For August, our Cloud of the Month is the variety known as ‘lacunosus’. The name means ‘full of hollows’ in Latin. The variety can appear at the low, mid and high cloud levels. This example is a mid-level one, and so it would be more fully classified as Altocumulus lacunosus. Since the formation consists of holes surrounded by fringes of cloud, it feels rather like a negative version of your typical layer of Altocumulus with clumps separated by narrow gaps. The lattice of holes in lacunosus, each typically around 30 km / 20 miles across, has the appearance of a celestial honeycomb. The holes look larger in lower examples, known as Stratocumulus lacuonusus, since they are closer. The higher, more distant examples of lacunosus, called Cirrocumulus lacunosus, look smaller.
Altocumulus lacunosus spotted over Haarlem, Netherlands, by Hans Stocker (Member 36,089).
And here we are explaining the lacunosus cloud of the month to The Weather Channel: