Tornadoes that occur in the Northern Hemisphere normally rotate anticlockwise, but in an estimated 1 percent of cases, they instead spin clockwise. Such anticyclonic tornadoes are normally fairly weak, tornado analyst Paul Robinson told the Washington Post in 2013.

Two such instances happened on April 30, when a supercell southwest of Oklahoma City produced a tornado whose track looped around on itself, and then spawned an anticyclonic tornado with winds spinning clockwise. DON'T MISS: How severe weather alerts are ...

A pair of odd twisters spun out from a supercell thunderstorm in Oklahoma Tuesday (April 30). An ultra-rare backward-spinning tornado was spawned Tuesday (April 30) from a powerful supercell thunderstorm that formed over the Oklahoma-Texas border.

In the Northern Hemisphere, the vast majority of tornadoes spin counterclockwise. But in rare cases—just 1 to 2 percent of the time—they rotate the “wrong” way, moving clockwise instead. That’s exactly what happened this week when powerful thunderstorms raged across southwestern Oklahoma.