Updated

The Los Angeles County Sheriff's Department says residents of more than 170 homes in two mudslide-prone foothill communities are being told to prepare to evacuate in anticipation of a storm system that's headed for Southern California.

Sheriff's spokeswoman Nicole Nishida said calls went out Thursday night to residents of 134 homes in La Canada Flintridge and 42 homes in La Crescenta. She says sheriff's deputies will begin going door-to-door at noon Friday and hope to have evacuations completed by 4 p.m.

The homes north of Los Angeles are threatened because they lie beneath slopes of the San Gabriel Mountains that were burned bare by wildfires.

Rainfall totals through Saturday are expected to range between a quarter and three-quarters of an inch. But forecasters say thunderstorms could bring downpours up to 1 1/2 inches in burn areas.