Recent National Weather Service and model guidance indicate a southerly flow advecting milder air into the Chicago area ahead of an approaching frontal boundary, supporting daily highs near the mid-70s on September 30. Increasing cloud cover and a low-probability afternoon shower risk introduce modest uncertainty in the precise maximum, as timing and coverage of any precipitation or thicker stratus could trim peak readings by a degree or two. Ensemble spreads remain tight around 72–75 °F, consistent with the market’s near-even split between those bins and lower probabilities for cooler or warmer outliers. Updated model runs and surface observations over the next 48 hours will refine the temperature profile and any late-day cooling effects from increased moisture.