Judging by the fact the asker's profile says "front-end developer & responsive web designer", I'm guessing this is to be published online - meaning motion can be used.
One of the best ways of visualising motion and flow is to use, well, motion and flow (or the illusion of it).
This wind map of the USA uses HTML5 canvas particle generation to give the impression of movement, speed, flow and volume. It's incredibly intuitive.
A handy thing to know about how motion is perceived is that you need very little to create the sensation of motion. Notice how, on that site, the particles simply grow then fade away - but you barely notice the fading unless you follow one particle. They don't actually move as such (if they did, it would cause problems) - but creates a consistent sense of movement in the chosen direction.