Trader consensus on Polymarket prices a 19°C overnight low at 30% implied probability for Shanghai on May 17, reflecting China Meteorological Administration (CMA) short-range forecasts clustering around 18–20°C after a cold continental air mass departed earlier this month, which had suppressed minimums to 13–15°C on May 9–10. Current high-pressure ridging promotes seasonal warming, with daily lows aligning to May climatological norms of 16–19°C, but model ensembles like GFS and ECMWF show divergence due to uncertain nighttime cloud cover—clear skies could drop temps toward 17–18°C via enhanced radiational cooling, while clouds or southerly winds might sustain 20–21°C. Key variables include evening humidity, light breeze persistence, and any late-developing showers; watch CMA's daily advisories through May 16 for refined guidance ahead of resolution.