What I mean in BW and BW2 you could encounter weather effects from the overworld, Rain, Sand, anf Hail. I'm sure in the natural world there are days where the sun is bright and blaring down especially in the summer seasons, so I feel the sunny day effect should have an overworld effect. --- B**** don't make me HM01 you!
They have things like this in previous games, like hail coming down during battles in snowy areas, sand storms picking up in desert areas, and rain falling in rainy areas. I don't think there are any sunny areas that cause the sunny day effect, though. That should be in the games, I agree.