This is what people saw above the Washington-Idaho border last week. It’s called a circumhorizon arc (or “rainbow of fire”), and it occurs when sunlight passes through ice crystals in cirrus clouds. Dr Fox from the National Weather Service in Spokane said, “It was even more spectacular than the Northern Light.” People who saw it felt privileged.
To create a rainbow of fire, clouds must be at least 20,000ft high and the ice crystals within them align horizontally instead of their usual vertical position. The sun also needs to be at least 58 degrees above the horizon. Then, the magic can begin.