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FARGO — About 98% of all tornadoes spin cyclonically, which in the Northern Hemisphere is counter-clockwise and clockwise in the Southern Hemisphere. This is because tornadoes tend to follow the rotation of the parent rotation in the storm from which it develops.
Contrary to popular belief, tornadoes are too small to be influenced much by the Coriolis Effect. This means sometimes a tornado can spin the wrong way. About 1 in 50 tornadoes will spin anti-cyclonically, which is clockwise in the Northern Hemisphere, and counter-clockwise in the Southern Hemisphere. Anticyclonic tornadoes tend to be weaker than cyclonic tornadoes. Nonetheless, like any tornado, strong ones do occur. The strongest known anti-cyclonic tornado occurred in West Bend, Wisconsin, on April 4, 1981, with F4 intensity. That tornado was unusual in that the parent thunderstorm was not particularly strong and did not appear to be capable of producing a violent tornado.
