• NASA has released picture of Mammatus clouds, hovering over Nebraska, US.

About Mammatus clouds

• They generally appear in connection with substantial cumulonimbus clouds, but they have also been sighted to form on other cloud types, such as stratocumulus, altostratus and altocumulus.
• Turbulence within cumulonimbus clouds often leads to formation of Mammatus clouds, particulraly on bottom of projecting anvil as it quickly descends to lower altitudes.
• Their shapes can vary greatly, from typical bulging shape to a more elongated tube dangling from the cloud above.