Dear Tom,

While almost all tornadoes rotate in a counterclockwise sense in the Northern Hemisphere, some do not. Has a clockwise tornado ever occurred in the Chicago area?
Bryan F.  Crest Hill

Dear Bryan,

It is true that about 95% of all Northern Hemisphere tornadoes rotate counterclockwise (cyclonically), but there’ve been many documented occurrences of anticyclonic twisters. At least two were in the Chicago area, one near 87th and Pulaski on July 22, 1962; the other a major F-4 tornado near Lemont on June 13, 1976 that killed two, injured 23, and caused $13 million of damage. 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 in the San Francisco Bay area that had spawned from an equally rare anticyclonic-rotating supercell thunderstorm. Several anticyclonic tornadoes were documented in Oklahoma during a severe weather outbreak on May 10, 2010.