I had half forgotten this at times. Could have used a pin job. 
I didn’t have any good ideas nor much time but I did manage to make something and more or less learned how post-processing and render targets work along way. This was very helpful: Mastering Render Targets.
After figuring out how to use Lumiere (very nice btw). I ported this cool rain thing from shadertoy to work with it.
HTML5: community-challenges 1.0
I also tried to port rain shader example over but after a lot of trial and error I gave up. 