Recent model guidance from the Korea Meteorological Administration shows a continental airmass from northern China moving across the peninsula, driving Seoul’s overnight low on May 21 into the 12–15 °C range. This cooler advection, combined with light winds and partial cloud cover, favors the market’s leading 13 °C-or-below outcome at 41 % implied probability. Historical KMA records place late-May minima around 13–16 °C on average, with the current setup sitting near the cooler end of that climatological envelope. Any strengthening of the flow or delayed frontal passage could shift the minimum upward into the 15–17 °C band, where the next three buckets each carry roughly 20 % odds. Updated KMA and ECMWF runs expected over the next 48 hours will provide the next clear signal for traders.