Current National Weather Service forecasts and ensemble guidance indicate a post-frontal airmass will deliver highs in the low-to-mid 60s across Chicago on October 3, with sunny skies and light easterly flow limiting afternoon mixing. This setup follows heavy rain and a cold front on October 1 that dropped temperatures into the upper 50s overnight, establishing a baseline several degrees below the 1991–2020 average high of 69°F. Trader emphasis on the 66–69°F brackets reflects lingering uncertainty in model timing of peak insolation and boundary-layer recovery, while lower bins price the risk of stronger northerly advection or earlier cloud return. Updated 12z runs and diurnal temperature curves from O’Hare and Midway will refine the exact maximum before market resolution.