Blowing snow and sub-zero temperatures are creating black ice on some roadways - ice that looks like darker pavement.
The Wisconsin Dept. of Transportation is advising drivers to reduce their speeds, in the event vehicles suddenly hit patches of black ice. Multiple accidents have been reported on the local interstate system.
Bridges and ramps are especially susceptible to the formation of black ice, according to the DOT, so are sections affected by blowing snow.
Crews have salted the freeways, but salt loses its effectiveness, as the temperature falls below zero.