**Cloud cover and widespread precipitation from an active monsoon trough or frontal boundary are the dominant near-term drivers capping Seoul-Incheon highs near 28–30 °C on 16 August.** Korea Meteorological Administration guidance and ensemble model consensus currently point to a daytime maximum of 30 °C under mostly cloudy skies, with 60 % probability of rain both morning and afternoon; scattered thundershowers and persistent low-level moisture limit insolation and promote evaporative cooling. This places the market-implied distribution—29 °C (29.5 %), 28 °C (23.5 %), 30 °C (18.0 %)— squarely within the envelope of official forecasts, where small differences in rainfall timing, cloud optical depth, or boundary-layer mixing can shift the peak by 1–2 °C. Historical August climatology for the region shows mean highs of 29–31 °C, but the current wet pattern has already produced measurable cooling relative to the early-August heatwave. Traders are therefore pricing the narrow scientific uncertainty around these threshold values rather than any single deterministic outcome, with resolution hinging on the precise 09:00–17:00 maximum recorded at Incheon International Airport.