A rare and powerful winter storm sweeping the West Coast is battering areas unaccustomed to snow and wintry mix, bringing parts of Portland, Ore., to a halt before moving south toward California.The varied precipitation, ranging from rain to snow to graupel, a slushier version of snow, was met with a mix of distress and marvel: Whiteout conditions shuttered roads in the mountains and stranded drivers, while beaches in areas like Santa Cruz, Calif., received a light dusting.