Halloween has been dry and the first day of November will likely be a mainly dry day. Things will change Tuesday night and through the day on Wednesday, though. A frontal boundary will essentially stall out over northern Illinois and southern Wisconsin Tuesday and waves of energy will ride along it into Wednesday. Those waves will support rain and potentially some thunderstorms late Tuesday night through Wednesday afternoon. It's rainfall that is needed with October ending roughly 1" below normal. In addition, most of the rain will fall Tuesday night and before lunchtime Wednesday, so many outdoor activities won't be affected too terribly much.
Rainfall totals could exceed 1" in many locations, but the more concentrated and heavy rain will likely be along and south of U.S. 20. A tool meteorologists use to analyze how much moisture is in the air is the precipitable water variable. For this time of year, values over 1" (PWATs over 1") are considered very high. Wednesday's PWATs will approach 1.5"! That is nearly record territory. As a result, some moderate to at times heavy rain is possible. However, severe weather is NOT expected, nor are flooding rains.