Following some bad weather recently, I saw the beautiful 'mackerel sky' above.
A mackerel sky can be used to forecast weather, but it is at the more challenging end of the weather lore spectrum.
The simple bit is this: a mackerel sky of any kind means change is likely. This is reflected in the associated weather lore:
'Mackerel sky, mackerel sky - never long wet, never long dry.'
However, if you want to work out whether it is a change for better or worse then we need to know the difference between the two types of cloud that can create a mackerel sky: altocumulus and cirrocumulus.
An altocumulus mackerel sky (altocumulus undulatus) will often have long thick lines running perpendicular to the direction the upper wind is blowing. The clouds themselves will be substantial and opaque (see main picture above). This indicates that an improvement is more likely.
A cirrocumulus mackerel sky is made up of wispier, patchier higher clouds (see picture below). There are no thick lines and the clouds appear translucent. These clouds can run before a front and the accompanying bad weather.
Cirrocumulus is often found with wispy cirrus, sometimes known as 'mares' tails'. Hence this lore:
'Mares' tails and mackerel scales make tall ships take in their sails.'
Soon after taking the top picture of the altocumulus mackerel sky... the sky cleared and we enjoyed a day and night of fair weather.
For a larger collection of weather lore sayings and their meaning see this page.
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