For those that feel inspired, there's a good article by Lucas Bebber that breaks down how this kind of rain effect can be made in WebGL here:
https://tympanus.net/codrops/2015/11/04/rain-water-effect-ex...
https://tympanus.net/codrops/2015/11/04/rain-water-effect-ex...
The page actually uses the exact same effect, so the article provides a decent breakdown of how it works, for those interested.