That sounds fun! You're very intrepid. Will it be cold?
Nah, probably not. Temperatures should be anywhere between 13°C (=mid fifties F) and 5C resp. 40F. I will take a light winter jacked however, so I won't have to buy one in case the weather takes a turn for the worse. Been there, done that. Twice. On Monika's and my summer trips, lol.
One time we got surprised by snow and the matching temps in South Dakota in early September and the second time no snow but icy temps in the Canadian Rockies.