Current ensemble forecasts from the Korea Meteorological Administration and global models place Seoul’s overnight low on May 21 near the seasonal late-spring baseline of 14–16 °C. This range arises from typical radiative cooling under a building high-pressure ridge, with light winds and limited cloud cover allowing surface temperatures to drop close to the climatological mean minimum for the date. Minor differences among 14 °C, 15 °C, and 16 °C brackets reflect small uncertainties in boundary-layer moisture, subtle warm-air advection, and resolution of local urban heat-island effects in the numerical guidance. Updated model runs over the next 48 hours will narrow the spread, while any unexpected increase in low-level cloud or a northerly flow could push the minimum lower or higher.