This is one of my father, Lloyd Sloan's favorite sayings. He taught me weather proverbs that reflected real world situations where fair weather day clouds can signal coming weather changes. A mackerel sky refers to cirrocumulus clouds, which often precede an approaching warm front, which will eventually bring veering winds (changing from northeast and east over to southwest and west) and precipitation. Tall ships were what they called the old sailing ships of a century and a half ago! Another weather proverb he often quoted was, "Red Sky at night, sailor's delight. Red sky in the morning, sailor take warning." If you want to learn more weather proverbs here is a link.
This morning the weather was cold and it is going to rain.