Numerical weather models from the Global Forecast System and European Centre for Medium-Range Weather Forecasts show a stable springtime pattern over eastern China that favors a Shanghai overnight low near 19–20 °C on May 18. Limited cold-air advection from the north combined with moderate radiative cooling under partly cloudy skies keeps temperatures in this narrow band, while boundary-layer moisture and light winds from the East China Sea add slight upward bias. Traders have priced 20 °C highest because recent ensemble guidance tilts toward marginally warmer conditions, yet modest model spread around wind speed and humidity leaves room for 19 °C or even 18 °C if the next update cycle strengthens nocturnal cooling. Historical mid-May climatology supports this range, with the next major model run expected within 24 hours poised to clarify the precise minimum.