Close clustering of market-implied odds around 19–23°C for Shanghai’s June 28 overnight low reflects substantial short-term forecast uncertainty typical of late-June East Asian monsoon conditions. Primary drivers include variable cloud cover modulating nocturnal radiative cooling, fluctuating humidity levels tied to southerly moisture transport, and subtle steering influences from the western Pacific subtropical high that can shift local wind patterns and marine-layer intrusions from the East China Sea. Official guidance from agencies such as the China Meteorological Administration shows model spread between GFS and ECMWF ensembles, with urban heat-island effects in Shanghai potentially raising minimums 1–2°C above rural baselines. Fresh model runs and updated surface observations expected within the next 24–48 hours are likely to narrow the range and move probabilities.