Why do tornadoes rotate counterclockwise?
Of course, it is true that most tornadoes counterclockwise in the Northern Hemisphere; in the Southern Hemisphere, most tornadoes rotate clockwise. About 99 out of 100 tornadoes rotate cyclonically (counterclockwise in the N. Hem., clockwise in the S. Hem.) because the initial weak circulations that go on to become tornadoes rotate cyclonically (recall Item #14, above). These vortices that eventually give rise to tornadoes rotate cyclonically because of the way the thunderstorm updraft interacts with vertical wind shear (see my Primer on Vorticity … WARNING: the “primer” can get pretty technical) … this process typically makes cyclonic rotation the preferred sense of rotation for vortices that go on to become tornadoes. It might be tempting to look for the preferred sense of tornadic rotation in the rotation of the earth. However, the Earth’s rotation is only indirectly related to the process that gives rise to tornadic rotation, through the way it influences vertical wind shear. I
