California officials and weather forecasters urged holiday travelers to avoid the roads on Christmas Eve and Christmas Day ahead of a series of powerful winter storms that threatened to slam the state with relentless rains, heavy winds and mountain snow through Friday.

Millions of people are expected to travel across the state. They will likely meet hazardous, if not impossible, traveling conditions as several atmospheric rivers were forecast to make their way through the state, the National Weather Service warned.

“If you’re planning to be on the roads for the Christmas holidays, please reconsider your plans,” said Ariel Cohen, a National Weather Service meteorologist in Los Angeles.

Forecasters said Southern California could see its wettest Christmas in years and warned about flash flooding, mudslides and debris flows in areas burned by last January’s wildfires. Los Angeles County officials said Tuesday they were knocking on the doors of some 380 particularly vulnerable households to order them to leave.

Most areas saw scattered showers Tuesday morning, and the system was expected to pick up in the evening and intensify into Christmas Eve. Some regions will see rain and winds taper off Wednesday before another storm moves in.