The snow happens when it happens. I was on a guided hunt for the elk opener (Sept. 26th) in the Gros Ventre in 2013, and 2 feet of snow was dumped the night before we rode in. The cook tent was collapsed, and it was hard hunting as the elk near this high camp moved out. It hurt us, but helped at the lower camp that was over-run with elk. Much of the snow melted, and the elk didn't move to the feed ground until much later. My other elk in the Gros Ventre was in mid-October, and I shot a 6x6 that was in the snow above timberline. So, I guess I am saying that you can't plan on any specific date.