A dense fog advisory was issued by the National Weather Service for coastal San Diego around 2 a.m. Friday. The advisory for areas within five miles of the coast will remain in effect until 9 a.m. Friday.
Visibility is expected to drop to one quarter mile or less.
Flights may be impacted at Lindbergh Field in San Diego, Palomar Airport in Carlsbad and John Wayne Airport in Orange County.
Driving may become hazardous on roads and freeways within five miles of the coast.
Drivers are asked to slow down, use low beam headlights and keep a higher than average distance from other cars.