Rain in Rust currently serves no function but to cause massive lag for most players.

You can activate it with weather.rain 0-1

Yes rain still comes thru everything sadly :(

I mean at this point you could use TimedExecute to make a schedule for weather, there used to be an addon but its been ages since Ive seen it... let me do some digging and might be able to find it... wether the addons working is another story XD

Zugzwang

 Maybe FacePunch will fix it some day.

thanks for the laugh this early in the morning

Goldie

thanks for the laugh this early in the morning

XTREMRUST

Variable weather is, however, important for a survival game. Strange that they don't take care of it.

You never know. They might fix it up as part of Farming 2 and HDRP.  But don't hold your breath.