The National Weather Service has issued the following alert that includes the Illinois Valley area:
Patchy freezing drizzle is possible across portions of northern Illinois and northwest Indiana early this evening, along with areas of fog.
Moist low levels combined with a weak upper level disturbance passing over the area this evening was resulting in areas of fog and patchy freezing drizzle occasionally alternating with a few light snow flurries where slightly deeper cloud layers develop.
Surface temperatures generally at or just below freezing may result in some minor ice accumulation where freezing drizzle occurs, particularly on untreated surfaces such as sidewalks, parking lots and lightly traveled roads, especially outside of the slightly warmer more urbanized areas of Chicagoland.
Light winds were also combining with the moist low level air to produce areas of fog, reducing visibility to 1-3 miles over portions of North Central Illinois and with a few areas experiencing visibility reduced locally to less than a mile.
Another upper disturbance approaching later this evening should produce deeper, colder clouds which should favor light snow or flurries rather than freezing drizzle.
If driving or walking across Northern Illinois or northwest Indiana this evening, be alert for the potential for some light ice accumulation from freezing drizzle and use appropriate caution.