Closely matched probabilities across 17–21°C for Seoul’s lowest temperature on June 27 stem from short-range ensemble model spreads in overnight radiative cooling under variable early-summer conditions. The Korea Meteorological Administration and global models show modest uncertainty driven by increasing humidity, scattered cloud cover, and the first influences of the East Asian monsoon, which can suppress nighttime temperature drops by 1–3°C compared to clear-sky scenarios. Historical climatology places late-June average lows near 18–19°C, with recent runs indicating sensitivity to precipitation timing and wind patterns that determine whether the minimum settles near 18°C or edges higher. Updated model guidance expected in the next 24–48 hours will likely narrow the distribution ahead of resolution.