Visibility is expected to be down to a quarter-mile in places.
Caltrans District 3
Heavy fog could make driving hazardous in Sacramento and other Central Valley communities for Thursday morning.
The National Weather Service issued a dense fog advisory at 2:30 a.m.
Visibility was expected to be down to a quarter-mile in parts of Sacramento, Modesto and Stockton.
The dense fog advisory also affects communities including Fresno, Merced, Kerman, Sanger, Selma, Tulare and Visalia.
Here’s what to know:
How long will fog last in Sacramento? Modesto?
The fog is predicted to continue through 10 a.m Thursday.
Patchy fog is forecast later Thursday morning, with partly sunny conditions Friday.
What about Fresno? Merced?
In the Fresno area, the dense fog advisory also was set to expire at 10 a.m. Thursday.
Fog may return to the San Joaquin Valley on Friday, according to the National Weather Service’s area forecast discussion. Warm and pleasant conditions are forecast, with rain expected to return early next week.
Why is it so foggy in Northern California and the Central Valley?
These 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.
Jan Null is a former National Weather Service forecaster in Northern California and current professor of meteorology at San Jose State University.
“The perfect recipe for radiation fog … is for there to be low-level moisture, clear skies and light winds,” Null said.
Null said Sacramento’s early fall weather patterns caused a perfect storm for a particularly heavy fog year.
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.
