Here's some optimism, as some others have mentioned, i think that image was supposed to be for the next update which may or may not get released in time for christmas. And that update may trigger the Snow weather in Online, i can't imagine it being difficult, since it's a cheat in SP anyway. Just copy pasterino some coding, i suppose.
Just to chime in here, no it is not that easy as copy and paste. At least not to do it right, like it appears in that small Vinewood sign picture. The snow cheat is nothing but a weather effect, a particle emitter at best.
Here's why there will never be a dynamic snow effect in Los Santos and Blaine County: imagine if you will for a moment, the weather going from 90* warm sunny beach day weather, to snowy and cold with dynamic snow layers all over San Andreas. Yeah, that's not even remotely realistic. It won't happen. Sorry to be that guy but don't ever expect Los Santos to look like North Yankton does in regards to snow.