Residents in burn scar areas should be ready to evacuate if needed. City and county agencies have readied streets for debris flow with K-rails and sandbags, as a storm moves in on Wednesday, Feb.

Forecasters released a breakdown Tuesday of where and when heavy rainfall this week is expected to hit areas of Southern California left burn-scarred by recent wildfires, raising the risk of potentially dangerous debris flows in those parts of the region.

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.