We've had the January thaw. Now it's the January fog. A dense fog advisory is in place for much of the state, including Door and Kewaunee counties, until 6 p.m. Friday. The National Weather Service says visibilities are expected to drop below ¼ mile at times with visibilities falling to a few hundred feet in some locations. Motorists are urged to slow down, use low-beam headlights, and keep plenty of distance between them and the vehicle in front of them.