1550s, navigator's word for violent windy thunderstorm in the tropical Atlantic, probably a mangled borrowing from Spanish tronada "thunderstorm," from tronar "to thunder," from Latin tonare "to thunder" (see thunder). Metathesis of -o- and -r- in modern spelling influenced by Spanish tornar "to twist, turn," from Latin tornare "to turn." Meaning "extremely violent whirlwind" is first found 1620s.
In meteorology, a storm in which high-speed winds move in a funnel-shaped pattern.
Note: Tornadoes occur chiefly during thunderstorms.
Note: If the tip of the funnel touches the ground, it can cause extensive damage.
Note: Tornadoes are common in the Middle West.