…never too wet and never too dry” goes the saying. I think it is one that my grandmother told me which I since discovered was fairly well-known. It is one of the bits of weather lore which has more than a grain of truth in it. The mackerel sky refers to alto-cumulus clouds which are said to make a pattern that resembles the skin of the fish. The “never too wet, never too dry” means that if it has been raining it won’t go on for much longer, and if it has been dry up till now then you should expect rain later that day. Apparently these medium-height clouds are often associated with rain-bearing weather fronts and they appear some time before or after the rain clouds. They do not guarantee rain but they do provide one clue as to what to expect. If it is showery weather then the nature of showers is that they are hit and miss affairs so you might get a mackerel sky, see the clouds build up but not necessarily benefit from the rain.  

In this instance, a few days ago, the mackerel sky was followed the next day with a notable drop in temperature and showers in our neck of the woods.