One form of bow wave can occur when strong wind flows over flat country against a large, uniform slope perpendicular to it (as often happens here at Crystal, for instance).   Smooth wavelike flow above and upwind of the mountain might carry a sailplane thousands of feet higher than the ordinary ‘ridge’ lift.   Meanwhile, because such waves often migrate downwind, they may periodic lift and sink down near the hill itself.   Also, you can bet there’ll be conventional wave on the other (downwind) side of the same mountain.