The National Weather Service has issued a frost advisory for low-lying spots in the East Bay from 1 a.m. to 9 a.m. Tuesday.
Sensitive plants might be damaged, but temperatures are expected to rise quickly after dawn.
The California Emergency Management Agency is urging state residents to get ready for winter.
"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," said Cal EMA Acting Secretary Mike Dayton.
The agency offers preparedness tips on its Winter Wise page.
(Bay City News contributed to this report. Patch garden blogger Angele Sweet has some tips for .)