Nights get cool to around freezing as the month goes by. Daytime temperatures drop from around 70 to 40. It is a low-use time and a time when larger groups are not around. Animals move more and are seen more often. Moose are seen often in September and can even be called.
Leaves begin to change toward the end of the month with the peak just at season's end.
Fishing is not as good as other times, but serious anglers can find something to bite. Trout-fishig is excellent at the end of the month. September is a very quiet time, when peace and serenity are the major attractions. Days get short, so plan to bring a good book and a headlamp. It is also a great month for star-gazing, watching the Aurora Borealis, and seeing the Milky Way.