A Winter Weather Advisory has been issued for all of Northern Illinois beginning at Noon on Friday and lasting through Saturday night. A Winter Storm Warning has been issued for Southern Wisconsin beginning at 2pm on Friday lasting through Saturday night.
Light snow has developed over eastern Iowa and northwest Illinois Thursday evening, but because the surrounding atmosphere is very dry it's not reaching the surface. During the overnight as a little more moisture is added back into the atmosphere, flurries and even light snow will be possible from about 1am/2am through sunrise. No accumulations are expected from this.
The bigger snow event arrives Friday and Saturday. As of Thursday evening the forecast calls for 3" to 6" of snow over northern Illinois with lesser amounts south of Highway 38. Higher amounts will occur just over the state line in Wisconsin but I wouldn't be surprised if totals near, or above, six inches were to occur just north of Rockford. Roads will become snow covered by the evening commute and heavy snow bands will lower visibility throughout the evening.
As low pressure passes to the south Saturday, heavy snow bands could once again set up over Northern Illinois. Within those bands additional snowfall amounts over three inches are very well possible. Winds increase from the northwest during the afternoon and evening causing any snow that is currently falling to blow around, and any snow that is on the ground to blow around. This will reduce visibility and have an impact on Saturday travel.