Trader consensus on Polymarket overwhelmingly favors 18°C as Shanghai's highest temperature on April 11, driven by morning observations from Xujiahui Observatory and Shanghai Pudong International Airport recording near 16°C amid persistent easterly winds carrying cool maritime air from the East China Sea. Overcast skies and light rain have suppressed solar heating, with forecast models from sources like the China Meteorological Administration and international agencies converging on a daily peak of 18°C—aligning with post-frontal cooling patterns common in early April, when average highs hover around 19°C. While inherent forecast uncertainty exists, a realistic challenge would require unexpected late-afternoon clearing and wind shift to southerlies, though current synoptic conditions make this improbable; end-of-day station data will confirm resolution.