Current ensemble forecasts from the Korea Meteorological Administration and ECMWF place Seoul’s May 20 overnight minimum in the 13–18 °C range, with the spread driven by uncertainty over cloud cover and boundary-layer moisture ahead of a possible weak frontal passage. Clear, dry conditions would favor efficient radiative cooling and push the low toward 12 °C or below, while increased cloudiness or southerly flow would limit cooling and support readings at or above 22 °C. Late-May climatology at the official station shows average lows near 16 °C, so the closely matched market probabilities for the warm and cool extremes reflect traders’ assessment of how model differences in humidity and wind will resolve over the next 48–72 hours. The next KMA medium-range update is expected to narrow the range by clarifying overnight stability and dew-point trends.