I was thinking though;
Noticed all the fall colored trees in the Cats and Dogs trailer?
It also seems some of the trees only have the tops of the trees in a fall color. I still think adding in rain only wouldn't really make sense, because it can also rain during spring and summer, and trees aren't going to changing into fall colors during Summer anyway.
So why would they give trees fall-like colors if they are only adding rain now? They could have just left the trees untouched.
Unless the different fall colored trees are just for the show, like Appaloosa Plains also had similar fall-like trees in the world.
So here is still hoping we will get a full weather/seasons EP/GP right after Pets. I am pretty sure they will never patch in all full Seasons for free, considering how much of a big seller that EP was in the past.
