It seems most significant rain events have passed over the northern or far southern portions of the Chicago area, leaving the southwest suburbs significantly drier. Is there a meteorological reason for this?
You have stated a version of the belief that rain seems to miss a location more often than surrounding places. Several people have recently voiced a similar belief for their location (north, northwest, west, south, southeast, etc). But it’s just not true. Averaged over a sufficiently long period of time, precipitation strikes all locations equally. There are exceptions, but they are minor. On average, there is slightly less precipitation to the far north than to the far south, for example. City temperatures also run higher than outlying areas and consequently rain/snow winter borderline events produce more rain in the city.