Recent forecasts from the Korea Meteorological Administration and global models point to overnight lows in Seoul near 20–21°C on June 18, aligning with the market’s tight clustering around those bins. Clear to partly cloudy skies expected under weak high pressure will allow moderate radiative cooling after daytime highs near 32°C, while light easterly winds and moderate humidity (around 60–70%) limit further drops. Early June climatology shows typical minima of 17–19°C, but current warm advection and reduced cloud cover have kept readings elevated. Traders appear focused on the narrow window between 19–21°C because small shifts in nocturnal cloud cover or wind speed—still uncertain within 48-hour model runs—could tip the official Incheon station reading by 1–2°C. Updated short-range guidance later today should clarify the exact minimum.