A dense fog advisory was in effect early Thursday for San Diego County's coastal and valley areas, where morning commuters faced low visibility — a quarter-mile or less at times.
The National Weather Service issued the advisory until 8 a.m., saying coastal mesas and higher terrain up to 15 miles inland were affected.
"Rapid visibility reduction will cause poor driving conditions at times," the weather service said. "Roads affected include the 5, 805, 163 ... and 15 freeways. Slow down and be alert!"
Motorists were also advised to use their low beam headlights and leave plenty of distance between vehicles.
