Formed by cold air sinking down, mammatus clouds are usually seen when there is turbulence in a cumulonimbus cloud. Two astronauts are returning home after nine months in space. Nick Beake of the ...

These clouds are often associated with thunderstorm clouds and accompanied by rain, hail and lightning. Mammatus is most often found at the base of a thunderstorm cloud called cumulonimbus.

Formed by cold air sinking down, mammatus clouds are usually seen when there is turbulence in a cumulonimbus cloud. A US Coast Guard rescue swimmer was lowered to pull the woman as high waters ...