A pre-Christmas storm with rain, wind and mountain snow will affect much of the western United States. While the storm will bring another dose of drought-denting rain and dump more snow onto the ski slopes, it has the potential to cause major travel disruptions. Enough rain can fall on the urban areas of California to cause sporadic flash flooding. Motorists should allow extra time to travel and reduce their speed on area highways and city streets. Airline delays are likely at the major hubs. Drenching rain will first arrive in southern Oregon and northern California early on Friday morning.