Official observations from National Weather Service stations in Chicago recorded a daily maximum of 80-81°F on October 10, 2026, confirming the market's sole 100% outcome. This aligned with National Oceanic and Atmospheric Administration forecast guidance and regional model consensus, which had projected mild autumn conditions under a high-pressure ridge with limited cloud cover and light southerly flow. Historical October averages near 65°F provided climatological context, but recent warm anomalies supported the elevated reading. Revisions to official data or station discrepancies remain the only realistic scenarios that could alter resolution, though such adjustments are rare once preliminary reports are validated.