Recent National Weather Service and model guidance indicate a warm air mass with southerly winds and increasing cloud cover will limit overnight radiational cooling in Chicago ahead of September 8. Forecast lows cluster in the low-to-mid 70s, well above the 1991–2020 climatological average of 62°F, as a departing high-pressure ridge allows warmer advection and reduced clear-sky cooling. This setup narrows the range of plausible minima, producing tightly bunched market-implied probabilities across the 60–71°F bins. Key differentiating variables include the exact timing of any late-day shower activity, boundary-layer moisture, and minor model differences in 2-meter temperature bias, which collectively sustain uncertainty between adjacent 2°F intervals while keeping extremes below 10% probability. Updated model runs and NWS forecast discussions expected in the next 24–48 hours will likely refine these thresholds.