The Los Angeles area is preparing for its first rain since wildfires first broke out weeks ago. But too much rain at once could bring its own set of significant issues.

Snow shut down a key interstate north of Los Angeles for hours on Monday while weekend downpours doused wildfires across Southern California in the first significant storm of the season for the region that had not seen rainfall for eight months.

Officials cautioned that ash in recent burn zones was a toxic mix of incinerated cars, electronics, batteries, building materials, paints, furniture and other household items.