A good many years ago, we went on a quick overnight hike to Bright Angel Camp. It was the middle of August. I lived in Phoenix at the time and thought, why carry all this gear? I took shorts and a t shirt and maybe a small tarp to rig a quickie shelter. Well, a monster cold front came through. Temp dropped through the floor and it rained, then poured, then rained some more. Canyon was beyond beautiful. Water cascading down everywhere. I have NEVER been so cold in my life.
I would not take a lot of heavy gear, but I would not leave it out altogether....