**Official National Weather Service forecasts for Chicago O'Hare project a Tuesday, October 13 low near 63°F**, with hourly guidance showing temperatures bottoming out in the low-to-mid 60s overnight into early morning as a cold front arrives. Southwesterly winds shift northerly after sunset, limiting mixing and allowing clearer skies initially before showers develop, which can moderate overnight cooling through increased cloud cover and latent heat release. Model consensus clusters the minimum in the 62–67°F range, with slight variations driven by exact frontal timing, dewpoint depression, and urban heat island effects around the observation site. The market’s leading 66–67°F bin at 43% implied probability reflects trader weighting toward warmer guidance runs, while the tight clustering of adjacent bins around 33.5% captures residual uncertainty in boundary-layer processes and precipitation onset that could shift the observed minimum by a few degrees.