Official forecasts from the National Weather Service and supporting model guidance indicate a high temperature for Chicago on September 30 in the upper 60s to low 70s Fahrenheit under persistent cloud cover, showers, and southerly flow. This positions the 70-71°F outcome as the market consensus, reflecting the narrow range where most ensemble members and observational trends converge given the day's mild advection and limited solar heating. Historical late-September baselines for the region support similar values absent strong ridging. A faster-than-expected clearing of clouds or a temporary wind shift could push readings into the 72-73°F range, while heavier rainfall or delayed mixing might cap the maximum below 70°F.