Converting Horizontal Vorticity into Vertical Vorticity

Kate alerted me to this remarkable video of the recent Compton, California tornado:

Vertical tilting of horizontal vorticity in its most dramatic form. Wow! Amazing footage of the Compton EF-0 tornado today. 

This is a fantastic illustration of how horizontally-oriented spin in the atmosphere gets tilted vertically to form a tornado that touches the ground.

I love this tornado video! The meteorology textbooks all say that tornadoes usually form from the tilting of a horizontal vortex tube. There is plenty of horizontal vorticity due to friction with the ground. Converting that horizontal vorticity into vertical vorticity is the trick, however, and usually requires a significant updraft. It's hard to picture that process but this video shows exactly how it happens!