Mackeral sky is associated with cloud type

A 'mackerel sky' is a meteorological phenomenon characterized by clouds that resemble the rippling pattern of fish scales [2]. This appearance is primarily associated with cirrocumulus clouds, which are high-altitude, small, white, and grain-like cloudlets. While altocumulus clouds can also occasionally form similar patterns, they are typically larger and darker. The term is famously preserved in maritime weather lore, such as the proverb 'Mackerel sky and mare's tails make tall ships carry low sails,' indicating that these high-level clouds often precede an approaching warm front and deteriorating weather conditions within 6 to 12 hours [1]. Cirrocumulus clouds are composed of ice crystals and appear at altitudes above 5,000 meters, creating the distinctive 'buttermilk' or 'scaly' texture that defines a true mackerel sky.

Sources

1. [1] https://en.wikipedia.org/wiki/Mackerel_sky
2. [2] https://www.bbc.com/weather/features/36702877