The National Weather Service warned of areas of locally dense fog, and possibly freezing fog, in Southwest Washington and Oregon's Willamette Valley on Saturday morning.
Visibilities of a mile or less are expected in that area, with the fog gradually dissipating around noon.
Temperatures at or below freezing will create areas of freezing fog, resulting in slick roadways. Caution is urged for those traveling this morning.
Snow at higher elevations has also prompted chain restrictions over mountain passes.