FWIW, I came across a description of what weather conditions were like around the time of the recent death:
http://mrhalfdome.wordpress.com/2011/08/01/half-dome-fall/#comments

Edit: Adding link to another SP thread---see pgs.2 &3 for attempts at explaining SIerra weather
http://www.summitpost.org/phpBB3/another-yosemite-fataility-t59358-15.html