Mackerel sky
A mackerel sky is a sheet of small, rippled clouds that resemble the scales of a fish. Old rhymes warned that the weather would change within a day, and as the clouds thicken, rain may be 6 to 12 hours away.
What it may mean
A mackerel sky is one of the prettiest warnings there is. High overhead the clouds break into hundreds of small puffs in rows, like the scales on a fish, and the light through them is often lovely. The old rhymes knew what that beauty can signal: "mackerel sky, not 24 hours dry." The ripples form high up, where the wind is already changing, often well ahead of a weather system that has not yet reached the ground. Not every mackerel sky brings rain, and the early notice is easy to miss precisely because the clouds are so pleasant to look at.
Depending on how you saw it
Scales that spread and thicken
When the cloudlets spread and merge into a gray sheet and the wind picks up, rain may be 6 to 12 hours away, a meteorologist told Spectrum News. Which slow thickening this week needs more of your attention than any single cloud?
A mackerel sky on a winter morning
Cirrocumulus, the highest kind, is common in winter and often comes with fair but cold weather, the UCAR science education center notes. When does a warning-looking sky simply mean a crisp day?
With mares' tails
A second rhyme pairs the scales with long, hooked streaks of cirrus called mares' tails and warns that together they send tall ships to shorten sail. Which two small signs, seen together, make you change course?
Why it happens in nature
A mackerel sky is made of small rounded cloudlets arranged in rows or ripples: cirrocumulus high in the sky or altocumulus at middle levels. The pattern forms where a thin layer of moist air is rippling in waves, which often happens as a weather front approaches. If the clouds thicken and lower, rain or snow can arrive within roughly 6 to 12 hours.
What folk beliefs say
Sailors' weather lore
Two sailors' rhymes warn of a change in the weather when a mackerel sky appears: "Mackerel sky, not 24 hours dry," and "Mare's tails and mackerel scales make lofty ships to carry low sails."
Source: Kristin Ketchell (Spectrum News NY1), Not a fish tale: What causes a mackerel sky? (2021), ny1.com. View the page
To reflect on
What is changing in your life at a height you rarely look up to?