A double rainbow is an awesome meteorological phenomenon on its own. But when mammatus clouds appear at the same time... It becomes epic. This is what happened in the sky of Newark, Delaware on April 7, 2016.
Double rainbow in Delaware
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In a double rainbow, a second arc is seen outside the primary arc, and has the order of its colours reversed, with red on the inner side of the arc.
Double rainbow
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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.
Mammatus clouds
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In fact, mammatus are usually seen after the worst of a thunderstorm has passed. Mammatus are long lived if the sinking air contains large drops and snow crystals since larger particles require greater amounts of energy for evaporation to occur.

Mammatus typically develop on the underside of a thunderstorm's anvil and can be a remarkable sight, especially when sunlight is reflected off of them.

Mammatus clouds
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