California's deadly wildfires could come to an end in the coming days when a weekend storm douses historically dry terrain, but the storm will come with the potential for a different problem: flash floods.

After weeks of windy and dry weather, rain has fallen in parched Southern California and is expected to aid firefighters who are mopping up multiple wildfires. But potentially heavy downpours on charred hillsides could bring new troubles such as toxic ash runoff.