More rain is falling on parts of Southern California after causing mudflows over the weekend. The rain is helping firefighters but boosting the risk of toxic ash runoff in areas scorched by Los Angeles-area wildfires.

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.

Much-need rain has begun to fall over Southern California, bringing relief to the drought-stricken region but also the threat of toxic runoff.