This is a cloud, all right—a dust cloud, and a fast-moving, dense, nasty one that stymied highway traffic, as it caught indirect sunset light reflected off clouds to the west. It also was a fascinating manifestation of fluid flow. The outflow that caused this blew a well-defined haboob through Tucson itself, before crossing some small mountain ranges that redirected the wind off into various channels and directions. One of those local currents focused onto a patch of desert a short distance to my southeast and lofted a strikingly dense dust bomb rapidly skyward for hundreds of feet, moving leftward (northward) and perpendicular to the westward aim of the haboob as a whole.
