Recent ensemble forecasts from global models point to Shanghai’s May 18 overnight low settling near 19–20 °C, reflecting a stable high-pressure ridge and light easterly flow off the East China Sea that limits strong radiative cooling. Typical May climatology shows overnight minima clustered between 17 °C and 22 °C, with the current 18–20 °C range favored by moderate humidity and minimal frontal activity. Key variables that could shift the outcome by one degree include cloud-cover changes overnight or subtle wind-direction shifts that either enhance mixing or allow clearer skies for greater cooling. With leading probabilities tightly grouped, traders are pricing the genuine forecast uncertainty inherent in short-range temperature resolution.