Lived in Rapid City for 4 years long ago but one thing we learned is the weather changes often and is unpredictable and will change a lot in a day or two. Only month we didn't generally have snow was July. Some things in Sep may be closing up but less crowds when school is in session. We have been back several times and We think Deadwood has become a tourist trap and the gambling has ruined the environment. Boot hill is still worth a visit. Also Crazy Horse has become expensive and touristy but worth a visit, best view is from the road. Lots of great scenery in the park and things to do, even a cave tour nearby.