What does altocumulus mean?
Altocumulus is a noun denoting one of the ten principal cloud genera in the international system used by meteorologists worldwide. It refers to mid-level cloud — generally found between about 2,000 and 6,000 metres — that appears as white or grey patches, sheets, or rolls composed of small rounded masses, sometimes arranged in waves or ripples. When laid out in regular rows, altocumulus produces the pattern long known as a 'mackerel sky', which folk tradition associates with approaching unsettled weather. The word derives from Latin roots: 'altus' meaning high and 'cumulus' meaning heap, reflecting both its altitude and its piled, billowy texture. Although primarily a technical term found in forecasts, aviation reports, and nature writing, altocumulus also enriches descriptive prose about the sky. Distinguishing it from lookalikes such as altostratus, cirrocumulus, and stratocumulus requires attention to height and the size of the individual cloud elements.
nounAltocumulus is a mid-altitude cloud type occurring in white or grey patches, sheets, or layers composed of small rounded masses or rolls, typically found between about 2,000 and 6,000 metres (6,500–20,000 feet). It is one of the ten principal cloud genera in the internationally recognised classification system.
- A genus of mid-level cloud occurring in white or grey patches, layers, or rolls made up of small rounded masses, typically between roughly 2,000 and 6,000 metres.
"A thin veil of altocumulus drifted across the morning sky, hinting at a change in the weather."
"By late afternoon the altocumulus had thickened into a broad grey deck across the western horizon."
"Photographers prize altocumulus at sunrise, when its rippled masses catch pink and gold light."
The Latin-style plural 'altocumuli' follows classical declension, but in practice most writers refer to multiple instances as 'altocumulus clouds' rather than using the plural directly.
"Several distinct banks of altocumuli were visible across the evening sky."
When altocumulus arranges itself into rippling rows, sailors call it a 'mackerel sky' — an old weather proverb warns that such skies often precede rain within a day.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of altocumulus
Altocumulus was coined in the early 19th century as part of the systematic cloud classification developed by Luke Howard and later refined by the International Meteorological Organization. The name combines the Latin 'altus' (high) with 'cumulus' (heap), placing this heaped cloud genus at middle altitudes alongside its sibling 'altostratus'. Its cognates include other compound cloud names built on the same Latin elements, such as cirrocumulus, stratocumulus, and cumulonimbus, all standardised in the modern international cloud atlas.
How altocumulus is actually used
Altocumulus is a technical term used chiefly in meteorology, aviation, and weather reporting, though it also appears in popular weather writing. The plural form 'altocumuli' exists but many writers simply use 'altocumulus clouds'. In everyday speech it is far less common than terms like 'cloudy' or 'overcast', so its use signals some meteorological knowledge.
Easily confused with altocumulus
Altostratus is a featureless grey sheet of mid-level cloud, whereas altocumulus consists of distinct rounded masses or patches.
Cirrocumulus forms at much higher altitudes and appears as very small white grains or ripples, while altocumulus elements are larger and sit lower in the sky.
Stratocumulus is a low cloud with larger, heavier-looking lumps, whereas altocumulus occurs higher up with smaller individual cloud elements.