A Freeze Warning is going up for the north bay valleys and mountains and also the eastern Santa Clara hills.
This could be the coldest night of the season so far and some cities may set or tie their records for the day.
This is the time to prepare for the chill and protect sensitive, bring in your pets and don't forget about the pipes.
Freeze and frost could cause damage to tender plants. Frost will form by morning and there may be some black ice on the roads so be careful.
Watch the latest AccuWeather forecast here and get the latest weather stories and videos here.