Temperatures dipped as low as the low 30s throughout most of the Bay Area overnignt into Wednesday.
It's not quite winter yet but the Bay Area woke up to the lowest temperaures of the season Wednesday.
A freeze warning was in effect until 9 a.m. Wednesday then a frost advisory remained in place.
The San Francisco Bay Area is expected to be partly cloudy in the afternoon. High temperatures in the mid to upper 40s and variable winds of 5 to 15 mph were anticipated.
Rain came back to the chilly region on Thursday and Friday, according to NBC Bay Area meteorologist Craig Herrera.
Wednesday night the Bay Area is expected to be partly cloudy in the evening and then become mostly cloudy. Low temperatures in the lower to mid 30s and northwest winds of 5 to 15 mph are anticipated.
The mercury dipped far below freezing in the Sierra Nevada, dropped to the mid-20s in the valleys north of the San Francisco Bay, and plunged into the 30s and 40s in valleys and some coastal areas of Southern California.
Blizzard conditions were reported along Interstate 5 over the Tejon Pass and the California Highway Patrol was escorting traffic over the summit linking Los Angeles and the San Joaquin Valley.
The mountains around Los Angeles were under a winter storm warning while the National Weather Service issued a freeze watch for the Santa Ynez and Antelope valleys.
The cold weather has prompted cold weather preparation for homeless shelters and warming centers in some cities.
State Office of Emergency Services deputy director Kelly Huston said rainfall has been keeping ground temperatures above freezing levels, but clear nights and low temperatures could push the state into a cold-weather emergency.
"I think the critical time is going to be Tuesday evening and Wednesday evening," Huston said.
EHC Lifebuilders, the largest provider of homeless shelter and services in Santa Clara County, operates the National Guard armories in Gilroy and Sunnyvale and a shelter in San Jose, spokeswoman Jennifer McEvery said.
The Gilroy shelter, 8940 Wren Ave., and Sunnyvale shelter, 620 East Maude Ave., each offer 125 beds nightly. The shelters open at 6 p.m. and close every morning at 6 a.m.
EHC Lifebuilders will extend the hours of the armories so people are not forced back each morning into cold weather once the agency is given the directive from the state, McEvery said.
California's citrus growers are scrambling to keep their groves warm to protect fragile trees from more unseasonably cold weather.
Many farmers with California Citrus Mutual are preparing to run wind machines Wednesday night to keep icicles from forming on the fruit. Some also may send up helicopters to push warmer air down toward their orchards.
A deep freeze in January 2007 caused some $1.3 billion in crop losses.
California is second only to Florida in orange production.