Recent atmospheric patterns featuring persistent southerly flow and reduced cold-air advection have elevated trader expectations for a mild overnight minimum in Seoul on May 20, driving the leading 49.5% implied probability for 22 °C or higher. Ensemble forecasts from the Korea Meteorological Administration and global models currently cluster projected lows in the 14–17 °C range, consistent with historical mid-May baselines near 13 °C but shifted warmer by the absence of strong northerly outbreaks. Key variables include the strength of the subtropical high and any late-May frontal passages; revised model runs over the next 72 hours could quickly alter positioning around the 12 °C-or-below and single-degree buckets if cooler air intrudes.