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How does a tornado form?

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Quick answer

A tornado forms when a strong thunderstorm's rising warm air meets winds blowing at different speeds and directions, setting the air spinning. That spin tightens into a narrow, fast-rotating column, and if it reaches the ground it becomes a tornado.

A tornado forms when a thunderstorm's rising warm air meets winds blowing at different speeds and directions, setting the air spinning. That spin can tighten into a violent, funnel-shaped column stretching from cloud to ground.

Step by step

  1. Warm, moist air near the ground rises quickly, feeding a tall thunderstorm cloud called a cumulonimbus.
  2. Winds at different heights blow at different speeds and directions, a condition called wind shear.
  3. That shear rolls the rising air into a horizontal tube of spinning air inside the storm.
  4. The storm's upward pull tilts the spinning tube upright, so it stands vertically.
  5. The spinning column tightens and speeds up, like a skater pulling in their arms.
  6. When the narrow funnel touches the ground, it is a tornado.

Key things to understand

  1. It starts with a strong thunderstorm and warm, moist air rising fast.
  2. Winds changing speed and direction with height (wind shear) start the air rotating.
  3. The rotation can tilt upright and tighten into a spinning column inside the storm.
  4. If that column reaches the ground, it is a tornado.
  5. The most powerful tornadoes come from rotating storms called supercells.

Labelled diagram

  1. Warm updraft

    Moist air near the ground rises fast into the growing storm cloud.

  2. Wind shear

    Winds at different heights blow at different speeds and directions.

  3. Spinning tube

    Shear rolls the rising air into a horizontal, rotating tube.

  4. Tilt upright

    The storm's updraft lifts the tube so it stands vertically.

  5. Tightening funnel

    The column narrows and spins faster as it stretches downward.

  6. Ground contact

    The funnel touches the ground and becomes a tornado.

How a thunderstorm spins up a tornado

Real-world examples

  • The 2013 Moore, Oklahoma EF5 tornado killed 24 people and caused billions of dollars in damage.
  • The 2011 Joplin, Missouri tornado was one of the deadliest in US history, killing about 160 people.
  • The 1925 Tri-State Tornado crossed Missouri, Illinois and Indiana on a path over 350 kilometres long.
  • Tornadoes also strike Bangladesh, Argentina and the UK, though most occur in the central United States.

Common mistake

✗ Myth: Many people think a tornado is simply a cloud that drops out of the sky.

✓ Fact: A tornado is a spinning column of air that starts inside the storm and only becomes visible when dust, debris or condensed water vapour wraps around it.

People also ask

What causes a tornado?
A tornado is caused by a strong thunderstorm combined with wind shear, where winds at different heights blow at different speeds and directions. This shear sets the rising air spinning. If the spinning column tightens and reaches the ground, it becomes a tornado. Warm, moist air near the surface and cool, dry air aloft increase the storm's energy.
How do tornadoes form?
Tornadoes form in stages. First, warm moist air rises into a thunderstorm. Second, wind shear rolls that rising air into a horizontal spinning tube. Third, the storm's updraft tilts the tube upright. Fourth, the spinning column tightens and speeds up. Finally, when the funnel touches the ground, it is a tornado.
Where do most tornadoes happen?
Most tornadoes happen in the central United States, a region nicknamed Tornado Alley, covering parts of Texas, Oklahoma, Kansas, Nebraska and nearby states. This area mixes warm, moist Gulf air with cool, dry northern air, creating frequent severe thunderstorms. Other tornado-prone regions include Bangladesh, Argentina and parts of Europe.
What's the difference between a tornado and a hurricane?
A tornado is small and short-lived, forming over land from a single storm; a hurricane is a vast ocean storm system hundreds of kilometres wide that lasts days.
Why do tornadoes form in 'tornado alley'?
Places like the central US mix warm, moist air from the south with cool, dry air from the north, creating the instability and wind shear tornadoes need.
How are tornadoes rated?
By the damage they cause, on the Enhanced Fujita (EF) scale from EF0 to EF5, which estimates wind speed from the destruction left behind.

Part of the guide: Water & Weather Phenomena →