Witcher 3 - CD Project Explains Changing Weather in Wild Hunt

In an interview with Game Informer, Kimberly Wallace talks with art producer, Michal Stec on how The Witcher 3's changing weather came to be:

What went into creating the weather and environments for The Witcher 3?

Hundreds if not thousands of hours of browsing through references: paintings, pictures, films, photos - everything, really. I remember this one time, Lucjan (one of the leads) and I were on our way to some party and he suddenly stopped the car, pulled a camera out of the glove box and started taking pictures of the setting sun to use as a reference. We drew a lot on photographs and movies. 

A quote on when the weather wil change:

How often will the weather change as you play?All the time - the weather is constantly changing. This is a randomized mechanism; working it out took us quite a while, since it required a lot of testing, checking if how it felt in the game was okay, or if it was too much. The weights given to particular weather conditions change depending on the region - in the swamps of No Man's Land it's practically always foggy and rains a lot, whereas in Skellige you can expect more thunderstorms near the coasts and sunshine up in the mountains.