What causes the unpredictable path of lightning?

[spliffter]

What's the math behind what you see in the picture..

Thanks for reading/replies

 

[Drakkith]

The current that causes lightning has to follow a path of ionized air. This doesn't happen in straight lines, or just in one spot, but branches out. Ever seen a plasma ball? The kind you can put your hand on and watch the plasma arc to your fingers. It a similar effect: air disturbances.