Here's a vaguely related question (that probably constitutes a thread hijack): when I walk on carpet, of course there's a static charge built up. When I get close to a Christmas tree with little threads of aluminum tinsel, the tinsel reaches out for me, attracted by the difference in charge. One of the threads gets me with an audible (and painful) snap. Is the flow of electrons going from me to the tree or the other direction? I know that shuffling my feet on the carpet causes electrons to move one way or the other, but never knew which way they were going (and never stopped to ask them, as they were in a hurry). The foot-shuffling surely pulls electrons one way or the other, but it isn't clear to me which way.
Well, obviously, the tree has been possessed by the Flying Spaghetti Monster, and is trying to reach out and touch you, using the tinsel as a substitute for His Noodly Appendage.
If you are an unbeliever, however, you might consider that if you are building up extra electrons by shuffling your feet on the rug, then you induce a positive charge on the tinsel, attracting it to you. Initially, the electrons start to move towards the tinsel (a leader), inducing a larger positive charge and creating a leader moving towards you. When they meet, current flows from you to the tinsel, but then there is a return stroke, from the tinsel to you, which is more powerful and, thus, brighter and louder. So, to answer your question, yes, it goes both ways.
At least that's what I think would happen if you're playing the role of the cloud and the tree is the tree.