More dense fog cloaks the Central Valley, experts say. How long will it last?

Drivers in Sacramento and other Central Valley communities could face hazardous conditions Wednesday morning due to dense fog, according to the National Weather Service.

The National Weather Service issued the dense fog advisory at 10:56 p.m. Tuesday.

Visibility may be reduced to a quarter-mile or less in cities including Sacramento, Chico, Fairfield, Modesto, Stockton, Marysville, Yuba City and Oroville, the weather service said.

The dense fog advisory also affects communities including Fresno, Merced, Kerman, Los Banos, Sanger, Selma, Tulare and Visalia, the weather service said.

The fog is predicted to continue through noon Wednesday.

More dense fog is forecast Wednesday night, with partly cloudy conditions the rest of the week.

Why is it so foggy in Northern California and Central Valley?

According to NASA, this weather phenomenon is called tule fog, named after a marsh plant that grows in the region.

Low-lying clouds typically form in the valley during the colder months when winds are light and the soil is moist.

Tule fog becomes especially dense when moist marine air, calm winds and clear skies come together.

“The Central Valley is fertile ground for the formation of tule fog, a persistent radiation fog, in late autumn and winter,” NASA said.

These weather patterns are common from November through February.

“Researchers have found, however, that tule fog has been forming less often in California in recent decades,” NASA said.

Tips for driving in foggy conditions

Take extra caution when on the road or avoid driving if possible.

If you must drive in foggy conditions, keep the following safety tips in mind, the National Weather Service said:

• Slow down and allow extra time to reach your destination.
• Make your vehicle visible to others both ahead of you and behind you by using your low-beam headlights since this means your taillights will also be on. Use fog lights if you have them.
• Never use your high-beam lights. Using high-beam lights causes glare, making it more difficult for you to see what’s ahead of you on the road.
• Leave plenty of distance between you and the vehicle in front of you to account for sudden stops or changes in the traffic pattern.
• To ensure you are staying in the proper lane, follow the lines on the road with your eyes.
• In extremely dense fog where visibility is near zero, the best course of action is to first turn on your hazard lights, then simply pull into a safe location such as a parking lot of a local business, and stop.
• If there is no parking lot or driveway to pull into, pull your vehicle off to the side of the road as far as possible. Once you come to a stop, turn off all lights except your hazard flashing lights, set the emergency brake, and take your foot off of the brake pedal to be sure the tail lights are not illuminated so that other drivers don’t mistakenly run into you.

The Modesto Bee’s Angela Rodriguez contributed to this story.