as the process repeats. As the air parcels curve they also rotate about their axis due to the wind shear's twisting motion. This curving, spiraling or rotating motion of the wind can exist without the air necessarily spinning as a vortex.

At this point, the updraft is then said to have differentially advected the momentum of the sheared flow; that is, the differences between the flowing air over a horizontal direction is translated to a vertical direction, resulting in curvature vorticity or the apparent curving and spiraling seen in