As a rule of thumb, a tornado in the Northern Hemisphere will rotate counterclockwise, while those in the Southern Hemisphere twist in a clockwise rotation. But, as with any rule, there are always exceptions. Anticyclonic tornadoes (rotating clockwise in the Northern Hemisphere) have occasionally been observed. When they do, they are typically weaker twisters associated with weak storm cells or sometimes appearing as waterspouts. One of the strongest anticyclonic tornadoes was observed in 1998 near Sunnyvale, California. Even rarer—but still possible—is an event when a supercell generates both cyclonic and anticyclonic tornadoes.