Weather is probably one of the easier problems to tackle. Sure, performance will be worse in a snowstorm, but that's true of humans too. Waymo has already showed they can filter out snowflakes. Maybe it wouldn't work in white-out conditions, but in that case, again, humans also can't really drive.

The more complex things that can happen in urban areas though, yeah that's hard. All kinds of weird shit can happen that takes social understanding to know how to deal with. Right now it looks like for those situations Waymo is relying on remote "coaches" that tell the cars what to do at a high level (guidance, but not directly control).