Recent ensemble forecasts from global and regional meteorological models reveal substantial uncertainty in Shanghai's overnight minimum temperature for May 21, driven by variable cloud cover, wind patterns, and the timing of a possible weak frontal passage that could either enhance radiative cooling or moderate it through warmer advection. With May climatology showing average lows near 17°C and historical extremes spanning 13–22°C this time of year, traders weigh the potential for clear, calm conditions favoring lower readings against the risk of increased humidity or southerly flow pushing values higher. This balance of factors sustains closely matched implied probabilities across the 15°C-or-below and 25°C-or-higher buckets, with fresh model runs expected to refine the outlook ahead of the 24-hour resolution window.