More info from one of our hiking books,

Snow can fall in higher elevations any time, rain in Colorado tends to be cold and unprepared hikers can become hypothermic at any time, monsoon season (mid-July to early Sept) brings occasional gray, rainy days and increased thunderstorms. Flash flooding and lightening (very dangerous out here) are 2 other problems with thunderstorms. It snowed on Monarch pass 2 weeks ago.

" Whatever the season, always bring layer of clothes and rain gear. Weather can change quickly and a temp drop of 10-20 degrees F in one hour is not unheard of. Be prepared!"

Another tidbit, for every 1,000 ft of elevation gained, the temp. drops 5.5 degrees F. If Denver at 5,280 is 80 deg.F it may be 53 degrees in Leadville at 10,190 ft! That's what got me the day I rode up there, temps were in the 50's Fortunately, I did have my arm and leg warmers with me and a light jacket.