National Weather Service officials are expecting areas of fog Saturday that may turn dense as the day continues across portions of Northern Illinois. Patchy fog is expected Saturday night and may turn dense mainly north of Interstate 80, officials said. While weather conditions are calm in Northern Illinois, other parts of the northwest are facing an atmospheric river expected to produce heavy rain and snow as a system moves in from the Southern Plains to the southeast, officials said. Officials said mild and above average temperatures are expected to continue across most of the country in the following days. Current conditions at O’Hare International Airport is mostly cloudy at 50 degrees. Farther south at Midway Airport conditions are the same at 51 degrees.