IIRC, for us it was in the 'teens near the top, just before the sun really came up. Medium-weight down parka, heavy mitts, and warm boots made our trip very pleasant. Can't say what temps you might hit, nor how cold you run.
I had a warm summit day but was happy to have a medium-weight down jacket (MH Subzero). My wife waited at the bottom of the glacier while a friend and I went for the summit and she wouldn't have been able to hang out for a few hours without her down.