Highest temperature in Chicago on August 9?

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Market context

Chicago’s heat on 9 August landed close to seasonal norms rather than in the extreme range, and the latest public observations point to a daily maximum around the mid-80s Fahrenheit at O’Hare. The National Weather Service’s Chicago-O’Hare climate report for 9 August lists a normal maximum of 83°F, with the previous day’s observed maximum at 84°F, while Weather Underground-linked market data has already shifted the crowd to the 84–85°F bin at 100% implied probability.[2][3][11]

That makes this market read more like a settled weather-observation question than a live forecast contest. August 9 at O’Hare has a long-run normal high of about 83°F, and historical records show that the date can still produce much hotter outcomes in rare years, with the all-time record at 97°F and several 90s-era heat spikes in the record books.[11][13] In that context, a mid-80s finish is consistent with a warm but not exceptional summer day in Chicago.[11][13]

The main things to watch are the final O’Hare station observations on Weather Underground’s Daily Observations table, because the market settles on that source rather than the summary high-low display. Late-updated readings, missing hourly data, or a revision before the first datapoint for 10 August could matter if the station’s highest recorded value is adjusted.[3] The latest National Weather Service update for the Chicago area showed thunderstorm rain and fog/mist at nearby Midway late on 9 August, which supports the idea that any end-of-day temperature movement would have come from local convective weather rather than a broad heat surge.[5]

Sources: 1 · 2 · 3 · 4 · 5

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