Dense fog swathed California’s Central Valley on Friday, putting more than 1 million residents under a dense fog advisory from the National Weather Service (NWS).
“As we start getting into fall, the cooler temperatures and the higher dew points across the region, especially in the Central Valley, tend to combine and create fog for our area,” NWS meteorologist Stephen McCoy told Newsweek.
Why It Matters
Sudden drops in visibility due to dense fog contribute to dangerous driving conditions and have historically played a role in multiple vehicle crashes, particularly during the morning commute.
The NWS issues dense fog advisories to alert drivers and help prevent traffic accidents by encouraging safer driving behavior under adverse conditions.
What To Know
The NWS office in Hanford, California, issued a dense fog advisory at 7:19 a.m. PDT on Friday. The advisory was scheduled through 10 a.m. PDT for a wide area including the cities of Le Grand, Madera, Kingsburg, Shafter, Lake McClure, Tulare, Visalia, Selma, Fresno, Lemoore, Wasco, Delano, Atwater, Merced, Sanger, Parlier, Corcoran, Kerman, Planada, Porterville, Alpaugh, Hanford, and Goshen, among others.
According to the alert, visibility in the affected regions is reduced to 3 to 4 miles in some locations due to dense fog. Many areas faced a chance of visibility at only one quarter mile or less, according to the NWS Hanford webpage.
London, Firebaugh, Fresno, Tulare, and Hanford faced the highest chances of such poor visibility.
However, the advisory ended earlier than expected as the foggy conditions improved. Residents should remain vigilant, as fog is common during this time of year.
McCoy said the fog was especially prevalent this week after heavy rain hit the Valley area and saturated the ground.
“Over the last day or two, all that moisture is evaporating out of the surface…which has caused this fog that has developed over the last two days for the San Joaquin Valley,” McCoy said.
There could also be fog tomorrow morning, according to McCoy.
The NWS warns that low visibility may make driving dangerous, particularly during the early morning commute. Motorists are urged to slow down, use headlights, and maintain a safe following distance to prevent collisions.
The Hanford area also saw fog on Wednesday. The dense fog advisory comes after many other states faced similar conditions earlier in the week.
“This is the time of year where this is most typical,” NWS meteorologist Kenley Bonner told Newsweek. “There’s always potential when the temperatures cool down to what the dew point is. That is when we’re going to get the fog formation. That’s why this time of year is more conducive to that, because we are getting the colder temperatures.”
What People Are Saying
NWS Hanford in a post on X: “High surface humidity in the San Joaquin Valley coupling with light winds and clear conditions aloft will result in chances for fog to return Friday morning. There is a 40-50% chance for visibilities to fall below 1/4 mile especially for the areas in and around CA HWY 99.”
NWS Hanford in a dense fog advisory: “Low visibility could make driving conditions hazardous.”
What Happens Next
Residents and travelers in the affected areas are advised to remain vigilant, especially during future early morning hours when fog development is common in the Central Valley during autumn and winter months. The NWS encourages the public to monitor official weather updates and to practice safe driving habits when advisories remain in effect.