A Dense Fog Advisory has been issued until 10am Thursday morning for the following counties, Black Hawk, Bremer, Butler, Cerro Gordo, Franklin, Grundy, Hamilton, Hancock, Hardin, Jasper, Marshall, Poweshiek, Story, Tama, Winnebago, Worth, Wright, Benton, Buchanan, Cedar, Clinton, Delaware, Dubuque, Iowa, Jackson, Johnson, Jones, Linn, Allamakee, Chickasaw, Clayton, Fayette, Floyd, Howard, Mitchell and Winneshiek. Melting snow along with nearly calm winds has led to a lot of low level moisture that is conducive to fog formation. Visibilities will drop under a quarter mile late tonight through tomorrow morning. Make sure to use low beams if you are traveling in these areas. Fog will begin to burn off by mid-morning.