Passage: Diaries and cameras found around their last campsite made it possible to track the group's route up to the day preceding the incident. On 31 January, the group arrived at the edge of a highland area and began to prepare for climbing. In a wooded valley they cached surplus food and equipment that would be used for the trip back. The following day (1 February), the hikers started to move through the pass. It seems they planned to get over the pass and make camp for the next night on the opposite side, but because of worsening weather conditions — snowstorms and decreasing visibility — they lost their direction and deviated west, up towards the top of Kholat Syakhl. When they realised their mistake, the group decided to stop and set up camp there on the slope of the mountain, rather than move 1.5 kilometres (0.93 mi) downhill to a forested area which would have offered some shelter from the elements. Yudin postulated that "Dyatlov probably did not want to lose the altitude they had gained, or he decided to practice camping on the mountain slope."

Question: Why made the group alter the course on the way up the mountain?
snowstorms and decreasing visibility