Snow and hail brought winter driving conditions to the Sierra on the last full day of summer — the earliest that Caltrans officials could ever recall — leading to a fatal 16-car collision on Interstate 80. The snow led to the chain-reaction pileup Thursday on westbound I-80 near Cisco Grove (Placer County) that killed one motorist when his car rammed a tree, shut down the road for more than three hours and created a backup of nearly 20 miles, a Caltrans spokeswoman said.