It’s the driest December in years — with no rain in sight.
A ridge of high pressure is causing stagnant air across the region
The Bay Area is in the midst of one of its most arid Decembers in years, and there’s no end in sight to the dry spell.
A ridge of high pressure remains entrenched over the West Coast, blocking the main storm track north to the U.S.-Canada border, according to the National Weather Service in Monterey.
The system is “keeping everything dry across the state of California,” said Roger Gass, a meteorologist with the weather service. “Unfortunately, it does not look like any kind of precipitation in the next seven days, and likely beyond that. It looks like the next two weeks will be dry.”
A fifth consecutive Spare the Air alert for poor air quality was called for Tuesday in the Bay Area as the high-pressure ridge continues to trap smoke and pollution near the ground. Wood fires in fireplaces or stoves will continue to be banned in the district, which includes seven counties plus southern Sonoma and southwestern Solano counties.
The system is causing stagnant air with chilly nights and moderately high temperatures in the 60s during the day.
“These conditions create a temperature inversion that acts like a lid,” the district said Monday, “causing unhealthy air pollution to build up. Smoke from the Southern California wildfires is currently offshore, but remains above the inversion layer, creating vivid sunsets but not contributing to already poor air quality.”
The high-pressure ridge is expected to break down late Thursday or early Friday, allowing for more wind to flush out and clean up the air, according to weather service forecasts.
Unlike Sunday, no heat records fell Monday in the Bay Area. San Francisco, Concord and Moffett Field in Mountain View all saw a high of 67 degrees. Elsewhere, the mercury topped out at 61 degrees in Oakland and 69 degrees in San Jose.
San Jose and Half Moon Bay on Sunday each broke their pre-
vious daily record of 69 by one degree.
The system has contributed to a dry start to December. San Francisco recorded just .02 of an inch of rain through Sunday, marking the driest first 10 days of the month since 2011, according to the weather service.
Overall, rainfall totals for the rainy season, which began Oct. 1, remain below average. Santa Rosa has recorded 6.27 inches (75 percent of normal), Oakland 3.15 inches (68 percent), San Francisco 3.16 inches (56 percent) and San Jose 1.5 inches (46 percent).
There is a bit of good news: The Golden State has received some rain where it really needs it.
Precipitation levels at eight key weather stations in Northern California, located in watersheds that feed Shasta, Oroville, Folsom and other major reservoirs, are at 98 percent of normal for the rainy season. But the high-pressure ridge is blocking storms there now, too.
Last year’s record rains helped fill many of those reservoirs after the state’s yearlong drought. The 201617 rainy season set a record for the eight-station index, which has been monitored continuously since 1920.
Contact Mark Gomez at 408-920-5869, Denis Cuff at 925-943-8267 and Jason Green at 408-920-5006.