So, I have been searching around and it seems that you can't get rain from the func_precipitation brush entity. However, I found an obscure video with no explanation that shows rain. https://www.youtube.com/watch?v=7Y1D2C0O2RU
It is possible that he is importing Portal 2 assets and using them in the default SDK editor then using func_precipitation and fooling me, but what if he isn't?
Arachnaphob says here (http://forums.thinking.withportals.com/mapping-help/func-precipitation-acting-wierd-t9004.html) that you can--probably--imitate rain with a info_particle_system entity, but I'm not quite sure how to do that to be honest. (I'm not saying it's not possible)
Anyway, any help at all would be appreciated as I'm trying to make a map that has rain.
On a similar note, I can't seem to change the animation speed of the Snowfall precipitation (which does work) Tell me if I'm wrong, but doesn't Minimum Speed and Maximum speed change the animation speed? There wasn't any documentation I could find on it. I'm asking this because it might be a nice substitute for the rain animation.

You could give it a try to the env_embers entity, with the proper settings you might get good results. Test it.

On the other hand, if you take a look on the wiki to the particles available for Portal2, you'll find some of them to try out:

Pretty sure you cannot set the sprite texture with an env_embers - unless of course you can override the default texture.

Try the sprinkler particle from the final boss battle.

FelixGriffin wrote:
Try the sprinkler particle from the final boss battle.

Yeah, I tried that. I couldn't ever get the sprinkler_funnel_ice particle to work (the only one that's positional and doesn't have mist)

It may require a control point, so you should put one below the particle system and on the ground. Also, I recommend starting it with a logic_auto instead of the parameter that has it automatically on.

Arachnaphob wrote:
It may require a control point, so you should put one below the particle system and on the ground. Also, I recommend starting it with a logic_auto instead of the parameter that has it automatically on.

I also tried that, too. I used a info_null as the control point and I tried it with logic_auto and "Start Active:Yes". Here are some screen shots if anyone cares. https://i.imgur.com/pi4vJLb.png https://i.imgur.com/0YApdne.png Also tried with control point on ground: https://i.imgur.com/klbYCBL.png

Info_nulls aren't compiled into the map, so they can't be used as control points. Use an info_target with Always Transmit checked.

FelixGriffin wrote:
Info_nulls aren't compiled into the map, so they can't be used as control points. Use an info_target with Always Transmit checked.

Tried this as well, did not work.

Lazauya wrote:
FelixGriffin wrote:

Info_nulls aren't compiled into the map, so they can't be used as control points. Use an info_target with Always Transmit checked.

Tried this as well, did not work.

OOPS! I had my control point in the ground, when the starting point of the particle isn't offset! Here's a quick pic of it working, for anyone wondering. I will post a later shot of the full thing. http://i.imgur.com/kHYRvEH.jpg