mackerel sky

Etymology

From mackerel +‎ sky.

Noun

mackerel sky (plural mackerel skies)

1. A sky filled with a regular pattern of altocumulus clouds somewhat resembling the skin of a mackerel.
   • 1717, Dictionarium Rusticum, Urbanicum & Botanicum, London: J. Nicholson et al., 2nd edition, “CLOUDS,”

     […] in a fair day, if the Sky seem to be dappled with white Clouds, which is usually termed, A Mackerel-Sky, it commonly predicts rain:

   • 1823, John Franklin, Narrative of a Journey to the Shores of the Polar Sea‎, London: John Murray, Appendix 3, p. 562:

     The clouds were of the fleecy kind, which sailors denominate a mackerel sky.

   • 1898, H. G. Wells, The War of the Worlds‎, London: Heinemann, Book 1, Chapter 13, p. 111:

     The sky was what is called a mackerel sky, rows and rows of faint down-plumes of cloud, just tinted with the midsummer sunset.

   • 1972, Richard Adams, Watership Down‎, Penguin, published 1974, Part 2, Chapter 25, p. 217:

     The clouds came racing over the ridge from the south as they had on the May evening when Hazel first climbed the down. But now they were higher and smaller, settling at last into a mackerel sky like a beach at low tide.