California’s Central Valley has been enshrouded in mist for more than a week thanks to the area’s infamous Tule fog.
The image below shows California as seen from space by a National Aeronautic and Space Administration satellite system. On the left is what the state looked like on Oct. 29, 2025 — before a major storm brought record-setting rainfall — and on the right is the same view on Nov. 27, in the middle of the days-long stretch of Tule fog.
Technically known as radiation fog, the weather phenomenon is the result of a combination of “a cool, moist layer of air from the Pacific close to the surface, clear skies above and light winds,” according to the National Weather Service. Most persistent in valleys where the wind can’t sweep it away, the Tule fog has been a main character in California for decades. It causes pile-ups, traps airborne pollutants and has even inspired poetry about its haunting beauty.
The NWS forecast shows most of the Central Valley — including Merced, Fresno, Visalia and Bakersfield — should be spared from the most hazardous conditions Monday evening, then the fog is expected to again thicken overnight and reach Level 3 of the weather service’s five-level fog severity index, indicating moderate risk and half a mile of visibility.
In past years, Tule fog has caused legendary and tragic pile-ups along Central California highways.
One of the worst such fog-caused chain-reaction accidents involved 108 vehicles and closed Highway 99 for more than 12 hours in November 2007. The collision unfolded over 10 minutes and resulted in two fatalities and 40 injuries.
As of Monday, no major pile-ups had been reported after nine straight days of fog.
The fog is not all bad: It is beloved by growers of crops such as almonds, apricots, cherries, peaches and pistachios because it helps the trees to satisfy the dormancy requirement necessary to produce flowers and fruit. The trees need this rest period to produce high yields during the growing season.
The California Highway Patrol suggests that, if possible, drivers postpone trips until the fog lifts. Those driving in foggy conditions should drive with lights on low beam, the CHP says. Drivers should not follow too closely behind other vehicles and should avoid crossing traffic lanes.
Visibility can be reduced to 10 feet, and the fog can be disorienting, causing motorists to drive faster than they realize. Drivers should not stop on highways except in emergencies. Drivers and passengers should move away from disabled vehicles. Drivers are urged to watch for CHP pace vehicles guiding cars through the fog.
Times staff writer Paul Duginski contributed to this report.
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