Fire rainbows, technically called circumhorizontal arcs, aren’t actually rainbows or related to fire. They occur when sunlight refracts through high-altitude ice crystals in cirrus clouds. These spectacular displays appear as horizontal streaks of bright colors in the sky.
Specific conditions are required:
- Sun must be at least 58 degrees above the horizon
- Cirrus clouds containing horizontal ice crystals must be present
- The ice crystals must be oriented parallel to the ground
The phenomenon is most common in the summer months when the sun reaches the required height. While called rare, they’re actually fairly common in certain locations where these conditions frequently align, particularly in middle latitude regions.