A powerful storm moved through the Los Angeles region Thursday, flooding streets, prompting evacuation warnings, and threatening mudslides in fire-ravaged areas. By Thursday evening, a debris flow had closed Mulholland Drive,

The Los Angeles fires were burning evidence of how dangerous this delusion is. The fires were a bonfire of bad ideas that had piled up over decades, from suburban sprawl into wildfire zones to the flammable plastics that now fill many people’s homes.

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.