Tornado season strikes again...

Tornado season strikes again...

Southern USA battens down the hatches and gets ready for some wild weather!

Every spring the southern states of the USA get ready to be battered by tornadoes.  These destructive towers of air, dust and debris are created by winds blowing at hundreds of miles per hour.

Let's take some time to learn more about this fearsome phenomenon...

To see a tornado in action, take a look at this video clip:

The key to a tornado is temperature - when air warms up it becomes less dense. Warmer air weighs less than the cold air. Just like a cork floats in water, the warm air floats on the heavier, colder air.

This causes a convection current to form, often called a thermal.  Glider pilots and birds use thermals to stay in the air. Birds are really good at taking advantage of thermals. They glide through them with outstretched wings, saving a lot of energy as they don't have to flap their wings as much.

We'd all be in trouble if tornadoes formed every time the temperature changed. Luckily, tornadoes only tend to happen when there are dramatic changes in temperature.

Unfortunately for people living in USA's Tornado Alley, they live somewhere where this happens pretty often...

When this happens, columns of air begin to spin as they rise. It's the spinning motion that reduces the density inside the column and this causes it to spin out of control!


All shapes and sizes...

Tornadoes aren't the only kind of twister. Dust devils, waterspouts and fire whirls are all types of tornado. Read on to find out more about each one.

Dust devils

You can find these in deserts, and they are nowhere near as dangerous as twister tornados. As they spin they pick up dust particles. They are formed in just the same way as twister tornados, but they generally form during good weather: blue skies with no clouds in sight.   As they spin, dust is picked up into a vortex.

To see a dust devil in action, take a look at the video clip:

Dust devils have even been recorded on Mars.  But the temperature change which causes them ranges between -60oC and -100oC! To see one in action, look at the video.


These occur over water, but they don't pick up water as they spin.  The water droplets inside them have been formed from condensation.  They normally occur in the tropics and also tend to be much weaker than land tornadoes.

To see a waterspout in action, take a look at the video clip:

Fire Whirl

These are very rare, but if they do occur it's usually during a wild fire. When there has been a drought and it is dry, it is easier for fires to spread.  But they don't normally last for very long.  Watch this video to see how fire whirls are created, but don't try it at home!

Or go directly to youtube.