Rainfall across Illinois and the central US has been substantial for June so far. This map represents the June rainfall through this morning. Large portions of the Missouri and Upper Mississippi River Basins have seen between 2 to 5 inches (yellows and oranges), while some spots in Illinois, Missouri, Nebraska, and Kansas have received 5 or more inches (red).
Zooming in on Illinois, the map below shows how far above average the wet areas have become. The areas in blue are 2 to 4 inches above average while the areas in green are 0.5 to 2 inches above average. Only small areas northwest of Chicago and south of Carbondale are below-average on rainfall.
The potential rainfall amounts over the next week are significant. The 7-day precipitation forecast from the National Weather Service shows that central Illinois could see between 4 and 6 inches of rain, while the northern third of the state could see 2 to 4 inches. The southern third of Illinois could see 1 to 3 inches. Since much of this rain will come from thunderstorms, local amounts could be much higher or lower.
The reason for this rain is that a somewhat stationary front is sitting over Illinois and will remain so over the next week. Rain will continue to develop along and south of that front as warm, moist air flows northward.