Ensemble weather models from the Korea Meteorological Administration and global centers currently cluster overnight minimum temperatures for Seoul on May 19 in the 15–17°C range, reflecting a transitional spring pattern with light northerly flow and minimal cloud cover that favors nocturnal radiative cooling. Small variations in boundary-layer humidity and wind speed across ensemble members create the tight spread among 15°C, 16°C, and 17°C outcomes, as even modest increases in mixing can raise the minimum by 1–2°C. Climatological normals for mid-May place average lows near 14–16°C, so traders are pricing the limited potential for either a brief cool surge or clearer, calmer conditions that would dip slightly lower. Updated short-range guidance expected within the next 24–48 hours will narrow the uncertainty as the event approaches.