Parts of Southern California and the U.S. Southwest on Monday faced the threat of flash flooding along with landslides and mudslides after storm Hilary unleashed record-breaking downpours overnight. Some 17 million Americans were under flood and high-wind advisories, watches and warnings as remnants of the storm moved north, dumping heavy rains from the California-Mexico border up through Las Vegas and into parts of the Northwest, the National Weather Service said.