# How Tornadoes Form

How wind shear, warm moist air and cold downdrafts combine to set a supercell spinning and bring a tornado down to the ground\.

By BigAl

Topic: Earth & Geography

[Open the interactive Jig](https://ask.jig.com/j/1kMwqOKN8P9u)

## Transcript

### 1. How tornadoes form

A supercell is a giant thunderstorm that spins\. From its dark base, a twisting column of air reaches all the way to the ground: a tornado\. Let's build one from scratch and see which ingredients it needs\.

The United States sees about 1,200 tornadoes in a typical year, most of them in spring\.

### 2. Warm, wet air rises

Near the ground, warm and moist air \(orange\) sits under cooler, drier air\. Warm air is lighter, so it rises in a strong updraft\. As it cools high up, its water vapour turns into cloud droplets \(white\)\.

A supercell updraft can rise at more than 40 metres per second, about 90 mph\.

### 3. Winds that turn with height

The yellow arrows on the weather mast show the wind at five heights\. Higher up it blows faster and from a different direction\. This change, called wind shear, rolls the air near the ground into an invisible spinning tube, like a rolling pin\.

### 4. The updraft tips the spin upright

When the rising updraft meets the spinning tube, it lifts the middle of the tube and tips it on its end\. Now the storm's updraft itself begins to turn\.

### 5. A spinning storm: the mesocyclone

The turning updraft is called a mesocyclone, roughly 3 to 10 kilometres wide\. Seen from above, it spins counter\-clockwise in the Northern Hemisphere\. Below it, part of the cloud base sinks into a rotating wall cloud\.

Only about one in four mesocyclones goes on to make a tornado\.

### 6. Cold air wraps around

Rain cools air at the back of the storm, and this cool air sinks in a downdraft \(blue\)\. It sweeps around the rotation and squeezes it tighter near the ground\. A little helps, but too much cold air cuts off the warm supply\.

### 7. Touchdown

As the spin is squeezed narrower it turns faster, like a skater pulling in their arms\. Air pressure drops in the core, and a funnel of cloud lowers from the wall cloud\. Once the spinning air reaches the ground, it is a tornado\.

The funnel is cloud made of water droplets\. The dust and debris swirl at the bottom is a separate debris cloud\.

### 8. Your storm

Your three sliders still shape this storm: warm air, wind shear and cold air\. Weak shear gives an ordinary storm with no tornado\. Start a new storm to watch the whole sequence again with your settings\.

Most tornadoes last less than ten minutes\. Their strength is rated from EF0 to EF5 by the damage they leave\.