Rainbow cloud in New Jersey
© Margie RaffMargie Raff captured this circumhorizontal arc, a rainbow-like feature in the clouds when sun passes through ice crystals in high altitude cirrus clouds.
Most of us would probably call them "rainbow clouds." To meteorologists, their name is a much more technical "circumhorizontal arc." Whatever you call them, they are a cool sight to see, and fairly rare features in the skies over South Jersey.

A rainbow forms when sunlight passes through a raindrop, and the light is refracted to form the multiple colors of the rainbow. Rainbows are best seen when the sun is lower in the sky, let's say the morning or evening hours. When the sun is higher in the sky during the midday hours, the rainbow will still form, but it will be below the horizon and unable to be seen.

Circumhorizontal arcs form the same way. Sunlight passes through plate-shaped ice crystals in high altitude cirrus clouds, causing a partial arc or rainbow. However, the sun must be high in the sky in order to create the arc. That means these rainbow-like clouds will only be seen during the middle part of the day, when the sun angle is the highest.

The light of the full moon can also cause the same effect, but the rainbow colors are naturally more difficult to see at night.
Fire rainbow in New Jersey
© Steffen KlenckSteffen Klenk of Ocean City caught the rainbow-like clouds over Ocean City.