Cold temperatures and frost are expected to continue through Tuesday and much of the week, with some parts of the Bay Area hitting freezing levels, the National Weather Service reported Sunday.
Forecaster Steve Anderson said a mass of high pressure air way out over the eastern Pacific Ocean is funneling the jet stream from Canada to the west and mid-western United States.
"It's dragging all that cold air straight down here," he said, adding that warmer temperatures won't return until Friday when the storms pounding the eastern parts of the country move on and bring weather patterns back to normal for December.
Meanwhile, the weather service has issued a freeze warning for the region lasting into Tuesday morning. That means people spending a lot of time outside face an increased risk of hypothermia. In addition, long durations of below freezing temperatures can kill crops, plants citrus trees and can harm outdoor pets.
Anderson said these parts of the Bay Area can expect the same until the massive cold front slamming the eastern part of the country peters out and allows the cold air hanging over the west to move on. That will open the region to warmer air from the south and Pacific.
Although the recent run of cold days and nights has not come close to setting records for low temperatures, some potted flowers and new plants can be damaged by frost over the next few days.
Grace Olson, who advises customers at the venerable Yamagami Nursery in Cupertino, said the most vulnerable are potted and tender plants like hibiscus and impatiens -- both Bay Area favorites -- and anything newly planted during our warm autumn. Potted plants, she said, should be moved to sit against the walls of houses and garages, and the newly planted should be covered with breathable, frost cloth.
"Don't cover plants with plastic," she said. "That's the worst thing you can do to them."
Olson said the recent cold snap doesn't come close to the severity of the winter of 1990-91, which she described as the worst she's seen on plant life in the Bay Area. The weather service said the harsh winter of 1972 was just as bad or worse in the region.
However, when warmer temperatures arrive later in the week, Olson said home gardeners should give their plants a good watering before the next cold front moves in. She said damp roots actually help plants survive frosty weather.
The National Weather Service said Monday morning should be the coldest of this recent spate, but things will warm up in the Bay Area only by one to four degrees Tuesday morning. Outside of the cold nights, afternoons will be looking as nice and warmer than Sunday, when bright sunshine and temperatures in the high 40s and low 50s drew Bay Area residents of all ages happily outside to play.
Contact Joe Rodriguez at 408-920-5767 and follow him at Twitter.com/JoeRodMercury.