'Fire rainbow' phenomenon seen around Puget Sound, Washington

KIRO 7
Tue, 31 May 2016 18:51 UTC

© Rakan AlDuaij Photography

What looks like a rainbow in the clouds and is sometimes called a "fire rainbow" isn't a rainbow at all.

It's a "circumhorizontal arc," a phenomenon that occurs when the sun interacts with ice crystals in high cirrus clouds overhead.

© Stevens Pass

The ice crystals in the clouds cause sunlight to refract or bend -- creating a rainbow appearance.

© Tara Ellis Photography

KIRO 7 viewers flooded Facebook Tuesday with images of a fire rainbow seen around northern Puget Sound.
Below, meteorologist Morgan Palmer explains the special conditions needed for a circumhorizontal arc to occur.

The ice crystals in the cirrus clouds high aloft must be shaped like plates and the wind aloft must orient those crystals at just the right angle to act as prisms for the sunlight. Also, the sun must be at an elevation above the horizon of 58 degrees or greater, which only occurs in the late spring through early fall in the Pacific Northwest. The rest of the year, the sun never gets high enough in our sky.

© Brandon Swervin Ervin