Hmm, I actually figured the wind in this mountain range (in between several mountain ridges) would be south-to-north... thus the north-facing plume (it's not going straight up, the view angle is perpendicular to the ground, not at an angle). I also took some artistic liberty, because I wanted the plumes shadow to be somewhat visible.

Perhaps I should make it a little lighter. Perhaps I should experiment with the direction... Cartography is full of choices!