the raindrops, and you end up with green. The size of the drops and the amount of rain or hail can make this color range from a washed-out yellow to a bright aquamarine. 

The green sky itself does not cause hail, nor is it caused directly by hail. But green skies can be a signal that severe weather is occurring nearby. There is no direct correlation between tornadoes and green skies.