Definition
Tornadoes are violently rotating columns of air that extend from the base of a thunderstorm cloud down to the ground, produced by the strong updrafts and wind shear inside severe thunderstorms. Wind speeds inside a tornado can exceed 200 knots, and the very low pressure in the core combined with the high rotational winds creates forces capable of destroying almost anything in the tornado's path. A funnel cloud is the same rotating column when it has not yet reached the ground; once it touches the surface it is called a tornado, and over water it is called a waterspout.
Plain English
Tornadoes are spinning columns of extremely fast wind that drop down from a thunderstorm and reach the ground. The winds and pressure changes inside them are strong enough to tear apart almost anything they touch.
Context Anchor
Encountered in aviation weather study, preflight weather briefings, convective weather forecasts, and decisions about avoiding severe thunderstorms.
Derivation
From the Spanish 'tronada,' meaning thunderstorm, which itself comes from the Latin 'tonare,' to thunder. The name reflects the fact that tornadoes form within thunderstorms, not as separate weather events.
Why Pilots Care
Tornadoes generate winds far beyond any aircraft's structural limits and create sudden, unpredictable changes in wind and pressure that can destroy an airplane in seconds.
Grounding Statement
Picture a severe thunderstorm producing a narrow, spinning column of air that reaches the ground and tears across a small area with extreme force.
Intuition Check
Do not assume the visible funnel is the whole danger. The surrounding severe thunderstorm and nearby wind changes can also be hazardous to an aircraft.
Example Sentence 1
The convective SIGMET warned of a line of severe thunderstorms with possible tornadoes, so the pilot diverted well clear of the area.
Example Sentence 2
Tornadoes can form and dissipate quickly, so pilots treat any supercell thunderstorm as a no-go area.