Across much of Central California, a cluster of stubborn clouds has lingered for more than two weeks, bringing periods of intense fog and unseasonably low temperatures — and officials say the stagnant weather pattern is likely to persist.
The low stratus clouds — which appear to stretch from Bakersfield through Chico and west into the Bay Area — continue to create visibility concerns on roadways and could help foster a record-cool December, said Carlos Molina, a meteorologist with the National Weather Service in Hanford. Temperatures have remained well below average the last few weeks, he said, with highs only in the upper 40s for much of the region, about 10 degrees below average for this time of year.
“If we continue to hold on to this pattern for a majority of this month,” Molina said, “it would definitely put us in the record books for how cool we’ve been this December.”
Already, the low, heavy clouds and fog have stuck around an abnormally long time — 16 days as of Tuesday, by Molina’s count. Forecasts show it could continue through the week.
“On occasion, when we do get this weather regime across Central California, typically it lasts about a week,” Molina said. So this year’s pattern is “on the extreme side.”
Before and during this 16-day stretch, some areas in this region have seen thick, dangerously opaque tule fog form briefly, slashing visibility to virtually zero. Weather service officials confirmed that the area’s signature fog developed on Nov. 20, 25 and 26, forming in spots that saw brief breaks from the clouds during the day, allowing the dense late-night and early-morning fog to develop. On Thanksgiving Day, parts of Kern County also experienced tule fog.
In these instances, the tule fog lifted relatively quickly, while the blanket of low clouds remained, creating ongoing visibility issues.
Dense fog has been an almost daily concern since late November, particularly on roadways that transition from higher elevations into the lower valleys, such as in the lower Sierra foothills, coastal ranges and along the Grapevine, Molina said. In those spots, drivers briefly enter the low clouds, where visibility becomes extremely limited, he said.
A dense-fog advisory remains in place across the Central California foothills through at least Tuesday morning.
But, Molina said, “we’re expecting to see this all of this week.”
A high pressure system lingering off California is helping to push any possible storms north toward the Pacific Northwest and Canada, leaving little to interfere with the tenacious clouds over Central California.
“There’s nothing to break up the low stratus,” Molina said.
Consequently, for now, there’s little chance that the dramatic tule fog will develop again.
That weather phenomenon requires some clearing of skies and some warming of the ground. Technically known as radiation fog, it can develop in any valley, but the geography of the Sacramento and San Joaquin valleys can make it particularly intense, resulting in several massive freeway pileups in recent years.
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