How do I make it rain slanty?

[morningstar]

When playing the Two Ship DM, I noticed that the rain was coming down at an angle, an effect that I really liked. 
I have been trying to figure out how to duplicate this with on a different gamemode with no success. 

Help please. 

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[Greek2me]

Either use the Sky_Slate_Storm sky file or create your own.

The variable is $EnvGuiServer::Skyfile.