MEMPHIS, Tenn. (WMC) -A mackerel sky is a beautiful site and a common term for clouds made up of rows of altocumulus and cirrocumulus clouds. It appears as a rippling type pattern in the sky and it can look like fish scales in the sky. This is caused by moisture in the mid levels that get trapped between dry air at the surface and dry cold air in high levels of in the atmosphere. The wind and gravity is what causes the rippled look.
Cirrocumulus can often show up ahead of a warm front and is a usually a decent indicator that the weather is about to change. When these high clouds take and the barometric pressure begins to fall, usually that means that precipitation associated with a disturbance is likely about 6 to 12 hours away. When the cloud start to thicken up and the cloud base lowers into altostratus or altocumulus, this is a good sign that the warm front may be closer and it may start raining in less than six hours.
Weatherlore says “Mackerel sky, not twenty-four hours dry”