Thunder/lightning clouds is one I can't quite figure out. Applying air/electricity to black smoke doesn't do it for me. But I've seen it happen a few times, and I'm not sure why.
Steam. Cast lightning on steam.
I'm not sure how to actually remove a static cloud, though. I had one appear via a trap in Black Cove and the stupid thing wouldn't go away on its own. Took a few minutes of slowly moving my character out of the cloud in between stun applications.
edit: I guess I could have teleported my guy out! But I'd still like to know how to remove a static cloud.