I'd be surprised if there were no weather effects at all. At the very least it might be scripted like in Divinity 1 where it rained only a few times for dramatic effects. Was hoping to hear from Larian about this, I'm sure there will be some rain or snow effects and lightning.

Every time there I run into trouble on the road, there is always a dwarf at the bottom of it. Don't they know how to drive above ground?