The weather shouldn't be that bad, but you're in the big mountains and need to be prepared for anything from real cold and snow to pleasant temps during the day. Up high even in September it will be cold at night and you'll need a good pad and sleeping bag. Montana actually just got 18" of snow yesterday, so you never what what you will run into in the mountains any month of the year!!! Also, you need to be in good shape, have well worn in boots and take care of your feet or you won't be going far. Cell phone may be poor to nonexistent and you may want to look into renting a satellite phone for the trip. Lastly, be bear aware and insure you follow all the requirements to hunt in the NF safely out there so you don't become a statistic. Have fun and good luck!