The National Weather Service in Chicago has issued a warning I don't recall ever seeing before today.
The NWS-C has a Freezing Fog Advisory in effect until noon Friday. Obviously that includes Kane County.
"A Freezing Fog Advisory means visibility will frequently be reduced to less than one-quarter mile. If driving, slow down, use your headlights and leave plenty of distance ahead of you," the advisory says.
"Also, be alert for frost on bridge decks, causing slippery roads."
You can also expect light mist or very light drizzle, which combined with below-freezing temperatures will result in icy patches developing on sidewalks and untreated roads — particularly bridges and overpasses.