# How Tornadoes Form A supercell storm over a miniature plain: warm air, wind shear and a rear\-flank downdraft spin up a tornado, shown with simulated air particles and adjustable ingredients By 玖阳 Topic: Earth & Geography [Open the interactive Jig](https://ask.jig.com/j/l6cFmwkWK5AY) ## Guide ### 1. How tornadoes form A tornado is a spinning column of air that reaches from a storm cloud down to the ground\. Every dot here is a parcel of air, pushed by the wind\. Follow how warm air, changing winds and a cool downdraft turn a thunderstorm into a tornado\. Drag anywhere to turn the storm\. Scroll or pinch to move closer\. ### 2. Warm, wet air below It starts with warm, moist air near the ground \(amber\) under cooler, drier air higher up \(blue\)\. Warm air is lighter, so once it starts rising it keeps going, like a hot\-air balloon\. The more warm, wet air there is, the stronger the storm can grow\. Most strong tornadoes come from supercells: long\-lived thunderstorms with a rotating updraft\. ### 3. Wind shear makes a roll Wind shear means the wind changes speed or direction with height\. Here the wind high up blows faster than the wind near the ground, so the air between them starts to roll over, like a pencil rolled between your hands\. The teal dots trace that invisible spinning tube\. The roll lies flat, along the ground\. It is not a tornado yet\. ### 4. The updraft stands it up A storm's updraft is a strong current of rising air\. As it lifts the rolling tube, it tips the spin upright\. Now the whole updraft turns: a rotating updraft called a mesocyclone\. A mesocyclone is usually 1\.6 to 10 kilometres \(1 to 6 miles\) wide, far wider than a tornado\. ### 5. The rear\-flank downdraft Rain\-cooled air sinks on the back of the storm \(deep blue\) and wraps around the spinning updraft\. This rear\-flank downdraft helps drag the spin down toward the ground\. A wall cloud lowers under the updraft, and a funnel starts to hang from it\. Scientists found that tornadoes are more likely when this sinking air is only slightly cooler than the air around it\. Very cold air tends to stop the spin reaching the ground\. ### 6. Touchdown The spin is squeezed into a narrower column, and it speeds up, just as a spinning skater turns faster by pulling in their arms\. Low pressure in the middle cools the air until water condenses, so we see a funnel\. When the spinning air reaches the ground and kicks up dust, it is a tornado\. Most tornadoes are about 80 metres \(250 feet\) wide\. The strongest winds can top 480 km/h \(300 mph\)\. ### 7. Roping out In the end, the cool downdraft wraps all the way around and cuts off the warm air feeding the tornado\. The column thins into a twisting rope and fades away\. Many tornadoes last only a few minutes, though a few last over an hour\. The visible funnel is a cloud of water droplets\. The dangerous wind spins wider than the funnel you can see\. ### 8. Your storm lab Grow a storm from calm air with the warm air, wind shear and downdraft you chose in the earlier steps\. The gauge on the plinth reads the result on the Enhanced Fujita \(EF\) scale, from EF0 \(green\) to EF5 \(purple\)\. Go back and change the ingredients, then grow another\. Weak shear or very cold sinking air often means no tornado at all\. Most storms, even spinning ones, never make one\.