Motorists on roadways along the coast and in the valleys were advised to use extra caution Thursday morning as dense fog blankets the areas.
A National Weather Service dense fog advisory for coast and valleys of San Diego County is set to remain in effect until 10 a.m. Thursday. Areas of fog are expected to extend up to 15 miles inland from the beaches through mid-morning.
"A shallow marine layer will continue to create areas of dense fog along the coastal plain and into the far western portions of the San Diego County valleys though about 10 a.m.," according to the weather service.
Forecasters said travel could be affected along portions of Interstates 5, 8, 15 and 805 and on state Routes 52, 56, 78, 94 and 163. Visibility could be reduced to a quarter-mile at times, and delays at area airports could be possible.
Drivers were urged to slow down, use low beams and leave plenty of distance in front of them.
Forecasters said more dense fog could roll into the same areas again Thursday night into Friday morning.