Current forecasts from NOAA and AccuWeather models place Chicago's August 20 high in the mid-to-upper 70s, near or slightly below the 82°F climatological normal, with traders assigning roughly equal implied probabilities across 74–83°F bins. Key differentiating factors include the strength and timing of a passing cold front, afternoon cloud cover that could cap insolation, and southwest winds near 10–15 mph that enhance mixing and limit peak heating. Ensemble guidance shows modest spread in boundary-layer moisture and subsidence, creating uncertainty between 76–77°F and 80–81°F outcomes. Updated National Weather Service model runs and local observations over the next 24 hours will narrow the range before market resolution.