I added this mod to my modpack. And used the weather machine to create storms to test it all out. And then I turned it off and cleared storms, the rain particles still appeared. If I move away from that area it's clear but I look back like this picture shows and the particles are still in that spot.

http://imgur.com/a/9JdDl

Using Minecraft v1.7.10
Forge 1614
Weather2 v2.3.10
Coroutil v1.1.5

Any help is appreciated. Thank you!

Does no one know what is going on here?

A known issue, aiming to take a look at it in further detail soon.