Chicago, Illinois – During some winter snowstorms, residents across the Midwest occasionally look up to see the sky glowing pink, rose, or even light purple instead of the usual gray. While the sight can feel unusual or even surreal, scientists say the explanation is rooted in basic physics and the way sunlight interacts with the atmosphere.
The color change happens because of how different wavelengths of light behave. Blue light has much shorter wavelengths, while colors such as red, orange, and pink have longer wavelengths. When the sun sits low on the horizon, typically around sunrise or sunset, sunlight must travel through a thicker slice of the atmosphere before reaching the ground.
During that longer journey, shorter blue wavelengths scatter more easily as they interact with air particles, clouds, and falling snow. As the blue light scatters away, longer wavelengths are left behind, allowing pinks and reds to dominate the sky’s appearance.
Cloud structure during a snowstorm also plays a critical role. Low clouds that are not especially thick can act as a filter, reflecting longer wavelengths back toward the ground. If the cloud deck is too dense or too tall, much of the light is scattered away and the sky remains gray. But when clouds are just thin enough, longer wavelengths can pass through and reflect off snow-covered surfaces, intensifying the pink glow.
The phenomenon is harmless, temporary, and most likely to appear when snow cover, low sun angles, and cloud thickness align just right during winter storms.
