Dense fog will develop tonight and last through Saturday morning over the coast and the coastal plain. Visibility will be reduced to 1/4 mile; in some spots even as low as 500 feet. When driving through fog, slow down, use your low beam headlights, and leave extra space between you and the vehicle in front of you. Be prepared for sudden reductions in visibility. Dense fog may also impact travel through coastal airports, including John Wayne Airport and Palomar Airport. It should be mostly clear by lunch time.