Shanghai’s late-May overnight lows typically settle near 17–19°C under dominant subtropical high pressure, light southeasterly flow off the East China Sea, and clear skies that promote radiative cooling after sunset. Current ensemble guidance from the China Meteorological Administration and ECMWF shows stable synoptic patterns persisting through May 22, with minimal cold-air advection or frontal passages that would otherwise depress minima below the seasonal baseline. Traders are therefore weighting the 18–19°C outcomes most heavily, reflecting both climatological frequency in the second half of May and the absence of any model run signaling a sharp deviation. Updated short-range forecasts issued in the next 48 hours will provide the next key test of this consensus, particularly any revisions to cloud cover or wind speed that could alter the nocturnal temperature drop.