What you’ll need for the tutorial (optional)

Here is my layout scene for the tornado. 6MB, Maya 7.0 and upwards.

Layout Scene

And the link for the tutorial itself is here:

tornadoLayout 

If you want to rig the tornado with joints and the spline IK with set driven keys then you might need this script.
I couldn’t find the bonus tools script for joints along a curve so I made one myself here:

jointsAlongCurve.mel