Cirrocumulus clouds: what they are and what they mean for weather

Cirrocumulus clouds are high-altitude cloud formations appearing as small, white patches or ripples above 6,000 metres. These ice-crystal clouds often signal atmospheric instability and may point to a change in weather patterns. Their scaly look is often called a mackerel sky.

Key takeaways

• Cirrocumulus clouds are high-level clouds made of ice crystals and sit in the upper troposphere.
• According to the Bureau of Meteorology (BOM), they are small, rippled clouds that do not produce precipitation.
• Their banded or rippled look is linked to atmospheric gravity waves and upper-level wind shear.
• Cirrocumulus can appear with cirrus and cirrostratus, which are also high-level ice-crystal clouds.
• They are often seen with a mackerel sky and can signal changing weather patterns aloft.

Cirrocumulus clouds in Australian skies

The Bureau of Meteorology (BOM) groups clouds into 10 main types across low, middle and high levels. Within that system, cirrocumulus clouds are high-level clouds, which means they form well above the lower cloud layers seen in everyday weather observations.

As BOM notes in its cloud types guide, cirrocumulus clouds are small and rippled, and they do not produce precipitation that reaches the ground. They are made of ice crystals and sit in the upper troposphere, where temperatures are well below freezing. For broader forecast reading, they are best treated as a sign of change aloft rather than a rain cloud at the surface.

What are cirrocumulus clouds?

Cirrocumulus clouds are high-altitude cloud formations made up of ice crystals. They appear as tiny white patches, grains or ripples across the sky and are often grouped with other cloud formations that form in the upper troposphere. This cumuliform lumpiness often lines up in rows across the sky. The common term for this pattern is a mackerel sky.

What do cirrocumulus clouds mean for the weather?

Cirrocumulus clouds can point to atmospheric instability high in the atmosphere. They may appear near changes in upper-level winds, including the jet stream, and can be seen ahead of larger weather shifts. They do not usually bring rain at the surface, but they can help with forecast reading when paired with other cloud signs. Occasionally, they are even associated with fallstreak hole phenomena if the cloud layer is disturbed.

Why a mackerel sky forms

The phrase mackerel sky refers to the cloud pattern’s fish-scale appearance. This look is often linked to atmospheric gravity waves moving through the upper troposphere. As air rises and sinks within these waves, moisture is organised into rows or patches that become visible from the ground.

Upper-level wind shear can also help shape the pattern. In some cases, the jet stream plays a role by setting up the wind structure that supports these ripples. According to Met Office cloud guides, these puffy shapes form when turbulent vertical currents meet a cirrus layer. The result is a spread of small cloudlets that can look like a sheet of textured white dots across the sky.

What causes the rippled look?

The rippled appearance, often technically known as undulatus, comes from waves in the air, not from the clouds themselves. Atmospheric gravity waves and wind shear organise the cloud into small cells or rows. When the air sinks between the wave crests, cloud formation weakens, leaving gaps between the brighter patches.

How cirrocumulus clouds form

Cirrocumulus clouds form in cold air high in the troposphere. At those heights, water vapour can freeze into ice crystals directly, and cloud glaciation is common. If supercooled water droplets are present, they can freeze as temperatures fall and the cloud develops into an ice-crystal cloud.

Research in the Arctic Report Card 2025 describes how lifting nutrient-rich waters to high levels can diminish winter sea-ice formation and lead to local instability, not cloud glaciation in the Australian Meteorological and Oceanographic Journal. The process is usually weak compared with the strong updrafts that build thunderstorm clouds. That is why cirrocumulus clouds stay thin, small and patchy rather than growing into tall convective towers.

These clouds are part of a broader set of weather patterns that often show what is happening higher up before anything changes at the surface. They can also form in bands associated with upper-air moisture and wind changes.

How do cirrocumulus clouds form?

They form when moisture in the upper troposphere cools enough for ice crystals to develop. Atmospheric lifting and wind shear then organise those crystals into rows, patches or ripples. Because the air is cold and usually dry at those heights, the clouds remain thin and short-lived.

Cirrocumulus clouds compared with cirrus and cirrostratus

Cirrocumulus clouds sit in the same high-level family as cirrus and cirrostratus. All three are made of ice crystals, but they look different and often point to different sky conditions. Cirrus clouds are wispy and streak-like, while cirrostratus clouds form a thin veil that can create halos around the sun or moon.

Cirrocumulus clouds are the most textured of the three. They appear as small white clumps or ripples, often spread in rows. Unlike cirrostratus, they do not make halo effects. Unlike cirrus, they are not drawn out into long strands.

Cirrocumulus versus altocumulus

Cirrocumulus clouds are higher and finer than altocumulus clouds. Altocumulus sits lower in the middle levels of the troposphere and can show more shading. Cirrocumulus is usually smaller, whiter and more delicate in appearance.

The BOM cloud guide places cirrocumulus above the middle cloud layer, while altocumulus is a mid-level cloud type. That difference in height is one of the clearest ways to separate them in the sky.

Cirrocumulus cloud types

BOM recognises several forms of cirrocumulus, including cirrocumulus stratiformis, cirrocumulus castellanus and cirrocumulus floccus. Cirrocumulus stratiformis appears as broad sheets or rows. Cirrocumulus castellanus shows small turret-like tops that can suggest stronger instability aloft. Cirrocumulus floccus appears as small tufted patches, often with a more ragged edge.

These forms can help weather observers track changes in the upper troposphere, especially when they appear with cirrus or cirrostratus.

What cirrocumulus clouds can mean for Australian rainfall patterns

Cirrocumulus clouds do not bring rain themselves, but they can sit ahead of broader weather changes. In Australia, cloud patterns high in the sky often reflect shifts in the jet stream, moisture flow and upper-air winds. Those changes can later affect rainfall patterns, especially when larger cloud systems move through.

On their own, cirrocumulus clouds are not a rain signal. But as part of a wider sky picture, they can help explain why the atmosphere is changing.