"Mackerel sky and mares' tails make tall ships carry low sails"
So goes the old sailor's proverb. Should you see these clouds, expect a swift breeze before the day is out – these clouds form high in the sky and indicate changing weather patterns, such as an approaching storm.
Mackerel scales is the name given to high level cirrocumulus clouds that are often arranged as ripples in the sky and have the appearance of the scaly skin of a fish. These high level clouds are mainly composed of ice crystals. The frequent glimpses of blue among these clouds tell us the clouds are unstable and breaking up.
The hole is known as a fallstreak hole.
A fallstreak hole (also known as a holepunch cloud) forms when part of the cloud layer forms ice crystals which are large enough to fall as a 'fallstreak'.
Photos: London skies over Harringay, November 6th