# How Tornadoes Form Watch warm air, wind shear and a spinning supercell build a tornado from thousands of simulated air parcels, then change the ingredients yourself\. By cal Topic: Earth & Geography [Open the interactive Jig](https://ask.jig.com/j/fv7OMjCZKJXb) ## Transcript ### 1. How Tornadoes Form Far above this prairie, a giant thunderstorm is quietly spinning\. Every speck you see is a parcel of moving air, pushed by the winds around it\. Let's find out how the storm turns that spin into a tornado\. Drag anywhere to look around\. Most tornadoes last only a few minutes, but a few keep going for over an hour\. ### 2. Warm, wet air near the ground The sun heats the ground, and the air just above it becomes warm and full of moisture\. Warm air is lighter than the cooler, drier air above it, so it wants to rise, like a bubble in water\. This rising air is the storm's fuel\. Turn up the warmth and watch it climb\. In the United States, tornadoes are most common from April to June\. ### 3. Winds that change with height Near the ground the wind is gentle and comes from one direction\. Higher up it blows faster and from another direction\. This change is called wind shear, and it rolls the air between into a long, invisible spinning tube lying on its side\. A difference of about 80 km/h \(50 mph\) between the surface wind and the wind 5\.5 km up is often enough for a spinning storm\. ### 4. The updraft tips the roll upright A strong rising current of air, called an updraft, pushes up through the middle of the spinning tube\. It bends the tube into an arch and tips the spin until it stands upright\. Now the rising air itself is turning\. Updrafts in the strongest storms can rise at around 160 km/h \(100 mph\)\. ### 5. A spinning storm The storm now has a huge rotating updraft inside it, called a mesocyclone\. Storms like this are called supercells\. Look under the cloud: a lower, slowly turning shelf, the wall cloud, often hangs beneath the spin\. A mesocyclone can be up to 16 km \(10 miles\) wide and reach 15 km \(50,000 ft\) high\. ### 6. Pulling the spin in tight Rain\-cooled air sinks down the back of the storm and wraps around the spin\. As the spinning column is stretched and squeezed narrower, it turns faster, just as a skater spins faster by pulling in their arms\. Switch the sinking air on and off to compare\. The sinking air is called the rear\-flank downdraft\. Blue specks show cooler air, orange specks warm air\. ### 7. Touchdown When the tight spin reaches the ground, a tornado is born\. Low pressure in the core cools the air until its moisture turns into a visible cloud funnel, and the winds around the base lift a swirl of dust\. Watch the funnel lower to the ground\. Most tornadoes are less than 2 km wide, and most have winds under 180 km/h \(110 mph\)\. ### 8. Your storm lab Now you control the weather\. Change the warmth, the wind shear and the sinking air in the panel and watch how the storm responds\. Not every spinning storm makes a tornado: the ingredients have to be just right\. In one study, only about a quarter of spinning storms seen on radar produced a tornado\. Wind estimates here are illustrative\. ### 9. The tornado fades Eventually the cool sinking air wraps all the way around and cuts off the warm air feeding the storm\. The funnel thins into a twisting rope and fades away\. Scientists still study storms like this to warn people earlier\. Tornado strength is rated from EF0 to EF5 by the damage it leaves, not by measuring the wind directly\.