Altocumulus Lenticularis Undulatus
Wave-like lenticulars soar over the shortgrass plains of Wind Cave National Park, on the southern periphery of the Black Hills. I don't know the cause for the constriction amidst each band; but it could be a slow-moving gravity wave or other subsident and nearly linear ripple running nearly perpendicular to the altocumulus wave train.
13 N Hot Springs SD (10 Jun 2) Looking SW