Rain fell on parts of Southern California on Sunday and the scattered showers were expected to continue overnight, boosting the risk of toxic ash runoff in areas scorched by Los Angeles-area wildfires.

The charred soil left by the wildfires could create conditions ripe for mudslides because the rain, which will last into Monday, will just run off, forecasters said.

Southern California’s first full rainy day of the winter has arrived. The day, months in the making, has brought steady storms across the region while the Southland experiences drought conditions. The mostly welcome rain began Saturday night and is expected to sustain until Monday evening.