Special Weather Statement issued August 15 at 12:55AM CDT by NWS

...Dense Fog Expanding over Far Northern Iowa... Areas of fog, patchy dense in spots, are likely to expand over portions of far north central iowa through early morning hours. The patchy dense locations could witness visibility down to less than a mile at times through 4 AM CDT. Areas along Interstate 35 north of Clear Lake and Mason City to the Minnesota border as well

from Current Watches, Warnings and Advisories for the United States Issued by the National Weather Service http://ift.tt/2i1hNsR