Snow levels will go down to 2,500 feet later in the night into Monday morning.
Mountain passes are expected to get 2 to 3 inches of snow, including the 5 Freeway near the Grapevine, Highways 14 (near Acton) and 33 (north of Ojai.)
Caltrans and the California Highway Patrol have activated 'Operation Snowflake,' ready if conditions take a turn.
"We're hoping it's not going to happen, but I have been watching the radar," said Sgt. Michael Kerr with CHP. "It looks like something will be coming pretty soon, couple hours, and lasting through the night. The precipitation amounts ... it's up in the air, but it looks like it will be something."
On Sunday afternoon, traffic was moving slowly, but drivers were already in prep-mode.
"Not bad, a little drizzle," said Eddie Sawyer from San Diego. "It's getting cloudy or foggy but no traffic, that's the amazing thing."
In the Inland Empire near the Cajon Pass, the same concerns are growing for I-15 drivers as snow is expected there as well. Snow plows were seen being used in Wrightwood as the snow began to fall earlier in the day.
Many residents were headed out to the mountains to enjoy the winter weather, but if Big Bear or Running Springs are in your plans, chains are a must.
Meanwhile, afternoon showers had residents out the San Gabriel Valley grabbing their umbrellas.
Residents are urged to monitor road conditions.