When calculating uplift pressures for a roof, it is important to understand that wind forces are not consistent as they move over and around structures. With a large commercial buildings, the corners and perimeter of the roof will experience far greater negative uplift pressures than the center will.
Wind is disrupted as it moves around and over objects; turbulence are created when it is no longer a smooth consistent force.
NATURE: An example in nature is the movement of air over a mountain. The air is initially forced upwards. When the air encounters the inversion, it is then deflected downwards. As the air is stable, it tries to return to its original level, so an oscillation motion is set up (see picture below).