**Forecast models show a southerly flow of warmer, more humid air reaching Chicago on September 15, lifting highs into the upper 70s to mid-80s after cooler conditions the prior two days.** Official guidance from sources like the National Weather Service and ensemble runs points to mostly cloudy skies with showers likely, especially in the afternoon, which could cap peak temperatures depending on timing and coverage. This setup follows a recent cooldown from mid-September heat earlier in the month, with historical averages near 76°F for the date. Trader consensus clusters tightly around 78–83°F outcomes, reflecting uncertainty in exact moisture advection, cloud persistence, and convective development that could either enhance or suppress the daily maximum. Updated model runs and short-term guidance over the next 48 hours will likely refine these probabilities before resolution.