Recent Korea Meteorological Administration guidance places Seoul’s daytime maximum on May 18 near 24–25 °C beneath a strengthening high-pressure ridge that promotes clear skies, subsidence warming, and modest southerly advection of milder air from the Yellow Sea. This pattern sits slightly above the mid-May climatological average of 22–23 °C, supporting the market’s tight clustering around the 24 °C and 25 °C or higher outcomes. Model ensembles show modest spread tied to the precise strength and timing of the ridge, while recent observations confirm steadily rising daytime temperatures through mid-May. Traders are therefore weighting the next 48-hour forecast updates most heavily, as any upward revision in the deterministic run would quickly shift volume toward the 25 °C threshold.