What causes a mackerel sky?

A mackerel sky is characterized by a pattern of small, white, rippled clouds, resembling the scales of a mackerel fish. This phenomenon occurs when altocumulus or cirrocumulus clouds form at high altitudes, typically indicating moisture in the atmosphere. The appearance often suggests that a change in weather is approaching, as these cloud types can precede storms or shifts in weather patterns. The name derives from the traditional association between the cloud pattern and the fish's scales.