OK...WOW...start with a game clock / calendar and vary the brightness based on the time and length of day (equinox reference). Now for weather...bit of work there (Indy coders).
Of course the characters will have to adjust their dialogue...there are no problems, only solutions...No important dialogue (or at least limited) during weather or other situational events, just "can we talk about this later" (or something like that). Lets not over-complicate that massive dialogue tree.
Now they can actually add content for "situational events"... sneaky mission, comments about the weather, ect.
P.S.: "This is important and I want to talk about it...can we seek shelter first?" Lines like this would only add value to the overall story. I don't think Larian gets that "immersive elements" reinforce each other.
