Dense Fog in California Keeps Causing Massive Highway Pile-Ups
California's Central Valley has been dealing with tule fog lately, and it keeps causing absolutely massive crashes.
Fifty-nine vehicles piled up on Highway 99 in Tulare County on January 31. Ten people got hurt. A few days before that, 43 vehicles crashed on Highway 58 near Bakersfield on January 27 resulting in nine more injuries. The fact that nobody died in either of these feels like luck more than anything when you're talking about crashes involving that many cars.
Tule fog—pronounced TOO-lee, named after tule grass—is way worse than regular fog. Visibility drops to near zero. Sometimes less than 10 feet. You can't see the car in front of you. You can barely see your own hood. And it rolls in fast with almost no warning.
NASA doesn't mess around with the description: "Tule fog is a major hazard to navigation and is the leading cause of weather-related accidents in California." The recent pile-ups back that claim up.
How It Forms
Tule fog is radiation fog that shows up on clear, calm nights when the ground is moist and wind is almost nonexistent. Ground cools rapidly. Moist air above it cools with it. Water vapor condenses. And boom, you’ve got fog.
Once it's there, air needs to heat up enough to either evaporate it or lift it off the surface. Until that happens, visibility stays terrible. Sometimes for hours.
NOAA says visibility often drops to less than 1/8th of a mile—around 600 feet—but can get way worse. Under 10 feet happens. And what makes this particularly brutal is how fast it changes. You're driving along fine, then suddenly there's just white. Nothing. No warning.
That's how you get 59-vehicle pile-ups. One car hits the fog bank and can't see. The car behind them does the same thing. Then another. And another. Until Highway 99 looks like a junkyard.
Intersections where cross traffic doesn't stop are especially bad. Someone's cruising on a major road, hits dense fog, and doesn't realize there's cross traffic until way too late.
This Week Looks Bad
National Weather Service in Hanford put out a forecast on February 4 that's pretty blunt. "High to very high transportation risk will continue through the week. Visibility will be near zero at times. Dangerous fog can move in quickly, before you have time to react."
Highways affected include Interstate 5 and State Routes 99, 41, 43, 46, 58, 59, 140, 152, 165, 180, and 198. So basically, every major road through the Central Valley.
Used to Be Even Worse
Back in 1985, Fresno dealt with 16 straight days of dense tule fog. Sacramento got 17 consecutive days. That’s weeks of not being able to see while driving.
Researchers say tule fog has been forming less often over recent decades. But "less often" doesn't mean "safe." When it shows up, it's still causing crashes like the two recent ones that put 19 people in the hospital.
How to Stay Safe In the Fog
NOAA has driving tips that mostly boil down to common sense people need to be reminded of.
Drive with lights on during the day, but use low beams. High beams reflect fog back at you and make things worse. Slow way down. Being late beats being in a 43-car pile-up. Listen for traffic you can't see. Stay away from intersections where cross traffic doesn't stop. Don't try passing anyone.
Don't stop on a freeway unless you absolutely have to. If you do, get away from your car in case someone slams into it.
Better plan: postpone your trip until the fog lifts, usually by late morning. Just wait.
If California Highway Patrol is running escorts in certain areas, follow them.
Tule fog is specific to California's Central Valley and vicious when it rolls in. Visibility goes to nothing in seconds. Recent crashes injured 19 people. Forecast says dangerous conditions last through the week. If you're driving through there right now, slow down, use low beams, or honestly just stay home until this clears.
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