Trader consensus on Polymarket reflects tight clustering around 78-85°F for Chicago's highest temperature on April 17, driven by National Weather Service forecasts indicating highs near 80-82°F amid a building upper-level ridge over the Midwest that promotes subsidence and sunny skies for peak heating. Recent severe weather and heavy rain on April 14-15 have cleared out, allowing southerly winds to advect warm, moist air from the Gulf, with 850mb temperatures supporting 80s potential per GFS and ECMWF model consensus. Differentiating factors include timing of any isolated thunderstorms or lake breeze onset, which could cap peaks at 78-79°F near the lakeshore versus 82-83°F inland at O'Hare; new evening model runs and morning soundings will refine this uncertainty before resolution.