Trader consensus on Polymarket has locked in 18°C as the highest temperature in Shanghai today at nearly 100% implied probability, driven by aligned forecasts from the China Meteorological Administration and global models like ECMWF and GFS. A recent cold frontal passage introduced persistent overcast skies, easterly winds of 10-20 km/h, high humidity near 80-90%, and scattered showers, sharply limiting solar insolation and capping daytime heating—observational data from Xujiahui station, the official recording site, shows morning temperatures struggling to rise above 15°C under these conditions. Early April climatology supports this with average highs around 18°C. Realistic challenges include unexpected afternoon cloud breaks allowing 1-2°C of additional warming, though low-level wind shear and moisture influx make this unlikely; final hourly observations will confirm by midnight.