Altocumulus Standing Lenticular Clouds: When sufficient moisture is present above mountain-top level, ACSL clouds develop within the crest of these mountain waves where the air is rising. ACSL clouds are continually developing and dissipating in the vicinity of the wave's crest and immediately dow...

A rainbow cloud can occur because of something called cloud iridescence. It usually happens in altocumulus, cirrocumulus, lenticular and cirrus clouds. Iridescent clouds happen because of diffraction – a phenomenon that occurs when small water droplets or small ice crystals scatter the sun's light.