I've just been playing with some examples for PureData and Supercollider (which you could probably run from a CLI, I was using their IDEs though):

These are two I've tried out:

http://sccode.org/1-e -- Rain and thunder (for supercollider)

http://www.obiwannabe.co.uk/tutorials/html/tutorial_rain.htm... -- for PureData

The rain does sound somewhat whitenoise-y though, I wonder if there are any simulations of rain, that take into account the actual physics of droplets hitting a surface.