3 Answers

 Lightning streaks inside a cloud, between clouds, and from clouds to the ground. Lightning is a flow of electrons (a negative charge) that zigzags downward in a forked shaped pattern (scientists call this a step leader). As it nears the earth, a stream of positive charges moves up to the charge of electrons (negative charge). When they meet, the power flows. We can't see this because it moves too fast (first stroke). The return flow (positive charge) moves upward more slowly. This is what we see and call lightning (return stroke). If there is a flicker, the upward stroke is repeating the process.

Try here...... http://www.newton.dep.anl.gov/askasci/wea00/wea00030.htm

I believe lightning goes either way, which ever has the strongest positive or negative from grownd to sky or sky to grownd.Until their both equal.