The Dense Fog Advisory for Winnebago, Boone, McHenry, Ogle, Lee and DeKalb Counties in northern Illinois has been extended until noon Tuesday. Green, Rock, and Walworth Counties in southern Wisconsin were also extended until noon. Visibilities will be down to a quarter of a mile or less at times. There are also some slick spots from temperatures falling under freezing level and wet roadways. Travel with caution into the afternoon.