Definition
A cloud formation characterized by rounded, pouch-like protrusions hanging from the underside of a parent cloud, most commonly the anvil of a cumulonimbus. Mammatus clouds are associated with strong vertical air currents and severe thunderstorm activity, and indicate an unstable, turbulent atmosphere.
Plain English
Bumpy, bag-like lumps hanging down from the bottom of a cloud, usually under a thunderstorm anvil. They're a visual warning sign of severe weather and turbulent air nearby.
Context Anchor
Seen during visual weather observation, preflight weather planning, and in discussions of thunderstorm clouds.
Derivation
From Latin mamma, meaning 'breast' or 'udder.' The name reflects the rounded, sagging pouches that hang from the cloud base — the appearance gave the formation its name.
Why Pilots Care
Signals strong vertical motion and the likelihood of turbulence, hail, or other severe weather inside the parent thunderstorm.
Analogy
Mammatus can look like upside-down bubble wrap or soft pouches hanging from the bottom of a cloud.
Grounding Statement
Picture looking ahead and seeing the bottom of a dark cloud covered with rounded hanging pockets; those pockets are mammatus.
Intuition Check
Mammatus does not automatically mean a tornado is present. It means the cloud is showing signs often linked with storm activity and possible rough air nearby.
Example Sentence 1
The pilot diverted around the storm cell after spotting mammatus clouds hanging from the anvil.
Example Sentence 2
Mammatus formations appeared on the satellite image during the morning weather briefing.