A tornado is a destructive weather phenomenon caused by storm fronts.
Once a common occurrence on Earth, by the 24th century, tornadoes could be dissipated by the planet's Weather Modification Net. In 2356, Amanda Rogers' mother and father were executed by the Q Continuum in the form of a single tornado, which spontaneously appeared and disappeared over their house in Topeka, Kansas, after destroying it. Upon hearing of the manner of their deaths in 2369, Jean-Luc Picard was surprised and questioned why the weather modification network failed to prevent the tornado, before learning of its unusual nature. (TNG: "True Q")
In 2365, Theta VIII's atmosphere was found to contain large concentrations of ammonia, among other gases, which formed ammonia tornadoes. Geordi La Forge agreed with William T. Riker's assessment that the planet was not suitable for vacations, unless one liked ammonia tornadoes. (TNG: "The Royale")
Yaderan folklore stated that Changelings could transform into tornadoes. In one story that Taya told Odo in 2370, the Great Minra tricked a Changeling by telling him tornadoes were easy to transform into. (DS9: "Shadowplay")
After the Reckoning began in 2374, the Bajoran city Tamulna was hit by a tornado. (DS9: "The Reckoning")
Tornadoes were sometimes used in a humorous way to describe destruction in a particular area. In 2370, Miles O'Brien joked that the only possible explanation for damage to the science lab was a tornado that no one on Deep Space 9 heard. (DS9: "The Alternate")