Latest ensemble forecasts from the Korea Meteorological Administration and global models like ECMWF and GFS drive the tight clustering of trader odds around 9–12°C for Seoul's March 21 high temperature, with 11°C leading at 21.5% implied probability amid mild southerly advection expected to moderate early spring chill. Differentiating factors include subtle model divergences on cloud cover and frontal timing—clearer skies could push toward 12–13°C via enhanced solar insolation, while increased low-level moisture favors 9–10°C. Historical March 21 highs average 10.8°C (1981–2023 baseline), but urban heat island effects in Seoul amplify readings by 1–2°C downtown; no signals for extremes like 14°C+ (low wind shear) or sub-7°C (no polar vortex intrusion) keep tails slim. Traders eye tomorrow's 12Z updates for shifts.