Fall is an ideal time to visit Montana. The crowds are down and the weather is beautiful. Expect cold nights and relatively warm days.  As you get into October, snow is possible at any time in the mountains, though unlikely to stick for too long. It's probably best to visit in September or early October, as locations, gateway communitites and park services start to close by the end of October.   Also, dressing in layers is recommended.

** Note:  The original information for this thread came from the following forum thread: http://www.tripadvisor.com/ShowTopic-...