We've been having some sunny days with snow occurring. Do we ever see a rainbow during these conditions?
— Donna Donovan, Fox River Grove
The fairly rare phenomenon is called a snowbow. It forms when sunlight is reflected and refracted by ice crystals in the air (just as a normal rainbow is produced by the reflection and refraction of sunlight by raindrops).
The colors in a snowbow are relatively faint because ice crystals are much poorer reflecting surfaces than raindrops.
It's possible to create a snowbow with a snowblower. On a cold day when the sun is low in the sky, aim the discharge plume vertically. The low temperatures will allow the snowblower blades to chew the snow into tiny crystals, and a snowbow will appear opposite the sun.