The National Weather Service has issued a freeze warning for interior valleys in the North Bay and a frost advisory for low-lying spots in the East Bay.
Both will be in effect from 1 a.m. to 9 a.m. Tuesday.
Temperatures of between 25 and 30 degrees are forecast late tonight through Tuesday in the North Bay, and lows in the East Bay are expected to be in the 30s.
Sensitive plants might be damaged, but temperatures are expected to rise quickly after dawn, according to the National Weather Service.
The California Emergency Management Agency is urging all state residents to accelerate their preparations for winter weather.
"As this weather tends to be the norm throughout the winter months, it is critical that Californians recognize the risks associated with freezing temperatures and take necessary steps to prepare if they have yet to do so," Cal EMA Acting Secretary Mike Dayton said.
The agency has compiled a list of steps residents can take to prepare for the cold and to prevent hypothermia, frostbite, dehydration and carbon monoxide poisoning. Those recommendations are available on the agency's website at www.calema.ca.gov.
The cold weather also threatens pets that are left unprotected.