Washington's Puget Sound skies dotted with 'fire rainbows'

© Jen Brazas

The thin, wispy clouds floating around the Puget Sound region Monday usually do nothing more than give the blue skies a little bit of character.

But today, they were giving the skies a little bit of color.

© Brian Willard Roetger

We had a number of reports of rainbow arcs in the sky -- both in a circular halo around the sun and just lighting up some clouds near the horizon -- a circumhorizontal arc, otherwise known informally as "fire rainbows."

They're both caused by the same thing -- those thin clouds are made of tiny ice crystals that at a certain angle to the sun will refract the sunlight like a prism. The type of arc they create are based on cloud position and shape of ice crystal -- and we had two rather common ones Monday.

© Krystie Baker

The sun halos, like these captured by @zargoman, can happen year round:

© @Zargoman

The circumhorizontal arcs only happen near the summer solstice near solar noon as the sun has to reach a certain height above the horizon for the angles to work. Sure enough, this arc was seen by Bob Hutchins around lunchtime near Boeing Field:

© Bob Hutchins

Many times these can be signals of approaching rain, as cirrus clouds like these will frequently precede a cold front. But not in this case, they're just some fair weather clouds passing through and no rain is in the forecast for at least the next few days.