An atmospheric river is expected to bring torrential rain to California this week, threatening parts of the state with flash floods and mudslides.

Flames burned through brush and vegetation, reducing the soil’s ability to absorb water — allowing water to possibly flow quickly, picking up debris and creating dangerous mudslides, debris flows and flash flooding.

Areas charred by last month's wildfires in Southern California now face a new threat from a powerful, but fast-moving Pacific storm. Here's what you need to know about this threat.