A dense fog advisory remains in effect until 9 a.m. as morning commuters navigate freeways clogged by traffic accidents.
The National Weather Service said dense morning fog could reduce visibility to one-quarter mile or less as a marine layer that's "not really playing by the rules" and low clouds inundate the region's valleys.
Conditions should clear up by midday as a weak high-pressue system moves in, bringing with it a slight warming trend heading into the weekend, according to the weather service.
