**Official National Weather Service observations from Chicago O’Hare on September 12, 2026, recorded a daily maximum of 88 °F under mostly sunny skies with light to moderate west-southwest winds, placing the high squarely in the market’s dominant 86-87 °F outcome.** Pre-event model consensus and climatological normals (historical September 12 average high near 77 °F) had pointed to mid-to-upper 80s, and the observed value aligned with that guidance rather than any late intensification from anomalous warmth or calm conditions. With resolution now based on verified station data, the near-100 % market-implied probability reflects the absence of measurement uncertainty or alternative reporting sources that could shift the result into the 88-89 °F bin. The only realistic challenges would involve a revised official climatological summary or a switch to a secondary station (such as Midway) showing a meaningfully different peak, both of which remain low-probability events given standard NWS procedures.