Mackerel and horsetail

Because of the sky mackerel and horsetails, tall ships carry low sails. In this proverb, "mackerel" means tall cumulus clouds, and "mare's tail" means cirrus clouds. Seen from the sky, this would indicate that a low pressure system is approaching. In the near future (about a day) sunny weather awaits you. However, the tails of mackerel and mare are the first visible signs of the approaching warm front, the matter of the storm. When the system works, it starts raining and clouds gather. When the ship saw this sign, they lowered the sails and opened the hatch to prepare for impending bad weather.