Circumhorizontal arc over VA
© Nora Lee Henderson
There wasn't any rain midday Wednesday, so you know it's not a rainbow. But some of the clouds did turn a vibrant!

These rainbow colored clouds are called a circumhoriztional arcs, or rather part of the arc.

While they're not exactly rare around our area, the circumstances have to be just right.

They can only happen certain times of the year (late spring through early fall) and during the midday because the sun has to be high enough in the sky.

The sunlight has to enter clouds made of flat, plate-shaped ice crystals at a steep angle. The ice crystals have to be oriented horizontally for this to work.

Circumhorizontal arc explainger
Circumhorizontal Arc Explainer
Circumhorizontal arcs generally happen with cirrus clouds because they are high enough in the sky to be made of ice crystals. They are typically thin, allowing the sunlight to shine through and get refracted and separate into the colors of the rainbow.

The band of colors runs parallel to the horizon. If the clouds were oriented all around you, the rainbow clouds could stretch across a large area. But, we generally we see them in little patches where these particular clouds happen to be.

Circumhorizontal arcs are often confused with something called cloud iridescence. You will know the difference because cloud iridescence colors look more like a soap bubble. They are not ordered like a rainbow and the clouds are typically closer to the sun in the sky.

These colors occur from the light being diffused by water drops or ice crystals in a cloud that is all very close in size and shape.

Happy cloud hunting! Thanks to everyone who shared their pictures!
Circumhorizontal arc over VA
© Betty Coulter
Ashburn, VA
A quick scan over social media, I've seen pictures on from as far north as Pittsburgh, Pa and as far south as Lynchburg, Va.