also: にゅうぼううん
noun
mammatus cloud; mammatocumulus; festoon cloud
A meteorological term for pouch-like cloud formations hanging beneath a cloud base, often associated with severe weather.
乳房雲は積乱雲の底によく見られる。
Mammatus clouds are often seen at the base of cumulonimbus clouds.
気象予報士が乳房雲の発生を報
The weather forecaster reported the formation of mammatus clouds.
Compound of 乳房 (ちぶさ, 'breast, udder') and 雲 (くも, 'cloud'), from the cloud's resemblance to a cluster of breasts or udders. The on'yomi reading にゅうぼううん follows the same pattern.