Pileus (meteorology)

Furthermore, the clouds are typically formed by drier air with a higher lifting condensation level, which often prevents vertical growth and leads to the smooth horizontal cap shape that the cloud is named for.

[6] Pilei form above some mushroom clouds of high-yield nuclear detonations.

[8] The bright iridescent colors seen in pileus are sunlight diffracted in water vapor.

Iridescent colors are strongest when the diffracting droplets are small and similar in size.

The newly formed pileus droplet all of similar provenance are ideal for iridescence.