Traders see the lowest temperature in Seoul on June 28 clustering tightly around 19–21 °C because ensemble forecasts from global models show a typical late-June monsoon transition pattern, with nighttime radiative cooling under partly cloudy skies and light southerly flow keeping minimums near the seasonal average of 20 °C. Recent upper-level ridging has suppressed widespread cloud cover, supporting the market’s slight preference for 20–21 °C outcomes, while any strengthening of the East Asian monsoon trough could increase humidity and raise overnight lows or, conversely, allow clearer skies and a dip toward 19 °C or below. Model spread remains modest two days out, with resolution hinging on the precise timing of frontal passage and local urban heat-island effects; updated KMA and ECMWF runs expected within 24 hours will likely tighten the distribution ahead of market close.