The Scales Of Things To Come

Today's image is of this wonderful sky that appeared overhead (mind you where else would it appear!) late this evening as I looked out at our back garden as dusk was approaching.
It's a mackerel sky and is a common term used to describe cirrocumulus or altocumulus clouds displaying an undulating, rippling pattern similar in appearance to fish scales which is caused by high altitude atmospheric waves. These clouds appear almost exclusively ahead of a warm front and this type of sky is a reliable forecast that the weather is about to change.
There are old rhymes and phrases that are associated to this cloud based phenomenon including:

Mackerel sky, mackerel sky, never long wet and never long dry

Mares tales (another type of cirrus cloud called cirrus uncinus) and mackerel scales make lofty ships carry low sails

Mackerel sky, not twenty-four hours dry

...and the rather more gnomic:

A dappled sky, like a painted woman, soon changes its face (?!)