Most tornadoes rotate in a counterclockwise sense. Have any clockwise tornadoes ever occurred in the Chicago area?
Approximately 95 percent of all Northern Hemisphere tornadoes rotate counterclockwise (cyclonically), but there have been many documented occurrences of anticyclonic tornadoes. At least two have occurred in the Chicago area, one near 87th and Pulaski on July 22, 1962; the other near Lemont on June 13, 1976.
Tornado researcher Dr. Ted Fujita, while investigating a June 3, 1980, storm in Grand Island, Nebraska, found three of the seven twisters produced by that storm to be anticyclonic. On May 4, 1998, rare anticyclonic tornadoes were documented by the WSR-88D Doppler radar in the San Francisco Bay area that had developed out of an equally rare anticyclonic-rotating supercell thunderstorm.