Altocumulus opacus (Ac op) - CEN 1930

A patch, sheet or layer of Altocumulus, the greater part of which is sufficiently opaque to mask completely the Sun or Moon. Most often, the base of this variety of Altocumulus is even and its apparent subdivision into merged elements results from the irregularity of its upper surface. The base is sometimes uneven and the elements then stand out in true relief, particularly with a low Sun. The variety opacus occurs fairly often in the species stratiformis.