Heavy rain and snow is in the forecast for California this week including local areas that are at risk of mudslides because of recent wildfires. But there is an upside. All that precipitation is chipping away at a snowpack deficit in the Sierra Nevada mountains – the source of one-third of the state’s drinking water supply. December, January and February were unusually hot and dry. But March has been a different story. Since the beginning of the month, the Sierra snowpack has gone from 23 percent to 48 percent of average in terms of its snow to water equivalent.