Traders have converged on 66-67°F as the highest temperature in Chicago on October 2 due to verified observational data from National Weather Service stations aligning precisely with that range. Post-event analysis of surface observations, including maximum readings from official sites, confirms this outcome with minimal variance across reporting networks. Model guidance issued in the preceding days accurately captured the stable atmospheric conditions, including moderate southerly flow and limited diurnal heating, that produced the observed peak. While final quality-controlled records from NOAA could theoretically shift by a degree if anomalies emerge in data processing, the tight clustering of preliminary measurements makes such revisions improbable before market resolution.