Ken, I agree. The second half Sept is risking early snows. I have been in the Wind River Range on Labor Day and it snowed us in for 3 days. I think a 20 degree bag in late August will be fine, especially in a tent. I have 2 down bags, and one is 5 degree, the other is a Western Mountaineering bag with a Micro Fiber outer shell which is rated for 15 degrees. The first one is overkill, and the second does'nt compress and pack as well. Also, Micro Fiber bags tend to make your evaporation rate much slower, thus waking up in the middle of the night all clammy. So I'm going to look at some of their Extreme Lite series bags. Getting one rated for 20 degrees with a full collar should keep me plenty toasty if the weather turns on us.