In 2008 it was overcast at the start but rain didn't start until you neared Barr Camp. Above timberline the temps were in the low 30s, 30 mph winds and freezing rain. It was a cold front that was predicted 5 days in advance and a major story on local TV news, but there were still many runners who showed up with only a top and shorts.
This year we have typical Colorado monsoon weather. There is enough moisture in the atmosphere to cause afternoon T-storms. I am a slower runner in wave 2 and if it looks like I will get wet above timberline, I have a very lightweight, long sleeve top with a hood that is water repellant, that I will wrap around my waist. The weather predictions have gotten a lot better than at the time of my original post.