Recent Korea Meteorological Administration guidance and ensemble model runs project Seoul’s May 18 daytime maximum in the 25–28 °C range, positioning the 25 °C or higher outcome as the clear market leader at 62 %. A broad high-pressure ridge over the peninsula is driving this outlook through sustained subsidence, clear skies, and modest southerly warm-air advection that exceeds the city’s mid-May climatological average of 22–24 °C. The secondary 24 °C bracket at 25.5 % captures residual spread across model solutions and possible localized urban cooling effects near the official station. With final short-range updates due within the next 24 hours, traders are closely monitoring any shifts in ridge strength or boundary-layer mixing that could alter the exact peak.