Wx would depend on elevation. Normally days are pleasant and in the 60s or 70s. You can never predict wx temps at higher elevations. (above 5000 ft) Could be just as nice or could he some snow. Around Cody WY we normally dont see constant bad wx until the end of the year. Although we may get a hard snow storm that lasts only a few days then warms again. Last winter we hardly had any snow all winter. Year before last we got -20 late Oct and lasted for a couple of months. My best bet is Sept would be pleasant.