Frigid Arctic air from northern Canada will bring sub-freezing temperatures to the North Bay beginning Tuesday and lasting through Thanksgiving, the National Weather Service said Monday.
Overnight temperatures will dip as low as 25 on Wednesday morning and 28 on Thanksgiving morning, forecaster Steve Anderson said.
"This is winter. Get the down blankets out, bring small pets and plants indoors," he said. "Get ready for a freeze."
Scattered showers are expected to continue through Tuesday morning. Daytime temperatures will be in the lower 40s to mid-50s on Tuesday, with snow falling above 1,500 feet in the North Bay hills.
As the weather dries out tonight, the mercury will plunge, bringing the coldest weather of the season with "near-record lows possible," the weather service said.
The coldest North Bay valleys will record overnight lows in the 20s from Tuesday night through Friday morning, with "several hours of freezing temperatures possible," according to a hazardous weather outlook issued by the weather service Monday morning.
Why the cold?
The airs pushing in from Northern British Columbia, where the temperature sank to 28 below zero on Monday, Anderson said.
It's not going to get that cold in Northern California, but with temperatures in the 20s Sonoma County will experience a "hard freeze," said John Feerick, a senior meteorologist with AccuWeather.
"I definitely think there's going to be problems with frost," Feerick said.
Citrus, tropical and other plants that favor temperate climates are at risk when temperatures drop below freezing, said Kris Kepa, a plant buyer with Harmony Farm Supply and Nursery.
"Make sure everything's well watered," Kepa said. "I know it's been raining but you never know."
String large-bulbed Christmas lights on citrus and avocado trees to help protect them from the cold air, Kepa said. She also recommended that gardeners cover smaller plants with frost blankets or spray an antitranspirant spray, such as Wilt Proof or Cloud Cover. Make sure the plants are well watered before spraying, she said.
Bring smaller plants, such as potted jade and other succulents, indoors when possible or cover with a blanket. Spreading mulch around perennial plants, leaving space around the stems, may help keep frost off their roots, she said.
Freezing temperatures also bring risk to pipes cracking as water freezes and expands.
Pipes within homes with insulation or heating should be fine, but exposed pipes, including irrigation pipes and water spigots, may crack if water freezes inside them, said Steve Brown, owner of Santa Rosa Plumbing in Cotati.
"Anything that's out of the ground is more susceptible to freeze than things under the earth," Brown said.
Wrap exposed pipes with rags, such as old T-shirts, and tightly secure them around all exposed pipe.
"Tape them to the pipes. The idea is to prevent the air from getting close to the pipes," Brown said.
Drain hoses of water and disconnect from the spigot, he said. And turn on the heat.