For those of you who don’t understand, he was asking how you enable/disable func_precipitation as the brush entity itself doesn’t have any options for this. Which is actually a good question that almost anyone who’s had to fuck with rain has had a problem with.
The answer to this is rather simple, just requires a bit of dodging around the system.
1. Name your func_precipitation entities “rain” without quotes.
2. Create a point_template entity, and name it “rain_on” without quotes.
3. Open up the Properties menu for the point_template, and under Template 1 list your “rain” entity. Next click the ‘Flags’ tab, and checkmark ‘Preserve entity names (Don’t do name fixup)’.
4. Now when you want to enable your rain (via another entity, say a button or trigger.), type in ‘rain_on’ as your ‘Target Entities Name’, and ‘ForceSpawn’ as your ‘Via this input’ in your button/trigger’s Output menu. In-order to disable your rain, simply kill the rain entity itself. You can still re-enable it, don’t worry.
If you want to start with the rain off, you should kill your ‘rain’ entity in a logic_auto. This method is used in Amsterville as someone mentioned before, and various other maps in-combination with other storm effects. As far as making it move, you should be-able to just use the Parent property in your func_precipitation. My suggestion would be to create a nodraw brush in an outside room that moves along a path_corner, and parent your rain brush entity to that.