Fog over east-central Minnesota and the Duluth area and snow in the northern part of the state will lead to harsh driving conditions and school delays Monday morning.

Conditions improved across the Twin Cities metro area, where fog prevailed early Monday. However, a dense fog warning was in effect until 9 a.m. for Aitkin, Pine, Itasca, Carlton and southern St. Louis counties, with visibility less than a mile in some places, the National Weather Service said.

Cities affected include Pine City, Duluth, Grand Rapids, Hill City and Aitkin.

To the north, a winter weather advisory remained in effect until midday for Koochiching, northern St. Louis and northern Cook and Lake counties, as well as Voyageurs National Park and the entire Boundary Waters. According to the National Weather Service in Duluth, up to 4 inches of snow could fall in the area.

Lower winds with gusty winds are expected in northwestern Minnesota, where a warning is also in effect until midday, the weather service said.

“Expect slippery road conditions,” the weather service warned.

Several school districts postponed classes Monday morning to allow for weather conditions to improve. Districts starting late include Aitkin, Bemidji, Brainerd, Cook County, Hill City, Nevis, Park Rapids, Pequot Lakes, Staples-Motley and Walker-Hackensack-Akeley.

Mild conditions will give way to arctic air by Wednesday, sending mercury levels into the minus teens from Brainerd to International Falls to Ely, and wind chill values ​​will be even lower, perhaps as low as minus 40 degrees, the weather service said.