Recent KMA short-range guidance and ensemble model runs place Seoul’s overnight minimum on May 18 squarely in the 14–15 °C range, with clear skies and light northerly flow favoring strong radiative cooling after sunset. A weak continental airmass trailing a weak front is expected to keep boundary-layer temperatures from climbing much above 13 °C pre-dawn, while the urban heat-island effect and minimal cloud cover prevent deeper drops below 13 °C. Historical May minima at the official station average 13.2 °C, so the current setup sits near the climatological center. With no strong warm advection or precipitation forecast through the night of the 17th, traders have clustered volume on 14 °C and 15 °C, leaving only modest implied odds for 13 °C or 16 °C. The next model update and 3 a.m.–9 a.m. KMA observations will decide the outcome.