Trader consensus on Polymarket overwhelmingly favors a highest temperature of 51°F or below in Chicago today (97% implied probability), aligned with National Weather Service (NWS) guidance projecting a daytime high near 45°F at O'Hare International Airport. This positioning stems from a recent cold front that swept the Midwest late last week, ushering in a cool maritime air mass from the northeast over Lake Michigan, combined with persistent low clouds, scattered showers, and 10-15 mph onshore winds suppressing daytime heating. Ensemble forecast models like GFS and ECMWF show strong agreement on subdued temperatures, 20°F below the May 1 climatological normal of 65°F. Realistic challenges include unexpected afternoon clearing allowing brief solar insolation for a 5-7°F bump, though current stability and short daylight remaining make warmer outcomes unlikely; monitor hourly observations through sunset for final resolution.