Altocumulus and cirrocumulus can both look like fields of small cloudlets, but cirrocumulus is usually higher, finer-textured and ice-rich; altocumulus appears at middle altitudes with larger-looking patches.
The visual clue
Hold your hand at arm’s length: cirrocumulus elements often appear tiny, while altocumulus cloudlets look larger and may have more noticeable shading. This is a rough field clue, not a precise measurement.
Why altitude matters
High cirrocumulus forms in colder conditions and commonly consists of ice crystals or very cold droplets. Midlevel altocumulus more often includes liquid water droplets, although freezing temperatures can change its composition.
What each may signal
Both can appear without severe weather. Altocumulus with growing towers can indicate instability aloft, while some high-level patterns accompany changes in broader weather systems. Interpret them alongside wind and forecast information.
Compare with stratocumulus
Stratocumulus is usually lower and shows larger, heavier-looking rolls or rounded masses. If patches are broad and noticeably dark underneath, you may be seeing a lower cloud deck.
Frequently asked question
Are ‘mackerel sky’ clouds always cirrocumulus?
No. The nickname can refer to repeating patterns of either cirrocumulus or altocumulus.
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