Clouds fill the skies above us and are part of our every day lives, often going unnoticed. However, there are some clouds that are so rare that you will be very lucky to see them in your lifetime. This is a list of the top 10 most rarest cloud formations (in no particular order) that for those lucky enough to see them, were caught on camera.
1. Nacreous Clouds
These rare clouds, sometimes called mother-of-pearl clouds, are 15 - 25km (9 -16 miles) high in the stratosphere and well above tropospheric clouds.
They have iridescent colours but are higher and much rarer than ordinary iridescent clouds. They are seen mostly but not exclusively in polar regions and in winter at high latitudes, Scandinavia, Alaska, Northern Canada. Lower level iridescent clouds can be seen anywhere.
Nacreous clouds shine brightly in high altitude sunlight up to two hours after ground level sunset or before dawn. Their unbelievably bright iridescent colours and slow movement relative to any lower clouds make them an unmistakable and unforgettable sight.
2. Mammatus Clouds
Mammatus are pouch-like cloud structures and a rare example of clouds in sinking air.
Sometimes very ominous in appearance, mammatus clouds are harmless and do not mean that a tornado is about to form - a commonly held misconception. In fact, mammatus are usually seen after the worst of a thunderstorm has passed.
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