113 - Reading the Sky: What Storm Colors Are Telling You

Why does the sky turn green when a tornado is coming? Why do storm clouds go black? And what does a 19th-century volcanic eruption in Indonesia have to do with one of the most famous paintings in the world? In this episode of Buzz, Blossom & Squeak, we finish our spectrometry series by bringing it closest to home — reading the colors of the sky itself, and learning what they’re telling us.

The Blue Sky: Our Baseline

A clear blue sky is the result of Rayleigh scattering — a process identified by British physicist Lord Rayleigh in the 19th century. Sunlight traveling through the nitrogen and oxygen molecules of the atmosphere scatters the short blue wavelengths far more powerfully than the long red ones. The result: blue light bounces in every direction, filling the sky, while red and orange travel a more direct path. Our eyes also favor blue over violet, which is why the sky appears blue rather than purple even though violet wavelengths exist.

Sunsets, Sunrises, and the Long Path Through Air

At sunset, the sun’s light must travel at a much longer diagonal through the atmosphere before reaching our eyes — roughly 30 times more atmosphere than when it’s directly overhead. That means more scattering. Blue goes first. Then green. Only the warm wavelengths survive: orange, crimson, deep red, pink, gold. Every sunset is Rayleigh scattering happening live.

Krakatoa, “The Scream,” and Volcanic Purple

When Krakatoa erupted in 1883 — one of the most violent volcanic events in recorded history — it injected billions of tons of sulfuric material into the upper atmosphere. For months afterward, sunsets around the world turned extraordinary shades of blood red, violet, and even green. In London, people thought it was a fire on the horizon. Fire departments were dispatched. And in Norway, a decade after the eruption, Edvard Munch described the blood-red sky he saw while walking with friends — the moment that inspired “The Scream.” That painting may be, in part, a spectral record of Krakatoa’s aftermath.

Dark Clouds and Why They Go Black

Clouds start white because tiny water droplets scatter all wavelengths equally, producing white light. As storm clouds grow taller and denser, their thickness blocks light from passing through entirely. A towering cumulonimbus reaching 40,000 to 60,000 feet absorbs rather than scatters — and the cloud that was white becomes gray, then dark, then nearly black. The darkness is measuring the cloud’s water content.

The Green Sky: A Warning You Can’t Ignore

The sickly yellow-green of a tornado sky is one of the most visceral color signals in nature. The leading explanation: the deep red-orange of late afternoon sunlight, already stripped of blue by the atmosphere, mixes with the intense blue light scattered inside the massive water column of a supercell. Red plus blue-green equals that unsettling cast. Hail intensifies it — ice crystals absorb red and scatter blue-green wavelengths. If the sky goes green, take cover.

The sky is a giant spectrometer, and it’s always telling us something. We just have to know how to read it.

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By choosing to watch this video or listen to this podcast, you acknowledge that you are doing so of your own free will. The content shared here reflects personal experiences and opinions and is intended for informational and educational purposes only. I am not a licensed biologist, ecologist, or wildlife professional. Any nature observations, identifications, or suggestions offered should not be considered a substitute for professional scientific or environmental guidance. Always follow local regulations when observing or interacting with wildlife and natural spaces. You are solely responsible for any decisions or actions you take based on this content.