Definition
A middle-altitude cloud type, generally found between about 6,500 and 20,000 feet AGL, appearing as white or gray patches, sheets, or layers of rounded masses or rolls. Altocumulus clouds are composed mostly of water droplets and often indicate moisture and instability at middle levels of the atmosphere.
Plain English
A layer of medium-height clouds that look like patches or rows of small puffy lumps, often with gaps of blue sky between them.
Context Anchor
Seen in aviation weather study, preflight weather planning, and cloud identification when judging what kind of weather may be developing along a route.
Derivation
From Latin altus meaning 'high' and cumulus meaning 'heap' or 'pile.' The name signals what the cloud is: piled, lumpy clouds at a higher level than ordinary low cumulus — but not as high as cirrus. 'Alto' in cloud naming does not mean 'highest'; it means 'middle level.'
Why Pilots Care
These clouds can signal areas of moderate turbulence or the potential for icing in colder conditions, affecting flight comfort and safety.
Analogy
Altocumulus can look like many small cotton balls or ripples spread across the middle of the sky.
Grounding Statement
If you look up and see many small, rounded cloud patches well above the low clouds but not as high and wispy as cirrus, you may be looking at altocumulus.
Intuition Check
“Alto” does not mean these are the highest clouds. In cloud names, “alto-” means middle-level clouds.
Example Sentence 1
The pilot noted patches of altocumulus during the preflight weather check and considered the possibility of afternoon thunderstorm development.
Example Sentence 2
The altocumulus layer at 12,000 feet prompted the pilot to request a higher altitude to avoid potential icing.