Official temperature observations from National Weather Service stations in Chicago recorded a daily maximum of 78–79°F on August 17, producing the near-certain market-implied odds. This outcome aligns with late-summer climatology for the region, where typical highs range 75–82°F under moderate humidity and light winds, with no significant heat advection or urban heat island amplification pushing readings higher. Forecast models from NOAA’s Global Forecast System and local mesonet data converged on this range days in advance, and post-event verification leaves minimal room for revision. Only an undocumented sensor malfunction or redefinition of the official reporting station could alter resolution, both of which remain statistically improbable given redundant monitoring networks.