Attached Link: Snowstorm with Particles 2

Particles 2'll do the trick, but I've already given myself one shameless plug today, so I'll link you an example and keep mum on it ;-) Ockham's method would probably yield pretty good results if you used multiple spinning torii. Another thing that you could try (if you're willing to brave the render time) would be using heavy atmosphere with clouds and noise nodes, and then animating the clouds and noise.