Drought-busting rains are possible as periodic showers/t-storms pass across the metro area. The opening salvo of downpours is expected to arrive Thursday afternoon and evening.
Conditions support storm development this afternoon, though heaviest activity is expected to move across S. Nebraska/N. Kansas, across S. Iowa/N. Missouri and into central Illinois bringing an enhanced risk of severe storms.
The nature of t-storm complexes is such that the timing, periodicity, and exact location of strongest storms can be hard to pinpoint more than about 12 hours in advance due to interactions with storm outflows, induced disturbances aloft, etc. It is safe to say that the Chicago area will likely see several inches of rain during the period from Thursday through Saturday.
At this time, it appears that the greatest likelihood of excessive rainfall in the Chicago area will be Saturday-Saturday night, although periods of heavy rain are possible beginning this afternoon. Through Friday night, current guidance suggests storm-scale interactions will focus the core of t-storm clusters just to our south, with periods of thundery, soaking rain extending north across the metro area. By Saturday, a larger scale frontal system to the west is expected to overcome storm-scale forcing, resulting in a more linear SW-NE axis of active, heavy-rain producing storms from eastern Kansas, across the Chicago area, and into lower Michigan.