Trader consensus on Polymarket favors 18°C (34.5%) as Shanghai's highest temperature on March 28, driven by the latest ensemble forecasts from global models like ECMWF and GFS, which cluster diurnal maxima around 17-19°C amid a building upper-level ridge over East Asia fostering mild southerly flow. Recent 48-hour updates reflect slight warming from prior cooler runs, as a fading cold surge gives way to seasonal spring advection, though model spread highlights uncertainty—18°C leads due to median projections, while 17°C (23%) accounts for potential persistent cloud cover, and 19°C (20.5%) for sunnier breaks enhancing urban heat island effects. Key variables include shortwave trough timing, which could suppress highs below 17°C (4.3-4.4%), or stronger ridging pushing 20-21°C (8-11.5%); extremes like 14°C or below (1.3%) or 24°C+ (1.1%) face climatological barriers in late March, with Shanghai's historical average high near 13°C. New CMA and international model outputs due within 24 hours could refine odds.