A stubborn cloud has persisted for more than two weeks across much of central California, bringing a period of thick fog and unseasonably cold temperatures — and officials say the stagnant weather pattern is likely to persist.
Carlos Molina, a meteorologist with the National Weather Service in Hanford, said low-level clouds — which appear to stretch from Bakersfield to Chico and west into the Bay Area — continue to cause visibility problems on roadways and could help contribute to record-breaking cool weather in December. He said temperatures have remained well below average over the past few weeks, with highs in much of the region only in the mid-40s, about 10 degrees below average for this time of year.
“If we continue this pattern for most of the month, our performance this December will certainly be one for the history books,” Molina said.
As of Tuesday, the low, dense clouds and fog had persisted for an unusually long time – 16 days, according to Molina’s count. Forecasts suggest this could continue for another week.
“Sometimes, when we do get these weather conditions in central California, it usually lasts about a week,” Molina said. So this year’s pattern is “extreme.”
Prior to and during this 16-day duration, some parts of the region briefly experienced dense, dangerously opaque Thule fog, resulting in near-zero visibility. Weather service officials confirmed that the region’s signature fog formed on November 20, 25 and 26, forming where clouds briefly broke away from the clouds during the day, resulting in thick fog late at night and early in the morning. Tule fog also occurred in parts of Kern County on Thanksgiving Day.
In these conditions, Tour fog dissipates relatively quickly, while low clouds remain, causing ongoing visibility problems.
Molina said dense fog has been a concern almost every day since late November, especially on roads transitioning from higher elevations into lower valleys, such as along the Sierra foothills, Coastal Mountains and Grapevine. At these locations, he said, drivers briefly enter low clouds where visibility becomes extremely limited.
A dense fog warning remains in effect for the central California foothills through at least Tuesday morning.
But, Molina said, “We expect to see that all week long.”
A high-pressure system near California is helping push any possible storms northward toward the Pacific Northwest and Canada, leaving little disturbance for the stubborn clouds over central California.
“Nothing can break the lower level,” Molina said.
So, for now, the chances of the dramatic Mists of Tour returning are slim.
This weather phenomenon requires clear skies and warming ground. Technically called radiation fog, it can form in any valley, but the location of the Sacramento and San Joaquin Valleys makes it particularly intense, leading to several massive highway pileups in recent years.
