Torrential rains inundated the California coast on Christmas Eve, sparking numerous flash flood and even short-lived tornado warnings, turning roads into rivers and sending debris cascading down hillsides.

Atmospheric rivers dumped heavy rains on large parts of California, causing floods and mudslides and leaving three dead as of Christmas night, according to local officials.

The Christmas Eve storm was expected to persist into Friday, posing unsafe driving conditions during what would normally be a busy holiday travel period, according to the U.S. National Weather Service...