Traders see the lowest temperature in Seoul on June 14 clustering near 20–21 °C because current model guidance and recent observations point to modest nocturnal cooling under partly cloudy skies and moderate humidity typical of early summer. Radiative heat loss overnight is tempered by lingering cloud cover that reduces longwave radiation escape, while higher dew points limit the temperature drop; light winds further mix the boundary layer and prevent stronger surface cooling. Official forecasts from sources such as the Korea Meteorological Administration and AccuWeather show morning lows in the 18–20 °C range, with slight day-to-day variability driven by shifting high-pressure influence and the early stages of the East Asian monsoon. The tight spread between the two leading outcomes reflects genuine uncertainty in the exact minimum, as small changes in cloud timing, wind speed, or urban heat-island retention can shift the recorded low by 1 °C. Historical June averages place Seoul’s morning lows near 19 °C, providing a baseline traders weigh against the latest short-range model runs.