Bright rainbow pileus cloud forms over cumulonimbus cloud in Zimbabwe, Africa

A quarter of an hour before sunset, a beautiful rainbow pileus developed on top of a cumulonimbus cloud over Chikanga Township, Mutare.

The four pictures, taken over a period of just three minutes show it appearing and then changing shape and color.

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Incredible rainbow pileus cloud taken by Peter Lowenstein on January 6, 2017 @ Mutare, Zimbabwe

One minute later it had disappeared behind the summit of the growing cumulonimbus cloud. This is a classic but awesome example of rainbow pileus formation.

A pileus is a small, horizontal, lenticular cloud that can appear above a cumulus or cumulonimbus cloud, giving the parent cloud a characteristic “hoodlike” appearance.

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Bright iridescent clouds over cumulonimbus taken by Peter Lowenstein on January 6, 2017 @ Mutare, Zimbabwe

They are formed by strong updraft at lower altitudes, acting upon moist air above, causing the air to cool to its dew point. Pilei clouds indicate that the parent cloud is growing rapidly, has plenty of moisture, and is highly unstable.

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This iridescent lenticular cloud above the cumulonimbus is sign of an impending storm. Taken by Peter Lowenstein on January 6, 2017 @ Mutare, Zimbabwe

As such, they are usually indicators of severe weather, and a pileus found atop a cumulus cloud often foreshadows transformation into a cumulonimbus cloud, as it indicates a strong updraft within the cloud.

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Epic rainbow cloud. Taken by Peter Lowenstein on January 6, 2017 @ Mutare, Zimbabwe

These clouds can cause severe weather and sightings of pilei should be viewed as a warning of an impending storm. Pilei also indicate strong and possibly damaging winds.

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