Direct answer
Objectives follow journal display order. Some depend on your choices; follow the active objective in the game.
Result
It turned out even the area around Kaer Morhen, a place which - one would think - Geralt knows by heart, can hide a great many interesting and undiscovered phenomena. Not far from the keep, Geralt came across an area where the weather differed remarkably from that of its surroundings. He decided to investigate what sort of forces were at work.
