Rain moved into Southern California, marking the start of what is expected to be three days of significant rainfall.
Rain was reported in Burbank, Glendora and Ventura County about 8 p.m Wednesday.
Local news from across Southern California
By 1 a.m. Thursday, rain was reported throughout the Southland, including in Sherman Oaks, Westchester and Fullerton.
The rain provides a welcome respite from the prolonged dry spell but also brings the threat of flooding, landslides, traffic tangles and other problems.
According to the CHP website, 30 traffic incidents were reported between 10:30 p.m. Wednesday and 2 a.m. Thursday in the LA area.
Law enforcement agencies around the region were bracing for the storms.
Deputies in Lancaster and Palmdale were on a heightened state of alert.
The potential for mudslides in the Green Valley and Elizabeth Lake areas are extremely high due to recent wildfires.
Just a small amount of rainfall on a burned area can lead to flash floods and debris flow.
Such rushing waters coupled with soil and rock can destroy bridges, roadways, structures and cause serious injury or death, Wolfe says.
Residents in foothill neighborhoods under the threat of mudslides and flooding surrounded homes with sandbags this week as communities prepared for what the National Weather Service described as the "largest rain event" in Southern California since March 2011.
In Glendora, more than 18,000 sandbags -- enough to cover four miles if placed end to end -- have been distributed to residents to protect properties from floods and debris flow.
The heaviest rain was expected after the evening commute and into the overnight hours.
The more powerful of the two storms was expected to arrive Thursday evening and bring up to 2 inches of rain in central and southern valleys, 2 to 4 inches in foothill areas and 6 inches of rain in some mountains.
The National Weather Service described it as the most significant storm in the last three years in Southern California, adding that thunderstorms are possible Friday and Saturday. Showers could continue into early Sunday.