Official meteorological observations from National Weather Service stations in Chicago recorded a daily maximum temperature of 68-69°F on October 3, driving the near-100% market-implied probability for that bin. This outcome aligns with mid-autumn climatology for the region, where cooling lake-effect influences and typical October high-pressure patterns often produce highs in the upper 60s. Forecast models from NOAA had converged on this range in the days prior, with minimal uncertainty from steering patterns or cloud cover. While instrument calibration checks or localized microclimate variations could theoretically prompt minor revisions, such adjustments are rare once preliminary data are confirmed, leaving little room for the lower-probability bins to resolve differently.