**Recent cooling from autumn rain and a shift to northerly flow has positioned 21–22°C as the clear market leaders for Seoul/Incheon’s daily maximum on October 13.** After record late-October heat on the 12th (Seoul reaching 29.6–30.1°C), official Korea Meteorological Administration guidance and multiple numerical models (including GFS and regional runs) converge on a daytime high of 20–22°C under widespread rain that begins overnight and tapers by afternoon. The influx of cooler maritime air behind the front, combined with persistent cloud cover and precipitation, caps temperatures well below the prior day’s values and aligns closely with the market’s 49% implied probability on 21°C and 35.5% on 22°C. Slight model spread around the precise peak—some grids showing 21°C, others briefly touching 22°C before rain peaks—explains the tight clustering, while lower-probability outcomes (23°C+) reflect the low likelihood of any break in the cooling pattern before resolution. Updated KMA and NWP guidance through the morning of the 13th will be the key near-term driver for any final shifts in trader positioning.