A tornado is a vortex born out of a large (supercell) thunderstorm that can grow to altitudes of over 40,000 feet.

Make a Tornado!

The purpose of this experiment is to observe a vortex.

Piece of wood (10 x 12 inches)

Glue gun

Vinyl sheets (.010" thickness) 9 x 10 inches (2 of them)

Small hand-held fan

Deli dish or cup

Clear plastic plant saucer (7" across). Cut out a hole 2" across in the middle of it

Water (1/2 cup)

Dry ice

1. Glue the cup in the center of the piece of wood.

2. Glue one of the vinyl sheets onto one side of the cup. Then glue the rest of the sheet in a half circle around but not touching the cup.

3. Glue the second sheet around the opposite side of the cup. Glue the rest of the sheet in a half circle. The two sheets must overlap, but not touch.

4. Pour about half a cup of water in the cup.

5. Using gloves, place a few small pieces of dry ice in to the cup.

6. Quickly place the plant saucer upside down on the top of the two pieces of vinyl.

7. Turn on the fan and place it in the hole in the saucer to draw the air up.

8. Watch the tornado spin!

Here are some students who did this experiment. (Requires an mpeg player like Microsoft ActiveMovie.) Did you make the same mistake they did?

The whirling fan at the top creates a spinning "updraft" or vortex. This pulls air in at the bottom of the container and out at the top of the plant saucer.

Dry ice is made of frozen carbon dioxide. It is very cold. As it warms, it turns from a solid (ice) into a gas. It cools the air above it, causing a little cloud of water vapor to condense from the air. The little cloud enters the updraft, allowing us to see the vortex. It looks like a little tornado!

We've discussed updrafts, but how would the column of air begin to rotate without a huge fan placed on top of the thunderhead?

This is not completely understood by scientists, but one way the rotation appears to happen is when winds at two different altitudes blow at different speeds creating wind shear. For example, a wind at 1000 feet above the surface might blow at 5 miles per hour (mph). A wind at 5000 feet might blow at 25 mph. This causes a horizontal rotating column of air.

If this column gets caught in a supercell updraft, the updraft tightens the spin, and it speeds up. This is much like a skater's spin speeds up, (much like a skator spins faster when the arms are pulled in close to the body). A funnel cloud is created.

The rain and hail in the thunderstorm cause the funnel to touch down. This creates a tornado.