By Betty Yu

SANTA ROSA (CBS SF) — San Francisco Bay Area residents bundled up early Monday as a cold front sent temperatures plunging, triggering a frost warning in the valleys and low lying regions.

The National Weather Service’s frost advisory for the North Bay Valleys will be in place until 9 a.m. with temperatures in the 30s.

Chilly overnight temperatures prompted a freeze warning in addition to a frost advisory from officials in Sonoma County, Monday evening.

Residents were advised to avoid prolonged cold weather exposure, and to shelter pets and livestock. The freezing conditions pose a risk for plants and crops, as well.

The chilly temperatures meant business was slow for restaurants in downtown Santa Rosa Sunday night. The Russian River Brewing Company just received heat lamps in time for the chilliest night of the season..

“We came up here to go wine tasting. It’s much colder than I was expecting, but they got the heaters out, and we don’t really care because Biden was elected president, so we’re just out here celebrating,” said Sam Larson of Moraga.

The popular downtown Santa Rosa spot had some empty tables Sunday evening.

“Usually at this time, I think we’d probably still have a pretty good waitlist, but it’s kind of sizzled down now, so I’m thinking that this is going to start affecting business a little bit as it goes, with how cold it’s getting,” said supervisor Alec Miller. “But overall, it’s still pretty busy compared to other places.”

Downtown was quiet, especially at restaurants without heat lamps. Mary’s Pizza Shack says business is down 30%, compared to a warmer Sunday during the pandemic.

Sonoma County is the only Bay Area county stuck in the state’s most restrictive purple tier, indicating widespread virus risk. That means indoor dining is not allowed.

“I knew there was a cold front coming and I wasn’t sure how cold it was going to be, it is kind of interesting being up here. San Francisco is like in the yellow tier, so a lot of indoor dining’s open. So I was kind of shocked that everything is outside here,” said Bailey Yuen of San Francisco.

The frost advisory warns that sensitive outdoor plants may be killed if left uncovered. It’s also advising residents to take extra care of their pets and livestock who may be outside.

“The fires are nice, I’m hoping that more of this outdoor dining will have fires after the pandemic,” said Dan Coming of San Francisco.

Still, not everybody out minded the chill.

“I’m from Russia, so I’m used to colder temperatures,” said Katerina Helmn of San Francisco.