How to make narration & dialogue (voices) always be loud enough?

We have a couple of dialogues and voice-overs in our project. The waves are normalized in volume and they usually can be heard very good.

However, we also have a dynamic weather system and other stuff that can make noise and become really loud, i.e. louder than nearby voices.

How can we assure that the voices can always be heard and that environmental sounds are toned down while narrations are running?