Northern Tier States, Best time for trip

Have been out that way in the summer months. Had snow on the ground in CO, WY & MT late May/early June. LOVE late August/early September in that area. Kids are heading back to school around mid-August in a lot of areas so after that point it does quite down SOME. And I emphasize SOME because it can still be busy. The bear jams and the like don't bother us-it adds a certain social aspect to the experience. Come September the male elk are bugling away, have their big racks and are beginning the rut. Baby animals aren't newborns anymore but are still babies and more visible than in the spring. If I had that kind of time I'd think about Jasper and Banff as well, but if you want to stay stateside don't miss WY and MT. The Rockies in CO are beautiful as well.